In-vitro study of the adhesive strengths of brackets on metals, ceramic and composite. Part 1: Bonding to precious metals and amalgam.

Adult patients often have fillings, artificial crowns and/or bridges that make fitting of conventional bands difficult or even impossible. In such cases bonding rather than banding would be preferable. The present paper presents the investigation of more than 25 resin/conditioner combinations with respect to their bond strength to different metals as well as to amalgam. For that purpose stainless steel lingual buttons were bonded with the various adhesives and their shear bond strengths and types of bond failure were determined after 24 hours. All specimens were air-abraded with 50 microns Al2O3 for 2 or 4 seconds by means of a Microetcher before bonding. For comparison, buttons were also bonded to bovine enamel after air-abrasion or conventional etching with 37% H3PO4. Results show that, on all metals investigated, several materials yield bond strengths which are similar to or higher than what is achieved with the conventional acid etch technique on enamel. Maximum adhesive strength is not always desirable, however, for bonding brackets. The type of bond failure and the risk of irreversible damage to the bonded material have also to be taken into consideration. Al2O3 abrasion may cause considerable damage to enamel within 4 seconds. Since the bond strength on air-abraded enamel is about the same as on acid etched enamel, conventional etching with H3PO4 is preferable to the sandblasting of enamel.