Bonding State of Metal-free CAD/CAM Restoration After Cyclic-loading w/o Immediate-dentin-sealing

Objectives: The purpose of this study was to examine the effect of immediate-dentin-sealing application on the bonding state of metal-free CAD/CAM onlay-restorations after in-vitro cyclic-loading.

Methods: Standardized MODB cavities were prepared in 24 extracted human lower molars. The intra-cavity dentin walls of a half cavity-specimens were immediately sealed (S+) with an all-in-one adhesive system (Scotchbond Universal Adhesive, 3M ESPE) and a flowable resin composite (Filtek Supreme Ultra Flowable Restorative, 3M ESPE). The other cavity-specimens were not sealed (S-). Optical-impressions for all cavities were taken by CEREC AC Omnicam (DENTSPLY SIRONA, SW ver.4.3), and then CAD/CAM onlays were fabricated from three types block, hybrid-resin-composite-block (L: Lava Ultimate, 3M ESPE), hybrid-ceramic block (E: VITA ENAMIC, VITA) and popular ceramic-block (V: VITABLOCS Mark II, VITA) by CEREC MC XL, eight each. Each onlay was cemented to individual cavity with an adhesive resin-cement (RelyX Ultimate, 3M ESPE). All restored specimens were subjected to cyclic-loading (157N x 300,000 times at 37°C water) simulating intra-oral environment. Four standardized beam specimens were trimmed from each restored specimen, and the 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.

Results: The μ-TBS(SD) of S+/S- restorations in MPa were L; 26.6(6.5)/21.2(6.1), E; 15.5(2.2)/15.2(3.3) V; 5.1(1.2)/3.5(1.6). The μ-TBS of S+ CAD/CAM restoration was statistically similar to or significantly greater than the values of S- restoration, regardless of milling-block type. Weibull modulus (Wm) of S+/S- restorations were L; 3.24/3.22, E: 7.91/4.60, V; 4.62/2.27. For E-restoration and V-restoration, the Wm-value of S+ specimens was significantly bigger than that of S- specimens. No difference was recognized in Wm for L-restoration between S+ and S- conditions.

Conclusions: Immediate-dentin-sealing application was effective to obtain excellent intra-cavity bond strength and good bonding reliability of metal-free CAD/CAM onlay-restoration compared with no-sealing treatment.