Effects of surface treatment and aging on the bond strength of orthodontic brackets to provisional materials

Purpose: The aim of this study was to evaluate the effects of different surface treatments and aging on the bond strength of orthodontic brackets bonded to provisional materials (autopolymerizing polymethylmethacrylate [PMMA] resins and bis-acryl composite). The mode of failure was also compared. Material: One hundred twenty flat-surfaced disks of each provisional material were fabricated and embedded in acrylic molds. The specimens were divided randomly into 3 groups of 40, according to the surface treatment rendered: control, polished with greenstone, and sandblasted. Brackets were bonded, and specimens were stored in water at 35°C. Half the specimens in each group were debonded after 1 week, and the other half were debonded after 1 month with a shear-peel load on a testing system with a crosshead speed of 0.5 mm/min. The amount of composite resin left on the specimen surfaces was analyzed and classified with the adhesive remnant index. Results: The bond strengths of brackets to bis-acryl composite resin for all 3 surfaces were clinically acceptable (9-12 MPa) when compared with PMMA (3-5 MPa). The bond strengths of both provisional materials were generally influenced by the kind of surface treatment and aging. The mode of failure was adhesive for PMMA and predominantly cohesive for bis-acryl composite provisional materials. Conclusions: The bond strength of orthodontic brackets to provisional restorations might depend on material, surface treatment, and time. Brackets should be bonded to bis-acryl composite provisional restorations within 1 week of fabrication.