The median age of the patients was 40.2 years (range 12.6–84.4 years). Patients were distributed almost evenly across the age groups (see Table 1).

Figure 3 clearly shows the median vestibular bone thicknesses (bt) at 2-mm intervals throughout the anterior to posterior course of the canal on both the right (bt2 r to bt66 r) and left (bt2 l to bt66 l) side of the mandible. The maximum distance between the mental and mandibular foramina was 6.6 cm. As shown in Fig. 3, the vestibular bone thickness on both sides is approximately 4 mm immediately behind the mental foramen, increases to 6 mm in further distal course and is approximately 3 mm towards the posterior at the mandibular foramen. Some individual measurements differed significantly from the median values. For example, immediately posterior to the right mental foramen, the bone thickness ranged from 1.6 to 8 mm.

We found some highly significant differences (p < 0.001) in bone thickness between the right and left side of the mandible in both men and women (see Fig. 4). Bone thickness also varied significantly between both men and women (p < 0.05), particularly in the first 30 mm posterior to the mental foramen (bt14 r to bt26 r and bt12 l to bt 28 l).

Bone thickness did not differ between the age groups among men. However, among women, significant differences were found in the first 40 mm posterior to the mental foramen on both sides of the mandible when comparing age groups 2 and 3, 3 and 4, and 2 and 4 (p < 0.01 in all cases).

In all CBCTs, the mental foramen was visible on the right and left side of the mandible and in two thirds of the cases (66.23% right, 67.66% left) was located near the second premolar. The location was not completely symmetrical: the foramen was more often mesial to the second premolar on the right side (27.87%) than on the left side (24.09%) and significantly more often distal to the second premolar on the left side (8.25%) than on the right side (5.91%) (p < 0.001) (see Figs. 5 and 6). Further analysis showed that gender did not affect the location of the foramen.