Bonding state of metal-free CAD/CAM onlay restoration after cyclic loading with and without immediate dentin sealing.

To examine the bonding state of metal-free CAD/CAM onlay restorations made from two popular resin composite blocks and a typical glass-ceramic block after cyclic loading, with and without immediate dentin sealing (IDS). Standardized mesial-distal-occlusalbuccal (MODB) cavities in 24 extracted human molars were prepared. The intra-cavity dentin surfaces of half of the cavities were immediately sealed with all-in-one adhesive and flowable composite, while those of the other half were not. All cavities were scanned, from which CAD/CAM onlays were fabricated from three types of block and cemented with an adhesive resin cement system. The restored specimens were subjected to cyclic loading and the intra-cavity microtensile bond strength was measured. IDS improves not only the internal bond strength, but also the bond reliability of metal-free CAD/CAM onlay restorations. The resin composite block seems to be more effective than a typical glass-ceramic block for achieving both high bond strength and excellent bond reliability.