Patterns of emergence of the human mental nerve.

This study investigated the path of emergence of the mental nerve in a number of human population groups. Skeletal material comprised 117 Negro skulls (53 males), 114 caucasoid skulls (62 males) and 100 pre-contact Maori skulls (70 males). In each case, the path of emergence was classified into posterior, anterior, right-angled or multiple. Those cases with severely resorbed alveolar ridges that made classification difficult were excluded from the study. Additionally, 56 cadaveric mandibles were examined, in which an osteotomy of 1cm was made on either side of the mental foramen to expose the nerve. The most common pattern of emergence in caucasoids and Maoris was a posterior direction (86.7% of caucasoid males, 90.2% of caucasoid females; 85.5% of Maori males, 93.1% of Maori females). In Negroes the most common pattern was a right-angled path of emergence (45.8% of males, 45.0% of females), with this difference between population groups being statistically significant (Pearson's chi(2): males=23.4, females=45-97; P<0.01). Multiple foramina were rare, with the highest incidence being in Maori and Negro males. Cadaveric data supported the findings of the skeletal investigation, with the dominant emergence recorded as posteriorly directed (80.7% of males, 86.6% of females). It was concluded that while the traditionally accepted ontogenetic explanation for the inclination of the mental nerve might be applicable to caucasoids and Maoris, it fails to explain the observed right-angled emergence pattern in Negroes. Hence, the nerve's emergence might be genetically, rather than functionally, determined. The study did not show a measurable anterior loop in the emergence of the mental nerve that would have any significant impact on treatment planning for implants in the anterior mandible.