Microtensile bond strength testing of luting cements to prefabricated CAD/CAM ceramic and composite blocks

Objectives. To investigate the Microtensile bond strength (μTBS) and failure mode of resin cements bonded to composite and ceramic CAD/CAM blocks following various surface treatments. Methods. Paradigm composite blocks and Cerec Vitablocs received three surface treatments following the control treatment of surface grinding with 600 SiC grit. (1) Application of adhesive resin (Adh), (2) etching with hydrofluoric acid and silanization (HF+S) or (3) combination of the previous two treatments (HF+S+Adh). Three resin cements (Tetric Flow, Nexus 2, RelyX ARC) were applied to these surfaces and built-up in layers. After 24 h water storage at 37 °C, the non-trimming version of μTBS test was used to produce 1 mm 2 microbars. The Microbars were subjected to a tensile load using a modified testing device. The broken specimens were examined with a stereomicroscope and SEM to determine the failure mode. Results. All control and adhesive treated groups of the ceramic substrate showed premature debonding during cutting. The overall mean μTBS for the three resin cements bonded to ceramic following HF+S and HF+S+Adh surface treatment, was 27 and 29.2 MPa and for the resin cements bonded to composite substrate was 42.3 and 54.2 MPa, respectively. The mode of failure was 98% adhesive with composite as a substrate and 68% mixed failures with ceramic as a substrate. Clinical significance. CAD/CAM restorations fabricated from processed composite blocks may have advantage over the ceramic blocks with regard to the higher bond strength with resin cements.