Muscle function as a determinant of mandibular growth in normal and hypocalcaemic rat.

The aim of the present investigation was to study the influence of low muscle function on the form, growth and structure of the mandible in rats with a metabolic bone disturbance due to hypocalcaemia. Growing rats were randomly divided into four groups where two factors were combined: hard or soft diet consistency to normal or calcium deficient diet. The experimental period was 30 days. At day 0 and day 15 the animals were injected with oxytetracycline. At the end of the experiment X-rays were taken from the mandibles for cephalometric analysis and the bone remodelling pattern was studied under a fluorescence microscope and with help of microradiograms. The cephalometric analysis showed that calcium deficiency was an unfavourable factor for the growth of the mandible as a whole, while muscle function was a significant factor affecting the angular and the condylar processes. General decreased bone apposition and increased endosteal resorption were found in the two calcium deficient diet groups. The cortical bone in these groups was thinner and the trabecular system sparser than in the two normal diet groups. The hard diet groups had higher bone apposition rate and better organized trabecular system than the respective soft diet groups. It was concluded that changes in the mechanical strain environment of the mandible, caused by reducing the vigorous mastication, is a powerful determinant of remodelling behaviour at certain sites, even in situations when a metabolic bone disturbance exists.