Some osteocytes released from their lacunae are embedded again in the boneand not engulfed by osteoclasts during bone remodeling

It is generally accepted that osteocytes derive from osteoblasts that have secreted the bone around themselves. Osteocytes are cells embedded in the l acunae in the bone, and they are characteristically in contact with other c ells by many slender cytoplasmic processes in canaliculi. During bone remod eling, many osteocytes in the bone are released from their lacunae by osteo clasts; however it remains unclear what happens to these released osteocyte s. The cortical bone of the rat mandibular body was used in this study. Man dibles were fixed, decalcified, and then embedded in Epon 812. Specimens we re sectioned in the frontal direction into serial 0.5 mu m-thick semithin o r 0.1 mu m-thick ultrathin sections, and then examined by light or transmis sion electron microscopy. Cells that fitted in the osteocytic lacunae with canaliculi extending to the bone were identified as osteocytes in this stud y. Among many osteocytes released by osteoclasts in cutting cones, there we re osteocytes half-released from their lacunae. These cells fitted in their lacunae with canaliculi extending to the bone and showed developed cell or ganelles in the cytoplasm. In closing cones, many osteocytes were situated in the bone away from cement lines; however, there were half-embedded osteo cytes in the bone formed on cement lines. These cells fitted in their lacun ae with canaliculi extending to the bone formed below cement lines and show ed developed cell organelles in the cytoplasm. These results show that half -embedded osteocytes in closing cones derive from half-released osteocytes in cutting cones. Osteocytes encircled by osteoclasts were sometimes observ ed on one section, but serial sections showed that these osteocytes fitted in their remaining lacunae in the bone on other sections. This shows that n ot all osteocytes released from their lacunae are engulfed by osteoclasts. Consequently, the present results suggests that some osteocytes released fr om their lacunae are embedded again in the bone and not engulfed by osteocl asts during bone remodeling.