An Analysis of Anterior Mandibular Anatomy Using Cone Beam Computed Tomography: A Study of Dentate and Edentulous Mandibles

Statement of Problem: The anterior mandible has conventionally been deemed as a relatively “safe zone” for dental implants due to perceived lack of innervation to the area as well as its relatively thick cortices and dense bone. However, with the evolution of cone beam computed tomography (CBCT), a number of anatomic challenges have been identified by clinicians that can lead to neuropathy and life-threatening hemorrhage if violated. The three critical anatomic structures in this area that pertain to implant placement are the sublingual artery (SLA), submental artery (SMA), and the mandibular incisive canal. Currently, there is a lack of knowledge regarding average measurements of these anatomic structures in relation to a specific non-variable landmark. Furthermore, it is not known if there are any significant variations of these anatomic structures in dentate and edentulous patients. While these structures may be identifiable on a CBCT scan, mandatory CBCTs are not required by practitioners in order to perform implant surgery in the anterior mandible. Purpose: To determine if standardized average values can be obtained for the sublingual artery (SLA), submental artery (SMA), and mandibular incisive canal (MIC), and if differences exist between dentate and edentulous patients. Materials and Methods: CBCTs of 125 edentulous and 100 dentate subjects were evaluated at the anterior mandible for incidence of visualization of the SLA, SMA, and MIC. Measurements of these three structures were also made from the inferior cortical border of the mandible to the superior border of each structure in order to gain average anatomical measurements. The cross-sectional shapes of anterior mandibles were also categorized and prevalence of each shape in this sample was calculated. Results: The incidence of visualization of the SLA on CBCT was found to be 100% for edentulous subjects and 98% for dentate subjects. The SLA was located approximately 15mm above the inferior border of the mandible. The incidence of visualization of the SMA on CBCT was 94% for edentulous subjects and 88% for dentate subjects. The SMA was located approximately 5mm above the inferior border of the mandible. The incidence of visualization of the MIC on CBCT was 61% for edentulous subjects and 59% for dentate subjects. The MIC was found to be approximately 1.5mm in diameter at the lateral incisor and canine regions. The MIC was located approximately 11mm above the inferior border of the mandible in edentulous patients, and approximately 14mm above the inferior border of the mandible in dentate patients. The edentulous mandibular ridge attained a buccal-lingual width of 6 mm at a mean distance of 4 mm below the ridge crest in this patient sample. A new classification system for the cross-sectional morphology of the anterior mandible was characterized and includes the following shapes: hourglass, ovoid, pear, sickle, and triangular. The pear was the most commonly visualized cross-sectional morphology among both edentulous and dentate patients. Conclusions: The sublingual artery and submental artery can be consistently identified in the anterior mandible using CBCT, both in dentate and edentulous patients. The SLA was located approximately 15mm above the inferior border of the mandible and the SMA was located approximately 5mm above the inferior border of the mandible. The mandibular incisive canal was not consistently visualized. The cross-sectional morphology of the anterior mandible is diverse in dentate and edentulous mandibles with pear shape being the most common in both situations. These findings should be taken into consideration when treatment planning for implants using CBCT or panoramic radiography