The in vitro effect of repeated bonding on the shear bond strength with different enamel conditioning procedures

The aims of this study were to evaluate the effect on shear bond strength (SBS), adhesive remnant, and enamel surface of repeated bonding of new brackets on the same tooth using different methods of enamel conditioning. One hundred and thirty-five bovine incisors were used. Brackets were bonded to enamel using one of the following conditioning procedures: (1) 37 per cent phosphoric acid, (2) 37 per cent phosphoric acid (prior to first bond but not for further bonds), (3) Transbond Plus Self Etching Primer (TSEP), and (4) non-rinse-conditioner (NRC). Brackets were sequentially bonded and debonded three times following the same conditioning procedure with the exception of group 2 where 37 per cent phosphoric acid was not reapplied prior to the second and third bonding sequences. SBS and adhesive remnant were evaluated for each debond. Scanning electron microscopy observations were made for each conditioning sequence. Statistical analysis was undertaken using ANOVA, Mann-Whitney, and Kruskal-Wallis tests. Bond strength and adhesive remnant values were similar across the four groups for the first and second bonding sequences. At the third sequence, SBS was significantly less (P < 0.008) for group 2 (5.71 +/- 1.56 MPa) than for group 1 (9.42 +/- 2.75 MPa) and the adhesive remnant was significantly lower (P < 0.008) for group 2 (6.93% +/- 3.34) than for the other groups (group 1: 16.95 +/- 4.99 per cent, group 3: 14.40 +/- 5.11 per cent, and group 4: 14.60 +/- 5.33 per cent). When comparing the SBS and adhesive remnant of the three bonding/debonding sequences within each group, both the SBS and adhesive remnant for group 2 (SBS: 5.71 +/- 1.56 MPa and adhesive remnant: 6.93 +/- 3.34%) at the third sequence were significantly less (P < 0.017) than at the first (SBS: 10.44 +/- 3.55 MPa and adhesive remnant: 13.81 +/- 5.59%) and second (SBS: 9.23 +/- 2.69 MPa and adhesive remnant: 15.32 +/- 6.85%) sequences. Enamel changes were similar across all groups. TSEP and NRC produced bonds that were similar to acid etching. When acid etching is used, it is possible to avoid etching for a second bond but not for following bonds.