The role of occlusal stress and gingival infection in the formation of exostoses on mandible and maxilla from Neolithic China.

Exostoses on the mandible and maxilla is a frequently observed bone growth of controversial aetiology. The aim of this study is to analyse environmental factors that may stimulate the formation of exostoses on different regions of the maxilla and mandible. Sixty-six well-preserved crania from Neolithic China were studied for the presence of buccal exostoses on the maxilla (BE) and lingual exostoses on the mandible (LME). Other oral health indicators, such as occlusal wear on molars, pathology of temporomandibular joint (TMJ), carious lesions, calculus accretion, periodontal disease, and antemortem tooth loss were recorded. Buccal maxillary exostosis was unusually common on the Neolithic skulls from China, which thus resemble the Sinantropus crania described by Weidenreich (1943). We report a significant Spearman correlation between BE and LME (rho = 0.54, P < 0.00001), suggesting a partially shared aetiology of these two types of exostoses. The highest correlations between either form of exostoses and any oral indicator of stress were found for pathology at TMJ (rho = 0.46, P < 0.0001 for both types of exostoses). Smaller but significant correlations were observed between LME and the age adjusted wear rate on lower molars, as well as between BE and indicators of oral/dental pathology, e.g. caries, calculus, periodontoses, and antemortem tooth loss. Both types of exostoses tended to increase in frequency with age, although a significant trend was observed only for BE. We conclude that formation of exostoses is a complex process that can be invoked by any agent causing damage and inflammation of gingival tissue. However, severe occlusal stress, which is often manifested in TMJ disorder, is the main environmental factor leading to exostosis development in genetically pre-disposed individuals.