Case Report: An association of the gubernacular canal, supernumerary tooth and odontoma with an impacted canine on cone-beam computed tomography

This report describes a clinical case of asymptomatic compound odontoma in the anterior left side of the maxilla associated with an impacted canine and supernumerary tooth with a gubernacular canal of a 47- year-old female with no relevant medical history. Cone-beam computed tomography (CBCT) was performed for precise three-dimensional localization of each structure and assessment of their spatial relationship with the associated structures before surgery. The treatment protocol involved surgical enucleation of the odontoma and open extraction of both impacted and supernumerary teeth. The patient had uneventful healing and proceeded with the prosthodontic treatment plan. The dentist should be aware of the probability of a close relationship between the development of odontoma and presence of the gubernacular tract, which could be used as a future radiographic diagnostic criterion of an odontoma. Also, we recommend that more studies be performed in this field to deeply analyze the imaging characteristics of GT and its spatial association with various pathological lesions in the future.


Introduction
Odontoma is defined as a benign odontogenic tumor containing enamel, dentin and cementum, and are classified by the World Health Organization into two main types: compound and complex 1,2 . Compound odontoma consists of a tumorlike malformation (hamartoma) with varying numbers of tooth-like elements (odontoids). The complex odontoma consists of a tumour-like malformation (hamartoma) in which the enamel and dentin, and sometimes cementum, are present 3 . Pathogenesis of odontoma is still unclear, although some etiologic factors have been suggested such as trauma during primary dentition, genetic factors, and chronic inflammation 4 . They are usually small, asymptomatic and discovered through radiographic examination when patients present with a missing permanent tooth 5,6 .
Odontomas may cause disturbances in the eruption of teeth such as impaction, delayed eruption, or retention of deciduous or permanent teeth, despite these critical disturbances only a few patients have been described 7 An impacted tooth is one that fails to fully erupt into the dental arch within the usual range of expected time. The tooth becomes impacted because abnormal tooth orientation, adjacent teeth, dense overlying bone, excessive soft tissue, or a genetic abnormality prevents eruption 8 . Exceptionally, it can be associated with the supernumerary teeth or an odontoma 1 .
The gubernacular cord is a structure composed of conjunctive tissue that connects the tooth follicle to the overlying gingiva, this cord guides or directs the course of the tooth eruption. A canal is formed within the bone by the osteoblastic activity to contain the gubernacular cord which is named gubernacular canal [9][10][11] We present a case of an impacted upper canine with compound odontoma and a supernumerary tooth accompanied by gubernacular canal, where we utilized cone-beam computed tomography (CBCT) to locate each structure precisely prior to surgical treatment.

Case report
A 47-year old female -of African origin -presented to the dental clinic to treat multiple carious teeth, and to replace multiple missing teeth. On Intraoral clinical examination, both the maxillary canines were missing as well as the third molars, and there was a bulge on the buccal cortex of the missing maxillary left canine, which was asymptomatic (Figure 1a). The patient's medical history showed no previous incidence of dental/maxillofacial trauma or infections. She was referred

Amendments from Version 1
The changes made were mainly at the discussion and conclusion areas, we added further literature about complications associated with odontomas, and syndromes associated with supernumerary teeth and also about the role of the gubernacular tract in differentiation between odontogenic and non-odontogenic tumors. The conclusion focused on gubernacular tract-odontoma connection where it can be used as a future radiographic diagnostic criterion. Histopathologic images 4a & 4b were marked with different sized arrows to point out different contents, also a more detailed description was added to image 4c along with the magnification. A minor edit was made to the title. Dr. Sara used to have both affiliations, but during executing this study, she was on a leave from Ain to the Oral and Maxillofacial Surgery clinic for management. Panoramic radiograph revealed the presence of an impacted maxillary left canine and two small radiopaque masses distal to the impacted canine ( Figure 1b) and the periapical radiograph showed that the apical mass is a supernumerary tooth and the coronal mass is a rounded denticle like mass (Figure 1c).
CBCT showed that tooth #23 was palatal impacted between teeth #21 and #22. There was a very small well defined rounded denticle like mass positioned distal to tooth #22 and coronal to the impacted supernumerary tooth (crown only), preventing its eruption. (Figure 2a, b, c).
The sagittal CBCT slice showed radiographic evidence of continuity of the follicular space of the supernumerary tooth along the bone up to its most inferior part at the alveolar ridge. This was determined to most likely be the gubernacular canal as it followed its possible eruption pathway through the bone. However, the denticle like structure was located inside this pathway and prevented the eruption of the supernumerary tooth. (Figure 2d) The most probable differential diagnosis would be a compound odontoma because of its denticle like density, organization, and coronal position.
Intraoral surgery was planned under local anaesthesia, based on the clinical, radiographic findings and multidisciplinary consultation diagnosis of the radiopaque mass as a compound odontoma.
Local infiltration of the area was performed, a full-thickness mucoperiosteal buccal flap was raised to expose both the mass and supernumerary tooth and soft tissue in between, a palatal flap was raised to expose the impacted canine. The cortical bone was removed utilizing rotary instruments accompanied by normal saline irrigation to minimize heat generation. The calcified mass was identified and ditched all around and then elevated with a Coupland elevator. The incompletely formed supernumerary tooth along with soft tissue attached to it was extracted using straight forceps, and for identification, the soft tissue was tagged with a black silk suture. By access from the palatal region, the impacted canine was sectioned horizontally and extracted (Figure 3 a, b, c), then the whole area was irrigated using normal saline and the flap was stitched back to its original position. A pre-surgical fabricated acrylic stent was placed to prevent falling of the palatal flap and to promote healing. Post-operative analgesia was prescribed in the form of acetaminophen 500mg every 6 hours. Clinical examination was performed 3 months post-surgical; patient was symptoms free and had uneventful recovery.
Histopathologic examination of the excised mass showed a tooth-like structure with dentin, and some enamel matrix confirming the diagnosis of compound odontoma (Figure 4 a,b).   Histological examination for the soft tissue mass showed epithelial lamina surrounded by collagenous connective tissue which confirms the diagnosis of gubernacular tissue (Figure 4c).

Discussion
Odontoma is a benign tumour that is usually asymptomatic, diagnosed clinically through routine radiographic examinations, or when investigating other events such as the delayed eruption of permanent teeth, or ectopic position of teeth 12-14 , as is the case in our findings.
Odontomas are mostly located at the anterior maxilla and associated primarily with permanent teeth, although they can also be associated with deciduous teeth and also can be associated with some complications such as impacted teeth, as in the present case, maxillary sinus complications 15-18 or/and cystic association 19 . Due to its rare recurrence, conservative surgical excision is the treatment of choice for odontomas 8,20 Supernumerary teeth occur most frequently at the anterior midline, causing malposition of neighboring teeth or preventing their eruption 1,6,21 . Occasionally, supernumerary teeth may be associated with some developmental syndromes like, cleidocranial dysostosis, Down's syndrome, Apert syndrome and Gardener's syndrome 22 In the present case, the supernumerary tooth was non-syndromic, incompletely formed, and it was extracted along with the impacted canine and odontoma.
Panoramic and periapical radiographs are conventional twodimensional radiographic techniques which are widely available and are frequently used for multiple diagnostic purposes like detection of impaction, odontoma, bone loss and various intraosseous lesions. Nevertheless, these radiographs have various limitations in revealing the buccolingual relationship, and presence of superimposition, also having geometric inaccuracy 23 . In the current case, we primarily detect the presence of impaction of a supernumerary tooth and odontoma through panoramic and periapical radiograph.
CBCT is an advanced 3D imaging modality that offers precise localization and detection of the spatial relationships of any dental structure with the surroundings, also it lessens the radiation dose in comparison with conventional CT and delivers high spatial resolution 24 . In our case, we used CBCT for 3D localization of the odontoma, impacted canine and supernumerary tooth before surgical removal 24,25 .
The role of gubernacular cord (GC) and the canal in tooth eruption is not clear, although it has been suggested that it may have a central role in inducing normal tooth eruption as it constitutes a pathway from the dental follicle to the gingiva for the eruption of permanent teeth 11 . Oda M. et al. 26 suggested that the presence of and contact with the gubernacular tract (GT) should be added as a characteristic CT finding of some types odontogenic masses including dentigerous cysts, calcifying odontogenic cysts (Gorlin Cyst), odontomas, Adenomatoid Odontogenic Tumor and perhaps others. Moreover, they concluded that dentists should pay more attention to the association between the GT and odontogenic masses 26,27 . Our case demonstrated an association between the GT and the odontoma where the odontoma was inside the GT of the supernumerary tooth with the same spatial relationship in agreement with Oda M. et al. 26 which reports that the majority of odontoma cases (about 70%) detected with CBCT were inside the GT of the unerupted teeth (Figure 2d). Also, Oda M. et al. 26 reported that the presence of GT helped in differentiating complex odontomas from bone dysplasia and cemento-ossifying fibromas.
Moreover, Ide F et al. 2011 28 stated that the Gubernacular cord may act as a source of epithelial remnants of the dental lamina which could be the basis of the development of some odontogenic tumors and/or cysts, Thus, the identification of imaging features of GT in CBCT may assist in the diagnosis of odontogenic cysts and tumors.
Furthermore, oda et al. 29 found that the continuity of the pathological lesion with the GT could be a characteristic differentiating imaging feature between some types of odontogenic and non-odontogenic tumors as this continuity was detected in CT of almost all of the odontogenic lesions (93.7%) in this study.
This was in harmony with our study, where during surgery, it was apparent that the GT was contiguous with the supernumerary follicle, suggesting that the GT was guiding the eruption of the supernumerary tooth, but the development of the odontoma prevented its eruption. Gaêta-Araujo H et al. reported that the most communal attachment site of GC was to the occlusal side of the dental sac of the unerupted tooth (93.2%) and was classified as a usual attachment. These findings were in agreement with our case, where we also found the GT to be attached to the occlusal aspect of the dental sac of the supernumerary tooth 27 .

Conclusion
The dentist should be aware of the probability of a close relationship between the development of odontoma and presence of the gubernacular tract, which could be used as a future radiographic diagnostic criterion of an odontoma. Also, we recommend that more studies to be performed in this field to deeply analyze imaging characteristics of GT and its spatial association with various pathological lesions in the future.

Consent
Written informed consent for publication of their clinical details and clinical images was obtained from the patient.

Data availability
Underlying data All data underlying the results are available as part of the article and no additional source data are required.

Open Peer Review
Reviewer Expertise: Oral Pathology, Histopathology, Oral Medicine

Version 1
Reviewer There are some points that could improve the quality of the article: a) The x-ray image is not clearly representative of a composite odontoma, it could also be a complex odontoma. Due to the aforementioned, I suggest that in the histopathological image 4a and 4b) the authors mark and mark each dental tissue that makes up the odontoma (dentin, enamel, cementum). In image 4c, the authors should put the following description: It is observed odontogenic epithelium arranged in islands and cords surrounded by mature connective tissue, suggesting the presence of epithelial lamina surrounded by collagenous. Please indicate the magnification of the image (for example 50X, 100X or 400X).
The reviewer suggests (in the discussion section) to go deeper into the imaging of the gubernacular tract with CBCT and the presence of odontomas or odontogenic tumors, I suggest reading in this article: Chaudhry and Sobti (2020 1 ). ○ c) I believe that the conclusion paragraph that says "The dentist should also be aware of the probability of a close relationship between the development of odontoma and the presence of the governmental tract, which in future could be used as a radiographic diagnostic criterion of an odontoma" is very ambitious. I suggest that the authors clearly explain why they believe that it could become a radiographic criterion for an odontoma and/or not for another odontogenic tumor that has the presence of mineralized tissue.

Minor points:
In the case report section, the authors describe the patient in the following way: "A 47-year old house wife -of African origin -" I think that this data is not important for the clinical case, I suggest describing only; "A 47-year old female ...".  Here are a few recommendations which could improve the manuscript: The 'A 47-year old housewife -of African origin presented' can be modified as 'A 47-year old female -of African origin presented' 1.
Supernumerary tooth and odontoma are also associated with syndromes. If the patient is non-syndromic, the phrase, 'an otherwise healthy and non-syndromic patient,' can be added to the case history section. A brief discussion on the syndromes associated with odontomas and supernumerary teeth may be a valuable addition to this report.

2.
In the conclusion section, the sentence "Thus, early detection and management of odontomas can help correct any dental irregularity and avoid further complications" has been included. When odontomas are asymptomatic entities and discovered incidentally during radiographic surveys taken for evaluation of missing permanent teeth, how is early detection achievable? Consider adding some info regarding the same and mention which are the further complications. 3.
Since the report mainly circles around GC, the conclusion paragraph could straightaway focus on the GC-odontoma connection. Consider avoiding conventional odontoma literature in conclusion. The below paragraph seems to be fitting: 'The dentist should be aware of the probability of a close relationship between the development of odontoma and presence of the gubernacular tract, which could be used as a radiographic diagnostic criterion of an odontoma.'

4.
The discussion section can also include a brief review of odontoma-GC literature and appropriate differential diagnosis.

5.
To avoid hype, the word 'unusual' can be removed from the title. The title 'Association of the gubernacular canal, supernumerary tooth, and odontoma with an impacted canine on conebeam computed tomography' seems fitting.

Is the background of the case's history and progression described in sufficient detail? Yes
Are enough details provided of any physical examination and diagnostic tests, treatment given and outcomes? Yes Is sufficient discussion included of the importance of the findings and their relevance to future understanding of disease processes, diagnosis or treatment? Yes Is the case presented with sufficient detail to be useful for other practitioners? Yes