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

Objective: To assess shear bond strength and failure mode (Adhesive Remnant Index, AR1) of orthodontic brackets bonded to polymethylmethacrylate (PMMA) blocks for computer-aided design/manufacture (CAD/CAM) fabrication of temporary restorations, following substrate chemical or mechanical treatment. Methods: Two types of PMMA blocks were tested: CAD-Temp (R) (VITA) and Telio (R) CAD (lvoclar-Vivadent). The substrate was roughened with 320-grit sandpaper, simulating a fine-grit diamond bur. Two universal adhesives, Scotchbond Universal Adhesive (SU) and Assure Plus (AP), and a conventional adhesive, Transbond XT Primer (XTP; control), were used in combination with Transbond XT Paste to bond the brackets. Six experimental groups were formed: (1) CAD-Temp (R) /SU; (2) CAD-Temp (R)/AP; (3) CAD-Temp (R)/XTP; (4) Telio" CAD/SU; (5) Telio (R) CAD/AP; (6) Telio (R) CAD/XTP. Shear bond strength and AR1 were assessed. On 1 extra block for each PMMA-based material surfaces were roughened with 180-grit sandpaper, simulating a normal/medium-grit (100 um) diamond bur, and brackets were bonded. Shear bond strengths and AR1 scores were compared with those of groups 3, 6. Results: On CAD-Temp (R) significantly higher bracket bond strengths than on Telio (R) CAD were recorded. With XTP significantly lower levels of adhesion were reached than using SU or AP. Roughening with a coarser 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.