This study investigated the effect of the strength and wetting characteristics of adhesives on the bond strength to dentin. The experimental adhesives containing various ratios of hydrophobic, low-viscosity Bis-M-GMA, with Bis-GMA and TEGDMA, were made and evaluated on the mechanical properties and bond strength to dentin.

Five experimental adhesives formulated with various Bis-GMA/Bis-M-GMA/TEGDMA ratios were evaluated on their viscosity, degree of conversion (DC), flexural strength (FS), and microtensile bond strength (MTBS). The bonded interfaces were evaluated with SEM and the solubility parameter was calculated to understand the wetting characteristics of the adhesives.

Although there were no significant differences in the DC between the experimental adhesives at 48 hr after curing (p > 0.05), the experimental adhesives that did not contain Bis-GMA exhibited a lower FS than did those containing Bis-GMA (p < 0.05). The experimental adhesives that had very little to no TEGDMA showed significantly lower MTBS than did those containing a higher content of TEGDMA (p < 0.05). The formers exhibited gaps at the interface between the adhesive layer and the hybrid layer. The solubility parameter of TEGDMA approximated those of the components of the primed dentin, rather than Bis-GMA and Bis-M-GMA.

To achieve a good dentin bond, a strong base monomer, such as Bis-GMA, cannot be completely replaced by Bis-M-GMA for maintaining mechanical strength. For compatible copolymerization between the adhesive and the primed dentin as well as dense cross-linking of the adhesive layer, at least 30% fraction of TEGDMA is also needed.

This study investigated the hypothesis that increasing light-curing time would leave the oxygen-inhibited layer (OIL) of the adhesive thinner, and in turn, result in lower shear bond strength (SBS) than those obtained by the routine curing procedures.

120 human extracted posterior teeth were randomly divided into three groups for bonding with three adhesives: All Bond 2®, One Step®, and Adper Prompt®. They were subsequently divided into four subgourps with different light-curing time (10, 20, 30 and 60 s). The assigned adhesives were applied on superficial occlusal dentin according to the manufacturer’s instructions and cured with one of the four curing times. Composite resin cylinder, 2.35 mm in diameter, were built on the cured adhesive and light-cured for 40 s. SBS were measured after 24 h from the bonding using a universal testing machine (crosshead speed 1.0 mm/min). The relative thickness of the OIL and the degree of conversion (DC) were determined from the adhesive on a slide glass using FT-NIR in an absorbance mode. Data were analysed with One-way ANOVA and Duncan’s multiple test (p < 0.05).

With increasing cure time, although there were no significant difference in th SBS of One-step and Adper Prompt (p > 0.05), those of All Bond 2 decreased significantly (p < 0.05). The relative thicknesses of the OIL on each adhesive were not affected by the cure time (p > 0.05). Although the DC of All-Bond 2 were statistically not different with increasing cure time (p > 0.05), those of One-Step and Adper Prompt showed an increasing trends with increasing cure time (p < 0.05).

Increasing light-curing time did not affect on the relative thickness of the OIL of the adhesives, and in turn, on the SBS to dentin.

The aim of this study is to evaluate the effect of light intensity variation on the polymerization rate of composite resin using IB system (the experimental equipment designed by Dr. IB Lee) by which real-time volumetric change of composite can be measured.

Three commercial composite resins [Z100(Z1), AeliteFil(AF), SureFil(SF)] were photopolymerized with Variable Intensity Polymerizer unit (Bisco, U.S.A.) under the variable light intensity (75/150/225/300/375/450mW²) during 20 sec. Polymerization shrinkage of samples was detected continuously by IB system during 110 sec and the rate of polymerization shrinkage was obtained by its shrinkage data. Peak time(P.T.) showing the maximum rate of polymerization shrinkage was used to compare the polymerization rate.

Peak time decreased with increasing light intensity(p<0.05). Maximum rate of polymerization shrinkage increased with increasing light intensity(p<0.05). Statistical analysis revealed a significant positive correlation between peak time and inverse square root of the light intensity (AF:R=0.965, Z1:R=0.974, SF:R=0.927). Statistical analysis revealed a significant negative correlation between the maximum rate of polymerization shrinkage and peak time(AF:R=-0.933, Z1:R=-0.892, SF:R=-0.883), and a significant positive correlation between the maximum rate of polymerization shrinkage and square root of the light intensity (AF:R=0.988, Z1:R=0.974, SF:R=0.946).

The polymerization rate of composite resins used in this study was proportional to the square root of light intensity. Maximum rate of polymerization shrinkage as well as peak time can be used to compare the polymerization rate. Real-time volume method using IB system can be a simple, alternative method to obtain the polymerization rate of composite resins.