Comparative evaluation of accuracy of cranial prosthesis designed by four different workflow protocols analysed by software

Background and rationale

Cranioplasty aims to reconstruct skull defects from tumours, congenital anomalies, decompressive craniectomies, and fractures in a cosmetically acceptable manner. In addition to attempting to safeguard underlying brain tissue from cranium defects, cranioplasty also seeks to re-establish normal calvarial shape in a way that is aesthetically appropriate. It can be carried out using either alloplastic devices for repair or osteoplastic reconstruction. Among the materials used for cranial alloplastic implants are metal, acrylic resin, polyethylene, and silicone.¹

Several centers now consider methyl methacrylate cranioplasty to be preferable to titanium mesh due to its radiolucency, cheaper cost, ease of shaping, light weight, and lower rates of infection when compared to titanium implants.¹ Previous studies have demonstrated the potential to transform a conventional workflow from one that is highly skill-dependent, time-consuming, labour-intensive, costly, and unpleasant for the patients due to discomfort of the procedure, to one that is straightforward and predictable digitally.¹

One of the earliest publications on digital maxillofacial prosthesis Penkener et al. in 1999 described a method for creating a patient’s unique, life-sized, three-dimensional ear model using a computer and a CT scan Endoplan (Medical Diagnostic Computing, Zeiss, Germany) with a semiautomatic contouring program for CBCT segmentation of the soft tissue, based on Hounsfield units (HU) thresholding.²

Recently, maxillofacial prosthodontics has adopted digital technology more and more. The studies on the production of maxillofacial prostheses with CAD and CAM (computer-aided design and computer-aided manufacturing) technology that have been published in the last 20 years² have shown that it is feasible to switch from a traditional workflow that is extremely skill-dependent, laborious, costly, and unpleasant for the patients to a digitized version.

Although there have been advances in digital fabrication for prosthetics, there are still some constraints that prevent a full transition to digital fabrication for the final stages of prosthesis construction. Advanced training and modification of current treatment procedures are required due to the introduction of new technologies and methods in the field of maxillofacial prosthodontics.³

As of right now, only highly skilled dental professionals or CAD engineers may utilise the interface and software used for processing and developing maxillofacial prosthesis as CAD software is expensive and requires a skilled personnel to carry out the fabrication process.⁴

Digital dentistry currently faces something of a split; industry-driven technological solutions (primarily in the CAD-CAM and imaging sectors) are already realities, whereas AI-technologies concentrating on diagnosis and treatment planning are currently theoretical rather than reliable applications. One important job in the future is to bridge this gap. There is great need for collaborative and interdisciplinary research that combines technology and dental care.

The purpose of this research is to develop a hybrid protocol for fabricating a prosthesis that could be more accurate than the conventional technique in terms of accuracy, precision and fit of the prosthesis, and provide ease for both the patient and the maxillofacial team. This research will help prosthesis providers understand the application of a digital workflow with the addition of a conventional workflow and how they could use this in providing the finest prosthesis.

Aim

The aim of this study is to evaluate the accuracy of cranial prosthesis designed with conventional, digital and hybrid workflow, using software analysis.

Objectives

The objective of this study is to evaluate the accuracy of prostheses fabricated from the conventional, two hybrid, and 3D workflow and then compare their accuracy with the help of software analysis, i.e. reverse engineering principle.

Ethics and consent

Ethical approval for this protocol was granted by Datta Meghe Institute of Higher Education and Research, Sawangi, Wardha, with IEC reference number DMIHER (DU)/IEC/2023/853 on 31^st March 2023.

Written informed consent will be taken from the participants. In the case of unconscious patients, the relatives including the parents or spouse can provide written informed consent instead. In the case of minors the parents can provide written informed consent.

Study design

This will be a hospital-based study with an observational and analytical design.

Study setting

This research comprises a hospital based observational and analytical study, carried out in the Department of Prosthodontics, Sharad Pawar Dental College, Sawangi (Meghe), Wardha, Datta Meghe Institute of Higher Education and Research (Deemed to be University).

Data will be collected after the IEC approval and this study will be completed in 2 years.

Inclusion criteria

Eligible patients will be those above 10 years of age, who have been referred from the Department of Neurology to the Department of Prosthodontics with a cranial defect, which may be due to a congenital or acquired anomaly. Only patients who have given full consent to participate in the study will be included.

Exclusion criteria

The exclusion criteria for the study will be the patients who are not willing to participate and give consent.

Variables

The study will measure the accuracy of all the prostheses made from the 4 different workflows, which will check the size, shape, and fit of the prostheses. As this study is an in vitro study, the fit cannot be checked on a patient. Since the prosthesis is fabricated with different protocols, the cost will differ for each prosthesis; the best fitting and most accurate prosthesis may be more expensive, so this is a variable that can act as a confounding factor and will be considered in the analysis.

Outcomes

The expected outcome of the study is that the hybrid prosthesis would be a better fit and more accurate than its conventional counterpart. For dental professionals the paradigm shift towards digital technology has many obstructions, such as in infrastructure and costly equipment, so for an accurate prosthesis opting for a hybrid solution is needed so that we can benefit from both technology and the conventional process.

Bias

Bias will be minimized by random selection of patients based on inclusion and exclusion criteria.

Study sample

The calculation of sample size is described in this section. The primary variable is the cranial prosthesis defect measurement.

Conventional method

Max (positive) deviation in conventional prosthesis = 3.5, max (negative) deviation in conventional mould = 1.0

Average deviation for prosthesis mould = (3.5+1)/2 = 2.25

Digital CAD method

Max (positive) deviation in CAD fabricated prosthesis mould = 2.5, max (negative) deviation in CAD mould = 1.0

Average deviation for prosthesis mould = 1.75⁵

Mean difference of deviation between two treatments = 0.5

Estimated standard deviation = (0.4) mean difference [mean difference between the two average deviations of prosthesis mould from conventional and digital method].

Assumption

${\mathrm{Z}}_{\mathrm{\alpha }}=1.64$

$\mathrm{\alpha }=\text{Type I error at 5\%}$

${\mathrm{Z}}_{\mathrm{\beta }}=0.84\mathrm{at}\text{equivalence}\left(1-\mathrm{\beta }\right)=\text{Power at 80\%}$

$\mathrm{\sigma }=\mathrm{std}.\mathrm{dev}$

Minimum sample size required N = 2 *[(1.64+ 0.84)²(0.4)²] / (0.5)² = 10 per group

Statistical analysis

All results obtained from the comparison of the prostheses fabricated from the four different workflows will be analyzed using R software version 4.3.2. Data collection from the prostheses fabricated for patients with congenital and acquired cranial defects who are undergoing cranioplasty, made with four different workflows, will be converted into point cloud i.e. the points of all four prostheses on 3 dimensional axis, X,Y, and Z. This data will be fetched from (point cloud) software and will be comparatively analysed for surface deviation in the 3 dimensional axes, defect significance (mean) in size, shape, fit and accuracy, using the one way ANOVA test. A p-value <0.05 will be considered as significant value for providing greater accuracy.

Dissemination

The findings related to this study will be published in indexed journals and presented in scientific tracks/conferences. This study will help us in standardizing a protocol for hybridization of digital technology with conventional methodology to establish a more accurate and precise treatment deliverance of maxillofacial prosthesis.

The craniomaxillofacial prostheses made with different workflows can be checked for their accuracy and cost efficacy, and the best suited one can be further used in patients.

Limitations

The limitations for this study are that only cranial defects will be considered, but the branch of maxillofacial prosthodontics as a whole deals with all the maxillofacial prosthesis. This is an in vitro study; as the prosthesis is not fitted in a patient its final fit cannot be assessed.

Study status

The study is not yet started. It will begin in September 2023.