PEER REVIEW DENTISTRY ARTICLE – Featuring Epica's Vimago™ A Veterinary Tomography Imaging Study

Localization of the First Mandibular Molar Roots in Relationship to the Mandibular Canal in Small Breed Dogs—A Tomography Imaging Study

Frontiers in Veterinary Science | www.frontiersin.org

May 2021 | Volume 8 | Article 684763

Han Chia1, Kendall Taney 1, Don Hoover 2, James B. Robertson3 and

Lenin A. Villamizar-Martinez 4*

1 Center for Veterinary Dentistry and Oral Surgery, Gaithersburg, MD, United States, 2 Veterinary Dental Clinic of North

Carolina, Durham, NC, United States, 3 Office of Research, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, United States, 4 Dentistry and Oral Surgery Service, Department of Clinical Science, North Carolina State University, Raleigh, NC, United States

Edited by: Serafeim Papadimitriou, Aristotle University of Thessaloniki, Greece

Reviewed by: Maria I. Kouki, Aristotle University of Thessaloniki, Greece

Yoav Bar-Am, The Hebrew University of Jerusalem, Israel

*Correspondence: Lenin A. Villamizar-Martinez lavillam@ncsu.edu

Specialty section: This article was submitted to Veterinary Dentistry and Oromaxillofacial Surgery, a section of the journal Frontiers in Veterinary Science

Received: 23 March 2021

Accepted: 19 April 2021

Published: 12 May 2021

Citation:

Chia, H., Taney, K., Hoover, D., & Robertson, J. B. (2020). Localization of the First Mandibular Molar Roots in Relationship to the Mandibular Canal in Small Breed Dogs—A Tomography Imaging Study. Frontiers in Veterinary Science. https://doi.org/10.3389/fvets.2021.684763

The intimate relationship between the mandibular canal (MC) and the first mandibular molar tooth presents challenges when performing dentoalveolar surgical procedures due to the probability of causing iatrogenic injury to the inferior alveolar neurovascular bundle. Superimposition between the MC and the first molar (M1) tooth roots is often observed on intraoral dental radiographs in small breed dogs. However, due to the radiograph’s bidimensional nature, it is impossible to determine the buccal or lingual localization of the first molar roots with respect to theMC. Thus, this study’s objective was to determine the localization of the first molar tooth’s roots in relation to the position of the MC and their overlapping percentage with the canal in small-bodyweight dogs (<15 kg) using tomographic diagnostic images. For this, cone-beam computed tomography and high-definition computed tomography exams from 103 small breed dogs (under 15 kg) were retrospectively assessed to determine the lingual or buccal localization of the first molar tooth’s roots with respect to the MC and the degree of overlap of the roots with the canal. In conclusion, most of the roots of M1 of dogs under 15 kg were located at the MC’s lingual aspect (82.7%) with an overall superimposition median with the MC of 100 and 90% for the mesial and distal roots, respectively. Straddle tooth roots were not a common anatomical presentation in the dogs of this study. Keywords: molar tooth, mandibular canal, tooth root, cone-beam computed tomography, high-definition computed tomography, small breed dogs

INTRODUCTION

The mandibular canal (MC) is a hollow space that carries the inferior alveolar neurovascular bundle, which innervates and provides blood supply to the gingiva, teeth, and rostral soft tissue of the mandible (1, 2). In the dog, the MC begins at the mandibular foramen located at the ventral region of the temporalis muscle insertion on the medial aspect of the ramus of the mandible. The inferior alveolar neurovascular bundle runs rostrally through theMC from the mandibular foramen to its end at the distal, middle, and rostral mental foramina on the buccal surface of the mandible at the level of the second premolar and canine teeth (1, 3). Knowledge of the MC’s position regarding the mandibular teeth is of paramount importance since iatrogenic trauma of the inferior alveolar neurovascular bundle

during dentoalveolar surgical procedures has been associated with intraoperative hemorrhage and temporary or permanent postoperative paresthesia or pain (4, 5).

The mandibular first molar (M1) is the largest two-rooted

tooth of the mandible in domestic canines, and portions of the roots are adjacent to the MC. The cusps contain both a sharp edge and a flat edge for its function. The mesial end is sharp and intended for shearing, whereas the distal end is flat and used for grinding (6). Due to this tooth’s size, it is common to see the M1 tooth roots and MC overlapping on the intraoral dental radiographs. A previous intraoral radiographic study evaluated the relationship between patient body weight and the M1 size. These authors showed that dogs under 10 kg presented larger M1s than the mandibular height, with the M1 tooth roots extending ventrally to the MC (7).

Further computed tomography (CT) studies, performed in mesaticephalic and brachycephalic dogs of different sizes, demonstrated the dorsal positioning of the roots of M1 in reference to the position of the MC. Although it was suggested that small brachycephalic dogs might have a lingual or buccal positioning of the roots of M1 in reference to the MC, the lack of small breed specimens used in these studies could not confirm this assumption (8, 9). More recently, a cone-beam CT (CBCT) study performed in mesaticephalic canine cadaver heads of different sizes showed that 66% of the assessed M1 roots presented some degree of superimposition with the MC, with 73.3% of lingual roots within cortical bone of the mandible. This study also suggested that small breed dogs may have a higher incidence of more than 50% of superimposition between the M1 tooth roots and the MC (10).

Although intraoral radiographs are widely used to assess the dentoalveolar complex in veterinary patients, distortion and superimposition of dental structures and surrounding tissues are associated with this diagnostic imaging technique’s bidimensional nature. CT and CBCT have been used in human and veterinary dentistry to evaluate the maxillofacial and dentoalveolar structures, where intraoral radiography has proven insufficient (10–14). Tomography imaging multiplanar reconstruction (MPR) and 3-D rendering provide the clinician superior visualization of anatomical structures and pathology without the superimposition of surrounded structures (10, 12–16).

While some tomographic studies have shown the positioning of the M1 tooth roots with the MC in different skull sizes and conformations in cadaver dogs, to the best of our knowledge, the relationship between the MC and the M1 tooth roots has not been clarified in small breed dogs. Thus, this research aimed to establish the lingual vs. buccal localization of the M1 roots in reference to location of the MC and determine the superimposition percentage between the M1 roots and the MC in small breed dogs (<15 kg), using tomographic images. We hypothesize that M1 roots are most likely to be located on the MC’s lingual side with a high likelihood of 100% superimposition with the MC.

MATERIALS AND METHODS

Diagnostic imaging records from 103 client-owned small-size adult dogs (<15 kg), who underwent CBCT or high-definition CT (HDCT) exams for dentoalveolar or maxillofacial structures evaluation at two veterinary dentistry and oral surgery facilities, were retrospectively evaluated. The demographic data collected from the medical record for each patient included weight, breed, and gender. Exclusion criteria included missing one of the M1 teeth, advanced periodontitis, mandibular fracture, malformation, or neoplastic process at the M1 region. This study did not involve the use of animals, and therefore, ethical approval was not necessarily required. Power calculations were performed to determine that a sample size of 100 specimens was needed for 90% power, assuming a 5% significance level.

All tomographic exams were performed with the patients under general anesthesia. Anesthetic protocols were determined by a board-certified anesthesiologist or primary surgeon for each patient according to their clinical status. Physical oral examination and blood panels (complete blood count and chemistry with electrolytes) were obtained before anesthesia induction. For each patient, the head was scanned with the long axis of the body of the mandibles parallel to the headstand using a CBCT mobile unit (1.) at 0.3-mm voxel size, 2 4 Å~ 14 cm field of view, 120 kVp, 57.6 mAs, and 20 s; and an HDCT scanner (2.) at 0.15mm voxel size, 16Å~16 cm field of view, 70 kVp, 70mAs, and 7 s. Multiplanar reformation (MPR) using suitable bony window and level settings was performed with a free DICOM viewer software for imaging evaluation. (3.) The images were reviewed by a board-certified veterinary dentist.

1. VetCATTM, Xoran Technologies, Ann Arbor, MI.

2. Epica Vimago veterinary CT scanner, San Clemente, CA.

3. Horos, version 3 (LGPL-3.0).

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