Marginal and Internal Adaptation Discrepancy and Microtensile Bond Strength of Cemented, Thermocycled 3D-Printed Ceramic-Filled Resin Inlays Processed with Four Post-Curing Protocols: An In Vitro Study

Background: Post-curing may influence the properties of 3D-printed ceramic-filled resin restorations. This study compared four post-curing protocols for adaptation and microtensile bond strength (µTBS) of cemented, thermocycled DLP-printed inlays. Methods: Seventy-six maxillary premolars with standardised MOD cavities received inlays randomised (n = 19) to standard post-curing in air (SP), glycerine-immersed post-curing (GP), or SP plus microwave heating in glycerine (MG; 800 W nominal, 50 s) or autoclaving (AT; 121 °C). After cementation and 5000 thermocycles, adaptation discrepancy—a composite of post-curing change, seating, cement layer and ageing—was measured at 11 points by triple-scan superimposition before µTBS testing of the inlay–cement–dentine complex and failure-mode analysis. Results: Discrepancy (F(3, 37.6) = 24.47, p < 0.001) and µTBS (F(3, 39.8) = 6.09, p = 0.002) differed among protocols. MG showed the largest discrepancy (104.42 ± 13.57 µm; p < 0.01 versus all groups), lower µTBS than GP and SP (15.04 ± 5.13 versus 21.58 ± 4.35 and 20.19 ± 5.33 MPa) and predominantly adhesive failures (68.4% of teeth; interface unidentified). GP had the numerically lowest discrepancy (77.09 ± 5.48 µm), but its 7.7 µm difference from SP was within measurement uncertainty and not robust to sensitivity analysis. AT did not differ from SP. Conclusions: The complete MG protocol was associated with greater discrepancy and lower µTBS; GP did not differ robustly from SP.