Effect of immediate dentin sealing on the fracture strength of lithium disilicate ceramic onlays

This study aimed to evaluate the effect of immediate dentin sealing (IDS) on the fracture strength of ceramic onlays when compared with delayed dentin sealing (DDS). Twenty extracted human maxillary premolars were randomly divided into 2 groups according to the dentin sealing technique (n=10). A standardized mesio-occlusal-distal cavity was prepared with reduction of the palatal cusp. The dentin surfaces of the IDS group were immediately sealed after finishing the preparation (before taking impressions, temporization, and 14-day storage at 37°C) using a bonding system (ALL-BOND 3®, ALL-BOND 3® RESIN) and flowable composite (Te-Econom Flow). Impressions were made and temporary restorations were fabricated using PRO-V FILL®. The wax patterns were milled and the onlays were fabricated by heat-pressing technique (IPS e.max Press). After bonding the final restorations with resin cement (Variolink N), the specimens were thermocycled. Fracture strength was measured using a universal testing machine (Testometric M350-10KN) at 1 mm/min until failure occurred. Student's t-test was used to evaluate the results of the fracture strength test. The failure mode was examined using a stereomicroscope. The mean fracture strength in the IDS group (1335 ± 335 N) was statistically significantly higher than that for the DDS group (931 ± 274 N) (p < 0.05). Fracture of the restoration with a small portion of the tooth was the most frequent mode of failure. Within the limitation of this in vitro study, there was an improvement in the fracture strength of ceramic onlays with the use of IDS. However, the ceramic onlays were strong enough to withstand the physiological mastication force in both groups.