The Effects of Immediate Dentin Sealing on the Enzymatic Activity and Bond Strength of Hybrid Ceramic CAD/CAM Onlays: A Comparative Study of Two Universal Adhesives

Background/Objectives: To elucidate the effects of immediate dentin sealing (IDS) with two universal adhesive systems on the microtensile bond strength (µTBS) and enzymatic activity (MMPs) of CAD/CAM hybrid ceramic onlays. Methods: Twenty-four human molars were assigned to one of the following groups (n = 8) according to IDS and the adhesives used: (1) Clearfil Universal Bond Quick (IDS QB; Kuraray); (2) Scotchbond Universal Plus (IDS SB; 3M); (3) no IDS (CTR). CAD/CAM onlays (Katana Avencia Block, Kuraray) were luted using a silane-containing universal composite cement (Panavia SA Cement Universal, Kuraray). µTBS tests and scanning electron microscope (SEM) analysis were performed after 24 h (T0) or 10,000 thermocycles (Tt). Three additional molars per group were processed to evaluate the effects of IDS on MMPs using in situ zymography at T0 and Tt. Data were statistically analyzed (α = 0.05). Results: At T0, IDS QB showed a significantly higher µTBS than IDS SB and CTR (p < 0.05). Artificial aging led to significant reductions in µTBS in IDS QB and CTR (p < 0.05), while µTBS remained stable in IDS SB. Both IDS groups demonstrated higher µTBS compared with CTR after aging (p < 0.05). At T0, the application of a universal adhesive system significantly increased the levels of MMPs (IDS QB > IDS SB > CTR; p < 0.05). At Tt, IDS QB exhibited higher MMP activity compared with CTR (p < 0.05). Conclusions: IDS had a positive effect on immediate and aged µTBS, while the level of MMP activity was found to be material-dependent.