Effect of different curing protocols of various dual-cure one-step self-etching adhesives on shear bond strength to dentin

Abstract

The purpose of this study was to evaluate the effect of curing protocols of four dual-cure one-step self-etching adhesives on shear bond strength (SBS) to dentin when combined with a self-cure composite. A total of 120 anterior bovine teeth were randomly assigned to 12 groups (n=10/group) according to the two experimental factors being investigated (adhesive type and curing protocol). Superficial labial dentin surfaces were exposed, embedded in acrylic resins and wet ground using #600-grit SiC paper. Adhesives were applied following the manufacturers' instructions and polymerized according to the respective curing protocol. The self-cure composite (Rebilda SC) was subsequently injected into polyethylene tubes (4 mm diameter x 2 mm depth) over the adhesives. The specimens were stored in 100% relative humidity at room temperature for 24 hours. They were submitted to shear bond strength test at 0.5mm/min crosshead speed until failure, then evaluated for fractographic analysis using a digital microscope x40. Representative debonded specimens were examined under SEM. For Vickers microhardness test (VMH), 60 composite cylinders (4 mm x 2 mm) were fabricated from Rebilda SC and divided into 12 groups (n=5/group) according to the two study levels mentioned earlier. VMH test was conducted on top surface with 500 g load and 15 seconds dwell time. Data obtained were statistically analyzed by ANOVA and Tukey's post-hoc tests (p=0.05). Two-Way ANOVA revealed that SBS results were significantly influenced by adhesive type, curing protocol and their interactions (p=0.000). For VMH, both experimental factors (adhesive type and curing protocol) had a significant effect on the VMH results (p=0.025 and p=0.000 respectively). The interactions between the two independent factors (adhesive type and curing protocol) showed also a significant effect (p=0.000). The failure modes observed were 82.5% adhesive, 15% mixed and 2.5% cohesive in dentin. SEM demonstrated that most of specimens had a fracture at the bottom of the hybrid layer.

Under the limitations of this study, several conclusions could be suggested: 1. Light activation of dual-cure self-etching adhesives prior to the application of the self-cure resin composite seemed to be an important step to enhance SBS. 2. Increasing light-curing distance showed no effect on SBS of two-bottle dual-cure adhesives; however, it negatively affected the SBS of the single-dose dual-cure adhesive. 3. It is preferable to include the DC catalyst in a separate bottle rather than within the adhesive composition. 4. The special-purpose adhesive (Gradia SE Bond dual-cure adhesive) showed inferior bonding performance compared to the universal adhesives, even in close proximity to the light-curing device.

Nevertheless, further studies should be conducted to evaluate the effect of dual-cure self-etching adhesives on different parameters critical to bond performance of both dual- and self-curing resin composites.