Methods: We randomly assigned 61 freshly extracted bovine incisors into three groups: 1) uncontaminated controls, 2) saliva contaminated before SEP application, and 3) saliva contaminated after SEP application but before cementing the bracket. We polished each tooth with pumice, rinsed it, and blotted it with a cotton roll. After applying the SEP (TransbondTM Plus Self Etching Primer, 3M Unitek; Moravia, CA; USA), we bonded metal brackets with an orthodontic cement (TransbondTM XT; 3M Unitek) using ~250 g finger pressure for 3 s. We removed excess cement with a sharp explorer and light cured for 20 s. We contaminated the bond site with 1.0 µl of human saliva. After storage in distilled water for 24 – 36 h, we used a tiltable mounting vice enabling alignment of a wire loop along a force vector parallel to the bonded surface. Using a mechanical testing machine, we sheared the bracket at 1.0 mm/min. We measured the force (N) to fracture the bond, calculated the bond strength (MPa), and at 20x magnification, assessed the adhesive remnant index (ARI).
Results: The mean shear bond strengths were: group 1: 9.68 ± 1.18 MPa (n = 20); group 2: 10.18 ± 1.45 MPa (n = 23); and group 3: 4.98 ± 2.39 MPa (n = 18). ANOVA showed that at least one treatment had a significant effect on bond strength (F = 53.79; p < 0.0001). The mean bond strength for group 3 was significantly lower than that of the controls and group 2 (Tukey HSD test; p < 0.05).
Conclusions: With this system, saliva contamination reduced bond strength only when it occurred after SEP application.