Titanium oxide (TiO_2) is known to exhibit photocatalytic activity by producing reactive oxygen species (ROS) when irradiated with light within an excitation wavelength band, in addition to strong oxidation-reduction effects and superior hydrophilic effects. In particular, an anatase-type TiO_2 shows a strong tendency for photocatalysis. In dentistry, although TiO_2 has been used for tooth bleaching, its application to other dental treatments has not been comprehensively studied because it is difficult to provide sufficient light for exciting TiO_2 within the confined space of the oral cavity. The present study aimed to examine the generation of ROS in addition to the antimicrobial and organic substance degrading effects of light-shielded TiO_2 after activation by irradiation with light. An anatase-type titanium oxide was used in this study. ROS generation by the light-shielded TiO_2 was measured by electron spin resonance. The results revealed that generation of ROS continued for 100min after light-shielding the TiO_2. The antimicrobial effect was evaluated with Streptococcus mutans, Staphylococcus aureus, Enterococcus faecalis and Candida albicans. After light irradiation of TiO_2 for 5h, a solution of each microbe was mixed with TiO_2 powder, then at a predetermined period, each solution was measured to determine the number of viable microorganisms. Results revealed that the viability of S. mutans and S. aureus decreased significantly from 1min after being exposed to the irradiated TiO_2, whereas the viability of E. faecalis and C. albicans decreased significantly from 2h. The organic substance degrading effect was evaluated using albumin as an organic sample. TiO_2 was irradiated under the same conditions as that used for examining the antimicrobial effect and mixed with an albumin suspension, which was subsequently retrieved at specified times for evaluation. Degradation of albumin, evaluated by polyacrylamide gel electrophoresis, was found immediately after exposure to the TiO_2 in the polyacrylamide gel. There was a significant post-exposure decrease in albumin volume as determined by the Lowry method. The results of the present study indicate that an anatase-type TiO_2 maintains a ROS-generating effect after irradiation with light even when subsequently shielded. Moreover, it was shown that antimicrobial and organic degrading effects occurred as a result of ROS generation.

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Cigarette smoking is one of most significant risk factor for periodontitis. The characteristics of smoking-associated periodontitis are loss of periodontal attachment, loss of alveolar bone and a higher rate of tooth loss. These characteristics result from tobacco products changing the host immune response. Nicotine is a major component and the most pharmacologically active agent in tobacco. Porphyromonas gingivalis (P. gingivalis) is the most representative periodontopathic bacteria. In this study, we investigate the immunological effects of nicotine and P. gingivalis LPS on cytokine production in the human gingival fibroblast cell line Gin-1. Gin-1 cells were exposed for 24-72 hours at the indicated concentrations (0, 1, 10, 100μg/ml, 1mg/ml) of nicotine and/or 1μg/ml P. gingivalis LPS. The cell morphology and viability of Gin-1 cells was assessed by micro-photo examination and cell viability test. The expression and production of cytokines were examined using Real-time RT-PCR and ELISA, respectively. In addition, mitogen-activated protein kinase (MAPK) inhibitor for p-38, extracellular signal-regulated kinase (ERK) and the c-Jun N-terminal kinase (JNK) pathway were used to identify the signal transduction pathway (s). A high concentration of nicotine (1mg/ml) changed the morphology and reduced the cell viability of Gin-1 cells. However, an intermediate concentration of nicotine (10, 100μg/ml) did not induce any morphological change or reduce the viability of Gin-1 cells, but did increase the expression and production of inflammatory cytokines in a dose-dependent manner, and decreased the OPG expression and production level in Gin-1 cells. Moreover, nicotine and P. gingivalis LPS in combination can additively up-regulate IL-6 production. A low concentration of nicotine (1μg/ml) had no effect on Gin-1 cells. Specific inhibitors of p-38 and the ERK pathway, but not that of the JNK pathway, could significantly suppress nicotine-induced up-regulation of IL-6 and IL-8 production. These findings demonstrate that cigarette smoking may exacerbate periodontitis by augmenting inflammatory cytokine production induced by periodontopathic bacteria. Moreover, cigarette smoking may augment alveolar bone loss as a feature of smoking-associated periodontitis by increasing inflammatory cytokine production and decreasing OPG production leading to osteoclastogenesis via p-38 and the ERK pathway.

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The purpose of this study was to evaluate the effect of C-factor on a resin-composite bond strength to a Class I cavity wall using three adhesive systems. Box-form occlusal cavities, 3mm wide, 5mm long, 2mm deep (C-factor=3.1), were prepared on flat dentin surfaces of human molars. For controls walls of cavities were removed in order to make flat dentin walls for bonding (C-factor=0.2). Each specimen was restored with one of three adhesives: Clearfil Mega Bond (Kuraray Medical), Single Bond (3M ESPE) or Clearfil Tri-S Bond (Kuraray Medical); followed by bulk filling or build up using Z100 resin composite (3M ESPE). After 600mW/cm² light-curing for 40s, specimens were stored in water maintained at 37 degrees centigrade for 24 hours under the dark condition. A specimen was cut parallel to cavity floor obtaining beams having bonding area of approximately 1mm². Control specimens were also cut obtaining beams. The micro-tensile bond strength (μ-TBS, MPa) was determined for flat dentin and cavity wall specimen. Data (n=9) were analyzed using Bonferroni test. Clearfil Mega Bond, Single Bond and Clearfil Tri-S Bond showed significantly lower μ-TBS to the cavity wall compared with the flat wall dentin group (p<0.05). Bonding to Class I cavity wall was affected by C-factor.

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Surface reaction type pre-reacted glass-ionomer (S-PRG) filler has been developed and is used for adhesive and restorative materials. The S-PRG filler might be most effective for inhibiting secondary caries around restorations, however, its biocompatibility is not well understood. The aim of this study was to evaluate the release of ions from the S-PRG filler and its cytotoxity for HeLa cells in culture solution. S-PRG filler (mean particle size: 3μm, 0.2g) was immersed in 20ml of distilled water and culture medium. The amounts of ions (F, Al, Na, B, Si, Sr) released from the S-PRG filler were measured by an inductively coupled plasma (ICP) spectro-chemical analyzer (Al, Na, B, Si, Sr), a fluoride ion electrode and pH/ion meter (F). The cytotoxity of the S-PRG filler was determined by evaluating the viability of HeLa cells in comparison to untreated controls (serum-free medium, cell viability=100%). HeLa cells in the culture medium were adjusted to a concentration of 5×10⁴ cells/ml. The cell viability of the S-PRG filler was measured by a Cell Counting Kit 8 after 24 hours. As a result, the release of each ion from S-PRG filler was affected by the solution of distilled water and culture medium (p<0.05, paired comparison t-test). The cell viability of the S-PRG filler was approximately 20% lower than that of the control (p<0.05, Scheffe's test), however, the cell viability with 10% diluted culture solution was similar to that of the control. These findings suggested that S-PRG filler components (F, Al, Na, B, Si, Sr) were released in the culture solution from the S-PRG filler, and the S-PRG filler showed very low cytotoxity.

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In recent years, one-bottle type one-step adhesives have been developed to simplify adhesion procedures. Although their adhesiveness has been investigated, details of the interaction between tooth component and acidic monomers employed in these adhesives have still not been clarified. This study examined the details of the interaction between the acidic monomer employed in G-Bond Plus and tooth component by comparing the changes in the ¹³C NMR profiles obtained before and after reaction with hydroxyapatite and dentin particles using carbon-13 nuclear magnetic resonance (¹³C NMR). The effect of the amount of tooth apatite demineralized by acidic monomer on the shear bond strength to enamel and dentin was then discussed by comparing the results obtained for G-Bond. Hydroxyapatite (HAP-200, Taihei Chemical Industrial) or bovine crown dentin particles of 0.400g was suspended in 2.000g of G-Bond Plus or G-Bond (GC), and these suspensions were then vibrated for 10 minutes. After centrifuging the suspensions, ¹³C NMR spectra of the supernatant solution of adhesives were observed using an EX 270 spectrometer (Japan Electron Optics Laboratory). The ratio of intensity of the NMR peak of the vinyl methylene carbon for the acidic monomer employed in G-Bond Plus or G-Bond to the NMR peak of that for TEGDMA (triethylene glycol dimethacrylate) detected in the ¹³C NMR spectrum was determined before and after reaction with hydroxyapatite or dentin particles. The reduction in the peak intensity for acidic monomer was determined by dividing the difference in the intensity ratio obtained before and after reaction by the intensity ratio obtained before reaction. The reduction was determined as a ratio of demineralization of tooth apatite by acidic monomer. The bond strength of G-Bond Plus or G-Bond to the ground enamel and dentin was measured. When G-Bond Plus interacted with hydroxyapatite or dentin, the demineralization ratio by acidic monomer was 22.0% and 66.0%, respectively. G-Bond Plus exhibited a greater demineralization ratio than G-Bond, and also exhibited a 28% greater shear bond strength than G-Bond. However, the bond strength of G-Bond Plus to the dentin was almost the same as that of G-Bond. It was concluded that G-Bond Plus, which exhibited a greater demineralization ratio of tooth apatite than G-Bond, provided enamel bond strength but not dentin bond strength.

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The removal of cast posts is difficult and involves risks (root fracture), so it is necessary to remove cast posts speedily, surely and safely (3S). This study basically investigated the methods of removing cast posts which might attain the 3S easily by comparing two kinds of post and core remover (PR, YDM). The subjects were 32 human extracted teeth with cemented metal post and core (cast post). The group in which cast posts were removed by standard-type PR was defined as Group R, while the group in which cast posts were removed by improved-type PR was defined as Group RS. The cast posts were removed by one of the following methods. The tooth was grooved at two locations, one on the buccal side and the other on the lingual side, on the metal core margin by a #1970 carbide bar for FG, then the two tips of PR were inserted into these locations and the cast post was slowly removed by gently clasping force of the PR. We evaluated the time taken to remove the cast post, the length of the post portion, and the existence of a root fracture line by the coloring matter flooding test. Almost all the cast posts were removed within 5 minutes [Group R: 16/16, Group RS: 16/16 (unit: piece)]. The average time taken to remove the cast post was 120±70 (Group R), and 103±76 (Group RS) (unit: second); the removing time in Group RS was a little shorter than that in Group R, and the removal time classified by PR was not significantly different (Mann-Whitney U test, p≧0.05). The average length of these post portions was 6.1±1.5mm (Group R), and 6.1±1.4mm (Group RS); the post portion length of the removed cast posts was not significantly different (Mann-Whitney U test, p≧0.05). Using a #1970 narrow carbide bar for FG decreases tooth matter only minimally. Furthermore, the coloring matter flooding test showed that using the PR for removing cast posts is unlikely to cause vertical root fracture after removal. These results suggested that cast posts might be removed speedily, surely and safely (3S). In addition, the improved-type PR was slightly faster than the standard-type PR.

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In order to evaluate the surface characteristics of composite resins as materials for restoring tooth color after final polishing, five composites having different filler compositions were investigated. The surface roughness and surface gloss were measured for the surface finished under different polishing conditions. The results were compared with SEM observations, and the following conclusions were obtained. 1. There were significant differences in surface roughness between the type of composite resin and the coarseness of final polishing paper. Although the surface roughness was small in the microfilled composite (SIL), submicrofilled composite (PAE) and a hybrid filled composite (APX), relatively large roughness was observed in two hybrid composites (Z250, TPH). As the coarseness of final polishing paper decreased, the surface of all composites tended to decrease, however, the difference in finishing state among composites became hardly distinguishable by the surface roughness. 2. The difference in surface state obtained by different final polishing was observed among the types of composite by gloss measurements. The gloss of the microfilled and submicrofilled composites increased rapidly as the grid number of the polishing paper decreased. Although the gloss of two hybrid composites, APX and Z250, also increased as the grid number of polishing paper decreased, the degree of decrease was relatively small. The surface of a hybrid composite (TPH) slightly increased with the decrease of grid number of polishing paper. 3. A strong negative correlation between surface roughness and gloss was found from the correlation analysis and a power function was obtained as a regression curve by regression analysis. From these results, although the state of the surface in the region of relatively rough surface should be estimated by the surface roughness, for a relatively smooth surface, which is important from the clinical point of view, the surface roughness in such a region could not easily be evaluated, therefore, the evaluation by surface gloss is suitable. 4. The results of SEM observations showed that the microfilled and submicrofilled composites possessed a smooth surface in accordance with the clinical evaluations. From these results, it is considered appropriate to use the surface gloss to evaluate the surface states of composite resins after final polishing.

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