Effect of different etching time and concentration on microshear bond strength of CAD/CAM glass-ceramic blocks to composite resin

Abstract

1. ObjectiveOptimal surface preparation techniques for chemical and/or mechanical bonding to ceramic substrates are crucial in order to ensure clinical success when placing indirect ceramic restorations. The purpose of this article is to evaluate the effect of different etching time and concentration on microshear bond strength of two different CAD/CAM glass ceramic blocks to composite resin.2. Materials and methods140 ceramic plates were prepared, 70 from leucite based IPS Empress® CAD and another 70 from lithium disilicate based e.max® CAD. The ceramic surfaces were assigned into 7 groups of different surface treatments. The variables were the hydrofluoric acid etching time (0, 20, 60, 120 seconds and 10 minutes) and the concentration of the gel (5% and 9.5%). After composite resin bonding, microshear bond test was carried out using INSTRON universal testing machine and all debonded specimens were observed under X40 stereoscope. Additionally specimens in each group with different hydrofluoric acid surface treatment were observed under scanning electron microscope for detailed evaluation of surface morphology.3. ResultThe mean microshear bond strength of IPS Empress CAD and e.max CAD was 43.38 and 36.43 MPa, respectively. In Empress blocks, all groups were homogenous with no statistical differences. Altered hydrofluoric acid etching time and concentration did not influence the results. However in e.max blocks, higher bond strength was associated with longer etching time and higher hydrofluoric acid concentration. In Empress blocks, cohesive fractures within ceramic occurred most frequently. On the other hand in e.max blocks, the failures were predominantly adhesive.4. Conclusion(1) In IPS Empress CAD, hydrofluoric acid conditioning time and concentration did not influence the microshear bond strength decisively.(2) In IPS e.max CAD, changing etching time and concentration had stronger effect on the surface microstructure, therefore resulted in positive relationship with microshear bond strength.