Effect of bone strain on cortical bone structure in macaques (Macaca mulatta)

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Abstract
The consistency of food significantly affects levels of bone strain in the mandible during mastication. Mandibular bone histology was examined to test the effects of a diet of hard food compared to a diet of soft food in 2 group of monkeys. One group of rhesus macaques (M. mulatta) was fed a diet of commercially prepared hard biscuits. The 2nd group was fed a soft diet the consistency of fudge. Both diets were nutritionally adequate for normal growth and development. As a control for other factors influencing cortical bone structure, fibular morphology was examined. At the end of the test period, mandibular and fibular tissue samples from the 2 groups were prepared to determine the amount of secondary Haversian bone present. Mandibular depth at M2 [mandibular morphological site] and fibular anteroposterior diameter were measured and compared between the 2 dietary groups. The soft-diet monkeys showed low levels of remodeling in their mandibles. There were large patches of unremodeled bone and resorption spaces were common. The hard-diet monkeys exhibited more extensive evidence of secondary Haversian remodeling in their mandibles. The hard-diet monkeys had deeper mandibles. The fibulae from the 2 groups had similar mean diameters and showed comparable levels of secondary remodeling. The higher mandibular bone remodeling levels in the hard-diet monkeys may represent an adaptive response to remove and replace fatigued mandibular bone due to higher stress levels associated with the ingestion and mastication of hard foods. Greater depth of the mandible at M2 found in the hard diet group apparently represents an adaptive response to higher stress levels associated with the ingestion and mastication of hard foods.