EXPRESSION OF OSTEOCALCIN IN CEMENTOBLASTS FORMING ACELLULAR CEMENTUM

To determine the phenotypic expression of cementoblasts responsible fo r acellular cementum, an immunohistochemical study was performed using a polyclonal antibody raised against the aminoterminal peptide of rat osteocalcin (OC). Maxillary first molars of Wistar male rats aged 2 a nd 3 wk were used for observations. Serial sections of decalcified par affin embedded specimens were stained either with hematoxylin and eosi n or with the anti-OC antibody. In 2-wk-old rats, apical roots were li ned with the epithelial root sheath. A thin layer of acellular cementu m was seen at most of the root surface, but was not seen near to root apex. In 3-wk-old rats, cellular cementum began to be formed at root a pex, and acellular cementum became more thick than in 2-wk-old rats. A cellular and cellular cementum were lined with the fibroblast-like cel ls. Osteocalcin staining was detected in cells lining root surface in both 2- and 3-wk-old rats. Almost all cells lining cellular cementum w ere positive for OC. In contrast OC positive cells lining acellular ce mentum and root surface devoid of cementum appeared at a specific site of the root. The cells at the interradicular area of root surface wer e positive but the cells at the outer area (the opposite side of the i nterradicular area) were negative for OC. Osteoblasts and odontoblasts were positive with the antibody. The present results suggest that the OC expression of cementoblasts forming acellular cementum is similar to that of cells forming cellular cementum as well as osteoblasts and odontoblasts, and has a role for calcification of acellular cementum.