Shear bond strength of rebonded orthodontic attachments using self-etching primers
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The purposes were to evaluate the difference in SBS of bonding and rebonding orthodontic attachments when using a CEP compared to a SEP and to evaluate if re-etching is necessary prior to rebonding with either a CEP or a SEP. Orthodontic metal buttons were bonded to extracted human molars according to 4 protocols: In Group A, teeth were bonded with the CEP for the first and second bondings. In Group B, teeth were bonded with the CEP for the first bonding but re-etching was omitted for the second bonding. In Group C, teeth were bonded with the SEP for both bondings. In Group D, teeth were bonded with the SEP for the first bonding but re-etching was omitted for the second bonding. The SBSs when the SEP was used for the first bonding were significantly lower (P<0.001; 10.65 ± 4.33 MPa) than when the CEP was used (14.04 ± 3.51 MPa). The second bonding omitting re-etching but still using the primer and adhesive generated significantly lower SBSs (P<0.001; 9.07 ± 4.53 MPa) than when re-etching was used (14.66 ± 3.70 MPa), but still above the "clinically acceptable" standard of 6-8 MPa for in vitro SBS testing. The second bonding SBS omitting re-etching and not using any primer or adhesive was very low (2.61 ± 2.34 MPa) and would definitely negatively effect the outcome of orthodontic bonding clinically. When rebonding a bracket, re-etching may be omitted but a primer and adhesive must be applied to obtain a "clinically acceptable" SBS.