Signs of the proximity of third molar roots to the mandibular canal: an observational study in panoramic radiographs.

The objectives of this study were to assess the relationship between mandibular third molars and the mandibular canal, establishing which radiographic signs are most prevalent in predicting contact between these structures, and to associate these signs and the proximity with the position of the third molar according to the classifications of Pell & Gregory and Winter. A retrospective, cross-sectional observational study was carried out on panoramic radiographs. From a dataset of 3289 images, a convenience sample of 1548 panoramic radiographs with a total of 2639 third molars was selected for evaluation. The inclusion criteria were patients of both sexes who had at least 1 totally formed mandibular third molar that was adjacent to a second molar. Radiographs were excluded if they were of poor quality or revealed evidence of cystic or tumoral processes or extensive caries. Seven radiographic signs were used to determine if there was contact between the third molar and mandibular canal. A proximity to the mandibular canal was verified for 1677 (63.5%) of 2639 third molars. The most frequent radiographic signs of proximity were darkened roots (767 teeth [29.1%]) and discontinuity of the mandibular canal (757 teeth [28.7%]). Third molar/mandibular canal proximity was found significantly more frequently in female patients and in patients aged 24 years and younger (P < 0.001). The tooth positions most frequently associated with proximity between the third molar and the mandibular canal were position C (highest point of the third molar located at or below the cervical margin of the second molar) and the mesioangular position (long axis of the third molar angled mesially toward the second molar).