F1000Research F1000Research 2046-1402 F1000 Research Limited London, UK 10.12688/f1000research.166989.3 Research Article Articles Fracture resistance of nanocomposite 3D-printed resins designated for teeth fabrication: An in vitro analysis before and after thermal aging

[version 3; peer review: 3 approved with reservations, 2 not approved]

 Y. Alshaikhnasser Farah Conceptualization Data Curation Investigation Methodology Writing – Original Draft Preparation 1 Y. Alboryh Shaymaa Data Curation Formal Analysis Investigation Methodology Writing – Original Draft Preparation 1 H. Al Dawood Zainab Formal Analysis Funding Acquisition Investigation Methodology Validation Writing – Original Draft Preparation 1 F. Almedarham Rawan Data Curation Formal Analysis Funding Acquisition Methodology Writing – Original Draft Preparation Writing – Review & Editing 1 A. Alhassan Fatimah Data Curation Funding Acquisition Investigation Methodology Visualization Writing – Original Draft Preparation 1 M. Alatiyyah Fatimah Data Curation Formal Analysis Software Supervision Writing – Original Draft Preparation Writing – Review & Editing 2 3 A. Nassar Essam Formal Analysis Investigation Methodology Supervision Writing – Original Draft Preparation Writing – Review & Editing 4 Akhtar Sultan Formal Analysis Funding Acquisition Methodology Writing – Original Draft Preparation Writing – Review & Editing 5 Q. Khan Soban Data Curation Formal Analysis Methodology Software Validation Writing – Original Draft Preparation https://orcid.org/0000-0002-8573-3080 6 A. Balhaddad Abdulrahman Formal Analysis Methodology Resources Software Writing – Original Draft Preparation Writing – Review & Editing https://orcid.org/0000-0001-6678-7940 7 Tharwat Al Ammary Ahmed Investigation Methodology Supervision Visualization Writing – Original Draft Preparation Writing – Review & Editing 3 M. Gad Mohammed Conceptualization Investigation Methodology Writing – Original Draft Preparation Writing – Review & Editing https://orcid.org/0000-0003-3193-2356 a 8 College of Dentistry, Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia Department of Genetic Research, Institute for Research and Medical Consultations (IRMC), Imam Abdulrahman Bin Faisal University, Dammam, Eastern Province, Saudi Arabia Assistant Professor of Operative Dentistry Department, Faculty of Dental Medicine, Al-Azhar University College for Boys' Faculty of Dental Medicine Assiut, Asyut, Assiut Governorate, Egypt Department of Preventive Dental Sciences, College of Dentistry, Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia Department of Biophysics Research, Institute for Research and Medical Consultations (IRMC), Imam Abdulrahman Bin Faisal University Institute for Research and Medical Consultations, Dammam, Eastern Province, Saudi Arabia Department of Dental Education, College of Dentistry, Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia Department of Restorative Dental Sciences, College of Dentistry, Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia Department of Substitutive Dental Sciences, College of Dentistry, Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia mmjad@iau.edu.sa

No competing interests were disclosed.

 23 3 2026 2025 14 894 10 3 2026 Copyright: © 2026 Y. Alshaikhnasser F et al. 2026 This is an open access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The author(s) is/are employees of the US Government and therefore domestic copyright protection in USA does not apply to this work. The work may be protected under the copyright laws of other jurisdictions when used in those jurisdictions. Background:

this study was to evaluate the fracture resistance and elastic modulus of modified 3D-printed resins containing zirconium dioxide nanoparticles (ZNPs) and silicon dioxide nanoparticles (SNPs).

 Methods:

Tooth-colored 3D-printed resin samples (ASIGA (AS)) and NextDent (ND)) were modified with silanized ZNPs and SNPs. Five groups (n=100) were prepared for each resin type, one without nanoparticles, and four groups (n=20 per group) with varying nanoparticles concentrations (0.5 wt. %ZNP, 1 wt.%ZNP, 0.5 wt.%SNP, and 1 wt.%SNP). Half of the specimens (110 samples) were subjected to thermal aging (TA; 5000 cycles). The fracture resistance and elastic modulus were evaluated, followed by Fourier-transform infrared and scanning electron microscopy analyses. An analysis of variance and Tukey’s post-hoc test were applied for data analysis.

 Results:

Incorporating SNPs and ZNPs into the ND material significantly improved the fracture resistance compared to that of the control group, with 1 wt.%SNP showing the highest resistance (1405.9±128.4 N) and 0.5 wt.%ZNP the lowest (1047.5±100.6 MPa). However, the elastic modulus decreased notably with these additions, with the ND control group (3097.5±115.9 MPa) exhibiting the highest elastic modulus and ZNP groups (1772.0±128.8 MPa) exhibiting the lowest. In between NPs-reinforced groups per NPs type, there were no significant differences between SNPs groups (p=0.064) as well as ZNPs groups (p=0.072). For the AS material, similar enhancements in fracture resistance occurred; however, reductions in the elastic modulus were more significant in the ND material (p<0.001*). For the AS material, SNP and ZNP addition improved fracture resistance relative to that of the control group. Post-TA, the elastic modulus significantly decreased in both the ND and AS materials (p < 0.05). Compared to ND material, the increase in fracture resistance was less pronounced in the AS material.

 Conclusion:

The addition of ZNPs and SNPs increased the fracture resistances of both materials. TA significantly reduced the fracture resistance and elastic modulus in most NP-incorporated groups. The ASIGA resin demonstrated superior performance and enhancements were more prominent which demonstrates promising characteristics for clinical use.

 3D printing; thermal aging; nanoparticles; fracture resistance; resin teeth The author(s) declared that no grants were involved in supporting this work. Amendments from Version 2

According to reviewer comments, all comments were addressed and modified mainly in the methods and discussion section.  all major modifications were changed using track changes and highlighted through the text. In addition to the added references with references reordered in the discussion and references section.

 Introduction

Artificial teeth for removable dentures are manufactured from various materials, including acrylic resin, ceramics, 3D-printed materials, and resin composites. 1, 2 These artificial teeth must be durable enough to withstand fractures induced by contact with the opposing teeth and abrasive foods. 2, 3 Conventionally, prefabricated denture teeth are made of acrylic resin, making them prone to fracture or chipping, particularly in situations in which a complete denture opposes natural teeth or an implant-supported overdenture. 4– 6 With growing demand for artificial teeth with enhanced fracture resistance, various approaches have been proposed, including the use of different monomers, cross-linking agents, and organic and inorganic fillers in polymer matrices. 7, 8 Despite these advancements, denture-teeth fractures continue to be a persistent issue, highlighting the need for the development of denture teeth fabricated using innovative methods capable of withstanding higher loads and forces. 8, 9

Digital dentures can be produced by using subtractive or additive manufacturing techniques. 3 In the additive process, a photopolymerized liquid resin is used to build removable prostheses layer-by-layer. 3, 4, 10 This method offers several benefits, including the significantly lower cost of 3D printers compared with milling machines, which facilitates its broader adoption in clinical practice. 3 Additionally, unlike subtractive milling, 3D-printing generates less material waste. 3, 11, 12 Occlusal stability, function, and esthetics are all reduced when the fracture resistance and elastic modulus of denture teeth are compromised, which is why high strength is crucial. 7, 8, 13 Moreover, 3D-printed denture teeth are typically manufactured from methacrylate-based photopolymerized resin, a material specifically designed for processing through 3D-printing technology. 11– 14 This method provides flexibility and precision, and improves functionality in the fabrication of removable dentures, making it a modern alternative to traditional techniques. Further advancements in digital dentistry are needed to further enhance the quality and durability of dental prostheses. 8, 14

Gad et al., 8 studied the fracture resistance of a specific type of 3D-printed teeth (NextDent), and showed that they exhibited greater fracture resistance than traditional prefabricated teeth. However, their strength decreased after exposure to thermal cycling. Similarly, Chun et al., 10 examined another variety of 3D-printed resin teeth (Dentca) and reported that their fracture resistance was comparable to that of prefabricated teeth. These studies 8, 10 identified the potential of 3D-printed resins and highlighted the need to improve their strength, especially after thermal aging (TA). The absence of nanoparticle (NP) reinforcement in previous research left a gap in the exploration of how NPs can enhance durability. 13 Therefore, exploring the incorporation of different NPs may be an effective approach for improving the mechanical properties of 3D-printed resin teeth.

Owing to the capacity of 3D-printed resins for reinforcement, zirconium dioxide nanoparticles (ZNPs) and silicon dioxide nanoparticles (SNPs) have attracted considerable interest. When added to a resin matrix, ZNPs, which are well known for their antibacterial properties, increase the mechanical strength and wear resistance of dental composites. 4, 13– 16 Similarly, SNPs enhance the hardness, fracture toughness, and elastic modulus of dental materials owing to their large surface area and compatibility with resin matrices. 15 By resolving the drawbacks of conventional materials, previous studies 4, 13 have shown that the addition of these NPs to interim resins has yielded encouraging results, resulting in long-lasting and resilient interim restorations.

The vitro testing of NP addition, with a shape that replicates clinical use through a standardized procedure, may provide valuable insights into material-specific properties that are critical for understanding their behavior. The addition of NPs to 3D printed resins was investigated in previous studies however, there is still a lack of information in the literature about the addition effect of ZNPs and SNPs with different concentrations to 3D printed resin designated for teeth fabrication. Up to author knowledge, no previous studies have thoroughly investigated the strength of 3D-printed nanocomposite teeth in comparison with prefabricated teeth; therefore, this study aimed to assess the fracture resistance and elastic modulus of newly introduced 3D-printed nanocomposite denture teeth before and after TA.

The study tested three null hypotheses: first, that incorporating zirconium dioxide (ZrO 2) and silicon dioxide (SiO 2) nanoparticles into 3D-printed denture-tooth resins would have no significant effect on their fracture resistance or elastic modulus; second, that thermal aging would not significantly influence these mechanical properties in any of the tested materials; and third, the interaction effect of variables has no significant effect on tested properties.

 Methodology

The sample size for this in vitro investigation was determined using data gathered from a prior study 8 that evaluated the mechanical characteristics of temporary crowns made of 3D-printed resin. The World Health Organization (Geneva, Switzerland) specified the formulae, and power analysis was used in the counting procedure. The study was conducted using a significance threshold of 5%, power of 80%, and marginal error of 5%. A total of 220 specimens were fabricated and subdivided as follows: 20 prefabricated teeth, 100 ASIGA, 100 NextDent. The prefabricated group (n = 20) consisted of mandibular molar teeth (Major Dent-V, MAJOR Prodotti Dentari S.P.A., Moncalieri (TO), Italy). For the printed groups, two types of photopolymerized resins were used to create the 3D-printed resin teeth (n = 100/resin): NextDent C&B MFH (NextDent, 3D Systems, Soesterberg, The Netherlands) and ASIGA (Asiga DentaTOOTH, Shade A1, ASIGA, Erfurt, Germany). Half of the prepared specimens (N = 110) were tested without thermocycling while another half (N = 110) were tested after thermocycling.

In this study, 3D-printed groups were reinforced with two types of NPs: ZNPs (Shanghai Richem International Co., Ltd., Shanghai, China) and SNPs (AEROSIL R812; Evonik-Degussa, Essen, Germany). Each NP type was incorporated into the resin fluid at two different concentrations (0.5 wt.% and 1 wt.%). The NPs were treated and silanized before being added to the resin. 13, 15, 16 The silanized NPs were carefully weighed using a digital balance (S-234; Denver Instruments, Gottingen, Germany) to ensure precise measurements. 15, 16 Subsequently, the resin/NP mixtures were thoroughly mixed using a magnetic stirrer for 30 min to ensure the homogeneity of the NPs within the resin matrix. 13 A total of five groups were prepared for each resin type: one control group without any reinforcement, and four experimental groups containing varying NP concentrations (0.5 wt.% ZNP, 1 wt.% ZNP, 0.5 wt.% SNP, 1 wt.% SNP). This design enabled a comprehensive evaluation of the effects of both the NP type and concentration on the mechanical performance of 3D-printed resin.

A standard tessellation language (STL) file was created by scanning the prefabricated mandibular molar teeth standardized to the dimensions of the mandibular molar (10.2 × 11.1 × 7.3 mm). Each STL file was printed in a horizontal orientation (0° build angle) with a desktop laser scanner (E3; 3Shape A/S, Copenhagen, Denmark), and the file was then exported to the respective 3D printer. 8 Each specimen was manufactured in a 3D-printer chamber in accordance with the digital blueprint and required standards. 8, 13 The manufacturer’s guidelines for the NextDent 5100 (3D Systems, Rock Hill, SC, USA) and ASIGA MAX (Asiga, Alexandria, NSW, Australia) 3D printers were followed to accurately convert the resin material into the specified dental components. All specimens were fabricated using two different additive manufacturing systems according to the manufacturer-recommended printing protocols. The first group was printed using the ASIGA MAX, which operates using digital light processing (DLP) technology with a 385-nm UV light source. Specimens were printed with a layer thickness of 50 μm, and the exposure parameters were automatically controlled through the printer’s validated resin profile to ensure consistent polymerization for each layer. The second group was fabricated using a NextDent 5100 with a 405-nm UV LED light source. Printing was performed using a 50 μm layer thickness, and the exposure time was set at approximately 5–6 s per layer according to the manufacturer’s resin profile for denture base materials. Once printing was completed, the specimens underwent post-processing using the post-curing units of each printing system with the recommended post-curing process and conditions. 13, 15, 16 The post-polymerization protocol for ND was using curing unit (LC-D Print Box, 3D systems Vertex Dental B.V., Soesterberg, Netherland) for 15 min with wavelength measured 360–435 nm and ASIGA underwent for (Asiga Flash UV Curing Chamber) for 20 min with wavelength 480–530 nm. After curing, a diamond disc was used to remove the support structure. Half of the specimens (N = 110) were subjected to 5000 TA cycles at 5°C and 55°C with a dwell time of 30 s ( Figure 1). The TA process was performed using a Thermocycler (Thermocycler THE- 1100, Mechatronik GmbH, Feldkirchen-Westerham, Germany), simulating intraoral temperature changes for six months of clinical use. 13, 17

Diagram illustrating the study design.

A stainless-steel ball indenter with a 7 mm radius was used to load the specimens at the occlusal surfaces using a universal testing apparatus (Instron model 5965, Massachusetts, United States) with a 5 kN load cell at a loading rate of 1 mm/min until failure occurred ( Figure 1). A 1.5 mm-thick rubber sheet was positioned between the occlusal surface and indenter to reduce contact damage and aid in distributing the load. 13, 17

Fracture resistance was recorded as the maximum load at fracture and expressed in Newtons (N). The elastic modulus was calculated from the linear portion of the load–deflection curve obtained from the universal testing machine using the following formula: (E = FL 3/4Ybd 3) Where: E = elastic modulus (MPa), F = applied load (N), L = span length (mm), b = specimen width (mm), d = specimen thickness (mm), Y = deflection (mm).

Essential data on the fracture behaviour of the modified 3D-printed denture teeth were obtained through fracture-site analysis using scanning electron microscopy (SEM; TESCAN VEGA3 LM model, TESCAN Orsay Holding, Kohoutovice, Czech Republic). To ensure optimal image quality, the fractured samples were cleaned and prepared by coating nonconductive polymer or resin materials with a thin layer of conductive gold (Quorum, Q150R ES, UK). This coating, applied at an accelerating voltage of 20 kV, prevented charging effects and enhanced image clarity. The specimens were then placed in the SEM chamber for analysis, where fracture surfaces were examined at a magnification of 2000× with a scale bar of 50 μm. Key fracture characteristics such as initiation sites, crack-propagation patterns, and interactions between the polymer matrix and reinforcing particles were identified. The NPs, with an average size of 40 nm and surface area of 9 m 2/g, were analyzed using both SEM and transmission electron microscopy (TEM).

Fourier transform infrared (FTIR) analysis is an essential tool for examining the bonding interactions between NPs and the polymer matrix because it offers comprehensive details on the chemical structure and functional groups present in the material. FTIR analysis assisted in identifying any changes in the molecular bonding caused by the addition of NPs. The specimens were placed inside an FTIR spectrometer for transmission spectroscopy (Hartmann & Braun, MB series), and two readings were obtained per specimen. FTIR spectra were obtained at a resolution of 4 cm −1, spanning a wavenumber range of 4000 to 400 cm −1. The resultant spectra showed distinctive peaks corresponding to certain functional groups; thus, the bond types and any matrix chemical changes caused by the presence of NPs could be identified.

The means and standard deviations of the data were calculated for a descriptive analysis by using SPSS v.23. The normality of the data was assessed using the Shapiro–Wilk test, with nonsignificant results indicating that the data followed a normal distribution. Consequently, parametric tests were applied for an inferential analysis. A two-sample t-test was used to evaluate the effect of TA on fracture resistance. To explore the effects of the NP concentration on the fracture resistance and elastic modulus, a one-way analysis of variance (ANOVA) was performed. If the ANOVA results were significant, pairwise comparisons were conducted using Tukey’s post hoc test. A three-way ANOVA was used to examine the interaction effects of the NPs, their concentration levels, and their properties. Statistical significance was set at p < 0.05.

 Results

Table 1 shows the three-way ANOVA of the three variables (NP type, material type, and impact of TA) and their interactions for fracture resistance. The combined interaction effect showed a significant interaction only between TA and the material type (P < 0.001) while no significant when combined with other variables (P > 0.05).

Three-way ANOVA results of combined factors for fracture resistance (N).
Source Type III sum of squares df Mean square F P
Intercept 516513388.282 1 516513388.282 3087.313 <0.001 *
concentration * TA effect 651393.526 5 130278.705 0.779 0.566
concentration * material 1224234.417 4 306058.604 1.829 0.125
TA effect * material 8297039.229 1 8297039.229 49.593 <0.001 *
concentration * TA effect * material 1140271.465 4 285067.866 1.704 0.151
Error 33125781.671 198 167301.928
Total 582653174.952 220

Statistically significant at the 0.05 level of significance.

The fracture resistance results are summarized in Table 2 and Figure 2. For ND pre-TA, in comparison to pure resin, the addition of both SNPs and ZNPs significantly increased the fracture resistance (p < 0.001) except 0.5%ZNPs (p > 0.05) which showed the lowest fracture resistance value (1047.5 ± 100.6 N). In between NPs groups, SNPs showed significant increase compared to ZNPs while SNPs groups demonstrated an insignificant difference in fracture resistance compared to the prefabricated teeth (p > 0.05). For ND post-TA, in comparison to pure resin, the addition of both SNPs and ZNPs significantly increased the fracture resistance (p < 0.001) except 0.5%ZNPs (p > 0.05) which showed the lowest fracture resistance value (984.5 ± 81.9 N). In between NPs groups, 0.5 wt.% SNPs with the highest fracture resistance value (1387.1 ± 101.4 N) significantly showed an increase in the fracture resistance compared to all reinforced groups and demonstrated an insignificant difference in fracture resistance compared to prefabricated teeth (p > 0.05). In terms of the TA effect on ND, the fracture resistance was significantly decreased (P < 0.05) except the prefabricated (p = 0.087) and 0.5%SNP (P = 0.656).

Variations based on material and NP types and thermal aging (TA) effect on fracture resistance (N).
Materials NPs/% Pre-TA Post-TA P
Prefabricated - 1517.1 ±121.9 a 1221.6 ± 103.5 a 0.087
NextDent (ND) 0 (pure) 1097.8 ± 167.7 b 844.4 ± 136.8 c 0.032 *
0.5 wt.% SNPs 1357.5 ± 110.1 a 1387.1 ± 101.4 a 0.656
1 wt.% SNPs 1405.9 ± 128.4 a 1102.7 ± 114.8 b <0.001 *
0.5 wt.% ZNPs 1047.5 ± 100.6 b 984.5 ± 81.9 c 0.034 *
1 wt.% ZNPs 1209.1 ± 140.9 1050.1 ± 75.8 b 0.012 *
P <0.001 * 0.003 *
Prefabricated - 1517.1 ± 121.9 1221.6 ± 93.5 a 0.087
ASIGA (AS) 0 (pure) 2346.6 ± 162.9 a 1437.3 ± 101.7 b 0.001 *
0.5 wt.% SNPs 2192.2 ± 181.5 a 1352.9 ± 116.4 a 0.004 *
1 wt.% SNPs 2250.1 ± 168.6 a 1691.3 ± 110.8 b 0.005 *
0.5 wt.% ZNPs 2185.2 ± 117.8 a 1498.6 ± 156.3 b 0.003 *
1 wt.% ZNPs 2321.6 ± 171.3 a 1492.9 ± 118.2 b 0.009 *
P 0.031 0.042

Statistically significant at the 0.05 level of significance. The same lowercase alphabets in each column indicate statistical insignificance between the pairs. NP) nanoparticles, TA) thermal aging, NTA) no thermal aging.

 Fracture resistance of prefabricated and 3D-printed resins before and after thermal aging.

For ASIGA pre-TA, the pure resin exhibited the highest fracture resistance value (2346.6 ± 162.9 N). In comparison to pure resin, the addition of both SNPs and SNPs showed no insignificant increase in fracture resistance (p > 0.05). In between NPs groups, no significance was found between all groups (p > 0.05); however, all reinforced groups and the pure group showed a significant increase in fracture resistance compared to the prefabricated group which showed the lowest fracture resistance value (1517.1 ± 121.9 N).

For ASIGA post-TA, the results showed the same behavior before TA, no significant differences were found between groups (p > 0.05) except 0.5%SNPs which showed a decrease fracture resistance recorded the lowest value (1352.9 ± 116.4 N). In comparison to the prefabricated group, all reinforced groups showed a significant increase in fracture resistance (P < 0.001) except 0.5%SNPs (p = 0.921) and the prefabricated group showed the lowest fracture resistance value (1352.9 ± 116.4 N). In terms of the TA effect on ND, the fracture resistance was significantly decreased per respective group (P < 0.05) except for the prefabricated group (p = 0.087).

The statistical T-test analysis for fracture resistance in Table 3 highlights the material-specific differences per respective NP type and concentration. Pre-AT, ASIGA significantly showed an increase in the fracture resistance (p < 0.05). Post-TA, significant differences in the fracture resistance were observed between the ND and AS materials across all NP-incorporated groups (p < 0.05), except for the pure resin (p = 0.387) and 1 wt.% SNPs (p = 0.657) groups.

T-Test compression of fracture resistance (N) between 3D-printed materials.
Materials NPs/% NextDent (ND) ASIGA (AS) P
Pre-TA 0 (pure) 1097.8 ± 167.7 2346.6 ± 162.9 0.000 *
0.5 wt.% SNPs 1357.5 ± 110.1 2192.2 ± 181.5 0.004 *
1 wt.% SNPs 1405.9 ± 128.4 2250.1 ± 168.6 0.001 *
0.5 wt.% ZNPs 1047.5 ± 100.6 2185.2 ± 117.8 <0.001 *
1 wt.% ZNPs 1209.1 ± 140.9 2321.6 ± 171.3 <0.001 *
Post-TA 0 (pure) 1221.6 ± 103.5 1221.6 ± 93.5 0.387
0.5 wt.% SNPs 844.4 ± 136.8 1437.3 ± 101.7 0.003 *
1 wt.% SNPs 1387.1 ± 101.4 1352.9 ± 116.4 0.657
0.5 wt.% ZNPs 1102.7 ± 114.8 1691.3 ± 110.8 <0.001 *
1 wt.% ZNPs 984.5 ± 81.9 1498.6 ± 156.3 <0.001 *

Statistically significant at the 0.05 level of significance. NP) nanoparticles, TA) thermal aging, NTA) no thermal aging.

Table 4 shows the three-way ANOVA of the three variables (NP type, material type, and impact of TA) and their interactions for the elastic modulus. The results showed a significant interaction between all variables (P < 0.05) and when the three variables were combined (P = 0.007).

Three-way ANOVA results of combined factor for elastic modulus (MPa).
Source Type III sum of squares df Mean square F P
Intercept 619284785.339 1 619284785.339 4469.913 <0.001 *
concentration * TA effect 10514215.811 5 2102843.162 15.178 <0.001 *
concentration * material 2097194.635 4 524298.659 3.784 0.005 *
TA effect * material 918520.695 1 918520.695 6.630 0.011 *
concentration * TA effect * material 2031145.360 4 507786.340 3.665 0.007 *
Error 27431940.310 198 138545.153
Total 1013871903.958 220

Statistically significant at the 0.05 level of significance.

The elastic modulus results are summarized in Table 5 and Figure 3. The prefabricated teeth significantly showed the highest elastic modulus values pre-TA (5002.0 ± 172.8 MPa) and post-TA (4255.5 ± 100.5 MPa). For ND pre-TA, the addition of SNPs and ZNPs significantly decreased the elastic modulus when compared with the pure resin (p < 0.001) and the lowest elastic modulus value was recorded with 1%ZNPs (1772.0 ± 128.8 MPa). In between NPs-reinforced groups per NPs type, there were no significant differences between SNPs groups (p = 0.064) as well as ZNPs groups (p = 0.072). When comparing NPs type, ZNPs showed a significant decrease in elastic modulus and the highest elastic modulus value was found with 1%SNPs (2048.2 ± 132.8 MPa) and the lowest values with 1%ZNP (1772.0 ± 128.8 MPa). For ND post-TA, in comparison to the prefabricated group, the elastic modulus of pure and NP-modified groups were significantly decreased (P < 0.001). While no significant differences between the pure and NP-modified groups (p < 0.05) and the pure group showed the highest elastic modulus value (376.6 ± 35.6 MPa). In terms of the TA effect, the elastic modulus of prefabricated, pure, and NP-modified groups was significantly decreased per respective NP type and concentration (p < 0.05).

Variations based on material and NP types and thermal aging (TA) effect on elastic modulus (MPa).
Materials NPs/% Pre-TA Post-TA P
Prefabricated - 5002.0 ± 172.8 4255.5 ± 100.5 0.002 *
NextDent (ND) 0 (pure) 3097.5 ± 115.9 376.6 ± 35.6 a <0.001 *
0.5 wt.% SNPs 1951.9 ±147.3 a,b 370.2 ± 36.4 a <0.001 *
1 wt.% SNPs 2048.2 ± 132.8 a 357.3 ± 31.9 a <0.001 *
0.5 wt.%ZNPs 1891.1 ±112.5 b,c 364.5 ± 35.1 a <0.001 *
1 wt.% ZNPs 1772.0 ± 128.8 c 359.8 ± 21.8 a <0.001 *
P <0.001 * <0.001 *
Prefabricated - 5002.0 ± 172.8 4255.5 ± 102.5 0.002 *
ASIGA (AS) 0 (pure) 2725.2 ± 115.3 a 2364.1 ± 42.2 a <0.001 *
0.5 wt.% SNPs 1951.1 ± 161.9 b 376.3 ± 25.6 a 0.001 *
1 wt.% SNPs 2608.1 ± 94.1 a 345.8 ± 91.5 a <0.001 *
0.5 wt.% ZNPs 2639.0 ± 93.0 a 362.0 ± 29.3 a <0.001 *
1 wt.% ZNPs 2201.8 ± 108.1 b 390.0 ± 25.1 a <0.001 *
P <0.001 * <0.001 *

Statistically significant at the 0.05 level of significance. The same lowercase alphabets in each column indicate statistical insignificance between the pairs. NP) nanoparticles, TA) thermal aging, NTA) no thermal aging.

 Elastic modulus of prefabricated and 3D-printed resins before and after thermal aging.

For ASIGA pre-TA, the pure resin and NP-modified groups showed a significant decrease in elastic modulus when compared with the prefabricated group (p < 0.001). In comparison to the pure group, the addition of both NPs showed a significant decrease in elastic modulus with 0.5%SNP and 1%ZNPs and 0.5%SNPs showed the lowest elastic modulus value (1951.1 ± 161.9 MPa). While no significant differences between pure resin and other NP-modified groups (pure vs. 1%SNPs and pure vs. 0.5%ZNPs, p > 0.05). in between NP-modified groups, 1%SNPs and 0.5%ZNPs significantly showed higher elastic modulus compared with 0.5%SNPs and 1%ZNPs and the highest values were recorded with 0.5%ZNPs (2639.0 ± 93.0 MPa) followed by 1%SNPs (2608.1 ± 94.1 MPa). For ASIGA post-TA, the elastic modulus was significantly decreased in pure and NP-modified groups when compared with the prefabricated group (p < 0.001). While no significant differences between the pure and NP-modified groups (P > 0.05) and 1%ZNPs showed the highest elastic modulus value (390.0 ± 25.1 MPa). In terms of the TA effect, the elastic modulus of prefabricated, pure, and NP-modified groups was significantly decreased per respective NP type and concentration (p < 0.05).

The statistical T-test analysis for elastic modulus in Table 6 highlights the material-specific differences per respective NP type and concentration. Pre-AT, pure ASIGA significantly showed a decrease in the elastic modulus compared with pure NextDent (p = 0.003). While NP-modified ASIGA groups showed a significant increase in elastic modulus except at 0.5 wt.% SNPs (p = 0.998). Post-TA and Pre-AT, pure ASIGA significantly showed a decrease in the elastic modulus compared with pure NextDent (p = 0.032*). While no significant differences in the elastic modulus were observed between the ND and AS materials across all NP-incorporated groups (p > 0.05).

T-Test compression of elastic modulus (MPa) between materials.
Materials NPs/% NextDent (ND) ASIGA (AS) P
Pre-TA 0 (pure) 3097.5 ± 115.9 2725.2 ± 115.3 0.003 *
0.5 wt.% SNPs 1951.9 ± 147.3 1951.1 ± 161.9 0.998
1 wt.% SNPs 2048.2 ± 132.8 2608.1 ± 94.1 <0.001 *
0.5 wt.% ZNPs 1891.1 ± 112.5 2639.0 ± 93.0 <0.001 *
1 wt.% ZNPs 1772.0 ± 128.8 2201.8 ± 108.1 0.022 *
Post-TA 0 (pure) 4255.5 ± 100.5 2364.1 ± 42.2 0.032 *
0.5 wt.% SNPs 376.6 ± 35.6 376.3 ± 25.6 0.531
1 wt.% SNPs 370.2 ± 36.4 345.8 ± 91.5 0.712
0.5 wt.% ZNPs 357.3 ± 31.9 362.0 ± 29.3 0.809
1 wt.% ZNPs 364.5 ± 35.1 390.0 ± 25.1 0.070

Statistically significant at the 0.05 level of significance. NP) nanoparticles, TA) thermal aging, NTA) no thermal aging.

Figure 4 shows the entire range of the infrared spectrum, 4000–500 cm −1, demonstrating the bonding of AS and ND with different types of NPs at varied concentrations. The FTIR spectra of the AS and ND materials revealed characteristic bonds attributed to carbonyl groups. All the groups of specimens exhibit the C-H bond at approximately 2900 cm −1 and C=O double bond at approximately 1703 cm −1. The most significant difference between the AS and ND groups was observed in the spectral region of 1144–1034 cm −1 in the FTIR spectrum. This range corresponded to the stretching vibrations of the C–O–C (ether) functional group. The differences in this region indicate that the chemical environment or bonding characteristics of the C–O–C group vary, suggesting structural or compositional differences between the materials.

FTIR spectra of modified pure and nanoparticle-incorporated resins.

(A) Modified pure and nanoparticle-incorporated ASIGA specimens. (B) Modified pure and nanoparticle-incorporated NextDent specimens. The important bands are labelled in each set of specimens.

Figures 5– 7 display the SEM images of both the occlusal and fracture surfaces. The fracture behavior of the occlusal surface showed more crack propagation in the NP-reinforced groups than in the pure-resin smooth fracture and absence of cracks. Prefabricated teeth ( Figure 5) include a smooth occlusal surface and smooth fracture line. An additional note regarding 3D-printed teeth is the stepwise effect, representing printing layers on curved surfaces, such as cusp tips and cusp slopes ( Figures 6 and 7). While comparing the two groups, pure ND and AS exhibited deep and multiple cracks. NP- incorporated AS are showing multiple and long propagated crack as compared to NP- incorporated ND. These SEM findings are useful while evaluating the mechanical strength of two types of specimens. Some cracks followed the line between the printed layers, which may be a reason for the weakened strength of printed teeth compared with prefabricated teeth that showed a smooth occlusal surface (absence of the staircase effect). In the cross-sectional surface analysis, most of the groups reinforced with NPs showed a rough surface with some lamellae as well as prefabricated teeth, whereas the pure teeth showed a smooth fracture side. Compared with AS groups the ND cross-sections showed higher surface roughness with several lamellar surfaces as marked with white arrows ( Figure 7).

Representative SEM images of prefabricated teeth.

a) Occlusal surface, b) fracture surface. SEM magnifications are ×11 (a) and ×10 (b).

 Representative SEM images of 3D-printed teeth for both materials showing the occlusal surface.

SEM magnifications from top row left to right are: ×35, ×22, ×35, ×35, ×40 and bottom row left to right are: ×40, ×40, ×32, ×38, ×33.

 Representative SEM images of 3D-printed teeth for both materials showing the fracture surface.

The cracks propagations are highlighted with red arrows while lamella structures are marked with white arrows. SEM magnifications top row are: ×40 and bottom row left to right are: ×33, ×39, ×40, ×40, ×40.

 Discussion

The aim of this study was to examine the fracture resistance and elastic modulus of 3D-printed denture-teeth pre- and post-TA with the addition of ZNPs and SNPs to the 3D-printing resins. The first and second null hypotheses were rejected because of the significant effect of NP addition and TA on the fracture resistance and elastic modulus when compared with the prefabricated teeth. For third null hypothesis, for fracture resistance, the null hypotheses of no interaction between thermal aging and material type were rejected due to the presence of a statistically significant interaction effect (p < 0.05). However, the null hypotheses related to interactions involving nanoparticle concentration were accepted, as these interactions were not statistically significant (p > 0.05). Therefore, while nanoparticle incorporation demonstrated certain effects at the main factor level, its interaction with other variables did not significantly influence the measured outcomes under the tested conditions. These findings indicate that the observed changes in material performance were primarily associated with the combined influence of thermal aging and material type, rather than synergistic interactions involving nanoparticle concentration. These findings are consistent with previous investigations that demonstrated the reinforcing effects of nanoparticle incorporation on 3D-printed dental resins. For instance, Alshamrani et al. 22 and Alhotan et al. 23 reported that adding silica or zirconia nanoparticles significantly enhanced the mechanical and thermal stability of photopolymer resins. In contrast, Yan et al. 24 noted that higher nanoparticle concentrations could disrupt polymer cross-linking, reducing the elastic modulus. Our results align with these reports, highlighting the importance of maintaining optimal nanoparticle concentrations (0.5–1 wt%) to achieve a balance between strength and flexibility. Furthermore, compared with Gad et al., 8 who examined the strength of unmodified 3D-printed denture teeth, our findings show superior fracture resistance due to nanoparticle reinforcement, confirming the benefit of composite modification.

In this study, the incorporation of SNPs at varying concentrations into 3D-printed denture teeth increased the fracture resistance at immediate testing prior to TA in 3D-printed ND materials. This enhancement occurred by reinforcing the polymer matrix, which increased stiffness, reduced crack propagation, and boosted toughness through mechanisms such as crack deflection and energy dissipation. 18– 20 The findings of the present study agree with those of previous studies 13, 17, 20 that have examined the potential benefits of integrating low concentrations of SNPs into 3D-printed interim resins to enhance their flexural properties. These studies reported that the addition of SNPs can effectively strengthen the mechanical properties of 3D-printed ND materials. In addition, previous studies have investigated the fracture resistances of 3D-printed resins containing 0.5 and 1 wt.% SNP concentrations. 20 The results indicate that the addition of 1 wt.% SNP significantly improved the fracture resistances of both the ND and AS 3D-printed resins.

Based on previous studies, 13, 16, 17 ZNPs have been recommended for incorporation into dental composites to improve their mechanical qualities, as ZNPs are well known for their remarkable hardness and capacity to reinforce resin composites. This investigation demonstrates that ZNPs improve the fracture resistance of 3D-printed ND only at 1 wt.% before TA. The improvements in fracture resistance resulting from ZNP integration align with previous studies, demonstrating the ability of ZNPs to enhance the mechanical properties of polymer-based materials. 13, 16 The primary mechanism proposed in previous studies is the ability of ZNPs to interact with polymer chains, distribute applied stress, and inhibit fracture formation. 16 For the ND material, the enhancement in fracture resistance at 1 wt.% concentrations is attributed to the stiffening effect of zirconia, which reinforces the polymer matrix by promoting crack deflection and energy dissipation. 21, 22

Before TA, the ND resin exhibited a greater increase in fracture resistance than the AS resin when the same amount of SNPs was added. While both resins benefited from SNP addition, ND significantly increased the fracture resistance with 1 wt.%SNP. In comparison to previous study, the fracture resistance of AS was reported to be 1305.7 ± 197.4.8. In contrast, significantly higher values were observed in the current study, with AS showing a fracture resistance of more than 2,000 N with and without NPs. Similarly, the fracture resistance of ND in earlier study 8 was 867.8 ± 108.4, whereas in the present study, it was 1097.8 ± 167.7. This difference may be due to the stronger intrinsic mechanical qualities of AS, a potentially higher cross-linking density, and variations in matrix-nanoparticle compatibility, making it less dependent on external reinforcements than ND. 12– 14 This finding also supported by FTIR analysis with shifts in C–O–C regions suggesting polymer–filler bonding differences between AS and ND.

No significant differences were observed (p = 0.981) in a comparison between the prefabricated teeth and ZNP-AS. In contrast, although ZNPs were incorporated into the AS resin, the overall improvement in fracture resistance was not as significant as that in the ND. This is because of the better baseline mechanical characteristics of the AS resin, which inherently has a higher fracture resistance. Previous studies investigating the fracture strength of different dental materials have shown similar findings, in which resin materials with higher intrinsic fracture strengths demonstrate less improvement when reinforced with NPs. 19– 23

It is important to investigate the strength of dental materials following artificial aging as many products experience decay in their strength after aging. In this study, the effect of thermal stress on the mechanical properties of the materials revealed significant differences between the pure and NP-modified groups in their fracture resistance. In pure groups, thermal stress generally led to a substantial reduction in the fracture resistance. This reduction in fracture resistance is attributed to the development of micro-cracks and other defects arising from repeated expansion and contraction under temperature changes. 24 These internal stresses lead to material weakening, making the material more prone to fracture. Owing to the addition of the NPs, the thermal stress caused thermal stability in the nanocomposite materials to some extent, thereby sustaining the properties of the materials and maintaining their elastic modulus. 22– 24

Following TA, the 3D-printed resins with 1 and 0.5 wt.%SNP maintained superior mechanical properties and were comparable to the performance of traditional prefabricated resins and higher than pure control in ND 3D-printed resins. In AS 3D-printed resins, 0.5 wt.% of SNP revealed higher strength than the prefabricated teeth and the pure control. These findings indicate that the incorporation of an optimal amount of 0.5 wt.% concentrations can enhance the ability of 3D-printed interim restorations from the ASIGA and NextDent manufacturers to endure thermal stresses in the oral environment, positioning them as a feasible alternative to conventional prefabricated resins. 23 These findings suggest that while developing nanocomposite 3D-printed resins for dental applications, attention must be given to the concentration of incorporated ZrO 2 nanoparticles, as higher levels may compromise color stability following thermal aging and beverage exposure, potentially affecting both esthetic durability and clinical performance. 21, 25 Such findings agree with previous studies indicating that the addition of SNP increased the fracture resistances of 3D-printed resins even after TA. 17, 20 After TA in the ZNPs groups, the incorporation of 1 and 0.5 wt.% of ZNPs in ND 3D-printed resin was associated with higher fracture resistance than pure control but not prefabricated teeth. While in AS 3D-printed resins, ZNPs incorporation did not offer additional strength following TA compared to pure control, but the fracture resistance was higher than prefabricated teeth. Such findings may suggest that NPs in general as reinforcing particles could be preferred to improve the strength of dental materials. The results found in this study may indicate that the incorporated NPs were more effective in maintaining the fracture resistance of the 3D-printed resins when compared to the pure control and prefabricated teeth.

For the elastic modulus, all the groups experienced significant reduction in their elastic modulus pre-TA compared to the prefabricated teeth, suggesting that the addition of NPs may alter the stiffness of the polymer network. The highest elastic modulus in the ND control group (3097.5 ± 115.9 MPa) indicates that the base resin formulation provides higher rigidity, which is reduced upon NP incorporation. 12, 22 This decline aligns with the findings who reported that, while ZNPs enhanced flexural strength, excessive concentrations may disrupt polymer cross-linking, leading to reduced stiffness. Also, there is frequently a nonlinear relationship between the mechanical properties of composite materials and their filler content. 22 Such an explanation could be applied as well when the elastic modulus values of the SNPs groups are observed. However, our findings contraindicate other studies showing that the addition of 1 wt.% SNP significantly improved the elastic modulus of 3D-printed resins compared with the control groups without the NPs. 17, 20 This may suggest that other parameters could affect how NPs may influence the elastic modulus of dental materials. This study revealed that TA significantly reduced the elastic modulus for pure control and experimental groups of 3D-printed resins, and prefabricated teeth. This significant reduction is mainly related to the 3D-printed resins rather than the incorporated NPs. The significant reduction in elastic modulus observed after thermal aging can be attributed to several material-related mechanisms. The reduction in elastic modulus observed after thermal aging can be attributed to several degradation mechanisms affecting resin-based dental materials. Exposure to a moist environment and repeated thermal fluctuations promotes water diffusion into the polymer matrix, leading to plasticization of the resin network and a consequent reduction in stiffness. 26 Water molecules penetrate the polymer structure and act as internal plasticizers, weakening intermolecular forces and increasing chain mobility, which ultimately lowers the elastic modulus of the material. In addition, hydrolytic degradation and swelling of the resin matrix may generate stresses at the filler–matrix interface, facilitating filler debonding or microstructural deterioration, which further compromises the mechanical integrity of the material. 24, 26, 27 It has been widely reported that artificial aging methods, such as thermocycling and long-term water immersion can significantly alter the mechanical properties of dental resins, including reductions in elastic modulus due to these physicochemical changes. Moreover, water sorption has been shown to negatively affect the mechanical behaviour of denture polymers by reducing their stiffness and structural stability over time. 26, 27 In summary, the repeated thermal cycling induces microstructural stress and hydrolytic degradation within the resin matrix, leading to plasticization and the gradual breakdown of polymer cross-links. 24 Similar findings were reported by Yan et al., 24 and Alhotan et al., 23 who observed that prolonged exposure to alternating hot and cold temperatures compromises the molecular integrity of polymer-based materials. In addition, the incorporation of nanoparticles at higher concentrations may interfere with polymer chain mobility and cross-linking efficiency, resulting in a more brittle and less elastic network. 22 These findings suggest that both intrinsic polymer degradation and filler–matrix interactions contribute to the observed decline in stiffness after aging, highlighting the need for further optimization of nanoparticle content to balance strength and flexibility.

Another factor that could affect the strength of 3D printed resin within the fabrication procedures is the post-polymerization conditions. 28– 30 Post-polymerization conditions are critical determinants of the final physicochemical and mechanical properties of photopolymerized dental resins. 29 Parameters such as light intensity, exposure duration, wavelength, and post-curing temperature significantly influence the degree of conversion (DC) and cross-link density of the polymer network. 29– 31 An insufficient or suboptimal post-curing protocol may result in a lower DC and higher residual monomer content, which can compromise the stiffness and long-term mechanical stability of the material. In additively manufactured dental resins, variations in manufacturer-recommended post-curing protocols between materials may therefore contribute to differences in their mechanical behaviour. Furthermore, materials with lower cross-link density are more susceptible to water sorption and hydrolytic degradation during thermal aging, which can lead to plasticization of the polymer matrix and a consequent reduction in elastic modulus. 29– 31 Accordingly, optimized post-curing procedures improve polymerization efficiency and mechanical performance of 3D-printed resins, whereas inadequate post-polymerization may accelerate degradation and reduction in stiffness after aging. 29, 31, 32 Therefore, differences in post-curing protocols between the evaluated materials may represent a potential confounding factor affecting the observed changes in elastic modulus following thermal aging.

In this study, two fracture modes are identified: brittle and ductile. The fracture mode serves as a guide for the material strength and microstructural properties. 8, 9 According to SEM findings, the fracture resistance of denture teeth with a ductile fracture pattern before breakage was greater than that of teeth without this pattern, such as in the AS group. The weakened structure of the teeth, which enables them to support their weight for an extended period, appears to be the cause of such outcomes. 8 Notably, the NextDent groups exhibited more pronounced structural degradation and surface defects following thermal cycling and staining, indicating lower resistance to aging compared to other tested resins. 25 As the material ages or is subjected to elevated temperatures, its degradation rate significantly increases. This accelerated deterioration is often due to thermal-oxidative processes and molecular changes within the polymer matrix. The primary consequence is a progressive weakening of the crucial interfacial bond between the reinforcing fibers and the surrounding matrix. This compromised adhesion leads to a shift in failure mode, where fibers tend to pull out effortlessly from the matrix rather than remaining firmly anchored and fracturing within the material. 8, 9 This phenomenon was empirically confirmed by microscopic observations revealing smooth fiber surfaces, notably lacking the typical embedded nanoparticles or matrix material. Such an appearance is a clear indicator that the interface between the fiber and the matrix has catastrophically failed, suggesting a loss of chemical bonding, mechanical interlocking, and overall load transfer capability at the critical interface. 13 Similar to the findings of the current study, Chung et al., 9 showed that quasi-plastic materials exhibited a more gradual loss of strength than stiff materials. Furthermore, Gad et al., 8 illustrated that the scattered fractures in AS demonstrated that these materials have a stronger fracture resistance, which is further corroborated by their higher strengths. However, the ND materials showed a fracture mode that was characterized by an early failure dominated by brittle fractures and a lack of dispersed fractures. This implies that the strength threshold of the ND material is lower, resulting in early breaking without the progressive deformation observed in stronger quasi-plastic materials. The existence of brittle fracture modes in the ND material emphasizes the necessity of strengthening its mechanical characteristics to increase its resistance to fractures.

In general, SNPs demonstrated greater strength in ND than ZNPs, but both NPs (SNPs and ZNPs) had similar ASIGA values per concentration. This highlighted the significance of NP type selection and the type of resin to be reinforced. Based on the findings of this study, the use of the investigated nanocomposites in clinical applications has both potential benefits and limitations. The practical importance of this project lies in its potential to enhance the durability and lifetime of 3D-printed denture teeth. As this is the one of primary project investigated 3D printed nanocomposite resin for denture teeth, the results should be interpreted with caution. The observed improvements in fracture resistance suggest that these nanocomposites may reduce the risk of denture fractures in high-stress areas. However, the decline in the elastic modulus post-TA indicates potential limitations in structural stiffness and durability over time. Therefore, further optimization is recommended to mitigate the effects of TA.

The findings of this study suggest several potential clinical applications for nanocomposite 3D-printed resins in removable prosthodontics. The enhanced fracture resistance of the nanoparticle-reinforced materials—particularly those containing 0.5–1 wt.% SNP or ZNP indicates their suitability for fabricating denture teeth in situations where high occlusal loads are expected. Such cases include complete dentures opposing natural dentition or implant-supported overdentures, where conventional acrylic teeth are more prone to fracture and wear. Additionally, these reinforced 3D-printed resins could be beneficial for partial denture prostheses or interim restorations that require improved mechanical strength and dimensional stability over time. The lower elastic modulus observed, may contribute to a more favorable stress distribution under masticatory forces, potentially reducing the risk of debonding or microfracture at the tooth–base interface. From a clinical standpoint, the combination of digital fabrication precision and improved material durability positions these nanocomposite resins as a promising option for custom-made prostheses, particularly when individualized esthetics and load-bearing performance are priorities. Further in vivo studies are recommended to evaluate long-term outcomes, wear behavior, and bonding integrity under functional conditions.

Despite the important findings of this study, some limitations exist. First, the study focused solely on two types of NPs and did not investigate additional potentially helpful NPs that may improve the mechanical characteristics of 3D-printed materials. Second, the study evaluated a narrow range of NP concentrations, which may not have captured the complete range of interactions between the NPs and polymer matrix. Furthermore, the long-term impacts of environmental elements such as saliva and oral-temperature fluctuations were not assessed, which may affect the longevity of materials in real-world clinical settings. Besides, the absence of long-term aging and fatigue testing in this study presents significant limitations. Without long-term aging tests, critical data on the materials’ performance over extended periods is missing, which can lead to an overestimation of their lifespan and reliability. Additionally, fatigue testing is essential for identifying failure modes that may only emerge under repeated stress. Therefore, further investigations on the effects of different NPs with different percentages added to different tooth resins are required. In addition, performing all tests under similar oral conditions and environments. At the printing-technology level, further research is needed to fully understand the synergistic interactions between the NP content, 3D-printing parameters, and fracture resistance of these materials in dental applications.

 Conclusions

In conclusion, this study demonstrates that the incorporation of ZNPs and SNPs enhances the fracture resistance of the tested materials. TA significantly decreased the fracture resistances and elastic moduli of most of the NP-incorporated groups, except at certain NP concentrations in both materials. AS exhibited the most favorable fracture resistance profile under the tested conditions, suggesting the need for further in vivo investigation. Further optimization is recommended to mitigate the effects of TA.

 Ethics and consent

Ethical approval and consent were not required.

 Data availability

Dataset available upon request from the authors.

 Acknowledgements

Not applicable.

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Mater. 2018 Feb;34(2):192–200. 29110921 10.1016/j.dental.2017.10.003 PMC5801146 Gekle S Mayinger F Kreitmair U : Impact of different post-polymerization protocols on the material properties of three printed dental resins. J. Mech. Behav. Biomed. Mater. 2025 Dec;172:107164. 40829201 10.1016/j.jmbbm.2025.107164 10.5256/f1000research.197538.r470325 Reviewer response for version 3 Aly Yasser Mohamed 1 2 Referee https://orcid.org/0000-0001-9119-1145 Conservative Dentistry Department, Alexandria University Faculty of Dentistry (Ringgold ID: 110139), Alexandria, Alexandria Governorate, Egypt Oral Rehabilitation Sciences, Beirut Arab University (Ringgold ID: 67025), Beirut, Beirut Governorate, Lebanon

Competing interests: No competing interests were disclosed.

 10 4 2026 Copyright: © 2026 Aly YM 2026 This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. recommendation approve-with-reservations

Review report

The research topic is up to date, with a well-structured experimental framework and in vitro design. Many tests were performed, which reflect the effort placed into conducting such research.

Abstract:

     1- The sample allocation and consistency are not clear in the method, particularly the exact subgrouping in relation to the total sample size (sample allocation must be mathematically consistent).

    2- Half of the specimens were thermally aged; what about the other half being tested directly following the same grouping? This should be mentioned in a clear, straightforward way.

    3- Results are written in a systematic way and are clear for the readers; however, the values reported for fracture resistance for 3D-printed resins are mentioned in MPa, which is not logical. It should be in newtons (N) rather than MPa. This should be clarified and corrected, as in the literature the range for fracture resistance in MPa is 70 to 200 MPa, not in the thousands.

Introduction:

The introduction effectively establishes the clinical importance of fracture resistance in denture teeth and appropriately presents additive manufacturing (3D printing) as a modern alternative to conventional fabrication methods. It also recognizes thermal aging as a critical factor influencing material performance and introduces zirconia and silica nanoparticles as potential reinforcement agents with beneficial mechanical effects.

     1- The research gap is not stated clearly, particularly regarding what is currently present and the flaws that need to be enhanced or modified.

     2- The first two paragraphs are nearly the same; rephrasing to avoid repetition is necessary.

     3- Limited justification of study variables: The rationale for selecting specific nanoparticle types, concentrations, and materials is not clearly explained.

     4- The mechanical improvements associated with zirconia and silica nanoparticles are presented as universal outcomes without acknowledging that effects depend on factors such as concentration, dispersion, and material compatibility.

     5- The third null hypothesis describing interaction effects is vague and unclear and should specify which variables are interacting.

Methods:

The methodology demonstrates a structured experimental approach but lacks critical details regarding sample size justification, group allocation clarity, nanoparticle dispersion validation, and specimen standardization, which may affect reproducibility and internal validity.

Sample size estimation is not relevant to the current investigation. The authors have nearly two tested materials, then five testing parameters, each divided into two subgroups; ten specimens for each subgroup may not be adequate for generalization. Alternatively, the authors should mention similar studies regarding the number of groups and subgroups used for calculating their sample size.

    1- Although 220 specimens were reported, the distribution of samples among subgroups (control vs. nanoparticle groups, thermocycled vs. non-thermocycled) is not clearly described, making the experimental design difficult to follow.

    2- Lack of randomization description: The method does not state whether specimens were randomly assigned to groups, which raises concerns about selection bias.

    3- No control for nanoparticle dispersion quality: The method states mixing for 30 minutes but does not include verification techniques such as ultrasonication, SEM, or particle distribution analysis (more details regarding the silanization process and the mixing technique employed are needed).

    4- Critical parameters such as temperature range, dwell time, transfer time, and the number of cycles equivalent to clinical aging should be mentioned in this section.

    5- The rationale for dividing specimens into thermally aged and non-thermally aged groups is implied. However, considering that all artificial teeth intraorally will be subjected to oral cavity changes, please clarify why some specimens were not thermally aged.

Results:

The Results section presents extensive and useful data but suffers from limited integration of mechanical, microscopic, and spectroscopic findings, which reduces clarity and interpretability of the main outcomes.

Discussion:

The discussion mostly reports agreement with previous studies but does not critically analyze differences and rarely discusses methodological variations.

    1- Several mechanisms—such as water sorption, hydrolytic degradation, and thermal aging effects—are repeatedly described, resulting in an overly lengthy discussion that could be streamlined for clarity and focus.

    2- Insufficient consideration of confounding variables: Potential influences such as post-curing conditions, printing parameters, and degree of conversion are acknowledged but not fully controlled or quantitatively assessed, which may affect the interpretation of mechanical property changes.

Why were prefabricated teeth used in the current study without even mentioning how they were fabricated or which manufacturing technique was used, especially since the reported values of prefabricated teeth are much higher than those of the two 3D-printed resin teeth groups?

Is the work clearly and accurately presented and does it cite the current literature?

Yes

If applicable, is the statistical analysis and its interpretation appropriate?

I cannot comment. A qualified statistician is required.

Are all the source data underlying the results available to ensure full reproducibility?

No

Is the study design appropriate and is the work technically sound?

Partly

Are the conclusions drawn adequately supported by the results?

No

Are sufficient details of methods and analysis provided to allow replication by others?

Partly

Reviewer Expertise:

Prosthodontics, Material science related to my specialty. Digital and Implant dentistry

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

Gad Mohammed Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia

Competing interests: none

 13 4 2026

The research topic is up to date, with a well-structured experimental framework and in vitro design. Many tests were performed, which reflect the effort placed into conducting such research.

Response: We would like to express our sincere appreciation to the reviewers for their thorough evaluation of our manuscript and for the constructive comments provided. All suggestions were carefully considered and have been fully addressed in the revised version. The feedback greatly contributed to improving the clarity, scientific rigor, and overall quality of the study. We believe that the revisions made in response to the reviewers’ insights have strengthened the manuscript and enhanced its contribution to the field. We are grateful for the time and expertise invested in reviewing our work.

Abstract:

Comment 1- The sample allocation and consistency are not clear in the method, particularly the exact subgrouping in relation to the total sample size (sample allocation must be mathematically consistent).

Response: Thank you for your comment. sample allocations and distribution were revised and addressed in the abstract and methods as well as modified figure 1.

Comment 2- Half of the specimens were thermally aged; what about the other half being tested directly following the same grouping? This should be mentioned in a clear, straightforward way.

Response: Thank you for your comment. specimen distribution for TA and no TA was clarified and how the specimens aged or immediately tested were added to methods. Please, see highlighted parts in the thermal aging section in methodology.  

Comment 3- Results are written in a systematic way and are clear for the readers; however, the values reported for fracture resistance for 3D-printed resins are mentioned in MPa, which is not logical. It should be in newtons (N) rather than MPa. This should be clarified and corrected, as in the literature the range for fracture resistance in MPa is 70 to 200 MPa, not in the thousands.

Response: Thank you for your careful review and suggestions. The unit per tested property was revised and modified through the text, tables, and figures.

Introduction:

The introduction effectively establishes the clinical importance of fracture resistance in denture teeth and appropriately presents additive manufacturing (3D printing) as a modern alternative to conventional fabrication methods. It also recognizes thermal aging as a critical factor influencing material performance and introduces zirconia and silica nanoparticles as potential reinforcement agents with beneficial mechanical effects.

Comment 1- The research gap is not stated clearly, particularly regarding what is currently present and the flaws that need to be enhanced or modified.

Response: Thank you for this important comment. The research gap has been revised to more clearly distinguish between what is currently available in literature and the specific limitations that require further investigation. In the revised manuscript, we have clarified that previous studies have primarily evaluated nanoparticle incorporation in 3D-printed resins using simplified specimen geometries and without focusing on denture teeth applications or clinically relevant conditions. In addition, limited data is available regarding the effect of specific nanoparticles, such as ZNPs and SNPs, at different concentrations. Furthermore, direct comparisons with prefabricated denture teeth and the evaluation of material performance under simulated aging conditions remain insufficiently explored. These points have now been explicitly stated to better define the research gap and justify the aim of the present study. Please, see highlighted paragraph for research problems at the end of introduction

Comment 2- The first two paragraphs are nearly the same; rephrasing to avoid repetition is necessary.

Response: Thank you for your comment. The first two paragraphs have been carefully revised to eliminate repetition and improve clarity. While both paragraphs were retained to address distinct aspects the first focusing on denture teeth and the second on printing technology, the content has been refined to ensure smoother flow and better coherence between them.

Comment 3- Limited justification of study variables: The rationale for selecting specific nanoparticle types, concentrations, and materials is not clearly explained.

Response: We appreciate the reviewer’s comment and have clarified the rationale behind selecting the nanoparticle types, concentrations, and materials. In the revised manuscript, we explain that the chosen nanoparticles were selected based on published evidence demonstrating their ability to enhance the mechanical, physical, or antimicrobial properties of denture base resins. The concentration ranges were based on previous studies showing that low‑to‑moderate nanoparticle loading improves performance without causing agglomeration or negatively affecting printability. These explanations have now been added to strengthen the scientific basis of the study.

Comment 4- The mechanical improvements associated with zirconia and silica nanoparticles are presented as universal outcomes without acknowledging that effects depend on factors such as concentration, dispersion, and material compatibility.

Response: Thank you for this important comment. The introduction has been revised to clarify the mechanical effects of ZNPs and SNPs nanoparticles in terms of nanoparticle concentration, dispersion quality, surface treatment, and compatibility with the resin matrix.

Comment 5- The third null hypothesis describing interaction effects is vague and unclear and should specify which variables are interacting.

Response: Thank you for this important comment. We agree that the third null hypothesis required clarification. Accordingly, it has been revised to explicitly specify the interacting variables. The updated hypothesis now states that there is no significant interaction effect between nanoparticle type, nanoparticle concentration, and thermal aging condition on the fracture resistance and elastic modulus of the tested materials. This clarification has been incorporated into the manuscript to improve precision and readability.

Methods:

Comment: The methodology demonstrates a structured experimental approach but lacks critical details regarding sample size justification, group allocation clarity, nanoparticle dispersion validation, and specimen standardization, which may affect reproducibility and internal validity.

Response: Thank you for your valuable comments and recommendations, which have significantly strengthened the methodological quality of the study. In response, we have carefully revised the methodology section to address the raised concerns. Specifically, additional details have been provided regarding sample size considerations, clearer description of group allocation, clarification of nanoparticle dispersion procedures, and improved standardization of specimen preparation.

Comment: Sample size estimation is not relevant to the current investigation. The authors have nearly two tested materials, then five testing parameters, each divided into two subgroups; ten specimens for each subgroup may not be adequate for generalization. Alternatively, the authors should mention similar studies regarding the number of groups and subgroups used for calculating their sample size.

Response: We appreciate the reviewer’s observation regarding sample size estimation. In this study, the sample size was determined using data from a closely related published investigation that evaluated the fracture resistance of 3D‑printed denture teeth fabricated from the same resin system but without nanoparticle reinforcement. Because fracture resistance was also the primary outcome in our work, the mean and standard deviation reported in that study provided the most appropriate and directly comparable estimates of variability for calculating the minimum required sample size. Although the referenced study did not include nanoparticle‑modified groups, it examined the same material category, printing technology, and mechanical test, making it the closest available model for estimating variability in fracture resistance. This approach is commonly used in in‑vitro dental materials research when identical datasets are not available. The sample size calculation section has been revised and expanded to improve clarity and accuracy.

Comment 1- Although 220 specimens were reported, the distribution of samples among subgroups (control vs. nanoparticle groups, thermocycled vs. non-thermocycled) is not clearly described, making the experimental design difficult to follow.

Response: Thank you for this important comment. The distribution of specimens among the different subgroups has now been clearly clarified in the revised manuscript. Detailed descriptions of the grouping have been added to the methods sections. In addition, the study design figure and flowchart have been revised to visually illustrate the sample allocation and experimental workflow more clearly.

Comment 2- Lack of randomization description: The method does not state whether specimens were randomly assigned to groups, which raises concerns about selection bias.

Response: Thank you for your valuable comment. In the present study, specimen grouping was not based on random allocation but was predetermined according to nanoparticle type and concentration for each 3D-printed resin. Therefore, randomization was not applicable, as each group represented a specific experimental condition defined by the study design. All specimens were fabricated under standardized conditions to minimize variability and reduce potential bias.

Comment 3- No control for nanoparticle dispersion quality: The method states mixing for 30 minutes but does not include verification techniques such as ultrasonication, SEM, or particle distribution analysis (more details regarding the silanization process and the mixing technique employed are needed).

Response: Thank you for your comment. Regarding mixing procedures, we followed the previous studies adding NP to 3D printed resins. More details about adding NPs to fluid resins were added and supported with references. In addition to the details of silanization process. Please, see highlighted changes in the methodology.

Comment 4- Critical parameters such as temperature range, dwell time, transfer time, and the number of cycles equivalent to clinical aging should be mentioned in this section.

Response: Thank you for your valuable comment. all details about TC protocols added and supported with references

Comment 5- The rationale for dividing specimens into thermally aged and non-thermally aged groups is implied. However, considering that all artificial teeth intraorally will be subjected to oral cavity changes, please clarify why some specimens were not thermally aged.

Response: Thank you for this important comment. The inclusion of both thermally aged and non-thermally aged groups was intentional to allow a baseline evaluation of the material properties prior to aging and to enable direct comparison with post-aging performance. The non-thermally aged specimens represent the initial mechanical behavior of the materials immediately after fabrication, while the thermally aged groups simulate the effects of intraoral temperature fluctuations over time. This approach is widely used in in vitro studies to assess the extent to which aging influences material degradation. By comparing both conditions, it becomes possible to determine not only the absolute performance of each group but also the magnitude of change induced by thermal cycling. This is particularly important in the present study to evaluate whether nanoparticle incorporation improves not only the initial mechanical properties but also their stability after simulated oral aging. Accordingly, this design provides a more comprehensive understanding of material performance and durability under both baseline and simulated clinical conditions. More discussion about this point is added.

Results:

Comment: The Results section presents extensive and useful data but suffers from limited integration of mechanical, microscopic, and spectroscopic findings, which reduces clarity and interpretability of the main outcomes.

Response: Thank you for this valuable comment. We would like to clarify that the microscopic (SEM) and spectroscopic (FTIR) assessments in this study were conducted as qualitative, supportive analyses rather than quantitative outcome measures. Accordingly, these findings were presented descriptively in the Results section to complement and contextualize the mechanical data, rather than to provide statistical integration across methods. The interaction between mechanical performance, microstructural features, and chemical characterization was addressed in the Discussion section, where the relationships among these findings were synthesized and interpreted.

Discussion:

The discussion mostly reports agreement with previous studies but does not critically analyze differences and rarely discusses methodological variations.

Comment 1- Several mechanisms such as water sorption, hydrolytic degradation, and thermal aging effects are repeatedly described, resulting in an overly lengthy discussion that could be streamlined for clarity and focus.

Response: Thank you for this helpful comment. We agree that the discussion section contained repeated descriptions of water sorption, hydrolytic degradation, and thermal aging mechanisms. In response, we have revised the section to streamline the narrative, remove redundancies, and present these mechanisms more concisely. The revised Discussion now focuses on synthesizing how these degradation processes relate to the mechanical, microscopic, and spectroscopic findings, improving clarity and interpretability of the main outcomes.

Comment 2- Insufficient consideration of confounding variables: Potential influences such as post-curing conditions, printing parameters, and degree of conversion are acknowledged but not fully controlled or quantitatively assessed, which may affect the interpretation of mechanical property changes.

Response: We appreciate the reviewer’s thoughtful comment regarding potential confounding variables. In this study, factors such as post‑curing conditions and degree of conversion were addressed in the highlighted section in discussion, as the curing units used for the two resins differ in their manufacturer‑specified protocols. In contrast, parameters including layer thickness and printing orientation were fully standardized for both materials and therefore did not vary across groups. Because these conditions were controlled rather than treated as experimental variables, they were not considered confounding factors that could obscure the interpretation of the mechanical outcomes.

Comment: Why were prefabricated teeth used in the current study without even mentioning how they were fabricated or which manufacturing technique was used, especially since the reported values of prefabricated teeth are much higher than those of the two 3D-printed resin teeth groups?

Response: Thank you for this valuable comment. Prefabricated teeth were included in the present study as a reference group because they represent the most used materials in conventional denture fabrication and are considered a clinical benchmark for comparison. The primary objective was to compare the mechanical performance of 3D-printed denture teeth with materials currently used in routine clinical practice. Regarding their fabrication, prefabricated denture teeth are industrially manufactured under controlled conditions using highly cross-linked acrylic resins and optimized polymerization processes, which typically result in superior mechanical properties. This may explain the higher values observed compared to the 3D-printed groups. The manuscript has been revised to clarify the type and commercial source of the prefabricated teeth and to acknowledge their manufacturing characteristics as a factor influencing the results.

 10.5256/f1000research.197538.r473238 Reviewer response for version 3 Ibrahim Yomna M. 1 Referee https://orcid.org/0000-0002-4541-6304 Alexandria University, Alexandria, Alexandria Governorate, Egypt

Competing interests: No competing interests were disclosed.

 8 4 2026 Copyright: © 2026 Ibrahim YM 2026 This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. recommendation reject

The authors in this article address an interesting and timely topic, where the authors devised a method of improving fracture resistance of denture teeth through the addition of two types of ceramic nanoparticles. While the study shows potential and the general concept is of scientific interest, there are several major methodological and reporting concerns that need to be thoroughly addressed before the work can be considered for indexing.

Major points:

A) Abstract

1. In the background section, an introductory sentence that defines the problem should be added before the aim.

2. The study groups are missing the prefabricated teeth group (n=20). This group is mentioned later in figure 1, but it should be mentioned in the abstract.

B) Introduction

The introduction is properly arranged with suitable references from the literature.

C) Methods

1. The details of the silanization process should be mentioned along with the type and concentration of silane used.

2. The homogeneity of the mixture is doubtful as 30 minutes is not considered an enough time for dispersion of the particles. Also, the rpm of stirring is not mentioned along with the brand name of the magnetic stirrer. It is also recommended to use an ultrasonic bath to help disperse the particles which was not used in this study.

3. Please provide evidence that supports your choice of support removal to be after post-curing and not before. What did the manufacturers recommend concerning support removal?

4. A major flaw in this study is the calculation of elastic modulus using values obtained from fracture resistance and using an equation that calculates flexural modulus of bar shaped specimens. Please remove any mention of the elastic modulus calculations from all sections of the manuscript.

5. Please check the consistency of reporting the post-curing parameters as what is written in the methods section conflicts with that reported in figure 1.

6. The SEM magnification is mentioned as x2000 which is contradictory to the SEM figure legends mentioned later. Therefore, please omit the magnification and scale bar details mentioned in the text. Also, the SEM and TEM micrographs of the particles should be provided in the manuscript.

7. The FTIR data could have been used not only to report the bonds, but also to calculate the degree of conversion which would be a valuable addition to your study.

D) Results

The ND group was always reported first in all tests except the FTIR and SEM. Please ensure consistent reporting of the groups in all figures where ND is mentioned first followed by AS.

E) Discussion

On page 15, the last paragraph suggests different uses for the reinforced denture teeth which are not supported by evidence from this study. Using reinforced resin against natural teeth or implant supported restorations should be evaluated in terms of wear and abrasion resistance in order to draw such conclusions.

Minor points:

1. A revision of the English language is required.

2. On page 5, the third paragraph of the methods section, the STL file preparation and printing procedure should be rewritten.

3. In figure 1, the label states "interim crown", while it should be "denture tooth".

4. In figure 2, the unit for fracture resistance should be (N) not (MPa)

Is the work clearly and accurately presented and does it cite the current literature?

Yes

If applicable, is the statistical analysis and its interpretation appropriate?

Partly

Are all the source data underlying the results available to ensure full reproducibility?

Partly

Is the study design appropriate and is the work technically sound?

No

Are the conclusions drawn adequately supported by the results?

Yes

Are sufficient details of methods and analysis provided to allow replication by others?

Partly

Reviewer Expertise:

Dental Biomaterials, 3D printing, Nanotechnology, Materials testing

I confirm that I have read this submission and believe that I have an appropriate level of expertise to state that I do not consider it to be of an acceptable scientific standard, for reasons outlined above.

Gad Mohammed Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia

Competing interests: Non-Financial Competing Interests'

 13 4 2026

The authors in this article address an interesting and timely topic, where the authors devised a method of improving fracture resistance of denture teeth through the addition of two types of ceramic nanoparticles. While the study shows potential and the general concept is of scientific interest, there are several major methodological and reporting concerns that need to be thoroughly addressed before the work can be considered for indexing.

Response: We would like to express our sincere appreciation to the reviewers for their thorough evaluation of our manuscript and for the constructive comments provided. All suggestions were carefully considered and have been fully addressed in the revised version. The feedback greatly contributed to improving the clarity, scientific rigor, and overall quality of the study. We believe that the revisions made in response to the reviewers’ insights have strengthened the manuscript and enhanced its contribution to the field. We are grateful for the time and expertise invested in reviewing our work.

Major points:

A) Abstract

Comment 1. In the background section, an introductory sentence that defines the problem should be added before the aim.

Response: Thank you for your comment. The research problem was added to background before the aim of study.

Comment 2. The study groups are missing the prefabricated teeth group (n=20). This group is mentioned later in figure 1, but it should be mentioned in the abstract.

Response: thank you for your valuable comment. Group allocation and distribution was revised in the abstract and methodology.

B) Introduction

The introduction is properly arranged with suitable references from the literature.

Response: Thank you for your positive feedback.

C) Methods

Comment 1. The details of the silanization process should be mentioned along with the type and concentration of silane used.

Response: Thank you for your valuable comment. In response, we have now added full details regarding the type of silane, its concentration, and the application protocol used in our study. Specifically, we have clarified the brand and chemical composition of the silane coupling agent, the concentration supplied by the manufacturer, the surface preparation steps prior to silane application. These details have been incorporated into the Materials and Methods section to ensure transparency and reproducibility of the procedure.

Comment 2. The homogeneity of the mixture is doubtful as 30 minutes is not considered enough time for dispersion of the particles. Also, the rpm of stirring is not mentioned along with the brand name of the magnetic stirrer. It is also recommended to use an ultrasonic bath to help disperse the particles which were not used in this study.

Response: Thank you for your comment. We have revised the mixing protocol and more details added with cited references. Unfortunately, we don’t perform Ultrasonication we immediately again do shake for 1 hour before printing. But after reviewing the comments we found some articles recommended Ultrasonication and we added to study limitation and further recommendation. Please, see updated study limitations and further investigations

Comment 3. Please provide evidence that supports your choice of support removal to be after post-curing and not before. What did the manufacturers recommend concerning support removal?

Response: Thank you for this important comment. The timing of support removal remains controversial, with some studies suggesting removal before post-curing and others after. However, in the pre-cured “green state,” the resin is not fully polymerized. Therefore, manufacturers commonly recommend post-curing prior to support removal to ensure optimal mechanical properties and dimensional stability, as early removal may result in deformation and surface defects. Based on these recommendations, we followed the post‑curing‑first protocol to ensure dimensional accuracy, minimize surface defects, and maintain the mechanical integrity of the printed specimens. We have now clarified this rationale in the methodology as well as the details of post-curing steps sequence and conditions.

Comment 4. A major flaw in this study is the calculation of elastic modulus using values obtained from fracture resistance and using an equation that calculates flexural modulus of bar shaped specimens. Please remove any mention of the elastic modulus calculations from all sections of the manuscript.

Response: Thank you for your valuable comment and recommendations. We totally agree with you regarding EM calculations. We followed previous study investigated elastic modulus for 3-unit bridge instead of bar and we cited this reference to support our method. The calculation method was added based on reviewer comment and suggestion in Version 2. After reviewing, all related statements related to elastic calculation were deleted and one reference supported this measurement method was cited. Also, our research team suggested deleting elastic modulus to overcome the methodology flaw and we are waiting for your suggestion regarding this point.

Comment 5. Please check the consistency of reporting the post-curing parameters as what is written in the methods section conflicts with that reported in figure 1.

Response: Thank you for your valuable comment and recommendation. Figure 1 has been completely revised. We hope that the updated figure presents the workflow more clearly and in an easily understandable flowchart format

Comment 6. The SEM magnification is mentioned as x2000 which is contradictory to the SEM figure legends mentioned later. Therefore, please omit the magnification and scale bar details mentioned in the text. Also, the SEM and TEM micrographs of the particles should be provided in the manuscript.

Response: Thank you for your valuable comment. The discrepancy between the SEM magnification reported in the text and that presented in the figure legends has been carefully reviewed. Also, the magnification and scale bar details are deleted from the text.

Comment 7. The FTIR data could have been used not only to report the bonds, but also to calculate the degree of conversion which would be a valuable addition to your study.

Response: Thank you for your valuable comment. In this study, only a subset of specimens was randomly selected for FTIR analysis; therefore, the degree of conversion test could not be conducted comprehensively, as not all specimens were evaluated. This limitation has been acknowledged and included in the recommendations for future investigations.

D) Results

Comment The ND group was always reported first in all tests except the FTIR and SEM. Please ensure consistent reporting of the groups in all figures where ND is mentioned first followed by AS.

Response: Thank you for your observation. We appreciate the need for consistency in the presentation of groups across all figures. All figures have now been revised so that the ND group is consistently reported first, followed by the AS group, in alignment with the order used throughout the text.

E) Discussion

Comment On page 15, the last paragraph suggests different uses for the reinforced denture teeth which are not supported by evidence from this study. Using reinforced resin against natural teeth or implant supported restorations should be evaluated in terms of wear and abrasion resistance in order to draw such conclusions.

Response: Thank you for this important comment. We agree that the suggested clinical applications in the last paragraph were not directly supported by the scope of our laboratory tests. The study did not evaluate wear behavior, abrasion resistance, or interactions with natural teeth or implant‑supported restorations. In response, we have revised the paragraph to remove unsupported implications and have limited the conclusions strictly to the laboratory findings. Additional studies assessing wear, antagonist contact, and long‑term functional stresses will be necessary before proposing such clinical uses.

Minor points:

Comment 1. A revision of the English language is required.

Response: Thank you for your suggestions. The manuscript was thoroughly revised and edited. 

Comment 2. On page 5, the third paragraph of the methods section, the STL file preparation and printing procedure should be rewritten.

Response: Thank you for your comment. The STL file preparation and printing procedure in the third paragraph of the Methods section has been fully rewritten for clarity and improved methodological transparency. The revised text now provides a clearer description of the design workflow, STL export, slicing parameters, and printing steps to ensure consistency and reproducibility.

Comment 3. In figure 1, the label states "interim crown", while it should be "denture tooth".

Response: thank you for your careful review. Figure 1 has been completely revised.

Comment 4. In figure 2, the unit for fracture resistance should be (N) not (MPa)

Response: Thank you for your careful review. The figure was modified.

 10.5256/f1000research.197538.r470324 Reviewer response for version 3 Uzunoglu Ozyurek Emel 1 Referee https://orcid.org/0000-0001-5032-9996 Hacettepe University, Ankara, Turkey

Competing interests: No competing interests were disclosed.

 3 4 2026 Copyright: © 2026 Uzunoglu Ozyurek E 2026 This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. recommendation reject

Dear Authors,

Thank you for your submission.This manuscript addresses a relevant and timely topic in digital prosthodontics, namely the mechanical performance of nanoparticle-reinforced 3D-printed resins intended for denture tooth fabrication. The subject is potentially of interest. However, after carefully reviewing the manuscript, I do not consider it suitable for indexing in its current form. My concerns are not limited to presentation or language issues; they involve methodological clarity, analytical consistency, and interpretation of the findings.

My first major concern is the lack of clarity in specimen allocation. The manuscript states that a total of 220 specimens were fabricated, including 20 prefabricated teeth, 100 ASIGA specimens, and 100 NextDent specimens, and that half of the prepared specimens (N=110) were thermocycled while the other half were not. At the same time, the manuscript describes five groups for each resin type with n=20 per group, which accounts for 100 specimens per printed resin. However, the exact subgroup distribution remains unclear, particularly regarding how the prefabricated group was allocated within the thermal aging scheme and comparison structure. In addition, the manuscript does not clearly report how many specimens were used for each outcome. It is left to the reader to infer that fracture resistance and elastic modulus were derived from the same loading procedure, but this should be stated explicitly and unambiguously.

A second major concern is the statistical workflow, which is difficult to follow and appears internally inconsistent. In the Methods, the authors state that a two-sample t-test was used to evaluate the effect of thermal aging on fracture resistance, that one-way ANOVA was used to explore the effects of nanoparticle concentration, and that three-way ANOVA was used to examine interaction effects. However, thermal aging is already one of the main study factors and is also presented within the three-way ANOVA framework in the Results. As written, it is unclear which model represents the primary inferential analysis and why an additional t-test was required for an effect that should already be addressed within a multifactorial design. This lack of analytical clarity weakens confidence in the reported findings.

Another important methodological concern relates to the calculation of elastic modulus. According to the Methods, elastic modulus was derived from the load-deflection curve using a formula that appears to be based on beam-type assumptions. However, the tested specimens were anatomically shaped denture teeth loaded on the occlusal surface, not standardized bar-shaped specimens typically used for modulus determination. Under such conditions, the validity and interpretation of the calculated elastic modulus are questionable. Since this is presented as one of the main outcomes, this issue directly affects the reliability of an important part of the study.

The manuscript also contains unresolved inconsistencies in data presentation. One of the previous reviewers had already raised concern regarding the inconsistent reporting of fracture resistance/load units in N versus MPa. Although the authors responded to this point, the revised abstract still includes an apparent fracture resistance value reported in MPa instead of N. This indicates that the revision was not fully implemented and raises concern regarding the accuracy of the final reported data.

There is also inconsistency between the description of the protocol and the graphical presentation. Figure 1 presents a generalized post-curing scheme, whereas the Methods describe different post-curing procedures for the two printing systems. This discrepancy should be corrected because it creates uncertainty about the actual protocol followed.

With respect to interpretation, the study is appropriately framed around denture tooth fabrication rather than natural tooth behavior. However, the conclusions still seem broader than the design can support. A single-load fracture test combined with relatively short-term thermal aging may provide useful preliminary laboratory data, but it does not reproduce the full clinical service conditions of denture teeth, including fatigue loading, wear, water sorption, antagonist contact, and prosthesis-level functional stresses. Therefore, the conclusions should remain more cautious and restricted to laboratory material performance.

In addition, the role of SEM and FTIR analyses is not sufficiently integrated into the overall argument. Although these methods are included, the manuscript does not clearly explain how many specimens were analyzed, whether the evaluation was qualitative or quantitative, or how these findings mechanistically support the reported mechanical outcomes. At present, these analyses appear supplementary rather than essential to the interpretation of the results.

Finally, the manuscript still requires substantial language editing. Several sentences remain awkward, unclear, or grammatically problematic, particularly in the Results and Discussion sections. These issues further reduce readability and make the analytical logic more difficult to follow.

Overall, although the topic is potentially relevant, I am unable to support indexing of the manuscript in its current form. The concerns involve core aspects of study design, outcome validity, statistical analysis, consistency of revision, and interpretation, rather than minor editorial issues alone. For these reasons, I do not consider the manuscript suitable for indexing in its present version. 

Best regards

Is the work clearly and accurately presented and does it cite the current literature?

Yes

If applicable, is the statistical analysis and its interpretation appropriate?

No

Are all the source data underlying the results available to ensure full reproducibility?

No

Is the study design appropriate and is the work technically sound?

No

Are the conclusions drawn adequately supported by the results?

Partly

Are sufficient details of methods and analysis provided to allow replication by others?

No

Reviewer Expertise:

Endodontics

I confirm that I have read this submission and believe that I have an appropriate level of expertise to state that I do not consider it to be of an acceptable scientific standard, for reasons outlined above.

Gad Mohammed Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia

Competing interests: None

 13 4 2026

Dear Authors,

Thank you for your submission. This manuscript addresses a relevant and timely topic in digital prosthodontics, namely the mechanical performance of nanoparticle-reinforced 3D-printed resins intended for denture tooth fabrication. The subject is potentially of interest. However, after carefully reviewing the manuscript, I do not consider it suitable for indexing in its current form. My concerns are not limited to presentation or language issues; they involve methodological clarity, analytical consistency, and interpretation of the findings.

Response: We would like to express our sincere appreciation to the reviewers for their thorough evaluation of our manuscript and for the constructive comments provided. All suggestions were carefully considered and have been fully addressed in the revised version. The feedback greatly contributed to improving the clarity, scientific rigor, and overall quality of the study. We believe that the revisions made in response to the reviewers’ insights have strengthened the manuscript and enhanced its contribution to the field. We are grateful for the time and expertise invested in reviewing our work.

Comment: My first major concern is the lack of clarity in specimen allocation. The manuscript states that a total of 220 specimens were fabricated, including 20 prefabricated teeth, 100 ASIGA specimens, and 100 NextDent specimens, and that half of the prepared specimens (N=110) were thermocycled while the other half were not. At the same time, the manuscript describes five groups for each resin type with n=20 per group, which accounts for 100 specimens per printed resin. However, the exact subgroup distribution remains unclear, particularly regarding how the prefabricated group was allocated within the thermal aging scheme and comparison structure. In addition, the manuscript does not clearly report how many specimens were used for each outcome. It is left to the reader to infer that fracture resistance and elastic modulus were derived from the same loading procedure, but this should be stated explicitly and unambiguously.

Response: Thank you for your valuable comment. The specimen’s distribution and allocation were revised and updated. Please, see highlighted in the abstract.

Comment: A second major concern is the statistical workflow, which is difficult to follow and appears internally inconsistent. In the Methods, the authors state that a two-sample t-test was used to evaluate the effect of thermal aging on fracture resistance, that one-way ANOVA was used to explore the effects of nanoparticle concentration, and that three-way ANOVA was used to examine interaction effects. However, thermal aging is already one of the main study factors and is also presented within the three-way ANOVA framework in the Results. As written, it is unclear which model represents the primary inferential analysis and why an additional t-test was required for an effect that should already be addressed within a multifactorial design. This lack of analytical clarity weakens confidence in the reported findings.

Response: Thank you for your comment. Reason of using t-test and one-way ANOVA along with three-way ANOVA is to study the effect of single factor while keeping the other factors fixed or constant

Comment: Another important methodological concern relates to the calculation of elastic modulus. According to the Methods, elastic modulus was derived from the load-deflection curve using a formula that appears to be based on beam-type assumptions. However, the tested specimens were anatomically shaped denture teeth loaded on the occlusal surface, not standardized bar-shaped specimens typically used for modulus determination. Under such conditions, the validity and interpretation of the calculated elastic modulus are questionable. Since this is presented as one of the main outcomes, this issue directly affects the reliability of an important part of the study.

Response: Thank you for your valuable comment. We totally agree with you regarding the elastic modulus for bar-shape specimens. We calculated the specimen surface area and mentioned the dimension in methodology that was used to calculate the elastic modulus that generated during the fracture test. A previous study calculated the elastic modulus for anatomical crown (3-unit-bridge) using same methods we followed. Moreover, this part was modified based on reviewers’ recommendations. The reference was added to the method however this part was clarified at the end of discussion.

Comment: The manuscript also contains unresolved inconsistencies in data presentation. One of the previous reviewers had already raised concern regarding the inconsistent reporting of fracture resistance/load units in N versus MPa. Although the authors responded to this point, the revised abstract still includes an apparent fracture resistance value reported in MPa instead of N. This indicates that the revision was not fully implemented and raises concern regarding the accuracy of the final reported data.

Response: Thank you for your valuable comment. The manuscript has been carefully revised, and an error in the abstract regarding the reporting of fracture resistance (in N) has been corrected. In addition, the entire manuscript has been thoroughly reviewed to ensure consistency and accuracy in this regard.

Comment: There is also inconsistency between the description of the protocol and the graphical presentation. Figure 1 presents a generalized post-curing scheme, whereas the Methods describe different post-curing procedures for the two printing systems. This discrepancy should be corrected because it creates uncertainty about the actual protocol followed.

Response: Thank you for your valuable comment and recommendation. Figure 1 has been completely revised. We hope that the updated figure presents the workflow more clearly and in an easily understandable flowchart format

Comment: With respect to interpretation, the study is appropriately framed around denture tooth fabrication rather than natural tooth behavior. However, the conclusions still seem broader than the design can support. A single-load fracture test combined with relatively short-term thermal aging may provide useful preliminary laboratory data, but it does not reproduce the full clinical service conditions of denture teeth, including fatigue loading, wear, water sorption, antagonist contact, and prosthesis-level functional stresses. Therefore, the conclusions should remain more cautious and restricted to laboratory material performance.

Response: Thank you for your insightful comment. We agree that the experimental design, which involved a single-load fracture test and short-term thermal aging, reflects laboratory conditions and does not fully replicate the complex intraoral environment. Accordingly, the conclusions have been revised to be more cautious and limited to the interpretation of laboratory-based material performance. In addition, the limitations of the study have been clearly emphasized to acknowledge these factors and to avoid overgeneralization of the findings to clinical scenarios.

Comment: In addition, the role of SEM and FTIR analyses is not sufficiently integrated into the overall argument. Although these methods are included, the manuscript does not clearly explain how many specimens were analyzed, whether the evaluation was qualitative or quantitative, or how these findings mechanistically support the reported mechanical outcomes. At present, these analyses appear supplementary rather than essential to the interpretation of the results.

Response: Thank you for this insightful comment. SEM and FTIR analyses were included as complementary techniques to provide mechanistic insight into the observed mechanical behavior rather than as primary quantitative assessment methods. In the present study, a limited number of specimens were randomly selected from each group for SEM and FTIR evaluation; therefore, these analyses were conducted on a qualitative basis. SEM observations were used to examine surface morphology, fracture patterns, and nanoparticle dispersion, while FTIR analysis was employed to confirm chemical interactions and assess polymerization characteristics. Accordingly, their role was to support and help interpret the mechanical findings rather than to serve as standalone outcome measures. This clarification has been added to the methodology and discussion sections to better integrate these analyses within the overall study framework.

Comment: Finally, the manuscript still requires substantial language editing. Several sentences remain awkward, unclear, or grammatically problematic, particularly in the Results and Discussion sections. These issues further reduce readability and make the analytical logic more difficult to follow.

Response: Thank you for your suggestions. The manuscript was thoroughly revised and edited.

 10.5256/f1000research.190325.r462252 Reviewer response for version 2 ALTINTAŞ EYYÜP 1 Referee https://orcid.org/0000-0002-7767-9694 Yalçın Elif 1 Co-referee Firat University, Elâzığ, Elâzığ, Turkey

Competing interests: No competing interests were disclosed.

 4 3 2026 Copyright: © 2026 Yalçın E and ALTINTAŞ E 2026 This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. recommendation approve-with-reservations

Referee Report

This manuscript evaluates the effect of zirconium dioxide (ZNPs) and silicon dioxide nanoparticles (SNPs), incorporated at two concentrations (0.5 wt.% and 1 wt.%), into two 3D-printed denture tooth resins (NextDent and ASIGA). Mechanical performance was assessed through fracture resistance and elastic modulus testing before and after thermal aging (5000 cycles). SEM and FTIR analyses were additionally conducted to explore fracture behavior and potential chemical interactions within the reinforced systems.

The topic is timely and relevant, particularly within the expanding field of additive manufacturing in prosthodontics and nanoparticle reinforcement strategies. The factorial design, relatively large sample size (n = 220), and inclusion of both mechanical and microstructural analyses represent strengths of the study. Previous literature supports the importance of post-processing conditions and nanoparticle dispersion in influencing mechanical performance of photopolymerized dental resins (Revilla-León & Özcan, 2019 - Ref 1; Tahayeri et al., 2018 - Ref 2). However, several issues related to clarity of reporting, statistical interpretation, and methodological transparency must be addressed to ensure scientific robustness and reproducibility.

A primary concern relates to the inconsistency in reporting fracture resistance units. In some sections, fracture resistance is presented in Newton (N), whereas in others it is reported in MPa. Since the described mechanical protocol involves compressive loading using a universal testing machine, clarification is required as to whether the analyzed parameter represents fracture load (N) or calculated stress (MPa). If stress values were derived, the method of stress calculation—including area assumptions—must be explicitly described. Consistent unit reporting is essential for transparency and scientific validity, and this issue should be resolved.

Regarding statistical interpretation, the three-way ANOVA indicates that the interaction between thermal aging and material type is statistically significant, while interactions involving nanoparticle concentration are not consistently significant. Nonetheless, the manuscript emphasizes enhancement associated with nanoparticle incorporation in generalized terms. Interpretation should more closely reflect the statistical outcomes, distinguishing between significant main effects and non-significant interaction effects. The rejection of null hypotheses should be aligned precisely with the statistical evidence.

The substantial reduction in elastic modulus observed in the ND control group after thermal aging warrants deeper discussion. While thermal aging is expected to affect mechanical properties, the magnitude of the reported decline is notable. The authors are encouraged to confirm the calculation method for elastic modulus and expand discussion of potential degradation mechanisms. It is well established that post-polymerization conditions significantly influence degree of conversion and mechanical performance in photopolymerized resins (Revilla-León & Özcan, 2019 - Ref 1), and the differing post-curing protocols between materials may represent a confounding variable that should be discussed more explicitly.

An inconsistency between the narrative discussion and tabulated results should also be corrected. The manuscript indicates that the elastic modulus of prefabricated teeth did not significantly decrease after aging; however, the corresponding table suggests a statistically significant reduction. Alignment between textual interpretation and statistical data is essential.

Although many methodological parameters are reported, additional detail would enhance reproducibility. Clear explanation of how elastic modulus was determined, clarification of fracture resistance calculation, and expanded reporting of printing parameters (e.g., exposure settings, curing conditions) would improve transparency. Providing a concise table summarizing subgroup allocation—including aging distribution—would further improve clarity.

Finally, while summary statistics are provided, the underlying raw data are not included. Sharing individual specimen values as supplementary material would strengthen transparency and allow independent verification of the statistical analyses, consistent with principles of open scientific reporting.

Overall, this study contributes valuable data to the field of nanoparticle-reinforced 3D-printed denture materials. The experimental framework is generally appropriate, and the inclusion of SEM and FTIR analyses adds depth. The identified concerns primarily relate to clarity, statistical alignment, and methodological reporting rather than fundamental flaws in study design.

In conclusion, the manuscript is potentially suitable for indexing following revision. Clarification of unit consistency improved statistical interpretation, correction of textual inconsistencies, and enhanced methodological transparency are required to ensure that the work is scientifically sound and fully reproducible.

Recommendation: Approved with Reservations.

Is the work clearly and accurately presented and does it cite the current literature?

Partly

If applicable, is the statistical analysis and its interpretation appropriate?

I cannot comment. A qualified statistician is required.

Are all the source data underlying the results available to ensure full reproducibility?

Partly

Is the study design appropriate and is the work technically sound?

Partly

Are the conclusions drawn adequately supported by the results?

Partly

Are sufficient details of methods and analysis provided to allow replication by others?

Partly

Reviewer Expertise:

Prosthodontics; Digital Dentistry; Dental Biomaterials

We confirm that we have read this submission and believe that we have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however we have significant reservations, as outlined above.

References : Additive Manufacturing Technologies Used for Processing Polymers: Current Status and Potential Application in Prosthetic Dentistry. Journal of Prosthodontics .2019;28(2) : 10.1111/jopr.12801 146-158 10.1111/jopr.12801 : 3D printed versus conventionally cured provisional crown and bridge dental materials. Dental Materials .2018;34(2) : 10.1016/j.dental.2017.10.003 192-200 10.1016/j.dental.2017.10.003 Gad Mohammed Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia

Competing interests: No competing interests were disclosed.

 8 3 2026

Response to reviewer 2

This manuscript evaluates the effect of zirconium dioxide (ZNPs) and silicon dioxide nanoparticles (SNPs), incorporated at two concentrations (0.5 wt.% and 1 wt.%), into two 3D-printed denture tooth resins (NextDent and ASIGA). Mechanical performance was assessed through fracture resistance and elastic modulus testing before and after thermal aging (5000 cycles). SEM and FTIR analyses were additionally conducted to explore fracture behavior and potential chemical interactions within the reinforced systems.

The topic is timely and relevant, particularly within the expanding field of additive manufacturing in prosthodontics and nanoparticle reinforcement strategies. The factorial design, relatively large sample size (n = 220), and inclusion of both mechanical and microstructural analyses represent strengths of the study. Previous literature supports the importance of post-processing conditions and nanoparticle dispersion in influencing mechanical performance of photopolymerized dental resins (Revilla-León & Özcan, 2019 - Ref 1; Tahayeri et al., 2018 - Ref 2). However, several issues related to clarity of reporting, statistical interpretation, and methodological transparency must be addressed to ensure scientific robustness and reproducibility.

Response: Thank you for this constructive and encouraging comment. We appreciate the reviewer’s recognition of the relevance of the topic and the strengths of the study design. The manuscript has been carefully revised to improve clarity of reporting, statistical presentation, and methodological transparency. The statistical analysis and presentation of results have also been rechecked and clarified, and the tables have been revised to ensure consistent reporting and interpretation of statistical groupings. These revisions were implemented to enhance the scientific rigor, transparency, and reproducibility of the study.

Comment: A primary concern relates to the inconsistency in reporting fracture resistance units. In some sections, fracture resistance is presented in Newton (N), whereas in others it is reported in MPa. Since the described mechanical protocol involves compressive loading using a universal testing machine, clarification is required as to whether the analyzed parameter represents fracture load (N) or calculated stress (MPa). If stress values were derived, the method of stress calculation—including area assumptions—must be explicitly described. Consistent unit reporting is essential for transparency and scientific validity, and this issue should be resolved.

Response: Thank you for this important observation. We agree that consistent reporting of mechanical test outcomes is essential for clarity and scientific transparency. In the present study, the parameter evaluated was fracture load, which was recorded directly from the universal testing machine (Instron) as the maximum load at failure and expressed in Newtons (N) while the elastic modulus was calculated from the load–deflection data generated by the universal testing machine. Please, see highlighted added statements in methodology.

Comment: Regarding statistical interpretation, the three-way ANOVA indicates that the interaction between thermal aging and material type is statistically significant, while interactions involving nanoparticle concentration are not consistently significant. Nonetheless, the manuscript emphasizes enhancement associated with nanoparticle incorporation in generalized terms. Interpretation should more closely reflect the statistical outcomes, distinguishing between significant main effects and non-significant interaction effects. The rejection of null hypotheses should be aligned precisely with the statistical evidence.

Response: Thank you for this valuable comment regarding the interpretation of the statistical findings. We appreciate the reviewer’s attention to the alignment between statistical outcomes and their interpretation in the manuscript. The three-way ANOVA results were reviewed again to ensure accurate interpretation, particularly with respect to the interaction effects. Furthermore, the null hypotheses were revised and modified as well as the acceptance or rejection of the null hypotheses has been aligned explicitly with the statistical evidence obtained from the ANOVA analysis.

Comment: The substantial reduction in elastic modulus observed in the ND control group after thermal aging warrants deeper discussion. While thermal aging is expected to affect mechanical properties, the magnitude of the reported decline is notable. The authors are encouraged to confirm the calculation method for elastic modulus and expand discussion of potential degradation mechanisms. It is well established that post-polymerization conditions significantly influence degree of conversion and mechanical performance in photopolymerized resins (Revilla-León & Özcan, 2019 - Ref 1), and the differing post-curing protocols between materials may represent a confounding variable that should be discussed more explicitly.

Response: Thank you for this detailed and insightful comment. We acknowledge the reviewer’s concern regarding the notable reduction in elastic modulus observed in the ND control group after thermal aging. In response, the calculation method for elastic modulus was carefully rechecked and confirmed to be correct, derived from the linear portion of the load–deflection curve generated by the universal testing machine (Instron) according to standard three-point bending calculations. No errors in the measurement or analysis were identified. Additionally, the Discussion section has been expanded to address potential degradation mechanisms. The observed reduction in elastic modulus may be attributed to water sorption, plasticization of the polymer matrix, hydrolytic degradation, and weakening of intermolecular bonds within the resin network, all of which are known to compromise stiffness over time. We also explicitly discuss the role of post-polymerization conditions, including differences in light intensity, exposure duration, wavelength, and temperature, which can affect the degree of conversion and cross-link density. Suboptimal post-curing can result in lower monomer conversion and higher residual monomer content, which may exacerbate the reduction in mechanical properties during thermal aging. These additions provide a more comprehensive understanding of both intrinsic material degradation and potential confounding factors affecting the ND control group, in line with previously reported findings (Revilla-León & Özcan, 2019; Tahayeri et al., 2018; Stansbury & Idacavage, 2016).

Comment: An inconsistency between the narrative discussion and tabulated results should also be corrected. The manuscript indicates that the elastic modulus of prefabricated teeth did not significantly decrease after aging; however, the corresponding table suggests a statistically significant reduction. Alignment between textual interpretation and statistical data is essential.

Response: Thank you for this careful observation. We appreciate the reviewer for identifying this inconsistency. After re-examining the results and the corresponding table, we confirm that the elastic modulus of the prefabricated teeth showed a statistically significant reduction after thermal aging, as indicated in the tabulated data. The statement corrected in the Discussion.

Comment: Although many methodological parameters are reported, additional detail would enhance reproducibility. Clear explanation of how elastic modulus was determined, clarification of fracture resistance calculation, and expanded reporting of printing parameters (e.g., exposure settings, curing conditions) would improve transparency. Providing a concise table summarizing subgroup allocation—including aging distribution—would further improve clarity.

Response: thank you for your valuable comment. Measurement details were added to the methods section as well as more details about printing parameters. Regarding subgroups allocations, this was clarified in the methods sections.

Comment: Finally, while summary statistics are provided, the underlying raw data are not included. Sharing individual specimen values as supplementary material would strengthen transparency and allow independent verification of the statistical analyses, consistent with principles of open scientific reporting.

Response: thank you for your comment and recommendation. Raw data uploaded as a supplementary file

Comment: Overall, this study contributes valuable data to the field of nanoparticle-reinforced 3D-printed denture materials. The experimental framework is generally appropriate, and the inclusion of SEM and FTIR analyses adds depth. The identified concerns primarily relate to clarity, statistical alignment, and methodological reporting rather than fundamental flaws in study design.

Response: Thank you for this positive and constructive assessment of our work. The manuscript has been carefully revised to improve clarity of presentation, consistency in statistical reporting, and methodological transparency. Specifically, the Materials and Methods section has been expanded to provide clearer descriptions of specimen preparation, nanoparticle incorporation, and testing procedures. In addition, the statistical analyses and the presentation of results have been rechecked, and the tables and corresponding descriptions in the Results section have been revised to ensure proper alignment and clarity. These revisions were made to enhance the overall readability, reproducibility, and scientific rigor of the study.

Comment: In conclusion, the manuscript is potentially suitable for indexing following revision. Clarification of unit consistency improved statistical interpretation, correction of textual inconsistencies, and enhanced methodological transparency are required to ensure that the work is scientifically sound and fully reproducible.

Response: Thank you for this constructive evaluation and for considering the manuscript potentially suitable for indexing following revision. We appreciate the reviewer’s recommendations aimed at improving the scientific clarity and reproducibility of the work. In response, the manuscript has been carefully revised to address the points raised. Unit consistency has been corrected throughout the manuscript, particularly regarding the reporting of mechanical properties, to ensure uniformity and clarity. The statistical analyses and their interpretation have been rechecked, and the presentation of results in the text and tables has been revised to eliminate inconsistencies. Additionally, the Materials and Methods section has been expanded to provide clearer and more detailed descriptions of specimen preparation, nanoparticle incorporation procedures, and testing protocols, thereby enhancing methodological transparency and reproducibility. We believe that these revisions have strengthened the scientific rigor and overall clarity of the manuscript.

 10.5256/f1000research.184057.r414809 Reviewer response for version 1 Tosun Büşra 1 Referee Bolu Abant İzzet Baysal University Faculty of Dentistry, Bolu, Turkey

Competing interests: No competing interests were disclosed.

 30 9 2025 Copyright: © 2025 Tosun B 2025 This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. recommendation approve-with-reservations

1. Abstract

Although the abstract briefly presents the study's objective and key findings, it lacks numerical data on statistical significance (e.g., p-values). The absence of these values makes it difficult for readers to assess the strength and reliability of the reported outcomes.

The results section in the abstract mentions the general effects of nanoparticle incorporation, yet it fails to highlight which specific group demonstrated superior performance or in which material these enhancements were more prominent. This weakens the interpretability and impact of the findings.

The final sentence of the abstract should be revised to clearly express the clinical relevance of the study. For instance, a conclusive statement such as “The ASIGA resin appears to be more suitable for clinical use” would provide a more concrete and impactful takeaway.

2. Introduction

While the introduction demonstrates a comprehensive understanding of the topic, it does not adequately emphasize the study’s novelty or specific contribution to the existing literature. The authors should clearly state what research gap this study fills or what unique question it attempts to answer that has not been addressed previously.

The null hypotheses are technically stated but should be presented in a more concise and isolated format to enhance the logical clarity of the study's objectives and to ensure readers can easily identify the guiding assumptions of the research.

3. Materials and Methods

Although the sample dimensions, geometric shapes, and build orientations are partially described, further clarification is necessary to ensure the methodology is reproducible by other researchers. Detailed specifications are essential for standardization and transparency.

The post-curing protocol is briefly mentioned; however, critical technical parameters such as the type of light source (LED/UV), wavelength, and total curing duration are missing. These details should be explicitly included, as they significantly influence the mechanical behavior of photopolymer resins.

The statistical software used for the data analysis (e.g., SPSS, Jamovi) is not specified, nor is the exact strategy for data interpretation. Without this information, methodological transparency is compromised, and it becomes challenging to assess the validity of the statistical approach.

Although the text mentions that a power analysis was performed, there is no information about the effect size used, or whether a post hoc power analysis was conducted. Including these details would enhance the statistical rigor and reliability of the findings.

4. Results

The results are presented only in tabular format, without any supporting graphical representations such as bar charts or error bars. The lack of visual data summaries makes it more difficult for readers to quickly interpret the findings and compare group performances.

FTIR and SEM analyses are discussed within the text, but the associated figures are lacking essential annotations, such as peak labels, magnification levels, and explanatory captions. These omissions hinder the reader’s ability to critically evaluate the microstructural and chemical characterization data.

In the SEM section, terms like “crack propagation” and “lamellar surfaces” are briefly mentioned; however, the specific groups where these fracture patterns occurred are not clearly identified, nor are they visually indicated on the figures. This limits the clarity and scientific depth of the microstructural analysis.

5. Discussion

The discussion follows the literature reasonably well, but the comparisons remain superficial in several areas. Each key finding should be more critically analyzed in light of previous studies, with proper referencing to enhance the scholarly depth of the interpretation.

The discussion should more explicitly address which type of nanoparticle (ZNP or SNP) was more effective within which resin system (ASIGA or NextDent). Presenting these outcomes with clear material-specific insights would improve the applicability and specificity of the conclusions.

Clinical implications are not sufficiently discussed. The authors should elaborate on how these materials might be implemented in practice—such as which types of dentures or patient scenarios would most benefit from the enhanced properties of these nanocomposite resins.

The observed decrease in elastic modulus following thermal aging should be analyzed more thoroughly. Possible mechanisms such as network degradation or disruption of polymer cross-linking due to increased nanoparticle content should be hypothesized and supported with relevant references.

6. Figures and Tables

In the FTIR spectra, significant peaks should be clearly labeled, and the corresponding functional groups identified. This would improve the interpretability of the chemical bonding analysis.

Statistically significant differences between groups should be visually summarized using bar graphs with standard deviation/error bars and appropriate significance indicators (e.g., asterisks). This would allow readers to more quickly grasp the magnitude and relevance of the differences reported.

Recommendation: Major Revision

The manuscript addresses a relevant topic and presents valuable findings. However, significant improvements are required in data presentation, methodological transparency, and clinical interpretation. I recommend major revision before the manuscript can be considered for indexing.

Is the work clearly and accurately presented and does it cite the current literature?

Partly

If applicable, is the statistical analysis and its interpretation appropriate?

I cannot comment. A qualified statistician is required.

Are all the source data underlying the results available to ensure full reproducibility?

Partly

Is the study design appropriate and is the work technically sound?

Partly

Are the conclusions drawn adequately supported by the results?

Partly

Are sufficient details of methods and analysis provided to allow replication by others?

Yes

Reviewer Expertise:

Prosthodontics

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

Gad Mohammed Imam Abdulrahman Bin Faisal University College of Dentistry, Dammam, Eastern Province, Saudi Arabia

Competing interests: The authors declare no conflicts of interest

 20 10 2025

Response to reviewer comments

Recommendation: Major Revision

The manuscript addresses a relevant topic and presents valuable findings. However, significant improvements are required in data presentation, methodological transparency, and clinical interpretation. I recommend major revision before the manuscript can be considered for indexing.

Response: We sincerely thank the reviewer for their thoughtful evaluation and constructive feedback. We appreciate the recognition of the relevance of our topic and the value of our findings. In response to the reviewer’s comments, we have thoroughly revised the manuscript to enhance the clarity and transparency of data presentation, provide more detailed descriptions of the methodology, and strengthen the discussion of the clinical implications of our results. We believe these revisions have substantially improved the overall quality and interpretability of the manuscript.

1. Abstract

Comment: Although the abstract briefly presents the study's objective and key findings, it lacks numerical data on statistical significance (e.g., p-values). The absence of these values makes it difficult for readers to assess the strength and reliability of the reported outcomes.

Response: Thank you for your comment. P values added to the abstract

Comment: The results section in the abstract mentions the general effects of nanoparticle incorporation, yet it fails to highlight which specific group demonstrated superior performance or in which material these enhancements were more prominent. This weakens the interpretability and impact of the findings.

Response: Thank you for your comment. The most superior performance material is added

Comment: The final sentence of the abstract should be revised to clearly express the clinical relevance of the study. For instance, a conclusive statement such as “The ASIGA resin appears to be more suitable for clinical use” would provide a more concrete and impactful takeaway.

Response: Thank you for your comment and recommendation. The statement was revised.

2. Introduction

Comment: While the introduction demonstrates a comprehensive understanding of the topic, it does not adequately emphasize the study’s novelty or specific contribution to the existing literature. The authors should clearly state what research gap this study fills or what unique question it attempts to answer that has not been addressed previously.

Response: thank you for your comment.  the research gap added at the end of introduction and the clarifying of novelty was highlighted

Comment: The null hypotheses are technically stated but should be presented in a more concise and isolated format to enhance the logical clarity of the study's objectives and to ensure readers can easily identify the guiding assumptions of the research.

Response: Thank you for your valuable suggestion. The null hypotheses have been revised to appear in a clearer and more concise format, presented in a separate paragraph within the Introduction section

3. Materials and Methods

Comment: Although the sample dimensions, geometric shapes, and build orientations are partially described, further clarification is necessary to ensure the methodology is reproducible by other researchers. Detailed specifications are essential for standardization and transparency.

Response: Thank you for your valuable observation. Additional details regarding the specimen dimensions, geometric configuration, and build orientation have been added to the Materials.

Comment: The post-curing protocol is briefly mentioned; however, critical technical parameters such as the type of light source (LED/UV), wavelength, and total curing duration are missing. These details should be explicitly included, as they significantly influence the mechanical behavior of photopolymer resins.

Response: Thank you for your valuable suggestion, the recommended topic was done.

Comment: The statistical software used for data analysis (e.g., SPSS, Jamovi) is not specified, nor is the exact strategy for data interpretation. Without this information, methodological transparency is compromised, and it becomes challenging to assess the validity of the statistical approach.

Response: the name of the statistical software has been added

Comment: Although the text mentions that a power analysis was performed, there is no information about the effect size used, or whether a post hoc power analysis was conducted. Including these details would enhance the statistical rigor and reliability of the findings.

Response: we added all the information while writing statements related to sample size, which was used to entire for the sample size computation.

4. Results

Comment: The results are presented only in tabular format, without any supporting graphical representations such as bar charts or error bars. The lack of visual data summaries makes it more difficult for readers to quickly interpret the findings and compare group performances.

Response: Thank you for your response. In reference to Tables 2 and 5, two supplementary charts have been added (figure 6 and 7).

Comment: FTIR and SEM analyses are discussed within the text, but the associated figures are lacking essential annotations, such as peak labels, magnification levels, and explanatory captions. These omissions hinder the reader’s ability to critically evaluate the microstructural and chemical characterization data.

Response: Thank you for your comment. Main peaks have labeled of each spectrum and corresponding groups are discussed in the relevant text. For SEM the given magnification for each image is provided along with figures captions as recommended.

Comment: In the SEM section, terms like “crack propagation” and “lamellar surfaces” are briefly mentioned; however, the specific groups where these fracture patterns occurred are not clearly identified, nor are they visually indicated on the figures. This limits the clarity and scientific depth of the microstructural analysis.

Response:  Thank you for your comment, we considered your suggestion and extended the results part with more details about the “crack propagation” and “lamellar surfaces”. The corresponding (fig. 5) is modified accordingly where crack propagation and lamellar surfaces are identified and marked with arrows (see modified fig. 5)

5. Discussion

Comment: The discussion follows the literature reasonably well, but the comparisons remain superficial in several areas. Each key finding should be more critically analyzed in light of previous studies, with proper referencing to enhance the scholarly depth of the interpretation.

Response: thank you for your Comment, comparison with other studies have been added in lines 324-337

Comment: The discussion should more explicitly address which type of nanoparticle (ZNP or SNP) was more effective within which resin system (ASIGA or NextDent). Presenting these outcomes with clear material-specific insights would improve the applicability and specificity of the conclusions.

Response: thank you for your valuable comments. Referral to NPs type effect was added to discussion 

Comment: Clinical implications are not sufficiently discussed. The authors should elaborate on how these materials might be implemented in practice—such as which types of dentures or patient scenarios would most benefit from the enhanced properties of these nanocomposite resins.

Response: Thank you for your insightful comment. To address this point, a graph illustrating the clinical relevance and potential applications of the nanocomposite 3D-printed resins has been added to the Discussion section (page 14).

Comment: The observed decrease in elastic modulus following thermal aging should be analyzed more thoroughly. Possible mechanisms such as network degradation or disruption of polymer cross-linking due to increased nanoparticle content should be hypothesized and supported with relevant references.

Response: thank you for the comment, more details have been added in lines 437-448

6. Figures and Tables

Comment: In the FTIR spectra, significant peaks should be clearly labeled, and the corresponding functional groups identified. This would improve the interpretability of the chemical bonding analysis.

Response: Thank you for your valuable comment, we have labeled the main peaks of each spectra and corresponding groups are discussed in the relevant text. However, these functional groups could not be mentioned within the figures due to limited space.

Comment: Statistically significant differences between groups should be visually summarized using bar graphs with standard deviation/error bars and appropriate significance indicators (e.g., asterisks). This would allow readers to more quickly grasp the magnitude and relevance of the differences reported.

Response: Thank you for this helpful suggestion. Bar graphs have been added to visually summarize the statistically significant differences between groups. These additions are now presented in Figures 6 and 7.