Effect of self-etchant pH on the shear bond strength of orthodontic brackets

Introduction: Self-etching primers (SEPs) have been used successfully during bonding to reduce technique sensitivity while minimizing the etching of enamel. Although serving the same purpose, SEPs differ in acidity and aggressiveness. Thus, the purpose of this study was to determine whether the pH of SEPs affects the shear bond strength of orthodontic brackets. Methods: Forty-five molars were cleaned, mounted, and randomly divided into 3 groups with different SEPs: in group 1 (control), 15 orthodontic brackets were bonded to the teeth with Transbond Plus (3M Unitek, Monrovia, Calif) with a pH of about 1.0; in group 2, 15 brackets were bonded with Adper Prompt L-Pop (3M ESPE, St Paul, Minn) with a pH of 0.9 to 1.0; in group 3, 15 brackets were bonded with Clearfil S3 Bond (Kuraray America, New York, NY), with a pH of 2.7. All teeth were bonded with Transbond XT paste (3M Unitek). The teeth were debonded within half an hour after initial bonding by using a universal testing machine. The residual adhesive on each tooth was evaluated. ANOVA was used to compare the shear bond strength (SBS) of the 3 groups, and the chi-square test was used to compare the adhesive remnant index (ARI) scores for the 3 groups. Results: ANOVA indicated significant differences between the groups. The Duncan multiple range test indicated that Clearfil S3 Bond produced a significantly stronger mean SBS (6.5 ± 1.9 MPa) than the Transbond Plus system (mean, 4.2 ± 1.9 MPa). No significant differences were seen between the SBS of the brackets bonded with Adper (mean, 5.9 ± 3.4 MPa) and the other 2 groups. The comparisons of the ARI scores between the 3 groups indicated that bracket failure mode was not significantly different. Conclusions: The SEP with the highest pH (least acidic), Clearfil S3 Bond, bonded brackets successfully and with the strongest SBS; this suggests that the pH of the SEP is not the primary determinant of the SBS. The clinician should be aware that some SEPs can leave the enamel surface healthier after debonding.