Effect of immediate and delayed dentin sealing on fracture resistance of lithium disilicate overlay

Abstract Statement of the problem Durable adhesion between ceramic restorations and tooth structure is crucial for long-term clinical success. Immediate dentin sealing (IDS) has been shown to enhance bond strength, but its impact on the fracture resistance and failure modes of ceramic overlays compared to delayed dentin sealing (DDS) remains uncertain. Purpose To evaluate the effect of IDS versus DDS on the fracture resistance and failure modes of lithium disilicate overlay restorations in extracted human premolars. Patients and methods Twenty extracted human maxillary premolars were prepared to receive ceramic overlay restorations and randomly allocated into two groups ( n = 10 each): group I (IDS) and group II (DDS). In the IDS group, acid etching, dentin primer, bonding agent, and flowable composite were applied immediately after tooth preparation. Digital impressions were taken, and both groups received temporary restorations. Lithium disilicate overlays were milled using CAD/CAM technology. During final cementation, IDS specimens were air-abraded while DDS specimens were polished prior to etching and bonding. All overlays were bonded with dual-cure resin cement. After 5,000 thermocycles, fracture resistance was measured using a universal testing machine, and failure modes were examined under a digital microscope. Results The IDS group exhibited significantly higher fracture resistance (2212.97 ± 224.14 N) compared to the DDS group (1434.86 ± 259.39 N) ( P < 0.0001). Most failures in the IDS group were limited to restoration (Mode I), whereas the DDS group experienced more severe failures involving both tooth and restoration (Modes II and III). Conclusion IDS significantly increases fracture resistance and promotes less severe failure modes in lithium disilicate overlays compared to DDS, indicating superior performance and longevity.