Abstract
The mandibular first molar (M1) tooth of the dog is commonly involved in dental procedures. Tooth roots and the mandibular canal can vary in location, which has not been described on a large scale. The objective of this study was to describe the three-dimensional anatomic relationship of the mandibular M1 tooth roots and the mandibular canal in dogs. Cone-beam computed tomography (CBCT) was used to evaluate the anatomic relationship between the M1 tooth roots and the mandibular canal. CBCT images were collected from 101 canine cadaver heads from a variety of unknown breeds. All skulls used in this study were mesaticephalic, confirmed by facial index calculations. The position of the apex in relation to the mandibular canal and in relation to the buccal and lingual cortices was recorded and analyzed in relation to mandibular bone height: root length ratio. When evaluating the apex in a buccal-lingual relationship, the tooth roots were found to be located closer to the lingual cortex in 73.3% of M1 roots. Tooth root apical positions were found to be symmetric between the right and left side of the mouth in 93% of mesial roots and 95% of distal roots. Apical positions relative to the mandibular canal within the same tooth were found to be consistent in 52% of teeth. Teeth with roots dorsal to the mandibular canal were associated with the largest mandibular bone height: root length ratio. CBCT provides a more precise overview than dental radiographs of three-dimensional anatomy. The tooth root position can be estimated in a clinical setting based on the ratio of mandibular bone height to tooth root length obtained from intraoral radiographs. Understanding the relative location of important anatomic structures is key to avoiding complications associated with various dental procedures. This study has documented that assessing anatomic structures with 2D imaging alone is flawed, and the large majority of dogs have M1 roots closer to the lingual aspect than the buccal aspect of the mandible.
Highlights
The carnassial teeth are recognized in dogs as the maxillary fourth premolar (PM4) and mandibular first molar (M1) teeth and are strategic teeth with an important role in chewing and grinding food [1]
A combination of the shorter mandibular bone height and shorter root length in the area of the distal root, combined with anatomic variation of the location of the mandibular canal within the mandible likely contribute to the higher rate of occurrence (82.2%) where the distal root apices are either found to be in apical position 0 or position 1 as compared to the frequency in the similar position for the mesial roots (65.3%)
This may play a role of clinical importance considering the mesial root apices occur in apical positions 2 and 3 more frequently than the distal root which, coupled with the lingual positioning of the root, suggests intraoperatively encountering the mandibular canal is more likely with the mesial root
Summary
The carnassial teeth are recognized in dogs as the maxillary fourth premolar (PM4) and mandibular first molar (M1) teeth and are strategic teeth with an important role in chewing and grinding food [1]. The mesial two-thirds of the crown is shaped to the premolars and is intended for shearing whereas the distal one-third of the crown is flat for grinding [2]. The close relationship between the M1 tooth roots and the mandibular canal is an important consideration when surgically manipulating structures in this location since the mandibular canal contains the inferior alveolar neurovascular bundle. Disruption of these structures can result in hemorrhage, paresthesia, pulp necrosis, and tooth nonvitality rostral to the disruption [9,10,11]
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