Tooth roots and the periodontal ligament: Morphology, modeling and behavior

The relationship between tooth roots and diet is relatively unexplored, although a logical relationship between harder diets and increased root surface area is suggested. Two studies were done to address the interaction between tooth root morphology, diet and bite force in small mammals. In bats there was a clear relationship between food hardness and root surface area. In contrast, no strong relationship was found between estimated bite force and tooth root surface area in rodents. In general though, these studies combined show that microCT successfully allows the non-destructive quantification of previously difficult-to-access tooth morphology and shows the potential for tooth roots to provide valuable dietary, behavioral and ecological information in small mammals. The study of root morphology by microCT inevitably ignores the PDL fibrous component, yet this is also critical for mechanical behavior. Therefore, simplified single-rooted tooth geometry was used to make predictions about PDL fiber bundle organization under two types of habitual loading. The architectural hypotheses generated by FEA were generally supported by histological findings. An unanswered question is whether PDL architecture can be modified in response to altered diet. A rabbit model was used to investigate the effects of reduced loading on the morphology and composition of the PDL. This is not a change in diet hardness per se, but it was assumed that the animals could not bite with normal force. The expected changes in PDL shape and size, as a result of reduced loading, were not seen. There was no reduction in PDL area or collagen content, nor was the complexity of either the PDL or bone affected. This could indicate that PDL morphology cannot adapt to changed circumstances or that the change in loading was not sufficient to trigger adaptation.