Effect of increasing the vertical dimension of occlusion in growing rats on masticatory muscles and craniofacial morphology

Abstract

I investigated histochemical changes in the masticatory muscles and morphological changes in the cranium induced by elevating the vertical dimension of occlusion in growing rats. One hundred and forty-four 4-week-old male Wistar rats were divided into three groups. In the experimental group, the vertical dimension of occlusion was elevated bilaterally 1.0 mm or 1.5 mm at the maxillary molars. The animals were observed at 5, 7, 10, 13 and 16 weeks of age. I weighed the temporal and masseter muscles from the left side. I then classified the muscles from the right side as type 1, 2A or 2B fibers based on ATPase staining, measured the fiber diameters, and calculated the percentage of each fiber type. I also measured the craniums on cephalograms.
Weights of the masticatory muscles and the mean diameter of the type 2B fibers had decreased at 7 weeks in the experimental animals, and the percentage of 2B fibers in these muscles had increased. The height of the mandibular angle region had significantly decreased at 7and 10 weeks.
These results suggest that elevating the vertical dimension of occlusion retards growth of the masticatory muscles and cranium, and that these changes might be related to a decrease in the diameter of, and an increase in the percentage of, type 2B fibers. Shika Igaku (J Osaka Odontol Soc) 1996 Mar; 59(1): 15-31.