Background: Molecular mechanisms of bone resorption during odontogenesis are entirely unknown. In this study, we investigated the expressions of receptor activator nuclear factor κB ligand (RANKL), osteoprotegerin (OPG) and tumor necrosis factor-α (TNF-α) during early-stage tooth germ development. Methods: Developing tooth germs in rats, including Hertwig's epithelial root sheaths (HERS) at prenatal day 20 and postnatal days 1, 3, 5, 7 and 9, were examined. Expressions for RANKL, OPG, and TNF-α in mRNA, as well as protein levels, were evaluated by RT-PCR and immunohistochemistry. Results: mRNA expression levels for RANKL were significantly increased at postnatal days 3 to 9. Those for OPG increased from 1 to 5 days. However, those for TNF-α did not change between prenatal day 20 and postnatal day 5. On each postnatal day, RANKL was immunohistochemically localized in dental follicle cells attached to HERS, as well as in the crown region. HERS cells were also immunopositive for RANKL at postnatal day 7 and later. OPG was weakly immunolocalized in dental follicle cells from postnatal days 1 to 5, whereas after postnatal day 7 it disappeared. Conclusions: These findings revealed that the RANKL-RANK signaling, but not TNF-α signaling, plays a major role during bone resorption in the dental follicle surface to the HERS during early-stage tooth development.

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Background: The purpose of this study was to investigate the differentiation and maturation of osteoblasts on surfaces with different roughnesses. Methods: Blasting a culture dish surface with Al₂O₃ particles of 25 μm, 50 μm or 180 μm diameter produces mean surface a roughness (Ra) of 0.48 ± 0.07, 1.02 ± 0.14 or 3.10 ± 0.36, respectively. Morphological changes of cells were compared, and the expression of mRNAs of osteopontin and osteocalcin were evaluated. Further, the ratio of alizarin red positive area was calculated. Results: Cells cultured on the 180 μm blasted surface had almost the same morphology as those cultured on the 50 μm blasted surface; however, cellular bridges tended to be much wider and more spread out. The expressions of osteopontin and osteocalcin mRNAs in cells cultured on the 180 μm blasted surface have greater up-regulation than the other cells. Further, the ratio of alizarin red positive area in180 μm blasted surface was significantly higher than those of others. Conclusions: These results suggest that the 180 μm blasted surface, with a surface roughness of approximately 3 μm in width, is the best surface for MC3T3-E1 cells to differentiate and mature in vitro.

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Sclerosing mucoepidermoid carcinoma (SMEC) has been rarely documented, and previously reported cases have suggested that this histologic variation is basically low-grade with a favorable prognosis. In an earlier report on the firstdescribed intraoral case of SMEC of intermediate grade that recurred as a nonsclerosed, high-grade tumor 13 years after the initial surgery, we presented a primary gingival tumor that occurred in a 28-year-old man as a non-ulcerated, polypoid, 2-cm mass on the retromolar pad. The present report, which briefly summarizes the further clinical course of that case, clearly demonstrates that stromal sclerosis is not a permanent feature of SMEC. Although SMEC has not been extensively studied, it is likely that the presence of extensive scar-like areas seems to have no prognostic significance.

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