Effects of masticatory movement on cranial bone mass and micromorphology of osteocytes and osteoblasts in developing rats.

In order to evaluate the influence of masticatory movement on cranial bone mineral density (BMD) and osteocyte and osteoblast micromorphology, we conducted a study in rats fed with solid feed (n=10) and powdered feed (n=10). Cranial BMD was measured by dual X-ray absorptiometry (DXA). Osteocyte morphology was evaluated by light microscopy. In addition, some of the tissue was treated with EDTA-KOH to digest the bone matrix and prepare osteocyte samples. Micromorphology of the osteocytes was examined by scanning electron microscopy (SEM). Bone mineral content (BMC) was significantly higher in the solid feed group (1.86 +/- 0.11 g) than in the powdered feed group (1.63 +/- 0.09 g) (p < 0.05). In the solid feed group, the maximum masseter muscle tension when crushing solid feed was 305 +/- 46.0 N. Immunohistochemical staining with DMP-1 showed greater positive localization of DMP-1 in bone lacunae in the solid feed group than in the powdered feed group. On examination of cranial bone sections by SEM, the lacunar area was significantly larger in the solid feed group (0.64 +/- 0.08 microm2) than in the powdered feed group (0.43 +/- 0.10 microm2) (p < 0.01). In the solid feed group, adjacent osteocytes were connected through cytoplasmic branches and reticular cell processes to form a 3-dimensional structure. In the powdered feed group, connecting osteocyte processes were sparser. Results suggest that masticatory movement stimulates mediator substances involved in dynamic interactions between osteocytes, increases cranial bone mass during the developmental period and influences osteoblast, osteocyte, and lacunar micromorphology.