The relationship between ante-mortem molar loss and mandibular ramus shape in an archaeological population from Korea

The relationship between age, ante-mortem tooth loss (AMTL) of molars, and mandibular ramus shape was examined in the context of function-induced alteration. It was hypothesized that age, as well as molar AMTL, would be significant factors for predicting ramus shape variation in an archaeological skeletal sample from Korea. Mandibles of 90 adults from the Joseon Dynasty in Korea were analysed using 3D geometric morphometrics. Molars were counted as functional units when mandibular–maxillary occlusion would have been possible, and the tooth socket was not shallow and remodelled. The relationships among age, AMTL, and ramus shape were tested, and nonparametric multivariate (rank-based) one-way tests were conducted to test the effects of age and AMTL on mandibular shape, both with and without considering age and AMTL as factors, respectively. The results showed that AMTL had no significant effect on mandibular shape variation irrespective of whether age was considered (without age: p =.104; with age: p =.088). In contrast, age had a significant effect on mandibular shape variation when AMTL was also considered (p =.044). Most of the shape variation among age groups occurred in the mandibular regions where the main masticatory muscles insert. However, the effect of age on mandibular shape among individuals with all three molar functional units intact was not statistically significant (p =.221). Thus, it is clear that age alone cannot explain all of the variation in mandibular shape. Rather, the results suggest that age and AMTL are highly correlated and combine to affect mandibular ramus shape variation throughout ontogeny.