Clinically Simulated Loading-conditions and Polymerization Mode on Cement-Dentin Adhesion

Methods: Dentin surfaces of extracted sound human molars (N=20) were prepared and composite-resin specimens (n=80) were cut using a low-speed diamond saw. Each tooth received four resin specimens. Composite-resin specimens were cemented on each tooth surface under 8 different loading conditions (n=10/group) with a dual-polymerized resin cement (Variolink II, Ivoclar Vivadent): G1: Under 240g load (simulating occlusion pressure) and immediate photo-polymerization; G2: Under 240g load, waiting for 5 seconds, removing the load and photo-polymerization; G3: Under 240g load, waiting for 4 minutes, removing load and photo-polymerization; G4: Under 240g load, no photo-polymerization; G5: Under 120g load (simulating finger pressure), waiting for 5 seconds and photo-polymerization; G6: Under 120g load, waiting for 5 seconds, removing load and photo-polymerization; G7: Under 240g load, waiting for 5 seconds, removing 120g, waiting for 4 minutes and photo-polymerization and G8: Cementation under 240g load, waiting for 5 seconds, removing 120g, waiting for 4 minutes, removing the remaining 120g and photo-polymerization. MSBS tests were performed using a Universal Testing Machine (Shimadzu AG-50 kNG). The data were statistically analyzed (ANOVA, Tukey’s, p<0.05). Failure analysis of the debonded surfaces were made using Scanning Electron Microscope. 

Results: Mean MSBS values (MPa±SD) were as follows: G1:5.6±0.6, G2:1.9±0.3, G3:3.9±0.6, G4:0.3±0.1, G5:21±0.5, G6:5.8±0.6, G7:5.2±0.5, G8:1.4±0.4. G5 demonstrated significantly higher MSBS values than those of other groups (p<0.05). Failure types were mainly adhesive.

Conclusion: Photo-polymerization while loading under finger pressure of 120 g showed dramatic increase in bond strength of the tested adhesive resin cement to dentin.