Natural teeth vary in color, transparency and other properties depending on the site of the tooth. When light-cured composite resin is used for fabricating crowns, the restoration needs to blend in with the natural tooth. However, because of the semi-transparent nature of light-cured composite resin, it is extremely difficult to mask background elements such as stained dentin and tooth discoloration. In the present research, a laminated filling consisting of an incisor shade (I), a standard shade (S) and an opaque shade (O) of various light-cured composite resins was assessed in order to decide the best method of laminated filling based on differences in the degree of brightness of the underlying dentin. A fundamental study was performed aimed at masking the underlying dentin color with the various light-cured composite resins. Samples of the incisor shade, standard shade (A3) and opaque shade (OA3) were prepared using three types of light-cured composite resins, Estelite Σ Quick (Tokuyama Dental), Clearfil® Majesty® (Kuraray Medical) and Beautifil II (Shofu). The samples were prepared at thicknesses of 0.5mm, 1.0mm, 1.5mm and 2.0mm. Each laminated sample was 2.0mm thick, and the lamination was done by changing the thickness of each sample to create laminated samples of O/S, S/I and O/S/I. The samples were placed on a white board, a black board and on mats of various shades of gray (L^* values ranging from 10 to 80) and measured with a Spectra Scan PR650 non-contact spectrophotometer (Photo Research, USA). The XYZ values and CIELAB values were calculated from the measurement results, and the following were determined: (1) the L^* values and C^*ab values on the white and black boards, (2) the translucency parameter (TP value), (3) the contrast ratio (CR value) and (4) the L^* values on the various gray mats.The results indicated that the transparency of Beautifil II was lower than that of Estelite Σ Quick and Clearfil® Majesty®, and that it effectively masked the underlying dentin color. In comparisons of individual shades, the opaque shade was less transparent and less affected by the underlying color, but when the thickness was 1.0mm or more, the color of the sample itself was more likely to have an effect than the underlying color. It was found that laminated samples with a thickness of 2.0mm masked the underlying color even without using the opaque shade, and a high degree of brightness could be obtained. The results confirmed earlier findings showing that with different types of composite resins, the brightness, color and transparency may differ even for the same shade. The color and transparency of natural teeth change as a person ages. Moreover, the brightness, color and transparency also differ depending on the site of the tooth and the type of tooth. In order to achieve more aesthetically pleasing crown restorations, it is first necessary to be aware of the color of the tooth being restored, the cavity preparation form and the optical properties of the composite resin, and then to select the appropriate material and lamination method.

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Nowadays many endoscopic systems with fiberscope (FS) are widely used in the field of medicine for clinical diagnosis and treatment. However, this system is still not so popular in dentistry. Direct, real-time visualization of subgingival hard and soft tissues may improve the efficiency of subgingival treatment. Therefore, we have been developing an original endoscopic system with FS since 1996 to employ it in clinical dentistry, especially for periodontics and endodontics. Many studies have concluded that the Er:YAG laser has excellent ability to remove subgingival calculus and superficial layers of infected cementum. The purpose of this study was to evaluate the usefulness of combining the Er:YAG laser and the FS for subgingival periodontal treatment. An original jaw model in which the artificial teeth were uniformly coated with nail enamel was attached to a simulator head. The experimental teeth were painted on the root surfaces of #12 and #14, and in the furcation of #46. The laser apparatus used in this study was the Er:YAG laser with contact tip. The C400F tip (φ400μm) was used in the non-FS group as for the contact tip, and the E200FL tip (φ200μm) was used in the FS group. The FS system (6,000 pixels, φ1.1mm) with a laser channel, water channel and light guide were used. The operators were five dentists who were experienced with using FS and Er: YAG laser. Initially, the experimental teeth were treated with laser only (non-FS group). A new set of experimental teeth which replaced the treated teeth from the non-FS group, were treated with laser using the FS (FS group). The laser beam was applied to each of the experimental teeth at 80mJ, 10pps with water for 1 minute. Then each root surface was observed to analyze the residual nail enamel. The residual rates of nail enamel (non-FS group: FS group) were as follows: palatal surface of #12 (82.48±13.57%:23.0±84.15%), mesial surface of #14 (79.74±11.60%:19.05±8.08%), furcation of #46 (80.16±8.12%:22.39±3.31%). The residual rate in the FS group was significantly lower than that in the non-FS group (Mann-Whitney U test, p<0.05). On the observation of root surfaces after Er:YAG laser irradiation, the FS group had little irradiation to the part except the nail enamel in comparison with the non-FS group. The results suggest that the application of Er: YAG laser treatment with FS leads to better outcome in comparison with laser treatment without FS for subgingival periodontal treatment.

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In previous reports, slightly acidic electrolyzed water (SAEW) produced by electro-disintegration of 2-6% HCl solution exhibited antibacterial effects similar to those of strongly acidic electrolyzed water. The purpose of this study was to investigate the bactericidal effects of SAEW at different concentrations against key oral pathogens and the cytotoxicity to adult human gingival fibroblasts (HGF). Streptococcus mutans (ATCC25175), Aggregatibacter actinomycetemcomitans (ATCC29522), Porphyromonas gingivalis (W83, ATCC33277) and Prevotella intermedia (ATCC25611) were selected for the bactericidal tests. HGF was obtained from the gingival tissue around extracted adult human teeth. Each genus of bacteria (initial concentration at 1×10^6 cell/ml) was incubated with SAEW for one minute at room temperature and their survival rates were measured by colony counting. Cytotoxicity of SAEW against HGF was studied by cell proliferation assessment with Alamar Blue assay. The results demonstrated that SAEW concentration over 25% had complete bactericidal effects on all tested bacteria. Compared with distilled water, undiluted SAEW showed significant inhibition of HGF proliferation. However, such effects were not found when the concentration was lower than 50%. The cytotoxicity (LD50) of SAEW determined by Alamar Blue assay was 70-80w/w%. These results suggested that 50% SAEW has ideal bactericidal ability without significant cytotoxicity.

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Tooth bleaching is a common esthetic dental treatment. Some enamel surfaces to be bleached contain white-spot enamel lesions, and the chemicals used in the bleaching process may increase the demineralization of these lesions. In order to characterize the changes of enamel subsurface lesions after exposure to a bleaching agent, we carried out an in vitro experiment in which bovine enamel specimens were exposed to a common in-office bleaching agent. The specimens were divided into four groups: a bleaching treatment group (BT), a subsurface lesion group (SL), a subsurface lesion+bleaching group (SLBT), and a control of sound enamel (CS). In the BT group, Shofu HiLite, an in-office bleaching agent containing 35% hydrogen peroxide, was applied to each specimen according to the manufacturer's instructions. One session consisted of three applications of the bleaching agent. This session was repeated six times, with rinsing after every session. In the SL group, an enamel subsurface lesion simulating a natural white-spot enamel lesion was made in each specimen by immersing it in demineralization gel (0.1mol/l lactic acid, pH 4.6) at 37℃ for 10 days. In the SLBT group, enamel subsurface lesions were made in the same way as for the SL group. After the lesions were produced, the specimens were subjected to the HiLite bleaching agent. In the CS group, untreated enamel surfaces were used. The mineral profile, integrated mineral loss (IML: vol%×μm) and lesion depth (LD: μm) of each specimen were obtained with a system that combined transversal microradiography with image-analyzing software (TMR 2000). Mineral profiles of SL specimens showed typical subsurface lesions. There was no observable difference between the microradiographic profiles of lesions in SLBT specimens and those of the SL specimens. The mean IML of SL specimens was not significantly different from that of SLBT specimens (3,816.5 and 3,675.1vol%×μm, respectively). Likewise, the mean LD of SL specimens was not significantly different from that of SLBT specimens (117.6 and 109.5μm, respectively). For both IML and LD, mean values of CS specimens were not significantly different from those of BT specimens. These results suggest that bleaching agents applied to enamel surfaces with white-spot lesions will not worsen the demineralization of these lesions.

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It has been reported that the bond strengths of enamel-resin adhesion reduced after tooth bleaching, although the mechanism remains unclear. The purpose of this study was to evaluate resin-enamel adhesion immediately after tooth bleaching. Shofu Hi-Lite® (Shofu, HL), Pyreness® (Mitsubishi Gas Chemistry, PY), and Shofu Hi-Lite Shade up® (Shofu, SU) were used in this study. Non-caries human extracted teeth were used. Bleaching agents were applied on the enamel according to the manufacturers' instructions. Specimens were divided into eight groups as follows: no bleaching with/without etching as controls, HL with/without etching, PY with/ without etching and SU with/without etching. After bleaching, the tooth surfaces were subjected to the 2-step self-etching adhesive system (Clearfil Mega Bond®, Kuraray Medical) and then were built up with resin composites (Clearfil AP-X® A3, Kuraray Medical). After storage for 24h in 37℃ distilled water, all specimens were trimmed with a diamond saw under running water (1.0×1.0mm at the bonded surface), and then subjected to a micro-tensile bond test at a crosshead speed of 1.0mm/minute (n=20). Data was analyzed by two-way ANOVA and Tukey's test (p<0.05). Bond strengths after bleaching were significantly decreased compared to the controls. There were no significant differences between PY and SU, but HL was significantly higher than PY and SU. The pH of HL was lower than that of other agents, so it is suggested that the bond strength of HL was not drastically decreased because the enamel surface was made rough. However, the bleaching effect was the same as that of the no-etching groups. From the results of this study, it is concluded that the bond strengths between resin and enamel were reduced after bleaching, and the rate of decrease in bond strength might depend on the type of bleaching agent.

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Dental X-ray photography is the most conventional and useful method for acquiring essential information on root canal morphology. However, due to restrictions on the direction of X-ray projection, traditional intraoral radiography cannot provide complete information on root canal morphology in situ. Recently, micro-focus X-ray computed tomography (CT) is considered useful for 3-D visualization of details of the pulp cavity. In order to evaluate the reliability of conventional dental X-ray photography compared with the results obtained by micro-focus X-ray CT imaging, we assessed the accuracy of conventional (orthoradial and eccentric projections) dental radiograms obtained from 14 extracted mandibular 1st molars in relation to micro-focus CT images of the same teeth. The results were as follows: (1) The number of root canals detected by conventional dental radiography was 75.0-87.5%, which was consistent with that shown in the CT images. Dental film images detected apical ramifications with low accuracy, while ramifications were clearly demonstrated by the CT images. (2) Orthoradial projection images of root bifurcation were 25.0-75.0% consistent with the CT images. With the eccentric projection technique, the consistency further decreased to 25.0-42.9%. (3) Orthoradial dental films detected denticles 4.5-10.7% consistent with the CT images. Eccentric-projection films showed overlapping images which decreased the consistency with the CT images. (4) The eccentric projection images provided more information than the orthoradial projection images, while showing a decrease in the consistency of the distal root canal (in particular, that containing denticles) with the 3D-CT imaging. The present 3D-CT imaging conducted on molars suggests that dental X-ray photography provides reasonable general information on root canals and bifurcations, but that it is difficult to identify details of the pulp cavity (in particular, that containing denticles) with a complex system of reticular root canal and apical ramifications.

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Diabetes mellitus is considered to be an important risk factor for periodontal disease, which is now regarded as the sixth complication of diabetes mellitus following retinopathy, diabetic nephropathy, neuropathy, microvascular disorder and macroangiopathy. All of these complications are attributed to angiopathy. In this study, for purpose of determining the effect of diabetes mellitus on recovery of microcirculation in the early wound healing process, localization of VEGF during wound healing was examined immunohistochemically for periodontal defects created artificially in the molar region of Goto-Kakizaki (GK) rats, which are model rats with type II diabetes mellitus, and the ultrastructural morphology of their microvessels newly developed was observed. Eight-week-old rats were separated between SD and GK and referred to as the control group and the experimental group, respectively. Palatal dehiscence defects were surgically created on the bilateral maxillary first molars in SD and GK rats. Six rats from each group were euthanized on each of days 3, 5 and 7 after surgery, and the periodontium including maxillary first molar was removed and decalcified after performing perfusion fixation. Following decalcification, paraffin sections were created for four rats of each group, immunostaining was performed on VEGF, and observations were made with a light microscope. For the remaining two rats, ultrathin sections were created by embedding them in Epon 812 with resin and were observed with a transmission electron microscope. As a result, localization of VEGF occurred to the rats of both groups in the periodontal defect region on days 3 and 5 after surgery. Additionally, VEGF was strongly localized, especially around the capillaries of the rats from the experimental group and active formation of new capillaries was also confirmed. Although VEGF was rarely localized in the rats of the control group on day 7 after surgery, localization occurred to the rats of the experimental group around the capillaries in the periodontal defect region, and the formation of new vessels was confirmed. It is suggested that the recovery of microcirculation for healing of defects in periodontal tissue is adversely affected since the expression of VEGF was promoted in the experimental group compared with the control group, and the continuous formation of new vessels and enhancement of vascular permeability in the surgical site were confirmed throughout the experimental period, and therefore stronger expression of VEGF occurred in the experimental group by creating hypoxia in the periodontal defect region.

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One-step bonding adhesives currently available on the market tend to decrease the bond strength of resin to dentin when stored for a prolonged time or at high temperature. To clarify the cause of the decrease of bond strength of resin to dentin when treated with one-step bonding adhesives, the influence on the degradation of monomer contained in one-step bonding adhesives was examined by shear adhesive strength and nuclear magnetic resonance (¹³C NMR) techniques in this study. Bond Force (Tokuyama Dental) was used as a one-step bonding material and was stored at 40℃ for 0, 3, 7 and 14 weeks in an incubator to serve as a test sample. Bond Force 300mg and dimethyl sulfoxide 250mg as a test sample for ¹³C NMR were weighed accurately in an NMR tube, followed by shaking and mixing before analysis by using the ¹³C NMR technique. The shear adhesive strength was also measured for the same storage period. As a result, it was found that two NMR peaks, one corresponding to the carbonyl carbon of carboxyl methacrylate and the other to the methylene carbon of ethylene glycol, were detected when Bond Force solution was stored at 40℃ with their augmented NMR peak strengths when the storage duration was prolonged. When Bond Force was stored at 40℃ for 14 weeks, the methacryloxy ester group of HEMA was degraded by 22.39%, that is, the ester group of HEMA was hydrolyzed, subsequently producing methacrylic acid and ethylene glycol. In addition, the bond strength to enamel was 16.2MPa when stored for 0 day (control), but the value decreased gradually with longer storage and markedly to 5.5MPa when stored for 14 weeks. Similar to the bond strength of enamel, the value of the bond strength to dentin decreased from 12.7MPa to 6.0MPa with longer storage. The bond strength of resin to dentin thus seemed to decrease when HEMA in the one-step bonding material was altered by hydrolysis in response to the prolonged storage period. These results suggest that the decreased bond strength of resin to dentin was attributable to the degraded one-step bonding material.

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Photocatalysis with anatase-type titania is a kind of photochemical reaction that shows catalytic action by irradiating light. A recent study applied photocatalysis of this anatase-type titanium to the bleaching of teeth in dentistry. This study was based on the application in dentistry of ST-01 (average particle size: 7nm) and ST-21 (average particle size: 20nm), which are anatase-type titanium with different particle diameter, and aimed to collect data, such as observation of particles, analysis of the crystal structure, and analysis of photocatalysis based on the data. The crystal structure was analyzed using an X-ray diffraction device (XRD) to observe the titanium particles with a transmission electron microscope (TEM). A mixture of ST-01 or ST-21 and methylene blue solution was irradiated by 365nm light (UV) using a transilluminator or 420-480nm light (LED) using a dental curing unit in order to analyze photocatalysis of ST-01 and ST-21. Photocatalysis was greater in ST-01 (small particle) than ST-21 (large particle), and was developed within 2 minutes after the light irradiation. The more the irradiation time was, the more the photocatalysis occured, which appeared as obvious in ST-01 than ST-21. Photocatalysis was developed by both UV and LED, however, UV showed higher effect than LED.

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In this study, the effects of CO₂ laser irradiation and nano-hydroxyapatite application to root dentin surface to coat it with hydroxyapatite were investigated. Firstly, the morphology of an experimental nano-hydroxyapatite (Pentax Newceramics) and a hydroxyapatite (Wako Pure Chemical) were characterized by SEM and TEM observations. The crystal structures were also analyzed using micro-X-ray diffractometry (micro-XRD) and Fourier transform infrared reflection spectroscope (FT-IR). The SEM and TEM observations demonstrated that both apatite crystals developed a clustering structure, yet the nano-hydroxyapatite cluster still exhibited nanoparticle size. Micro-XRD and FT-IR pictures revealed that the nano-hydroxyapatite had exactly the same crystallinity as the hydroxyapatite. Secondly, the effects of CO₂ laser irradiation in conjunction with nano-hydroxyapatite application on dentin surface were investigated to examine the meltability of the apatite pastes, the crystalline changes of the melted apatite particles and their adhesion to dentin surfaces. #2000-grit flat root dentin surfaces were prepared on extracted human premolars, and were conditioned with 10% citric acid for 10 seconds, followed by the application of either the hydroxyapatite or the nano-hydroxyapatite paste to the surfaces. These experimental surfaces were then irradiated using CO₂ laser (Panalas CO5Σ, Panasonic Health Care) with an output power of 3W (34.3J/cm²), 2W (24.2J/cm²), or 1W (14.1J/cm²) at a "Repeated Pulse Mode (0.5 second)", irradiating three times at the same spot. Then, those lased surfaces were observed by SEM without sputter-deposition in the wet condition, and were analyzed using micro FT-IR to identify and evaluate the crystallinity. Furthermore, the specimens were subjected to ultrasonic irrigation for 5, 10, 20 and 30min, and the conditions of residues of the apatite were examined using SEM. Five groups were classified according to the surface treatments: Nano-HAP (Citric acid/Nano-hydroxyapatite/Laser), HAP (Citric acid/Hydroxyapatite/Laser), L (Lased-only), C (Citric acid-conditioning), and Control. Morphological analysis revealed occlusion of the dentinal tubules and fusion of the dentin surface and the nano-apatite paste. The degree of occlusion and fusion varied with the energy density of the irradiation. Analytical chemical investigation revealed that the crystallinity of the Nano-HAP and HAP groups were almost the same, while the crystallinity of the L, Control, and C groups were lower, in that order. The results of this study suggest that CO₂ laser irradiation in conjunction with the nano-hydroxyapatite application on dentin surface might be effective for coating hydroxyapatite on dentin such as the exposed root surfaces of dentition among geriatric people.

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An understanding of the characteristics and reliabilities of dental materials and devices prior to clinical use is one of the responsibilities required of all general practitioners in order to give high-quality dental treatment to patients. The purpose of this study was to examine the bonding characteristics and reliabilities of all-in-one resin adhesive systems based on their immediate tensile bond strength (ITBS). Six typical all-in-one resin adhesive systems on the market were selected. The ITBS of those systems to both enamel and dentine surfaces of a standardized V-shaped cavity prepared in the buccocervical region of extracted human upper premolars was measured with an in vivo/in vitro bi-use portable adhesion tester. Furthermore, debonded surfaces after the bond test were observed with a digital microscope. The data of the ITBS were examined using two-way ANOVA, Tukey's q-test and Weibull analysis. The six systems indicated significantly higher bond strengths when the bonded surface was dentine rather than enamel. The reliability of acquiring bond strength peculiar to each system varied among the systems. The systems could be divided into two groups by reliability: those which exhibited excellent reliability when the bonded surface was enamel and those which demonstrated higher reliability for the dentine surface. The adhesion of the six systems to enamel and dentine characterized by the ITBS depended on the differences in oral environmental factors and systems. When the bonded surface was enamel, there were significant differences in the reliability of acquiring bond strength peculiar to each system among the six systems, but no remarkable superiority or inferiority of specific systems was found. When the bonded surface was dentine, significant differences in the reliability were found, and also the superiority or inferiority of specific systems was confirmed. The influence of oral environmental factors on bonding durability to both enamel and dentine varied among the systems. Mixed fracture was mainly observed on the debonded surfaces after the bond test.

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