The purpose of this study was to establish a new external landmark of mental foramen to help facilitate prediction of the location during local anesthesia and during surgery of mandibular region.

One hundred and ten adult Thai cadavers of 61 males and 49 females from Department of Anatomy, Faculty of Science, Mahidol University were included in this study. The anatomy of mental foramen in 110 adult Thai cadavers (220 sides) was studied from 2008 until 2011. Measurements in vertical plane were made: (i) From gingival sulcus to mental foramen = A, (ii) from mental foramen to inferior border of mandible = B, and (iii) the ratio of A/A + B = D.

Measurements in horizontal plane were also made: (i) From symphysis menti to the mental foramen = S (in straight line and not related to mandibular curvature), and (ii) from symphysis menti to the mental foramen = C (in curved line related to mandibular curvature), and (iii) in relation to position of lower tooth/teeth, and (iv) in relation to cheilions (corners of the mouth).

The results included 61 male and 49 female cadavers. On the right side, the proportion of A/A + B (D) of male and female was 0.50 and 0.46. On the left side, the proportion of A/A + B (D) of male and female was 0.50 and 0.46. The location of right and left cheilion was related with the position of mental foramen, mostly at center (male: 63.93 and 70.49%, female: 61.22 and 73.47%). If center ± 0.3 cm it was possible to find the mental foramen more easily than the point of the center (male: 95.08 and 91.80%, female: 87.76 and 93.88%). If center ± 0.5 cm, it could find the mental foramen more easily than the point of the center ± 0.3 cm (male: 98.36 and 98.36%, female: 95.92 and 97.96%).

The knowledge gained from this study is quite important, since it helps the surgeon to easily identify the mental foramen prior to surgery which is halfway between gingival sulcus and inferior border of mandible in vertical plane and at the cheilion position in horizontal plane.