Bond strength comparison of moisture-insensitive primers

The objective of this in vitro bonding study was to evaluate the effectiveness of 2 moisture-insensitive primers, Assure (Reliance Orthodontic Products, Itasca, Ill) and MIP (3M Unitek, Monrovia, Calif) compared with a control hydrophobic primer, Transbond XT (3M Unitek). Six groups of 40 premolars were acid etched and bonded using metal orthodontic brackets with the following in vitro protocols: (1) Transbond XT primer and adhesive applied to a noncontaminated surface; (2) Assure primer applied after saliva contamination; (3) MIP primer applied after saliva contamination; (4) Assure primer reapplied after saliva contamination; (5) MIP reapplied after saliva contamination; and (6) Assure adhesive applied after saliva contamination of the primer. All bonded specimens were stored in deionized water at 37 degrees C for 30 days and thermocycled for 24 hours before debonding. Brackets were debonded using a shear-peel load on a testing machine, bond strength was measured in megapascals, and bond failure was analyzed by using the adhesive remnant index. In vitro shear-peel bond strengths were acceptable for all groups, and the bond strengths for Assure and MIP were not significantly affected by saliva contamination. The mean shear-peel bond strength of the control (14.82 MPa) was significantly higher (P <.001) than the contaminated groups with the exception of MIP group 5 (14.02 MPa). The values of the Assure primer and adhesive were less than the MIP primer and its respective adhesive; however, the hydrophilic Assure adhesive resin applied to a saliva-contaminated surface had acceptable bond strength. Bond failure analysis (adhesive remnant index) mainly showed adhesive bond failures. An increased frequency of enamel fractures at debond was noted, with the control group (1) and the MIP groups (3 and 5) having 22.5%, 12.5%, and 15%, respectively. The Assure groups had no enamel fractures.