Bonding reliability of CAD/CAM onlay restoration using hybrid-resin-composite milling block

Objectives: The purpose of this study was to examine the bonding reliability of CAD/CAM onlay restoration using hybrid-resin-composite milling block under a cyclic-load-stress condition simulating intra-oral environment.
Methods: A hybrid-resin-composite CAD/CAM milling block(L: Lava Ultimate, 3M ESPE) and a popular feldspathic-glass-ceramic block(V: VITABLOCS Mark II, VITA, as cotrol) were used. 16 standardized-duplicated MODB cavities were prepared in extracted human lower molars from an original-master cavity. For a half of cavities, the dentin surface of the cavity wall was pretreated with an all-in-one adhesive system(Scotchbond Universal Adhesive, 3M ESPE) and immediately sealed with a flowable-resin-composite(Filtek Supreme Ultra Flowable Restorative, 3M ESPE) (S+). The other cavities were not sealed(S-). Optical-impressions for all cavities were taken by CEREC AC Omnicam(ver.4.3), and then CAD/CAM onlays were milled from L and V blocks by CEREC MC XL(SIRONA Dental Systems). Each onlay and individual cavity are cemented with an adhesive-resin-cement(RelyX Ultimate, 3M ESPE). All restored specimens were subjected to cyclic-load-stress(157N x 300,000times at 37°C water) simulating intra-oral environment. 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 of μ-TBS were examined using Student’s t-test and Weibull analysis with a level of significance set at 0.05.
Results: The mean μ-TBS(SD) in MPa and [Weibull modulus (Wm)] of L/V-restorations were S+ specimens; 26.6(6.5)[3.24]/5.1(1.2)[4.62], S- specimens; 21.2(6.1)[3.22]/3.5(1.6)[2.27]. No pretesting failure was occurred in all beam specimens. Both the mean μ-TBS and the stress value for 10% probability of failure of L-restoration were significantly greater than the values of V-restoration, regardless of immediate-resin-sealing mode. The inequality in Wm between L and V-restorations was reversed by sealing mode.
Conclusions: The bonding reliability of CAD/CAM onlay L-restoration using a hybrid-resin-composite milling block was superior to that of V-restoration using a popular feldspathic-glass-ceramic block.