Bracket bonding to polymethylmethacrylate-based materials for computer-aided design/manufacture of temporary restorations: influence of mechanical treatment and chemical treatment with universal adhesives

Objectives: To assess shear bond strength and failure mode (Adhesive Remnant Index, ARI) of orthodontic brackets bonded to polymethylmethacrylate (PMMA) blocks for CAD-CAM fabrication of temporary restorations, following substrate chemical or mechanical treatment.

Methods: Two types of PMMA blocks were tested: CAD-Temp® (VITA) and Telio® CAD (Ivoclar-Vivadent). The substrate was roughened with 320-grit sandpaper, simulating a fine-grit diamond bur. Two universal adhesives, Scotchbond Universal Adhesive (3M ESPE, SU) and Assure Plus (Reliance, AP), and a conventional adhesive, Transbond XT Primer (3M Unitek, XTP, control), were used in combination with Transbond XT Paste (3M Unitek) to bond the brackets. Six experimental groups were formed: 1) CAD-Temp®/SU; 2) CAD-Temp®/AP; 3) CAD-Temp®/XTP; 4) Telio® CAD/SU; 5) Telio® CAD/AP; 6) Telio® CAD/XTP. Shear bond strength and ARI were assessed. On 1 extra block for each PMMA-based material surfaces were roughened with 180-grit sandpaper, simulating a normal/medium-grit (100 μm) diamond bur, and brackets were bonded. Shear bond strengths and ARI scores were compared with those of groups 3, 6.

Results: On CAD-Temp® significantly higher bracket bond strengths than on Telio® CAD were recorded. With XTP significantly lower levels of adhesion were reached than using SU or AP. Roughening with a more coarse bur resulted in a significant increase in adhesion.

Conclusions: Bracket bonding to CAD-CAM PMMA can be promoted by grinding the substrate with a normal/medium-grit bur or by coating the intact surface with universal adhesives. With appropriate pretreatments, bracket adhesion to CAD-CAM PMMA temporary restorations can be enhanced to clinically satisfactory levels.