Enamel hypoplasia in the deciduous teeth of great apes: Variation in prevalence and timing of defects

The prevalence of enamel hypoplasia in the deciduous teeth of great apes ha s the potential to reveal episodes of physiological stress in early stages of ontogenetic development. However, little is known about enamel defects o f deciduous teeth in great apes. Unresolved questions addressed in this stu dy are: Do hypoplastic enamel defects occur with equal frequency in differe nt groups of great apes? Are enamel hypoplasias more prevalent in the decid uous teeth of male or female apes? During what phase of dental development do enamel defects tend to form? And, what part of the dental crown is most commonly affected? To answer these questions, infant and juvenile skulls of two sympatric gene ra of great apes (Gorilla and Pan) were examined for dental enamel hypoplas ias. Specimens from the Powell-Cotton Museum (Quex Park, UK; n = 107) are r eported here, and compared with prior findings based on my examination of j uvenile apes at the Cleveland Museum of Natural History (Hamman-Todd Collec tion; n = 100) and Smithsonian Institution (National Museum of Natural Hist ory; n = 36). All deciduous teeth were examined by the author with a X 10 h and lens, in oblique incandescent light. Defects were classified using Fede ration Dentaire International (FDI)/Defects of Dental Enamel (DDE) standard s; defect size and location on the tooth crown were measured and marked on dental outline charts. Enamel defects of ape deciduous teeth are most commo n on the labial surface of canine teeth. While deciduous incisor and molar teeth consistently exhibit similar defects with prevalences of similar to 1 0%, canines average between 70-75%. Position of enamel defects on the canin e crown was analyzed by dividing it into three zones (apical, middle, and c ervical) and calculating defect prevalence by zone. Among gorillas, enamel hypoplasia prevalence increases progressively from the apical zone (low) to the middle zone to the cervical zone (highest), in both maxillary and mand ibular canine teeth. Results from all three study collections reveal that among the great apes, gorillas (87-92%) and orangutans (91%) have a significantly higher prevalen ce of canine enamel defects than chimpanzees (22-48%). Sex differences in c anine enamel hypoplasia are small and not statistically significant in any great ape. Factors influencing intergroup variation in prevalence of enamel defects and their distribution on the canine crown, including physiologica l stress and interspecific dento-gnathic morphological variation, are evalu ated. (C) 2001 Wiley-Liss, Inc.