Effect of immediate dentine sealing on the aging and fracture strength of lithium disilicate inlays and overlays

Objectives: The objectives of this study were to compare the in vitro, laboratory aging, fracture strength, failure mode and reparability of molars restored with lithium disilicate inlays and overlays in conjunction with or without immediate dentin sealing (IDS). Methods: Forty extracted, sound human molars were selected and divided into four groups: 1) Inlays with IDS; 2) Inlays without IDS; 3) Overlays with IDS; 4) Overlays without IDS. Standard MOD preparations were made (3 mm wide, 5 mm deep) and in groups 2 and 4, all the cusps were reduced by 2 mm. Directly following tooth preparation, IDS was applied in specimens belonging to groups 1 and 3. The indirect restorations were luted with a heated composite. The restored teeth were subsequently challenged during aging (1.2 million cycles) and thermocycling loading (8000 cycles, 5-55 degrees C). Subsequently, the fracture strength was tested by a load to failure test at 45 degrees. A failure analysis was performed using lightand scanning electron microscopy. The results were analyzed using two-way ANOVA and a Fisher exact test. Results: Mean fracture load + SD (N) were: Group 1 (n = 12): 1610 +/- 419; Group 2 (n = 12): 1115 +/- 487; Group 3 (n = 12): 2011 +/- 496; Group 4 (n = 12): 1837 +/- 406. Teeth restored with an onlay were stronger than those restored with an inlay restoration (p < .001). Teeth with IDS were stronger overall than those without IDS (p = .026). The interaction between preparation type and the mode of dentin conditioning had no statistically significant influence on fracture strength (p = .272). Subsequently, custom hypothesis tests showed that there was no statistically significant difference in fracture strength between inlays with IDS and overlays without IDS (p = .27). Overlays tend to fail in a more destructive, non-reparable way (p = .003). Significance: Both variables IDS and overlay preparation improve overall fracture strength. Inlays with IDS and overlays without IDS didn't differ in fracture strength. Both inlays and overlays are strong enough to withstand physiological chewing forces.