In a study comparing measurements between cadavers and CT images, the distance between the upper edge of the mandibular canal and the alveolar ridge showed possible over- and underestimations. The quantification showed a possible overestimation of up to 1.05 mm and a possible underestimation of up to 1.36 mm [34]. This discrepancy is of relevance in preoperative planning. Intraoperatively, a risk of bone block harvesting is the damage to the IAN, depending on the depth or angulation of the osteotomy. Hanser and Dolliveux describe further complications like bone overheating and damage due to chisel placement. Such complications can be avoided, knowing about the patient’s individual anatomy with regard to the mandibular canal and the osteotomy [35].

In the present study, the median bone thickness between the mandibular canal and the buccal surface of the mandibular cortical plate was approximately 4 mm immediately posterior to the mental foramen. This distance increased up to 6 mm in the first 30 mm posterior to the mental foramen and decreased to about 3 mm at the most posterior measurement at the level of the mandibular foramen. Large inter-individual differences in bone thickness were found. The findings of this study indicate that the vestibular bone thickness, i.e. the vestibular distance to the mandibular canal, is generally greatest 30 mm posterior to the mental foramen.

Significant differences in bone thickness between the right and left mandibular side support the known asymmetry of the two halves of the face [36]. The significant differences between men and women, mainly in the region of the first 30 mm posterior to the mental foramen, indicate that the mandible is wider in the area of the mental foramen in men. In contrast to women, males did not show significant age-related differences in bone thickness within this study.

In two thirds of the cases, the mental foramen was located in the region of the second premolars (66.2% right, 67.7% left) (see Figs. 5 and 6). Interestingly, the location was not completely symmetrical: the mental foramen was distal to the second premolar significantly more often on the left side than on the right side and mesial to the second premolar more often on the right side than on the left side. This finding is in agreement with those of Phillips et al. [37] and Pyun et al. [38]. In the present study, gender showed no effect on the position of the mental foramen; however, there was a trend towards an effect for age.