The effect of retraining hypofunctional jaw muscles on the transverse skull dimensions of adult rats.

OBJECTIVE: To experimentally investigate the effects of increased masticatory muscle function on the transverse cranial dimensions on adult rats with an earlier reduced masticatory muscle function.

MATERIAL AND METHOD: Sixty young male rats were used. The experimental group received soft diet for a prolonged period, so that the animals developed weak masticatory muscles. A control group received ordinary hard food during the whole experimental period (27 weeks). After 21 weeks when the animals had nearly ceased their body growth the rats in the experimental group were divided into two groups. One group continued with soft diet until the end of the experiment (hypofunctional group). The other group received ordinary hard food to get the possibility to retrain their masticatory muscles (rehabilitation group). At week 21 and at the end of the experimental period (week 27), axial cephalograms were taken. Fourteen landmarks were defined to measure seven transverse distances of the skull.

RESULTS: The increase of the anterior zygomatic arch width and interzygomatic width during the experimental period were larger in the rehabilitation group compared to both the normal and the hypofunctional group.

CONCLUSION: Retraining of masticatory muscles in adult rats leads to increase of some transverse cranial dimensions.