Effect of at-home bleaching gels with different thickeners on the physical properties of a composite resin without bisphenol A

To investigate, in vitro, the influence of at-home bleaching with 16% carbamide peroxide (CP) gels containing different thickeners on the color, gloss, roughness, and microhardness of a composite resin with bisphenol A (BPA) and without bisphenol A (BPA-free).

Cylindrical samples (7 × 2 mm) of a composite resin with BPA (Filtek Z350 XT®; 3M/ESPE) and composite resin BPA-free (Vittra APS®; FGM) were subdivided into six subgroups (n = 12), according to the bleaching gel used: no bleaching (control), commercial gel with 16% CP and carbopol, experimental gel with 16% CP and carbopol, experimental gel with 16% CP and natrosol, experimental gel with carbopol and experimental gel with natrosol. At the end of the experimental phase, the specimens were analyzed for color (ΔE*_ab and ΔE₀₀ ), surface roughness (Ra), gloss (GU), and surface microhardness (SMH). The data for all analyzes were submitted to Levene's test, Shapiro-Wilk's test and ANOVA.

For ΔE*_ab and ΔE₀₀ no statistically significant differences were found between all groups evaluated. Bleaching with experimental 16% CP gel with carbopol resulted in the lowest GU values for both composite resins evaluated. 16% CP experimental gel with natrosol resulted in higher Ra for the BPA composite resin and the bleaching with natrosol resulted in higher Ra for BPA-free. About 16% CP experimental gel with carbopol and 16% CP experimental gel with natrosol resulted in the lowest final SMH for composite resin with BPA. For the BPA-free composite resin, no differences were found between the groups in SMH for the same resin, however they presented the lowest values compared with all others groups.

The effects on physical properties are dependent on the composition of the composite resin and the thickener/bleaching gel used. The BPA-free composite resin showed less changes after exposure to bleaching agent, although its initial physical properties were worse compared to a bleached BPA.

The hydrogen peroxide and thickener of the at-home bleaching gel does impact the properties of composites with BPA or BPA-free such as gloss, roughness and surface microhardness, extremely important factors for maintaining an aesthetically and physically satisfactory restoration. BPA-free composite resins have inferior properties after at-home bleaching with different thickeners.