Chronic periodontitis is a common dental inflammatory disease partly attributed to environmental factors in the oral cavity. As the genetic background of the host also plays a part in the etiology of this disease, the possible relationships between polymorphisms of several genes and periodontitis have been studied. Interleukin (IL)-13 is functionally and genetically implicated in inflammatory and immune systemic diseases, including asthma and atopy. We investigated whether polymorphisms of the IL-13 gene are associated with chronic periodontitis. Our study included 105 Japanese individuals, of which 52 were controls and 53 were periodontitis patients. Genomic DNA from subjects was assessed for polymorphisms of the IL-13 gene at positions -1510, -1111 and +389 using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). We found that genotype frequencies between the controls and periodontitis patients at positions -1111 and +389 were statistically significant (P= 0.00724 and 0.0313, respectively). Allelic distributions at positions -1111 and +389 between the two groups were also statistically significant (P= 0.0398 and 0.0432, respectively). These results suggest that polymorphisms of the IL-13 gene at positions -1111 and +389 are associated with periodontitis in the Japanese population.

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Tooth enamel is composed of nano-scale, needle-like biological apatite crystallites. These crystallites constitute the enamel prisms. The generally accepted Meckel's model of arrangement of crystallites in enamel prism might be slightly revised according to the variations in tooth enamel chemical composition and structures. An x-ray diffraction method was proposed to survey the three-dimensional crystallite orientation instead of electron microscopy. Preliminary results showed clear difference in the convergence and broadening of enamel crystallite orientations of human tooth enamel. This method has high potential in analyzing partial deviation in crystallite orientation as well as easy sample preparation and operation.

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The study investigated the remineralization effect of calcified seaweed with large amounts of calcium (Ca), magnesium (Mg), sodium (Na), fluorine (F) and phosphorus (P). Human third molars were used in the experiment with the approval of the Ethics Committee of Tokyo Dental College. Cementum was removed from the cervical area around the teeth exposing the dentin. Small dentin blocks were prepared and immersed in acetic acid-sodium acetate buffer for 24 hours. Samples were immersed in remineralized liquid or saliva solution with or without calcified seaweed for 2 weeks. Structural changes in remineralization, depth of demineralization and loss in mineral volume were evaluated by contact microradiogram (CMR). Qualitative analysis was carried out with electron probe microanalyzer (EPMA). Morphology of crystal was observed using high-resolution transmission electron microscopy (HR-TEM). CMR image analysis revealed that part of the samples immersed in the solutions underwent remineralization. However, there was no significant difference in the degree of remineralization. EPMA observation of dentin partly detected Ca and P but not Mg or F. HR-TEM analysis revealed changes in crystal structure caused by Mg and F, which influenced remineralization in a small amount.

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During palatine rugae development in mice, a cell cluster appeared transiently in the palatine rugae epithelium. The characteristics of these cells were examined histologically and immunohistochemically for anti-cytokeratin (CK) and anti-protein gene product 9.5 (PGP9.5) antibodies using mice from embryonic day 15 (E15) to postnatal day 1 (PN1). At E15, the epithelium of both palatine rugae located in the anterior portion and inter-rugae area consisted of 2-3 cell layers, and palatine rugae have papillae under the epithelium. However, palatine rugae located in the posterior portion have cell clusters in the epithelium. These cells expressed immunopositive reactions for anti-CK18, although they did not react with anti-CK14. Under the anti-CK18 immunopositive cell cluster in palatine rugae epithelium, anti-PGP9.5 immunoreactivity was observed in papillae. Moreover, the basal cells of the cell cluster showed anti-CK7 immunoreactivity. The cell cluster in palatine rugae epithelium disappeared gradually and anti-CK18 immunopositive cells also disappeared. However, anti-PGP9.5 immunoreactivity in the papilla was maintained after the disappearance of anti-CK18 immunoactivity in the palatine rugae epithelium. At PN1, the epithelium of the palate, including the palatine rugae, was stratified and keratinized. These findings suggested that the cell cluster in the palatine rugae epithelium may be considered as a taste bud-like structure according to the expression pattern for anti-CK and may play an important role in nerve innervation to the papilla under the palatine rugae epithelium.

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Histopathological and immunohistochemical studies were conducted to elucidate the organization and remodeling of the extracellular matrix (ECM) and important factors in the early stromal reaction of oral precursor lesions and oral squamous cell carcinoma (OSCC). Gingivae from 36 cases (5 normal, 7 hyperkeratosis, 7 mild dysplasia, 7 moderate dysplasia, 5 severe dysplasia, and 5 OSCC) were examined. Histopathologically, hyperkeratosis demonstrated more desmoplastic areas than normal gingivae. Edematous changes and inflammatory cell infiltration were increased in cases of hyperkeratosis as compared to moderate dysplasia. Histo-morphological analysis revealed that the ratio of mature collagen stained by picro-sirius red was the most predominant in hyperkeratosis, and it decreased with advanced dysplastic grading. The greatest microvessel count occurred in moderate dysplasia, and the greatest microvessel area occurred in OSCC. Severe dysplasia and OSCC exhibited vasodilatation rather than increased microvessel count. The immunohistochemical analysis of ECM revealed that anti-collagen I had the most intense staining in hyperkeratosis, and the intensity of staining decreased with advanced dysplastic grading. The appearance of tenascin-c (tenascin) under the basement membrane was gradually increased from mild dysplasia to OSCC, and tenascin appeared scattered in the subepithelial zone of moderate dysplasia, severe dysplasia and OSCC. The up-reregulation of lysyl oxidase (LOX) and heparan sulfate proteoglycan (perlecan) in the subepithelial zone gradually increased along with the increase in dysplastic grading from moderate dysplasia to severe dysplasia to OSCC. Thus, in the present study of oral precursor lesions, inflammation, neovascularization and up-regulation of ECM-related proteins have reinforced from moderate dysplasia. Based on these results, it appears that moderate dysplasia is the stage at which the switch to malignant transformation occurs.

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Parametric X-ray (PXR) is a new type of radiography with variable monochrome wavelength and high coherent characteristics. The Laboratory for Electron Beam Research and Application (LEBRA) at Quantum Science Institute, Nihon University generated LEBRA-PXR, a system that irradiates Si crystal with electron accelerated by linear accelerator (LINAC). LEBRA-PXR is uniquely developed for world-wide application experiment. X-ray images of tooth samples were taken with flat panel detector using LEBRA-PXR. As a result, images were captured as short as 1 sec. LEBRA-PXR uses LINAC with micro-macro pulse electron beam structure. Imaging time of 1 sec is equivalent to about 0.025 msec when x-ray is converted to actual radiation exposure. The effective dose point estimates of x-rays were about 1 μ Sv/5 sec. Results show that LEBRA-PXR can be used to generate low dose x-ray imaging advocating the possibility of its application in biological studies and medical treatment.

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It has been reported that glycerol enhances susceptibility to radiotherapy and chemotherapy by a chemical chaperone-like effect which restores mutated protein higher-order structures of the p53 protein because p53 functions are recovered to induce p53-dependent apoptosis through radiotherapy and chemotherapy. On the other hand, based on in vitro and in vivo experiments glycerol alone has not been considered to inhibit growth and invasion of cancer cell lines. In the present in vitro study, glycerol alone was added to oral cancer cell lines (tongue cancer, cervical lymph node [CLN] metastasis of tongue cancer, mandibular gingival cancer) and a cisplatin (CDDP) resistant cell line. The results showed that glycerol inhibited the growth and invasive capacities of the cancer cell lines concentration-dependently. Further, it was demonstrated that the mechanisms of glycerol for inhibiting growth and invasion of the cancer cell lines are inhibition of G1/S phase transition of the cancer cell lines, apoptosis induction, and an inability of cancer cells to use glycerol as an energy substrate. Clinically, this may suggest that glycerol has a potential inhibitory effect on the growth and invasion of CDDP-resistant oral cancer as well as primary and CLN metastatic lesions of oral cancer.

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This study focused on the antibacterial activity of the fluoride ions corted titanium. The profile of the elements of the modified material were analyzed with a X-ray photoelectron spectroscopy analysis system. At the same time, in vitro bacteria culture model was established to evaluate the influence of the modified titanium on the colonization and adhesion of Porphyromonas gingivalis (P.g.). It was confirmed by bacterial colony counting assays and SEM observations that fluoride ion-corted titanium could effectively influence the adhesion and growth of P. g. The current results indicated that fluoride ion corting could improve the antibacterial activity of titanium.

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Oxide film was obtained on a NiTi shape memory alloy by a chemical method. In vitro bioactivity of the oxidized NiTi shape memory alloy was studied. Cell culture showed that both non-oxidized and oxidized NiTi shape memory alloy did not have cell toxicity while the oxidized displayed higher cell viability. More L929 cells were found to adhere and proliferate on the oxidized samples surface than that on the non-oxidized. Cell number increased slowly for the test alloy samples'. Oxidized NiTi shape memory alloy possesses equal cell-activating properties to the pure titanium. More intercellular substance was observed for the cells on the oxidized NiTi alloy. The oxidized NiTi alloy shows better cell response than the non-oxidized. Surface oxidation improves the bioactivity of NiTi shape memory alloy.

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