In recent years, Use of dental implants is becoming more widespread; however, not all patients can receive implant treatment without bone grafting. Bone grafting is frequently performed in implant treatments, and graft materials include autogenous bone, allografts, xenografts, and alloplasts. The healing mechanism of the autogenous bone graft is not well known; therefore, this study examines the healing mechanism surrounding grafted bone, at both cellular and molecular levels, employing tissue derived from transgenic mice expressing red fluorescent protein in vivo to monitor cellular kinetics in situ and to elucidate the healing mechanism. Results of our study suggested that mineralized tissue regeneration was induced by the transplanted bone representing autogenous bone graft but occurred from the margin of the existing bone.

Purpose: Platelet-Rich Fibrin (PRF) is a product prepared from the patient's peripheral blood, containing several growth factors and fibrins, potentially stimulating tissue regeneration. The purpose of the present study is to examine the stability of PRF in vivo.

Methods: Under anesthesia, a small amount of blood was collected into a small glass tube from the superficial femoral vein of a Wistar rat and PRF was immediately prepared after spinning down. Then, the PRF was transplanted and stitched to the back muscle of the same animal. The animals were sacrificed at 1, 3, 5, 7, 14, 21 and 28 days. The transplanted region was examined histologically and immuno-histochemically with an antibody against rat PDGF.

Results: Histological and immunohistochemical results demonstrated that the PRF became small and sparse at 21 days, almost disappearing at 28 days.

Conclusion: Although PRF can potentially stimulate tissue regeneration, its degradation time should be considered in its clinical applications. It is also obvious that PRF alone cannot work as a scaffold or a barrier membrane for maintaining the space of regeneration.

The safety of fluoride use to prevent dental caries has been controversial. To clarify the risk of embryotoxicity of fluoride influencing human fetuses/newborns, we investigated the embryotoxicity levels of 4 fluorides (NaF, KF, SnF₂, and CuF₂) using the EST method, which is an in vitro embryotoxicity screening test developed by Spielmann et al. in 1997. Of the fluorides, NaF and SnF₂ are used to prevent dental caries in Japan. All substances were "non-embryotoxic", but SnF₂ and CuF₂ were close to the borderline of "weak embryotoxic". Since many young people use fluoride to prevent dental caries, further investigation of the embryotoxicity of fluorine is desired.

Development of the salivary gland is characterized by extensive branching morphogenesis and lumen formation as well as differentiation into acinar and ductal cells. Although various molecules have been implicated in salivary gland development, transcription factors regulating the expression of those molecules and salivary gland development are largely unknown. The GRHL2 transcription factor and its target gene product SPINT1 as well as the SPINT1-regualted protease matriptase play crucial roles in epithelial development in several organs. Here we examined the expression of these epithelial regulators in developing mouse SMG. Of the three Grhl gene members, Grhl2 was the most abundant in embryonic SMG. The expression levels of GRHL2, SPINT1 and matriptase were increased during development of the gland. All of these molecules were expressed exclusively in the epithelial tissue. The present data may suggest the involvement of these molecules in SMG development and give a clue to developing a regenerative therapy of damaged salivary glands.

Purpose: Coral is a porous and bioabsorptive material with physical strength that could possibly be effectively used as scaffolding for bone augmentation. To compare the characteristics of cultured and natural coral, we examined the physical characteristics and internal structure of porous corals as a scaffold material. Materials and methods: Dried blocks of cultured and natural coral (velvet finger coral) were immersed in 1N NaOH to remove protein. We then observed the exoskeleton and surface of these cultured and natural corals using micro-CT and SEM. We also measured the specific gravity, the proportion of internal cavities, and the physical strength (compressive strength, hardness) of the cultured coral when wet, and in comparison with the natural coral in the sea. Results: Cultured coral was a porous structure with tubular cavities measuring 100-250 μm in diameter and natural coral was 100-200 μm. The specific gravity and proportion of cavities, were 1.02, and 66.9%, respectively, for cultured coral, and 1.32, and 52.8%, for natural coral. The compressive strength and hardness of cultured coral were 9.3 MPa, 52.4 and those of natural coral were 26.6 MPa, 60.1, respectively. These findings suggest that cultured coral may be useful for bioabsorbable scaffold, and natural coral for bone augmentation.

In the Japanese regenerative dental field, some original ideas were favorably evaluated, but many were a reworking of studies performed in other countries, and the contents were mostly combinations or slight modifications of preceding studies. It may be time to return to the starting point and reconsider the study objective. Various studies on regeneration have been performed in the regenerative dental field, but very few results have actually been clinically applied, and many new ideas have already been disregarded. To overcome this situation, studies based on original ideas not per-formed in other countries may be initially necessary to promote regenerative dental research in Japan.