"Smile-Obates": Permanent Dental Development in the White-Handed Gibbon (Hylobates lar carpenteri)

Tooth formation is not as well known as eruption among the Hylobatidae. To expand knowledge of variability in dental development in hylobatids, we described the relative timing of upper and lower permanent tooth initiation, mineralization, and completion in the white-handed gibbon (Hylobates lar carpenteri).

Using a wild-shot, known-sex sample of H. lar carpenteri, we micro-CT scanned 44 crania with permanent teeth forming, including a subset of 16 skulls with mandibles. We used these data to assess crypt, crown, and root formation. Each tooth received a dental score from 0 (no crypt initiation) to 12 (root apices closed). We used principal component and cluster analyses, among other tests, to examine variance and covariance among scores.

First molar and central incisor formation was advanced over the rest of the dentition, while the premolars and second molar developed concurrently with one another. The canine crown initiated before the third molar yet reached root apical closure last. Overall patterns among dental scores were similar between upper and lower jaws, but the formation of lower anterior and premolar teeth was advanced by up to three formation stages. These patterns appeared invariant with respect to sex or pathology.

H. lar carpenteri is characterized by relatively advanced central incisor formation, catch-up growth of the lateral incisor, and protracted canine development. Adjacent molar crown formation timing is staggered, as in other primates. The development of the relatively large canines in these short-faced apes highlights the myriad influences and competing demands on tooth formation and emergence.