This in vitro study aimed to evaluate the effect of flowable composite resin as a restorative material on regional tensile bond strength to cervical wedge shaped cavity walls. Wedge-shaped cavities were prepared in the buccal cervical dentin of eighteen extracted intact human molars. The teeth were divided into two groups according to the adhesive systems used (Clearfil Mega Bond, MB, (Kuraray), or One-up Bond F, OB, (Tokuyama)). After the application of the adhesive systems, the teeth were further subdivided into two groups, and the cavities were restored with a flowable resin composite (the flowable group, Palfique Estelite LV High Flow, Tokuyama) or a hybrid resin composite (the hybrid group, Palfique Estelite, Tokuyama). After 24h in water at room temperature, the teeth were serially sliced and alternately trimmed (0.7?-1.4mm) to test either the occlusal or gingival walls of the each bonded restoration, and micro-tensile bond strengths (μTBS) were determined. The data were analyzed by one-way and three-way ANOVA, and Fisher's PLSD test (p<0.05). For both adhesive systems, and both sides of the cavity walls, μTBS of the flowable group was higher than the hybrid group. Flowable resin composite used in this study could be recommended as the adequate restorative material for improved bonding to the wedge shaped cavity.

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The purpose of the current study was to evaluate the adhesive performance of bonding between resin modified glass ionomer luting agents and a silver-palladium-copper-gold alloy. One luting agent (Ionotite F) contained 6-methacryloyloxyhexyl 2-thiouracil-5-carboxylate (MTU-6), whereas the other five agents (Fuji Lute, Fuji Lute BC, Fuji Luting S, Vitremer Luting Cement Fast Set, Xeno Cem Plus) were conventional materials. Cast disk specimens made of a silver-palladium-copper-gold alloy (Castwell M.C. 12) were airabraded with alumina then bonded with the six luting agents. Shear bond strengths were determined before and after thermocycling (20, 000cycles). Bond strength was significantly reduced by application of thermocycling for all groups (p<0.05). The Ionotite F material exhibited the greatest bond strength both before and after thermocycling (50.4, 14.3MPa). It is notable that the post-thermocycling bond strength of the Ionotite F material was statistically comparable to the pre-thermocycling bond strength of the Fuji Lute and Fuji Lute BC materials.

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Recently, good bonding performance to dentin has been demonstrated by means of development and improvement of the adhesive systems. The purpose of this study was to evaluate the effect of operating experience on dentin bond strengths of three dentin bonding systems. Eight graduate students and two instructors were selected as the group with and without experience of bonding test respectively. Ground bovine dentin was bonded with one of three dentin bonding systems, Clearfil SE Bond (SE), Single Bond (SB), and AQ Bond (AQ). The specimens were subjected to the conventional tensile bond testing at crosshead speed of 2.0mm/min after 1day storage in water. The highest bond strength were obtained in SE, in which there were no significant differences between instructors and the graduate students. On the other hand, the instructors group recorded a statistically higher bond strengths of SB and AQ than those of the graduate students group. The bond strengths were material and operator dependent. SE showed less technique sensitivity than the other bonding systems.

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This in vitro study aimed to evaluate the micro-shear bond strengths of the newly developed fluoride releasing one-step bonding system (Fluoro Bond Shake-One, FB, Shofu), and Reactmer Bond (RB, Shofu). Sixteen bovines' labial crowns were sectioned to make eight enamel plates and eight dentin plates (12×6×2mm). After the preparation with #600 grit SiC paper, FB or RB was applied to these enamel or dentin surfaces according to the manufacturers' instructions. Then, cylinders of Beautifil (Shofu) were adhered according to the Shimada's method. After 15min or 24 hrs, the micro-shear bond strengths (MSBS) to enamel and dentin of the adhesives were measured (n=10). Two human molars were used for SEM observations of the enamel and dentin surfaces after the treatment with FB or RB. The resin-enamel and resin-dentin interfaces of FB were also observed by SEM. For both 15min-group and 24hrs-group, MSBS to enamel and dentin of FB were significantly higher than those of RB. The dentin bond strengths of 15min-group and 24hrs-group of FB were almost same, and the enamel bond strength of 15min-group of FB was significantly higher than that of 24hrs-group of RB.

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Assuming the initial molecular interactions in the resin infiltrated layer formation at a dentin surface, an interaction between type I collagen and 2-hydroxyetyl methacrylate (HEMA) was investigated using a chromatography and a calorimetry techniques. It was found that at lower HEMA concentrations, the collagen helix tended to dissociate and became less stable with increasing HEMA concentration. It was supposed that the internal hydrogen bonds that had stabilized the helix were exchanged with those between collagen and HEMA, which meant the binding of HEMA onto collagen. On the other hand, an excess of HEMA deprived collagen of water, leading to the shrinking of collagen and a rise of its denaturation temperature, at higher HEMA concentrations. At a balanced concentration of 30 wt%, HEMA might be taken up into collagen fibers most effectively, which is strongly supported by the previous experimental fact that the tensile strength at a dentin surface was the strongest when 30 wt% HEMA was applied (Suzuki and Nakai, 1993).

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The purpose of this study was to evaluate the microhardness of the matrix part of a commercially available dual-cure resin cement: Panavia Fluoro Cement (Kuraray Medical). The effect of curing methods (with or without light irradiation), storage conditions (either in the dry chamber, distilled water or artificial demineralizing solution: pH4.5) and storage periods (1 day or 1 week) on the microhardness of dual-cure resin cement matrix was investigated. Microhardness of the matrix resin part of each specimen were measured using a nano-indentation tester (ENT-1100, Elionix) with 5gf load. The data of each group were statistically analyzed and then the factor curing methods was revealed to have significant effect on the microhardness of the resin cement matrix, while storage conditions and storage periods had no significant effect.

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An experimental single-step bonding system, RZII (Sun Medical), has been developed as a resin coating material. The purpose of this study was to evaluate the dentin bonding of RZII using micro-tensile bond strength (MTBS) test and a SEM observation. RZII was applied to the human molar dentin once or twice for “resin coating”. After storage in water for 1 day, a cured composite was cemented to the coated dentin using a resin cement, Chemiace II (Sun Medical). For the control group, a cured composite was cemented to the dentin surface using Chemiace II without resin coating. After storage in water for 1 day, MTBSs were measured at a crosshead speed of 1mm/min. Number of the specimens for each group was twenty. The data were analyzed using one-way ANOVA and Fisher's PLSD test (p=0.05). The interface between the indirect composite and resin-coated dentin was also observed using a SEM. The MTBSs with RZII were approximately 25 MPa, which were significantly higher than that without resin coating (p<0.05). The thickness of the resin-coating layer and the hybrid layer were 5-6μm and less than 1μm, respectively. RZII could be useful as a resin coating material for crown preparation.

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In this study, the influence of the heat-treatment of the bovine dentin, on the adhesion ofthe dentin to adhesive resin cement was evaluated using frozen storage bovine teeth. Afterperforming thermal cycling 10, 000 times between 4 and 60°C, or thermal treatment for 10hours at 100°C, shear bond strength of the specimens adhered to Super bond was measured.Furthermore, scanning electron microscopic observation of the polished surface of thethermal treated dentin, the dentin surface pre-treated by 10-3 solution, and resin tags of the Super bond was performed, and Knoop hardness of the dentin was measured. Shear bondstrength of the dentin to adhesive resin cement decreased after thermal treatment. Further-more, the effects of pre-treatment agents on the removal of the smeared layer decreased, and decreases in Knoop hardness were noted, suggesting the influence of thermal treatmenton the changes in dentin collagen.

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The purpose of this study was to examine the shear bond strength of composite resin core build up by indirect method to the human dentin. The shear bond strength was measured before and after 5, 000 thermocycling when various dentin conditioners and two types of cements were used. Furthermore, scanning electron microscopic observation was performed on the dentin surface after applying various dentin conditioners and on the dentin/resin interface after cross-sectioning the specimens.
In comparison with the direct method, the groups of the indirect method indicated almost the same or significantly higher bond strength. Bond strength after thermocycling did not indicate any significant differences among all groups. Scanning electron microscopic images showed that there were some kinds of morphological change on each pretreated dentin surfaces and on the cross sectional surfaces of each bonding area. That means there are some differences of the adhesion system in each experimental condition.

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The aims of this study were to estimate the thickness and structure of hybrid layer formed with a self-etching bonding agent (AQ Bond) by SEM and TEM observations.
Various chemical modifications on specimens were useful for the observation of both SEM and TEM to study the hybrid layer. Less than 1μm of hybrid layer was discerned in TEM although it could not be observed clearly by SEM. According TEM observations, a demineralized dentin and resin-reinforced dentin were discernible in the hybrid layer. But if larger amount of bonding agent was placed on the prepared surface and cured, the demineralized smear layer was identified in the bonding layer and it could be adverse effects on the bonding.
It was concluded that smear must be scattered during the application of the self-etching bonding agent.

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Recently, the AQ Bond Plus has been developed with the improvement on the previous AQ Bond by Sun Medical Co. The AQ Bond Plus does not have to be applied to the cavitywalls twice, and can be cured with any kind of the visible light curing unit such as a halogenlamp unit, a xenon lamp unit, or an LED unit. The purpose of this study was to examinethe interfacial ultrastructure between the AQ Bond Plus and enamel/intact dentin/caries-affected dentin under the FE-SEM by means of the Ar-ion beam etching technique. The AQ Bond Plus showed a tight interfacial junction to enamel/intact dentin/caries-affecteddentin without creating hybrid layer which was revealed in the SEM images of theconventional resin bonding systems. From the results of this study, there was a doubtwhether the resin impregnated dentin, namely hybrid layer was an indispensable factor forresin bonding to dentin.

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