Dental enamel crystallites consist of relatively highly crystalline biological apatite, which include a large amount of carbonate ions in the apatite crystal lattice. However, this common understanding was achieved only after a great deal of research because of the wide variation in the chemical composition of dental enamel. In this paper, the difference between biological and mineral apatite is briefly reviewed, and how to obtain information easily concerning the chemical composition of dental enamel, which is a major factor in determining the physical-chemical properties, using non-destructive high-accuracy analytical instruments, such as FT-IR spectrometry, FT-Raman spectrometry and X-ray diffraction. Variations in the enamel structure observed by instruments other than optical or electron microscopes were not reported in relation to tooth type differences. These variations are referred to herein as variations in enamel micro-structure, such as micro-pores. Finally, a number of problems with respect to variations in dental enamel that cannot be ignored when treating dental enamel are discussed.

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Aim: To observe the age-related three dimensional morphological and quantitative changes in the pulp cavity and root canal orifices of mandibular first molars by Micro-CT. Methodology: In each age group (20’s, 40’s and 60’s), ten mandibular first molars without any substance defects or caries were examined using Micro-CT. The pulp cavity of each tooth was reconstructed in three dimensions. Then, the volume ratio of the pulp cavity and the diameter and angle of root canal orifices were examined. Results: With age, the volume ratio of the pulp cavity decreased, and the diameter of root canal orifices also decreased. With regard to the root canal angle in the orifice region, the angle of the mesio-buccal and mesio-lingual root canals decreased, but there was no marked change in that of the distal root canals. Conclusions: The morphology and volume ratio of the pulp cavity of the mandibular first molar changed with age. The morphological changes of the orifice region were particularly specific. The angle of mesio-buccal and mesio-lingual root canal increase was age-related, but with the distal root canal, the degree of change was small and insignificant.

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The junctional epithelium at the interface between the tooth and gingiva is the site first exposed to pathogenic factors. This can lead to the onset and progression of periodontitis. Integrin α₆β₄ is an adhesion molecule associated with the connections between gingival epithelial cells and teeth. However, the expression of adhesion molecules, such as integrin α₆β₄, P-cadherin, and E-cadherin, and the occurrence of apoptosis are not well understood in diseased human gingival epithelial cells (HGEC).
We stimulated cultured HGEC with the periodontal bacterium Porphyromonas gingivalis (P. gingivalis) and examined immunohistochemical staining for integrin α₆, integrin β₄, P-cadherin and E-cadherin. In addition, we examined the apoptosis caused by P. gingivalis stimulation using ELISA and evaluated the number of viable cells using the MTS assay.
The localization of integrin α₆, integrin β₄, P-cadherin, and E-cadherin was observed in the cell membrane of HGEC with P. gingivalis stimulation. However, although the expression of these adhesion molecules did not appear in detached HGEC with stimulation, chromosomal condensation of the nucleus was observed. On the other hand, the localization of these adhesion molecules in the cell membrane of detached HGEC without stimulation was the same as in the experimental group. However, no chromosomal condensation of the nucleus was observed in the supernatant of controls. The appearance of apoptosis in HGEC induced by P. gingivalis stimulation indicates that the same phenomenon occurs in the junctional epithelial cells (JEC), with a resulting loss of adhesion molecules and possible desquamation of JEC. This can increase susceptibility to periodontal bacterial invasion.

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Acquisition of substantial amounts of carbonate, acid phosphate and other impurities is encountered universally in biogenic apatites in vertebrates. To date, however, much still remains to be elucidated about the driving force behind carbonatoapatite formation in physiological environments and whether the solubility of carbonatoapatites depends on their stoichiometric composition and types of carbonate substitution. We here used discrete groups of carbonatoapatites prepared under various aqueous conditions and determined their solubility during acid equilibration. We selected a stoichiometry model to describe these crystal compositions, i.e., (Ca)_5-x(HPO₄)_v(CO₃)_w(PO₄)_3-x(OH)_1-x. All apatite products were equilibrated in phosphoric acid solutions at 25°C for a maximum of 28 days under a constant partial pressure of CO₂, i.e., 1.8% CO₂/N₂. After this long-term equilibration, each of the apatite samples was verified to reach a plateau of the ionic activity product (IP), which was calculated on the basis of the experimentally determined stoichiometries. Notably, the solubility product values of carbonatoapatites were confirmed to depend primarily on their carbonate contents. Importantly, analysis of the solubility data and electron microscopic observation validated that the incongruent equilibration, i.e., dissolution of the original crystal and co-precipitation of projections formed on the original crystals, was most prominent for batches of B-type carbonatoapatites originally prepared at alkaline conditions. In contrast, the solubility of A, B-type carbonatoapatites, which were originally prepared at neutral conditions, yielded the so-called central-core dissolution without morphologic evidence for projection-type precipitation. The results obtained support the hypothesis that the stoichiometry and solubility properties of carbonatoapatites depend primarily on the solution environment, including the gas atmosphere, where crystal precipitation has occurred, so that a congruent equilibration of biogenic or synthetic carbonatoapatites might be pursued under conditions similar to the originally precipitating milieu.

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We examined whether Saireito, a Chinese herbal medicine, inhibits nifedipine-induced gingival fibroblast proliferation. Nifedipine (10μM) significantly enhanced proliferation from the ninth day of the culture period. When added together with nifedipine, Saireito dose (0.05-0.2%)-dependently inhibited nifedipine-induced proliferation. Saireito at the highest concentration (0.2%), inhibited normal proliferation on the ninth and fourteenth days. Sole application of nifedipine (10μM) augmented bFGF release. Saireito concentration (0.05-0.2%)-dependently reduced the level of bFGF in the nifedipine-containing culture medium. In the case of Saireito at concentrations of 0.1% and above, there was a significant difference between the control (nifedipine alone) and test (nifedipine+Saireito) groups. Saireito had no effect on normal bFGF release. Nifedipine (10μM) increased the production of collagen compared with that of the control (normal medium), and Saireito at 0.1% and above significantly reduced nifedipine-induced production of typeI collagen. Saireito did not inhibit the normal production of typeI collagen. Our findings indicate that Saireito indeed inhibits nifedipine-induced proliferation by depressing the release of bFGF, and reduces nifedipine-induced collagen synthesis in the gingival fibroblasts. Administration of Saireito may thus be clinically effective for the treatment of drug-induced gingival overgrowth.

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To characterize osteodentin in the pre-functional rat incisor, we performed histological and histochemical evaluation of the anterior apex of the incisor in 3-day-old rats. The unerupted incisor was composed of osteodentin, with numerous cells present in the anterior apex. The osteodentin was immunopositive for osteocalcin, bone sialoprotein, and dentin sialoprotein, with an immunolocalization pattern similar to that of dentin. Back-scattered electron microanalysis (BSE) and electron probe microanalysis (EPMA) showed that osteodentin was not uniformly calcified. These results indicate that osteodentin in the rat incisor possesses dentin-like characteristics, and may be fragile in structure.

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