Microtensile bond strengths to cavity floor dentin in indirect composite restorations using resin coating

The aims of this study were (1) to evaluate the effect of a resin coating on the microtensile bond strengths (mu-TBSs) of indirect composite restorations bonded to dentin with resin cement and (2) to compare the mu-TBSs with that of a directly placed composite.

Class I cavities were prepared in extracted human molars. The specimens were divided into five groups: For the indirect restorations, the cavity surfaces of the control group were left uncoated (group 1), while the surfaces of the experimental groups were resin coated with a dentin bonding system, Clearfil Protect Bond (PB; groups 2 and 3), or with a combination of PB and a flowable resin composite, Protect Liner F (PLF; group 4). The cavities were temporized for 1 day. Indirect composite restorations (Estenia) were cemented with a resin cement (Panavia F). Pretreatment with ED Primer II was performed in the groups 1, 3, and 4. For the direct restorations, the cavities were restored with PB and a direct composite (Clearfil AP-X; group 5). After 24 hours of water storage, mu-TBSs were measured at a crosshead speed of 1 mm/min. The data were analyzed with one-way analysis of variance and Sheffe's test (p < 0.05). In addition, fracture modes were determined visually and by scanning electron microscopy.

A combination of PB and PLF showed significantly higher bond strengths compared with the original bond strength of Panavia F and the single use of PB (p < 0.05). However, the highest bond strengths were obtained when PB was used for direct composite restorations (p < 0.05).

The application of a resin coating consisting of a self-etching primer dentin bonding system and a flowable resin composite significantly improved the mu-TBS of indirect restorations bonded to dentin using resin cement.

A resin coating should be required to improve dentin bonding performance of Panavia F in indirect restorations. However, direct composite restorations still provide higher bond strength compared to indirect restorations.