Titanium (Ti) dental implant(IP)s were embedded within 3-D cultured cell clusters of human mesenchymal stem cells (HMS0014) in Cellmatrix Type I-A collagen gel scaffold; the cells were induced to differentiate into mature osteoblast(Ob)-like cells. Subsequently, we examined hard tissue formation around the Ti-IPs. After phase contrast microscopic examination of diachronic changes in the peri-IP tissue, the IPs and the surrounding scaffold were dissected, resin-embedded, ground-sectioned and prepared for light microscopy (LM). Frozen sections and ultrathin sections were further processed for LM and transmission electron microscopy (TEM) studies of the peri-IP tissue. The results demonstrated attachment of the Ob-like cells and deposition of calcifying nodules on IP surfaces. The fine structure TEM study observed secretion of type I collagen fibrils by the Ob-like HMS0014 cells along the Cellmatrix 3-D meshwork, and the occurrence of collagen-mediated mineralization in the scaffold; the cells essentially regulated ECM turnover of the engineered tissue. The present study suggests the utility of collagen gel as a tissue-engineering material to enhance contact and distant osteogenesis for the IP therapy.

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The authors previously reported that when nano-hydroxyapatite (nano-HA) was applied to artificial demineralized root canal dentin inside the root canal, the nano-HA particles naturally penetrated into the root canal dentin within approximately 24 hours, and the root canal dentin rehardened to largely the same degree of hardness as undecalcified dentin. However, the kinds of changes that take place in rehardened artificial demineralized root canal dentin over time remain unclear and no published reports have addressed this issue. Therefore, we investigated the time-dependent changes that take place in artificial demineralized root canal dentin that has been rehardened by applying nano-HA. The results indicated that over time, the hardness of the rehardened artificial demineralized root canal dentin tends to increase.The fact that there was no change in the hardness of the rehardened demineralized dentin over the long term when the dentin was rehardened to the hardness of undecalcified dentin using nano-HA suggests that it may be possible to conserve demineralized root canal dentin, which must normally be removed.

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The present study aimed to develop a method for conserving dentin that has been demineralized, which in principle is completely removed, by rehardening it. It has been reported that artificial demineralized root canal dentin was prepared when bovine dental root was demineralized from within the root canal using a rapid-decalcification agent (K-CX). Furthermore, when this artificial dentin was applied inside the root canal using nano-hydroxyapatite (nano-HA), the artificial demineralized root canal dentin was found to reharden to the same degree of hardness as undecalcified dentin. However, while the artificial demineralized root canal dentin that had been prepared as the test sample was free of bacterial infection, infected root canals seen in the clinical setting often contain large numbers of bacteria, and it is unclear how these bacteria affect the rehardening of demineralized root canal dentin using nano-HA. Consequently, we prepared artificial demineralized root canal dentin that had been in contact with oral saliva, and then applied nano-HA in the same manner. The results demonstrated that the artificial demineralized root canal dentin that had been in contact with oral saliva rehardened to the same degree of hardness as undecalcified dentin.The fact that the quintessential strength of dentin could be obtained regardless of whether or not bacteria were present suggests that it may be possible to conserve demineralized root canal dentin, which until now it has been necessary to remove, for reuse in later prosthetic therapy.

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The purpose of the present study is to examine the relationship between the periodicity of incremental lines in dentin of teeth and the role of melatonin. In this experiment, 5- and 6-day, 7- and 8-days after birth SD rats were used. In the low melatonin concentration group, the light staining layer became narrow. In the high melatonin concentration group, this layer disappeared. The number and size of calcospherites in predentin increased in proportion to the concentration of melatonin administered. The new incremental line was confirmed in both the incisor and molar dentin of the melatonin treated groups. In SEM-EDS analysis, Ca and P content were increasing by the melatonin treated group compared with the control group. It is considered that melatonin participates in the formation of incremental lines and the calcification mechanism of the odontoblast. The work was supported by KAKENHI (23592727).

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