Comparative study of enamel adhesion between RelyX Unicem(R) (3M), a self-adhesive bonding agent, and the combination of MIP(R) (3M), a hydrophilic adhesive, and Transbond Supreme Low Viscosity(R) (3M), a traditional hydrophobic adhesive.

Although the bond strength of self-adhesive bonding agents is inferior to that of other families of adhesives, it is still adequate for orthodontic purposes provided prior enamel etching is performed. AIM: To determine the efficacy of RelyX Unicem((R)) (3M) self-adhesive cement both in vitro and in vivo and to compare it with the combination of MIP((R)) (3M), a moisture-insensitive primer, with a traditional hydrophobic adhesive, Transbond Supreme Low Viscosity((R)) (3M). IN VITRO: Comparison of bonding results on 23 trial dentures using RelyX Unicem((R)) (3M) with bonding results on 29 trial dentures using a combination of MIP((R)) and Transbond Supreme Low Viscosity((R)) (3M), by means of a multipurpose Instron((R)) 4444 testing machine. RESULTS: the breaking force of MIP((R))/Transbond Supreme Low Viscosity((R)) (3M) (mean: 144+/-37.5 Newtons) was significantly higher than that of RelyX Unicem((R)) (3M) (mean=110+/-26 Newtons) (P=0.001). IN VIVO: A 12-month prospective, randomized, monocentric, single-blind clinical study in order to investigate the failure rate of orthodontic attachments according to the type of adhesive used, and the precise site of the debonding. Bracket bonding was performed on 16 patients with randomized allocation of the two adhesives to each of the semi-arches. RESULTS: The failure rates were: 15.3% for the MIP((R))/Transbond Supreme Low Viscosity((R)) (3M) combination and 8.2% for the RelyX Unicem((R)) (3M), with a significant difference (P=0.039). The more posterior the bonded teeth, the greater the superiority of RelyX Unicem((R)) (3M). The in vivo results did not concord with those obtained in vitro. RelyX Unicem((R)) (3M) exhibited lower adhesion values in vitro and yet it presented a debonding rate almost half that of the MIP((R))/Transbond Supreme Low Viscosity((R)) (3M). The viscosity of RelyX Unicem((R)) (3M) and its moisture tolerance would appear to account for these results. CONCLUSION: With prior etching, RelyX Unicem((R)) (3M), a self-adhesive, self-etching bonding agent is compatible with use in the orthodontic indirect bonding technique. The MIP((R))/Transbond Supreme Low Viscosity((R)) (3M) combination, though very effective, still remains sensitive and requires special care during usage.