The natural history of tooth wear, continuous eruption and periodontal disease in wild shot great apes

Abstract

Wild-shot great apes comprising 65 lowland gorillas, 67 orang-utans and 60 chimpanzees were studied to explore the interrelationship between tooth wear, continous eruption and periodontal disease with increasing age. Observations on stages of tooth wear for upper and lower I1, M1, M2 and M3 were used as a broad scale of the increasing time a tooth was judged to have been in functional occlusion during the lifetime of the animal. Three measurements of combined alveolar and basal bone heights were made on mandibles and maxillae of male and female orang-utans and gorillas. These measurements suggest that there was no change in alveolar bone height during the period between young adulthood and old age in either sex or taxon. Measurements of total tooth height above the alveolar crestal bone remained more or less constant in all teeth measured in all taxa through successive stages of wear. Measurements of enamel height and of the amount of root exposed above the level of the alveolar bone demonstrate that with increasing tooth wear, tooth root emerges above the alveolar bone in a compensatory manner to maintain a constant height of tooth tissue. Eventual degeneration of the functioning dentition occurred in older animals when enamel was completely lost from the occlusal surfaces of the molar teeth and from the crowns of the incisors. Combined chronic pulpo/periodontal infections were judged to underlie final vertical alveolar bone and tooth loss in these great apes (probably at about 30–40 years of age).