The effects of internal tooth bleaching regimens on composite-to-composite bond strength

Background. The authors conducted an in vitro study to investigate the influence of several internal bleaching regimens on the composite-to-composite shear bond strength of a dental core buildup material. Methods. The authors fabricated 72 specimens from a resin-based composite core buildup and assigned them randomly to six groups (four experimental and two control groups) (n = 12 per group), according to the following bleaching agents: sodium perborate mixed with distilled water (SP/W); sodium perborate mixed with 3 percent hydrogen peroxide (SP/HP-3); sodium perborate mixed with 30 percent hydrogen peroxide (SP/HP-30); 35 percent hydrogen peroxide (HP-35). After the 12-day bleaching procedures, the authors applied a calcium hydroxide dressing for two weeks. The two control groups consisted of unbleached specimens that either did not receive (C1) or did receive (C2) the calcium hydroxide dressing. The authors cleaned and silanized the resin-based composite specimens and coated them with an intermediate adhesive resin before applying fresh composite material. They measured composite surface roughness and shear bond strength and performed statistical analyses of the data. Results. Unbleached specimens in groups Cl and C2 exhibited significantly lower composite-to-composite bond strength and significantly lower surface roughness than did specimens in groups SP/W and SP/HP-3. Bond strength in group HP-35 was significantly lower than that in group SP/W. Conclusion. Internal bleaching regimens that involve the use of sodium perborate mixed with water or 3 percent hydrogen peroxide might increase the composite-to-composite interfacial bond strength. Clinical Implications. None of the internal bleaching regimens in this study had an adverse effect on the composite-to-composite interfacial bond strength.