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PURPOSE: The aims of this study were to (1) evaluate the effect of a resin coating consisting of a dentin bonding system and a flowable resin composite on the microtensile bond strength (micro-TBS) of a resin cement to dentin in indirect composite restorations and (2) compare the bond strengths of direct and indirect composite restorations. MATERIALS AND METHOD: Occlusal surfaces of human premolars were ground to obtain flat dentin surfaces and were divided into seven groups. For indirect restorations, the dentin surfaces of the experimental groups were bonded with a dentin bonding system (DBS), Clearfil SE Bond (SE) or Single Bond (SB) with and without a flowable resin composite, Protect Liner F (PLF), temporized for one day and cemented with a resin cement (Panavia F) according to the manufacturer's instructions. The dentin surfaces of the control group were temporized without prior treatment, and indirect composite (Estenia) was bonded with Panavia F. For the direct restorations, either SE or SB was applied to the dentin surface and the entire surface was built up with direct composite (Clearfil AP-X). After 24 hours in water storage, micro-TBS was measured at a crosshead speed of 1 mm/min. The data were analyzed with one-way analysis of variance and Fisher's protected least significant difference test (p < .05). RESULTS: The original bond strength of the resin cement (Panavia F) to dentin significantly improved with the use of a resin coating technique in indirect restorations (p < .05). The combination of DBS + PLF showed significantly higher bond strengths compared with the single use of DBS. The combination of SE + PLF as a resin coating provided the highest bond strengths in indirect restorations (p < .05). However, the best bond strengths were observed when SE and SB were used for direct composite restorations (p < .05). CONCLUSIONS: The application of a resin coating consisting of a dentin bonding system and a flowable resin composite on the dentin following cavity preparation significantly improved the micro-TBS of the resin cement Panavia F to dentin in indirect restorations. However, the bond strengths of indirect composite restorations were significantly lower than those of direct composite restorations even with the resin coating technique. CLINICAL SIGNIFICANCE: Indirect composite restorations may require a resin coating to improve the bonding performance of the resin cement Panavia F to dentin. However, adhesive systems with direct composite restorations still provide superior bond strengths compared with indirect restorations.
Jayasooriya et al. (Sat,) studied this question.