An equation has been proposed describing the relation between √KHN and mineral content for demineralized enamel (vol%=4.3(√KHN)+11.3). However, it is unknown whether mineral content profiles of remineralized enamel are equivalent to hardness profiles. Our objective was to compare profiles of transversal microradiography and hardness for remineralized enamel cross sections using a nano-indentation technique. Bovine enamel subsurface lesions were created in a lactic acid gel system at pH4.6 for a ten-day period. After the period, lesions were remineralized for two weeks at 37℃. Before and after the remineralization, 150μm specimens were cut from the enamel blocks and transversal microradiographs were taken. Simultaneously, nano-indentation testing was performed on cross sections of the lesions into the underlying sound enamel, starting from 10μm in from the anatomical surface at 10μm intervals. Microradiography of the thin specimens and nano-hardness values at the cross section resulted in similar subsurface lesion profiles after demineralization. Although mineral volume percent of the remineralized surface and lesion body gave recoveries up to 68-87%, recovery rates of nano-hardness value were limited to 30-50%. Further, while the recovery rate of 30μm depth nano-hardness value was 30.5%, the recovery rate of conversion from mineral volume% using the formula was 39.1%. Though the mineral volume percent of remineralization recovered remarkably, the nano-hardness values did not recover to the same degree as the volume percentage mineral. From an ultrastructural point, the remineralization process seems to be more complex than the demineralization process. Therefore, remineralization strategies to recover the mineral should be developed with concomitant recovery of lesion consolidation.

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The purpose of this study was to determine the influence of operator variability on dentin bond strengths of single-step self-etch adhesive systems, notably: Bond Force (BF) , Clearfil tri-S Bond (CT) , and G-Bond (GB). Shear bond strengths to bovine dentin were measured and failure modes after testing were evaluated. Resindentin bonding interfaces were also observed with SEM. Six operators, whose clinical experiences were different, were enrolled to make bond strength specimens. The dentin bond strengths ranged from 6.7 to 18.4 MPa for BF, 11.0-18.6 MPa for CT, and 6.9-14.5 MPa for GB. When the specimens were made by operators with clinical experience exceeding five years, the coefficients of variation tended to be lower. From the SEM observations, many bubbles and flaws were detected inside the adhesives, when the specimens were made by the operators whose clinical experiences were two years. From the results of this in vitro study, the operator variability might be one of the technique sensitive factors of single-step self-etch systems used in this study.

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In order to improve the durability of the adhesive layer, we experimentally prepared an HEMA-ethanol base primer containing 4-META (ME) or MDP adding a fluorine compound, and a bonding agent consisting of Bis-GMA/TEGDMA (Bis/3G), and evaluated its adhesive strength. As a result, it was found that the addition of 2,2,2-trifluoroethyl methacrylate (FM) was useful in improving the durability of adhesion to dentin. Affinity of the primer containing FM for bonding agents is not completely clear as yet, however. In the present study, the durability of the adhesive layer using bonding agents of different viscosities, i. e., Bis/3G, UDMA (UD) and UD/3G, was evaluated with the aim of improving the penetration and diffusion of bonding agents within the dentin treated with the primer containing FM. Five kinds of experimental primer containing MDP with addition of no FM and containing ME with addition of 0, 0.5, 1.0 and 5.0 wt% FM were applied to the dentin of the crown of bovine teeth, respectively. Three kinds of experimental bonding agent, Bis/3G, UD, and UD/3G, were applied, and photo-irradiated. Then, they were filled with Clearfil AP-X and used as specimen. After 1 day and 6 months of water storage and a 4℃/60℃ thermal cycling test, the shear bond strength of each specimen was measured with a cross head speed of 1 mm/min. Under all experimental conditions, the ME primer showed a significantly stronger adhesion to the dentin than the MDP primer. Irrespective of the different kinds of bonding agent applied, the ME primer containing FM showed no significant decrease in adhesion to dentin after water storage for 6 months or after a thermal cycling test, and maintained a nearly stable adhesive strength. In addition, the combined use of 5.0 wt% FM containing ME primer and UD/3G showed the strongest adhesive strength. On the other hand, the MDP primer used in combination with different bonding agents showed no effectiveness. Thus, the results showed that combination of a self-etching primer containing ME with the addition of FM and a UD/3G bonding agent formed an adhesive layer of the highest durability.

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Aim: The purpose of this study was to evaluate the influence of γ-irradiation of teeth on the effectiveness of root canal irrigation and the sealing ability of root canal filling materials. Methodology: <Experiment 1> Twenty bovine teeth were divided into four groups : those subject to no irradiation, 60 Gy, 3 kGy, and 30 kGy of radiation, respectively. All teeth were split longitudinally and irrigated with 6% NaClO or distilled water. After irrigation, SEM images of the root canal wall dentin were evaluated and scored. The results of the score evaluation were statistically analyzed based on logistic-regression analysis (p<0.05). <Experiment 2> Ninety extracted single rooted human teeth were allocated to three groups: those subject to no irradiation, irradiation before root canal filling, and irradiation after root canal filling raspectively. The roots in each group were divided into three subgroups of 10 teeth each and obturated with gutta-percha point (GP) with Sealapex (Group A), Resilon™ with Epiphany™ sealer (Group B), or GP with MetaSEAL™ (Group C). After the canal sealers were set, a polypropylene tube containing a 0.06% methylene blue dye solution was attached to the coronal portion of each root. Two millimeters of the apical portion were immersed in distilled water within a glass bottle. The amount of dye emerging through the root into the water was measured with a spectrophotometer at 1, 4, 8, 15, and 30 days after immersion. Data obtained were statistically analyzed using ANOVA and Tukey-Kramer at 5% significant level. Results: <Experiment 1> The degree of irrigation scoring differed significantly between the no irradiation group and the 3 kGy group, and between the no irradiation group and the 30 kGy group. Significant differences were also found between the two irrigation methods in all groups irrespective of the dose of irradiation (p<0.05). <Experiment 2> Statistical analysis revealed that the amount of leaked dye on the 30th day differed significantly between the Sealapex group and the MetaSEAL™ group. There were no significant differences in the amount of leaked dye among the no irradiation group, the irradiation before root canal filling group, and the irradiation after root canal filling group. Conclusions: Under the conditions of this study, the sealing ability of root canal filling materials was not affected by irradiation of the teeth. When a root canal was irrigated, dentin exposed to high dosages of radiation showed different features compared to normal dentin.

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The aim of the study was to assess the effects of Er: YAG laser irradiation equipped with a cone-shaped tip (300μm inner-diameter) on root canal walls of extracted human teeth and on bovine dentin slices. Human teeth mechanically prepared using K-files were irradiated by Er: YAG laser at the output powers of 30 mJ and 40 mJ without air and water cooling. Subsequently, the samples were split longitudinally and observed under a scanning electron microscope (SEM). SEM showed the crater formation with the removal of smear layer and open dentinal tubules, free of melting, crack, and carbonization. The size of open tubules by laser was smaller than that by chemical irrigation using EDTA. In addition, Er: YAG laser was applied to bovine dentin surfaces with a thickness gauge (50, 100, or 150μm) between the tip and dentin slices. Laser microscopic analysis revealed that the ablation effect of Er: YAG laser largely decreased by distance between the tip and dentin wall. These results indicate that the Er: YAG laser in conjunction with a cone-shaped tip is a suitable tool for removing the smear layer in root canals. Moreover, it was suggested that in the apical third of the root canal the use of a tip which fits the size of enlarged canals is necessary for the efficient cleaning of the mechanically prepared canal wall.

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The purpose of this study was to investigate the influence of Ca(OH)₂ on NaClO in the dissolution of organic tissue. In this study, we used gelatine as a protein which was treated with 5% NaClO[0 mg-Ca(OH)₂ group], 5% NaClO+1 mg/ml-Ca(OH)₂[1 mg-Ca(OH)₂ group], 5% NaClO+0.1 mg/ml-Ca(OH)₂[0.1 mg-Ca(OH)₂ group], or 5% NaClO+0.01 mg/ml-Ca(OH)₂ [0.01 mg-Ca(OH)₂ group], respectively. The dissolution of gelatine was greater in the 0 mg-Ca(OH)₂ group than in the 1 mg-Ca(OH)₂ group (p<0.01). In addition, increases in pH were dependent on Ca(OH)₂ concentration. Free radicals were measured using the ESR spin-trapping method. Generation of DMPO-X was found to be increased by Ca(OH)₂ concentration, and diminished time dependent. These results suggested that gelatine dissolution with NaClO was inhibited by Ca(OH)₂ concentration.

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Recently, various resin-based root canal filling materials with adhesive properties have been introduced, whereas removal of these materials may cause serious problems during root canal retreatment. Nickel titanium (NiTi) rotary instrumentation has been applied in the removal of gutta-percha, while only a few studies have evaluated the efficacy of this technique with respect to resin-based materials. In this study, we compared the working time, canal wall cleanliness and frequency of iatrogenic events when different resin-based root canal filling materials were removed with either K3 or ProTaper rotary instrumentation. Resilon (RE) and gutta-percha points with a taper of 6% (GP) or 4% (04GP) were used as core materials, and Epiphany (EP), SuperBond sealer (SB), and Canals N (CA) were used as sealers. Ninety-six simulated canals with a 30-degree curvature in resin blocks were prepared with NiTi instruments to a size 25/06 taper and were randomly divided into RE+EP, RE+SB, GP+SB, 04GP+SB, GP+CA and 04GP+CA groups (n=16, each). The canals were then filled with a single cone technique and each group was further subdivided (n=8, each) according to the use of either K3 or ProTaper Retreatment Files (PT). Removal was performed with a standardized crown-down technique. Working time for each removal attempt was measured, and the amount of residual material on the canal wall at 0-2, 2-4 and 4-6 mm levels from the apex was imaged and evaluated using a 5-point score system. Frequencies of file fracture and ledge formation were also recorded. PT was faster than K3 in all groups (ANOVA and Fisher's PLSD test, p<0.05). RE+EP required significantly longer working time compared with 04GP+CA and RE+SB for PT and GP+SB for K3 (ANOVA and Fisher's PLSD test, p<0.05). GP+CA and 04GP+CA showed significantly greater amounts of remaining materials at 2-4 and 4-6 mm levels, compared with certain groups with resin-based materials (Steel Dwass test, p<0.05). File separation occurred in three canals and a ledge was formed in three canals. It was concluded that ProTaper and K3 instruments may be applicable to the removal of resin-based root canal filling materials. However, safety issues remain to be fully evaluated before routine usage can be recommended.

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The recent growth of aesthetic demand among patients and the concept of Minimal Intervention (MI) have begun to attract attention to the use of composite resin for restoration after minimum grinding. This has also made composite resin popular for aesthetic restoration. For high-grade aesthetic restoration to resemble a natural tooth enough to satisfy a patient, the tone should be selected in consideration of the influence of the ambient color on the composite resin. Composite resin is a semitransparent material known to be subject to the influence of the background color. Therefore, investigation into the tone of composite resin filled into cavities of various conditions is important for understanding tonal harmony between the composite resin and the natural tooth. In this study, we conducted an experiment to investigate the influence of the color and size of a cylindrical cavity on the composite resin used for restoration. Considering white and black cylindrical cavities of different diameters and depths as standard cavities, we measured the colors of three types of composite resin in order to investigate the influence of the cylindrical cavity size and the cavity wall color on the color of the composite resin. In conclusion: 1. The color of composite resin used to repair a cylindrical cavity is subject to both the influence of the cavity wall color and the cavity form. 2. The influence of the cavity floor and wall colors on composite resin color varies with cavity size and depth. 3. Consideration of the influence of the cavity walls and cavity form is necessary when selecting the color of composite resin for restoration.

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The purpose of this study was to examine the relationship among the tensile bond strength of three adhesive systems (Clearfil Mega Bond (Cleartil SE Bond), Tri-S Bond, ABF/Kuraray) to carious dentine, DIAGNOdent™ value and dyeing-degree with Caries Detector®. In addition, efficiencies of DIAGNOdent™ were investigated as a substitute for Caries Detector®. A shade guide consisting of 15 continuous diluted solutions of Caries Detector®, 1/2ⁿ (n=1-15) concentration was prepared. Preliminary survey of clinical acceptable caries affected-dentine for the adhesive restoration was performed by 25 clinicians, and as a result, the mean acceptable dyeing-degree for caries affected-dentine were C=10. Thirty extracted human canines and premolars with cervical caries were used. The DIAGNOdent™ value (D₁-value) of the carious dentine was measured. Then the carious dentine (cariesinfected dentine) was stained with Caries Detector® (C-value) and measured with DIAGNOdent™ (D₂-value). Each adhesive system was applied to the dentine, according to the manufacturer's instruction, and tensile bond strength tests were performed using a Portable Adhesion Tester (BST value). Dyed caries-infected dentine was removed using a round steel bur, following standard clinical procedure. The above-mentioned procedure was continuously performed until the C-value of the carious dentine became 10 or greater. The data were analyzed using the Pearson's correlation coefficient test. The results are as follows. 1. Though there was a significant difference between D₁ and D₂-values, there seems to be no difference in use as an indicator for removing caries dentine. 2. The correlation coefficient was statistically significant between the D₂-value and C-value (p<0.01). However, the correlation coefficient was -0.238. 3. There were significant positive correlations between the C-value and BST values of the three adhesives. 4. Though there was a significant negative correlation between the D₂-value and BST value of CMB (p<0.01), there was no correlation between the D₂-value and BST value of TRS or ABF. 5. The mean BST values of the C=10 dentine were: CMB 25.3 MPa, TRS 20.5 MPa, ABF 25.1 MPa, respectively. There was no significant difference between the adhesives. 6. Compared to the C-value, the regularity of the D₂-value seemed to be low. So single use of DIAGNOdent™, as a caries-removing indicator, is not an adequate choice.

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When investigating of vital tooth bleaching, it is considered difficult to simply apply a clinical result as an index for evaluating the bleaching effect, because of individual variations as well as varied staining substances and degrees of staining. Even in the case of in vitro bleaching experiments, it is also difficult to obtain evenly stained enamel with no individual variation in a relatively short term due to the structural properties of enamel. Thus, an alternative sample that can serve as a standard for evaluating the effects of bleaching is desired. Based on the assumption that a brown eggshell could serve as an effective sample for evaluating vital tooth breaching, we had previously examined the eggshell structure and the stability of staining in relation to the bleaching effect using a colorimetry the result of which suggested its possibility. In the present study, therefore, the bleaching effect in relation to light irradiation time was examined using two commercially available office bleaching agents in Japan, in order to elucidate the possible utility of brown eggshell as an evaluation sample with the aid of a halogen lamp light irradiator for composite resin polymerization. With regard to the bleaching effect, L*, a*, b* value at each irradiation time was calculated by colorimetry, and the effect was then evaluated based on ΔL*, Δa* and Δb* as well as the difference in coloration before and after bleaching to examine a possible approach for evaluating the bleaching effect achieved using brown eggshells. As a result, the following conclusions were obtained: 1. With the aid of light polymerization irradiator used in this study, it was revealed that light irradiation lasting about 4 minutes is most suitable for bleaching in the case of Shofu Hi-Lite 2. With the aid of light polymerization irradiator used in this study, it was indicated that the bleaching could be done more effectively with a prolonged irradiation time in the case of Pyrenees. In the present experiment condition, the most effective time result could be obtained in maximum 9 minutes. 3. In the breaching of the brown eggshell, it was considered that the bleaching effect could be evaluated using ΔL* values before and after bleaching.

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It is known that the remnants of temporary cement decrease the bond strength of luting cement. Although self-adhesive luting cements have recently become available, little is known about the influence of removal methods of temporary cement on the dentin bond strengths of the cements. The purpose of this study was to evaluate the influence of temporary cement removal methods on the shear bond strengths of luting cements. An experimental temporary cement and four luting cements were used. After removal of temporary cement using different removal methods, the luting cements were inserted into a mold and hardened. Shear bond strength tests and scanning electron microscopic (SEM) observations were done. The results were as follows: 1. When the luting cements were applied according to each manufacturer's instructions, the dentin bond strength was found to range from 6.0 to 10.5 MPa. On the other hand, dentin bond strength after the removal of temporary ranged from 2.8 to 9.0 MPa. 2. The method used to remove the temporary cement together with the type of luting cement used were significant factors affecting dentin bond strength. 3. The highest bond strength was obtained when the temporary cement was removed using an ultrasonic tip. The predominant mode of failure was the adhesive regardless of the method used to remove the temporary cement. 4. Different morphological features of the dentin surface were observed under the SEM.

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