Effect of Different Post-Processing Techniques on Bonding Strength and Marginal Fit of 3D-Printed Resin Inlay Restorations (An In Vitro Study)

Background: Post-curing may influence the fit and bonding performance of 3D-printed ceramic-filled resin restorations. This study evaluated the effects of post-curing protocols on marginal and internal fit and dentine microtensile bond strength (µTBS) of 3D-printed resin inlays. Methods: Seventy-six maxillary premolars received MOD inlay cavities and DLP-printed resin inlays and were allocated to post-curing protocols (n = 19): standard air (SP, control), glycerine-shielded (GP), microwave-assisted glycerine (MG; 800 W, 50 s), and autoclave-assisted thermal (AT; 121 °C, 58 min). Marginal and internal discrepancy were measured at 11 points using triple-scan superimposition. Microtensile bond strength (µTBS) was assessed per tooth. Results: Post-curing protocol significantly affected fit (F(3, 37.6) = 24.47, p < 0.001, η² = 0.494) and µTBS (F(3, 39.8) = 6.09, p = 0.002, η² = 0.195). GP showed the lowest discrepancy (77.09 ± 5.48 µm) and highest µTBS (21.58 ± 4.35 MPa), whereas MG showed the highest discrepancy (104.42 ± 13.57 µm) and lowest µTBS (15.04 ± 5.13 MPa). Adhesive failures were more frequent with MG than GP (68.4% vs. 0%; χ²(6) = 25.65, p < 0.001). Fit and bond strength were weakly correlated. Conclusions: Glycerine shielding improved fit and dentine bond strength, whereas microwave post-curing resulted in inferior performance.