Yoshihiko Hayashi

Chitosan and fish collagen as biomaterials for regenerative medicine.

This chapter focuses and reviews on the characteristics and biomedical application of chitosan and collagen from marine products and advantages and disadvantages of regeneration medicine. The understanding of the production processes of chitosan and collagen and the conformation of these biomaterials are indispensable for promoting the theoretical and practical availability. The initial inflammatory reactions associated with chitosan application to hard and soft tissues need to be controlled before it can be considered for clinical application as scaffold. Further, as chitosan takes too long for biodegradation in vivo, generally it is not suitable for the scaffold for degenerative medicine in especially dental pulp tissue. The collagen extract from the scales of tropical fish has been reported to have a degeneration temperature of 35°C. The properties of biocompatibility and biodegradation of fish atelocollagen are suitable for the scaffold in regenerative medicine.

Synchrotron radiation microbeam X-ray fluorescence analysis of zinc concentration in remineralized enamel in situ

OBJECTIVE Remineralization is an indispensable phenomenon during the natural healing process of enamel decay. The incorporation of zinc (Zn) into enamel crystal could accelerate this remineralization. The present study was designed to investigate the concentration and distribution of Zn in remineralized enamel after gum chewing. METHODS The experiment was performed at the Photon Factory. Synchrotron radiation was monochromatized and X-rays were focused into a small beam spot. The X-ray fluorescence (XRF) from the sample was detected with a silicon (Si) (lithium (Li)) detector. X-ray beam energy was tuned to detect Zn. The examined samples were small enamel fragments remineralized after chewing calcium phosphate-containing gum in situ. The incorporation of Zn atom into hydroxyapatite (OHAP), the main component of enamel, was measured using Zn K-edge extended X-ray absorption fine structure (EXAFS) with fluorescence mode at the SPring-8. RESULTS A high concentration of Zn was detected in a superficial area 10-microm deep of the sectioned enamel after gum chewing. This concentration increased over that in the intact enamel. The atomic distance between Zn and O in the enamel was calculated using the EXAFS data. The analyzed atomic distances between Zn and O in two sections were 0.237 and 0.240 nm. CONCLUSION The present experiments suggest that Zn is effectively incorporated into remineralized enamel through the physiological processes of mineral deposition in the oral cavity through gum-chewing and that Zn substitution probably occurred at the calcium position in enamel hydroxyapatite.

Challenges to the clinical placement and evaluation of adhesively-bonded, cervical composite restorations

OBJECTIVES The incidence of non-carious cervical lesions (NCCLs) has been increasing. The clinical performance of resin composites in NCCLS was previously unsatisfactory due to their non-retentive forms and margins lying on dentin. In order to address this problem, a lot of effort has been put into developing new dentin adhesives and restorative techniques. This article discusses these challenges and the criteria used for evaluating clinical performance as they relate to clinical studies, especially long-term clinical trials. Polymerization contraction, thermal changes and occlusal forces generate debonding stresses at adhesive interfaces. METHODS In laboratory studies, we have investigated how these stresses can be relieved by various restorative techniques and how bond strength and durability can be enhanced. Lesion forms, restorative techniques, adhesives (adhesive strategies, bond strengths, bond durability, and the relationship between enamel and dentin bond strengths) were found to have a complex relationship with microleakage. With regard to some restorative techniques, only several short-term clinical studies were available. RESULTS Although in laboratory tests marginal sealing improved with a low-viscosity resin liner, an enamel bevel or prior enamel etching with phosphoric acid, clinical studies failed to detect significant effects associated with these techniques. Long-term clinical trials demonstrated that adhesive bonds continuously degraded in various ways, regardless of the adhesion strategy used. SIGNIFICANCE Early loss of restoration may no longer be the main clinical problem when reliable adhesives are properly used. Marginal discoloration increased over time and may become a more prominent reason for repair or replacement. Reliable and standardized criteria for the clinical evaluation of marginal discoloration should be established as soon as possible and they should be based on evidence and a policy of minimal intervention.

Early gene expression analyzed by a genome microarray and real-time PCR in osteoblasts cultured with a 4-META/MMA-TBB adhesive resin sealer

OBJECTIVES Adhesive resin sealer systems have been applied in endodontics to seal the root canal system. This study was designed to confirm the mechanism of intracellular molecular events in an in vitro cell culture system with a 4-methacryloxyethyl trimellitate anhydride/methylmethacrylate-tri-n-butyl borane (4-META/MMA-TBB) adhesive resin sealer. STUDY DESIGN The gene expression patterns relating to cell growth and differentiation were examined using a human genome expression microarray and real-time polymerase chain reaction analyses in hard tissue-forming osteoblasts cultured with and without a 4-META/MMA-TBB resin sealer. RESULTS There was no significant difference in the cell number between the control and adhesive sealer groups. An increased expression of integrin beta, transforming growth factor beta-related protein, craniofacial development protein 1, and PI3K genes was demonstrated. The integrin beta and PI3K genes showed extremely high ratios. CONCLUSIONS The signal transduction pathway, at least through the PI3K/Akt cascade for cell proliferation and differentiation, can be controlled by some components of this type of adhesive resin sealer.