Effect of Metal-free-block on Bonding of CAD/CAM Restoration Under Thermomechanical-cyclic-stress

Objectives: To examine the effect of metal-free-block on the bonding of CAD/CAM onlay-restoration under thermomechanical-cyclic-stress simulating intra-oral environment.
Methods: Standardized MODB cavities in 24 extracted-human-molars were prepared. The 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 by CEREC AC Omnicam(SIRONA Dental Systems), and CAD/CAM onlays were fabricated from three types of metal-free-block, hybrid-resin-composite-block(L: Lava Ultimate, 3M ESPE), hybrid-ceramic-block(E: VITA ENAMIC, VITA) and popular feldspathic-ceramic-block(V: VITABLOCS Mark II, VITA), by CEREC MC XL, eight each. Fabricated-onlays were cemented with an adhesive resin cement system. The restored-specimens were subjected to thermomechanical-cyclic-stress(157N x 3 x 10⁵ times at 37°C water). Four standardized beam-specimens were trimmed from each restored-specimen, and micro-tensile-bond strength(μ-TBS) to pulpal-dentin-wall were measured. The data were examined using the Kruskal-Wallis test, the Steel-Dwass test and Weibull analysis with a level of significance set at 0.05.
Results:
The median(mean) values of μ-TBS in MPa, [Weibull modulus(Wm)] and the stress value in MPa for 10% probability of failure level{PF10} of L/E/V-restorations for sealed specimens were 29.2(26.6)[3.2]{15.1}/15.5(15.5)[7.9]{12.4}/5.0(5.1)[4.6]{3.4}, and for none-sealed specimens were 23.7(21.2)[3.2]{11.9}/15.5(15.2)[4.6]{10.2}/3.9(3.5)[2.3]{1.5}. The μ-TBS was influenced by the block-type, regardless of sealing-mode. The values of L and E were significantly greater than that of V. The Wm of E indicated the greatest value compared to L and V, regardless of sealing-mode. The PF10 of L and E were significantly greater than that of V, regardless of sealing-mode.
Conclusions: The CAD/CAM onlay-restorations with L and E-blocks were significantly superior in intra-cavity-bond-strength to the restoration with V-block, regardless of sealing-mode. The bond-reliability of E-restoration exhibited statistically superiority compared with the other restorations, regardless of sealing-mode. The L and E-restorations were significantly superior in bond durability to V-restoration, regardless of sealing-mode.