Compensatory response of molar eruption for environment-mediated tooth wear in sika deer

Abstract

Teeth move continuously in the occlusal direction after they have approached the occlusal plane, which is considered a compensatory mechanism for loss of tooth crown by wear, although quantitative data have been inadequate. To clarify phenotypic correlation of tooth eruption and wear 10 populations of wild sika deer (Cervus nippon) in Japan were investigated. Mandibles, with ages assigned by cementum annuli of incisor roots, were used to estimate molar wear rate and eruption timing. Molar eruption status was assessed by observation of the buccal side of molars and coded as 3 ordinal levels according to the appearance of a cervical line (a boundary between molar crown and root). Logistic regression of the eruption status revealed that eruption timing of the lower 3rd molar (m3) was significantly different among populations (P < 0.0001) and correlated with m3 wear rate; faster molar wear resulted in faster molar eruption (P < 0.01). Eruption timing of lower 1st (m1) and 2nd (m2) molars did not show significant correlation with wear rate, possibly due to less variation in eruption timing in m1 and m2 than for m3. These findings indicate that the compensatory response of molar eruption occurs for m3 in accordance with wear mediated by environments.