Retromolar foramen of the human mandible.

Analysis of retromolar foramen (RMF) in a large series of mandibles (N 2500) was undertaken to provide descriptive statistics for this variant. RMF of diameter 0.5 mm or greater were scored. Consistent with other data on accessory canals in the facial skeleton, RMF was found to occur more commonly in native populations of North America than in other populations (Africa, Europe, India, northeast Asia). The ratio of bilateral to unilateral occurrences was shown to increase with population incidence, a pattern consistent with the theoretical model of an epigenetic (threshold "quasicontinuous") variant. Male-female differences were not found. Age profiles were characterized by a marked peak in the adolescent cohort. In some populations RMF showed a positive intertrait correlation with accessory mandibular foramen and with accessory mental foramen, but correlations with presence/absence of third molar and three-rooted first molar were not found. With refinements in scoring criteria and, ideally, better evidence of its heritability, RMF should be useful along with other minor cranial variants for ethnohistorical studies.