Radiographic proximity of the mandibular third molar to the inferior alveolar canal.

Objective: To determine the panoramic radiographic distance from the mandibular third molar tooth to the inferior alveolar canal.
Study Design: Five hundred sixty mandibular third molars were evaluated by panoramic radiography. The teeth were grouped into erupted vs unerupted and further subdivided by tooth angulation. The distance from the most inferior aspect of the mandibular third molar tooth to the superior border of the inferior alveolar canal was measured with digital calipers. A t test was performed to compare erupted and unerupted teeth, and ANOVA was used to determine if a significant difference exists based upon tooth angulation. A record review was performed to assess the incidence of inferior alveolar nerve paresthesia based upon measured distances.
Results: The mean distance from erupted mandibular third molar teeth to the inferior alveolar canal is 0.88 mm. This distance was significantly different from unerupted teeth (P=.002). The mean values for unerupted teeth indicated that the most inferior portion of all teeth measured was below the superior border of the canal (negative values) as follows: mesioangular (-0.97 mm), vertical (-0.61 mm), distoangular (-0.31 mm), and horizontal (-0.24 mm). The position of mesioangular impactions were significantly different than all other impaction groups (P=.0125). The incidence of inferior alveolar nerve paresthesia was 3.33% (18/541), most commonly associated with mesioangular impactions (-0.66 mm) in female patients.
Conclusions: Unerupted mandibular third molar teeth are closer to the inferior alveolar canal than are erupted teeth. Mesioangular mandibular third molar impactions are most closely positioned to the inferior alveolar canal, and this may represent an independent risk factor for postoperative paresthesia.