The purpose of this study was to evaluate the effect of the polymerization shrinkage and modulus of elasticity of composites on the cusp deflection of class V restoration in premolars. The sixteen extracted upper premolars were divided into 2 groups with similar size. The amounts of cuspal deflection were measured in Class V cavities restored with a flowable composite (Filtek flow) or a universal hybrid composite (Z-250). The bonded interfaces of the sectioned specimens were observed using a scanning electron microscopy (SEM). The polymerization shrinkage and modulus of elasticity of the composites were measured to find out the effect of physical properties of composite resins on the cuspal deflection. The results were as follows.

The amounts of cuspal deflection restored with Filtek flow or Z-250 were 2.18 ± 0.92 µm and 2.95 ± 1.13 µm, respectively. Filtek flow showed less cuspal deflection but there was no statistically significant difference (p > 0.05).

The fracture toughness test is believed as a clinically relevant method for assessing the fracture resistance of the dentinal restoratives. The objectives of this study were to measure the fracture toughness (K_1C) and microtensile bond strength of dentin-resin composite interface and compare their relationship for their use in evaluation of the integrity of the dentin-resin bond.

A minimum of six short-rod specimens for fracture toughness test and fifteen specimens for microtensile bond strength test was fabricated for each group of materials used. After all specimens storing for 24 hours in distilled water at 37℃, they were tensile-loaded with an EZ tester universal testing machin. Statistical analysis was performed using ANOVA and Tukey's test at the 95% confidence level, Pearson's coefficient was used to verify the correlation between the mean of fracture toughness and microtensile bond strength. FE-SEM was employed on fractured surface to describe the crack propagation.

Fracture toughness value of Clearfil SE Bond (SE) was the highest, followed by Adper Single Bond 2 (SB), OptiBond Solo (OB), ONE-STEP PLUS (OS), ScotchBond Multi-purpose (SM) and there was significant difference between SE and other 4 groups (p < 0.05). There were, however, no significant difference among SB, OB, OS, SM (p > 0.05). Microtensile bond strength of SE was the highest, followed by SB, OB, SM, OS and OS only showed significant lower value (p < 0.05). There was no correlation between fracture toughness and microtensile bond strength values. FE-SEM examination revealed that dentin bonding agent showed different film thickness and different failure pattern according to the film thickness.

From the limited results of this study, it was noted that there was statistically no correlation between K1C and µTBS. We can conclude that for obtaining the reliability of bond strength test of dentin bonding agent, we must pay more attention to the test procedure and its profound scrutiny.

This study compared the microtensile bond strength (µTBS) of three single step adhesives to dentin.

Occlusal superficial dentin was exposed in fifteen human molars. They were assigned to three groups by used adhesives: Xeno group (Xeno III), Prompt group (Adper Prompt L-Pop), AQ group (AQ Bond).

Each adhesive was applied to dentin surface, and composite of same manufacturer was constructed. The bonded specimens were sectioned into sticks with an interface area approximately 1 mm², and subjected to µTBS testing with a crosshead speed of 1 mm/minute. The results of this study were as follows;

The µTBS to dentin was 48.78 ± 9.83 MPa for Xeno III, 30.22 ± 4.52 MPa for Adper Prompt L-Pop, and 26.31 ± 7.07 MPa for AQ Bond.

The mean µTBS of Xeno group was significantly higher than that of Prompt group and AQ group (p < 0.05).

There was no significant difference between the µTBS of Prompt group and AQ group.

This study was done to evaluate the shear bond strength between light-cured glass ionomer cement (GIC) base and resin cement for luting indirect resin inlay and to observe bonding aspects which is produced at the interface between them by SEM.

Two types of light cured GIC (Fuji II LC Improved, GC Co. Tokyo, Japan and Vitrebond™, 3M, Paul, Minnesota, U.S.A) were used in this study. For shear bond test, GIC specimens were made and immersed in 37℃ distilled water for 1 hour, 24 hours, 1 week and 2 weeks. Eighty resin inlays were prepared with Artglass® (Heraeus Kultzer, Germany) and luted with Variolink® II (Ivoclar Vivadent, Liechtenstein).

Shear bond strength of each specimen was measured and fractured surface were examined. Statistical analysis was done with one-way ANOVA.

Twenty four extracted human third molars were selected and Class II cavities were prepared and GIC based at axiopulpal lineangle. The specimens were immersed in 37℃ distilled water for 1 hour, 24 hours, 1 week and 2 weeks. And then the resin inlays were luted to prepared teeth. The specimens were sectioned vertically with low speed saw. The bonding aspect of the specimens were observed by SEM (JSM-5400®, Jeol, Tokyo, Japan). There was no significant difference between the shear bond strength according to storage periods of light cured GIC base. And cohesive failure was mostly appeared in GIC. On scanning electron micrograph, about 30 - 120 µm of the gaps were observed on the interface between GIC base and dentin. No gaps were observed on the interface between GIC and resin inlay.