Evaluation of Varied Repair Methods Applied to CAD/CAM Blocks

Objectives: The study aim was to determine the best repair method for three types of CAD/CAM blocks.

Materials and Methods: 3 types of CAD/CAM materials, two ceramic (Vitablocs Esthetic Line, Vident and ProCAD, Ivoclar Vivadent) and one composite (Paradigm MZ100, 3M ESPE), were sectioned into 48 specimens (5X2X3mm), then embedded and randomly divided into 12 groups (n=12). Specimen surfaces were either roughened by a fine diamond bur (Brasseler, USA) or air abraded by 30mm aluminum oxide particles (CoJet System, 3M ESPE). Clearfil Repair (Kuraray America) was applied and polymerized according to manufacturers' instructions. A cylindrical mould (2.3798X4mm) was used to fabricate composite cylinders from either flowable (Esthet X Flow, Dentsply) or hybrid (Filtek Z250, 3M ESPE) composite resin. Specimens were stored in water at 37'C for 24 hours and sheared using the Ultradent method with Zwick Z010 Compression Tester set to move at 1mm/minute. Data were analyzed using ANOVA single factor (a=0.05). Scanning Electron Microscope (SEM) was used to assess the modes of fracture.

Results: ProCAD and Paradigm blocks yielded statistically significant higher shear bond strengths as compared to Vitablocs (p<0.05). There was no statistically significant difference between bond strengths for bur and CoJet abrasion (p>0.05) or between hybrid and flowable resins (p>0.05). Failed specimens showed mostly cohesive fractures within the blocks

Conclusions: Within the study's limitation, the significant difference found in the reparability of CAD-CAM blocks may be attributed to block composition; however, all block/surface preparation/resin combinations yielded clinically acceptable shear bond strengths when bonded by Clearfil Repair. Both fine diamond bur abrasion and CoJet abrasion may be used to roughen CAD/CAM restorations after which either flowable or conventional hybrid composite resins can be bonded to repair the material.

Acknowledgements: NORTH/IMHA/CIHR; Kuraray America; Ultradent; 3M ESPE; Brasseler USA; Ivoclar Vivadent