The prevalence of enamel hypoplasias in the bonobo, Pan paniscus

Enamel hypoplasia (EH). is a dental enamel defect that is often used as an indicator of non-specific systemic stress during the early stages of development. There are few reports of this enamel defect in non-human primates and little is known about the prevalence of this defect in the bonobo, Pan paniscus. The frequency and distribution of EH within the bonobo are investigated using skeletal specimens from the Royal Museum for Central Africa in Tervuren, Belgium. All permanent teeth were examined with a 5-20X pocket hand lens in oblique incandescent and natural light. Linear defects were scored as mild, moderate, or severe and defect distances from the cemento-enamel junction were measured with digital calipers. Pit-type hypoplasias were counted and recorded as present or absent. At the level of the individual (N=82), the vast majority of bonobos in this skeletal sample (98.8%) are affected to some degree with linear enamel hypoplasia (LEH) and there is no significant difference in the expression of LEH between the sexes. Pitting is observed in 13.4% of these individuals with no significant difference between the sexes. The anterior teeth are more affected with hypoplasias than the posterior teeth although maxillary and mandibular differences are noted. The incisors express the greatest frequency of enamel hypoplasias, closely followed by the canines. In contrast to previous studies, the mandibular canine does not demonstrate a marked difference in the expression of LEH when compared with the maxillary canine. Comparisons with the common chimpanzee are made and it appears that the bonobo is more developmentally stressed. Etiological factors such as locality and seasonal stress are examined. This macroscopic inventory of EH provides the necessary insight into the prevalence of this defect within the bonobo and serves as a foundation for the current micro-incremental analysis of EH within this endangered species. Research funded by Natural Sciences and Engineering Research Council of Canada (OGP0171168).