The purposes of this study were to examine and compare the effectiveness of tooth bleaching and influences on teeth of laser-assisted office bleaching material with other office bleaching materials. One hundred and four human extracted anterior teeth were used in this study. The teeth were divided into three groups: in the first group (group 1) teeth were treated with the material including 35% hydrogen peroxide (Shofu HiLite™), second group (group 2) with 3.5% hydrogen peroxide (Pyrenees®), and third group (group 3) with 55% hydrogen peroxide (Smart-bleach®). Color changes of enamel surfaces were measured, surface morphology was observed by scanning electron microscopy (SEM), and calcium ion release from enamel surfaces and microhardness on enamel surfaces before and after tooth bleaching were measured. Statistical analyses were performed using the Kruskal-Wallis or Mann-Whitney U test, and a probability of less than 1% was considered significant. All bleaching materials showed bleaching effects that depended on number of repeated times, but there was no significant difference in bleaching effect among the three groups. The surface morphology in group 2 was very similar to that of the control group, but rough surfaces were observed in groups 1 and 3 by SEM, and the roughness of group 1 in particular was severe compared with that of group 3. Calcium ion release from enamel surfaces after bleaching was similar among the three groups, and there was no significant difference compared with the control group. The microhardness of enamel surfaces before and after bleaching was also similar, and there was no significant difference among the three groups. The three bleaching materials used in this study showed similar bleaching effects and there were no significant differences in the influence on teeth of calcium ion release and microhardness among the three groups.

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The aim of this study was to evaluate in vitro the wear, output-energy, and ablation efficiency of a flatend, quartz-fiber tip of 600μm diameter for Er:YAG laser. Four different conditions were used regarding the distance and angle between the tip and dentin plates prepared from extracted bovine teeth. Group 1 was irradiated at 0.5mm and 60 degrees. Groups 2, 3 and 4 were irradiated at 1mm and 60 degrees, 0.5mm and 45 degrees, and 1mm and 45 degrees, respectively. In all groups, the tip surface morphology revealed damage after 120min irradiation under scanning electron microscopy. However, the output energy showed no change by analysis using a power meter. Laser microscopic examination showed that group 3 had the highest ablation efficiency. The results indicated that when the tip was used without contact and at oblique irradiation for a long time there was no reduction in output-energy, although the tip surface was damaged. In addition, the ablation efficiency depended on the distance and angle between the tip and dentin.

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To improve the bond strength and durability against hydrolysis of the silica-resin interface, a novel silane coupling agent containing a hydrophobic fluoroalkyl and/or phenyl group, 3-{4-[di(trifluoromethyl)-4'-methacryloyloxyphenylmethyl]phenoxy}propyltrimethoxysilane (p-MBFBS), was synthesized. The silane coupling agents used in this study were 3-methacryloyloxypropyltrimethoxysilane (3-MPS), nonafluorohexyltrimethoxysilane (4F), 3-{4-[di(trifluoromethyl)-4'-methacryloyloxyphenylmethyl]phenoxy}propyltrimethoxysilane (p-MBS), and p-MBFBS. The concentration of each silane solution was adjusted to 2 mass% with ethanol, and then the contact angles of a resin monomer mixture (Bis-GMA:TEGDMA=50:50) to glass plates modified with each silane and the tensile bond strength of resin composite were measured. The glass surface modified with 4F/3-MPS showed significantly higher affinity than 3-MPS, p-MBS and p-MBFBS. The contact angle of the monomer mixture to the p-MBS or p-MBFBS modified glass plates was the same as that modified with 3-MPS. The tensile bond strength of the resin composites to glass plates modified with 4F/3-MPS, p-MBS or p-MBFBS was significantly higher compared with 3-MPS after water immersion for 360 days. Furthermore, the bond strength of 4F/3-MPS and p-MBS showed no significant difference after water immersion or thermal stress compared with those stored at room temperature in air for 1 day. These results suggest that the novel silane coupling agent containing both hydrophobic fluoroalkyl group and phenyl group has better water resistance than 3-MPS, however, the silane coupling agent containing only a hydrophobic group produces a coupling layer with the best water resistance over the long term.

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The purpose of the present study was to evaluate the damage to adjacent artificial teeth in class II metal inlay cavity preparation during approximal box-cavity practice. Five dental students and five dentists from Asahi University prepared the maxillary and mandibular right first molar (distal) using a mannequin head with lighting from a dental unit. The instruments consisted of two tapered flat-end diamond points (TF21, 22; Mani), and two experimental tapered flat-end diamond points (diamond-coated end only, S1, 2; Shofu) using a high-speed handpiece. The experimental instruments (S1, 2) and procedure for finishing the cavosurface margins has been described. The damaged teeth were classified into four groups (n=5): G1 (Student, TF21, 22), G2 (Student, TF21, 22, S1, 2), G3 (Dentist, TF21, 22), and G4 (Dentist, TF21, 22, S1, 2). The degree of damage to adjacent surfaces was determined by using a digital image analyzer, designed to calculate the damaged area (mmm²). The cavity form prepared teeth was measured by a 3D measuring system (Surflacer, Unisn). For each group, five specimens were measured and means were determined. Data were examined for significance by ANOVA, Scheffe's test (p<0.05). As a result, there was a significant difference between G1 and G4 in the maxillary right first molar (distal) preparation, and between G1 and G2, G4 in the mandibular right first molar (distal) preparation. The results indicated that trauma to surfaces adjacent to the approximal preparation site was reduced when experimental instruments (S1, 2) were used.

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The presence of biofilm and microbial contamination of dental unit water lines (DUWL) has been reported since 1993. A dental chair unit with new built-in water line cleaning system for decontaminating the DUWL was developed in 2008. This study evaluated the effect of the cleaning system on a new dental chair unit that was set up in Tsurumi University Dental Hospital in November the same year. The cleaning system treats the DUWL daily with hydrogen peroxide (1,000ppm), which is drawn through the DUWL and left there over night. Before using the dental unit every morning, the hydrogen peroxide is drained completely and tap water is pumped through the lines. There are two high-speed handpiece lines: one of them is part of the cleaning system (H-1), while the other is not part of the cleaning system (H-2), to compare the results. Water samples from H-1, H-2 and the cup filler were periodically taken after one day of use. All the samples were measured for residual chlorine and were incubated on R2A agar plates at 25℃ for seven days and the number of CFU/ml was counted. The bacteria predominantly isolated from H-2 were identified by analysis of 16S rDNA sequence. Furthermore, the inside wall of the small tube parts that were cut from the DUWL tubes were observed using SEM. The results were as follows: 1. Compared to H-1 and the cup filler, H-2 showed a reduction in residual chlorine of 0.1-0.4ppm and in the number of CFU/ml detected on the R2A agar plates from the fourth month. 2. The dominant bacteria isolated within the heterotrophic bacteria were identified as Methylobacterium populi, Sphyngobium chiorophenolicum and Caulobacter vibrioides through analysis of 16S rDNA sequence. 3. Small amounts of structures such as biofilm on H-1, H-2 and the cup filler tube walls were observed by SEM after 6 months. After 18 months, the structures showed no signs of enlarging. This study suggests that this new dental unit water line cleaning system is effective for maintaining clean water of the DUWL.

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Objectives: Sometimes esthetic problems occur around the margins of tooth-colored inlays because of the discrepancy in color or transparency of resin cements. We investigated flowable resins as a substitute for resin cements and their effectiveness. In our previous study, most flowable resins satisfied the standard of film thickness as a luting cement and could be polymerized by light through composite resin inlays. However, polymerization of the flowable resins decreased as the inlay thickness increased. The purpose of this study was to estimate the dentin bond strength of flowable resins polymerized with light through composite resin inlays. Materials and Methods: Aeliteflo™ LV (ALV), Filtek™ flow (FTF), Metafil flo (MTF), Palfique estelite LV low flow (PEL), Revolution™ formula 2 (REV), Tetric® flow (TTF), Unifil® flow (UNF), Xeno flow paste (XFP), Laminabond composite paste (LMB) and Panavia® F2.0 (PNB) as a control were used in this study. Adhesive systems were used according to the manufacturer's recommendations. Clearfil® CR inlay was used to prepare five kinds of cylindrical inlays: 1, 2, 3, 4 or 5mm in height and 4.3mm in diameter. After the dentin surfaces of extracted human molars were treated with each adhesive system, the inlays were set using the materials tested and shear bond strength was determined. With the PEL and LMB adhesive systems, there are no air-blow instructions after application of the bonding agent. Therefore, both air-blown (PEL-a and LMB-a) and non air-blown (PEL and LMB) specimens from these two adhesive systems were tested. Results: No material tested showed a significantly lower shear bond strength compared with PNB within 3mm in height of the CR inlay. PEL-a and LMB-a showed a much lower shear bond strength than PEL and LMB, respectively. FTF, PEL, REV, UNF and LMB did not show significantly different shear bond strengths until 3mm in height. Furthermore, ALV, MTF, TTF and XFP did not show significantly different shear bond strengths until 4mm in height. Conclusion: Flowable resins could be used as a substitute for resin cements. From our previous study and this study, ALV, FTF, MTF, TTF and UNF are suitable as resin cement substitutes.

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Disinfection and chemical sterilization of dental instruments have been widely practiced in clinical dentistry. Recently, peracetic acid has received much attention as an alternative disinfectant to glutaraldehyde, which has allergenicity, mutagenicity and strong irritability to skin and mucous membrane. This disinfectant solution is effective for a wide range of microorganisms including bacterial spores, and can be used for powerful disinfection and chemical sterilization in a short time. In addition, there has been no report of peracetic acid having allergic potential, suggesting that the disinfectant is harmless to those who handle it. Since dental instruments are repeatedly disinfected and sterilized, peracetic acid solution should not induce significant changes in the appearance and quality of instruments. However, the corrosion behavior of dental metallic instruments in peracetic acid solution has not been systematically investigated. In the present study, the corrosion resistance of six alloys (carbon steel, two stainless steels, brass, aluminum alloy and tungsten carbide) used for dental metallic instruments was evaluated in peracetic acid solution by an electrochemical method, analysis of released metal ions by ICP emission photometry, and analysis of the corroded alloy surfaces by X-ray photoelectron spectroscopy and visible-ray spectrocolorimetry, and the corrosion resistance was compared with that in other disinfection solutions and deionized water. The effectiveness of adding a corrosion inhibitor to peracetic acid solution for lowering the corrosion rate of instruments was also examined. The following results were obtained. 1. The corrosiveness of peracetic acid solution to ferrous alloys (carbon steel, stainless steel) was sufficiently low to be used as disinfectant solution for instruments made of these alloys. 2. The corrosiveness of peracetic acid solution to brass and aluminum alloys was significantly higher than that of deionized water and alkaline glutaraldehyde solution with pH buffer agent. Thus, peracetic acid solution can not be used as a disinfectant solution for instruments made of these alloys. 3. The corrosion rate of brass was decreased to 1/100 in peracetic acid solution with 3% Na₂HPO₄ due to the formation of a protective surface film composed of Cu(OH)₂. 4. The corrosion rate of aluminum alloy and tungsten carbide was not significantly decreased by the addition of Na₂HPO₄. 5. The pH of peracetic acid solution was increased from 3.8 to 5.2 by the addition of Na₂HPO₄ (3%) and the effective duration of sterilizing power was reduced from 7 days to 2 days. In conclusion, peracetic acid solution is suitable for disinfecting instruments made of carbon steel and stainless steel. The solution with 3% Na₂HPO₄ can also be employed as a useful disinfectant solution for instruments made of brass, though the effective duration of sterilizing power of the solution is short (2 days) compared with that of the solution without Na₂HPO₄ (7 days).

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