Effect of Gallic Acid Addition on Mechanical Properties of Resin-cements

Objectives: The clinical usage of self-adhesive resin cements (RC) have considerably increased for possessing simplified adhesive techniques. Gallic acid (GA) which is extracted from green tea leaves was shown to inhibit the activity of both matrix metalloproteinases and cysteine cathepsins. Mechanical properties of resin cements influence the clinical behavior which is significant for the long-term survival of the bonded restorations. The purpose of this study was to evaluate Vickers hardness and biaxial flexural strength of self-adhesive resin RCs after addition of two different concentrations of GA.
Methods: Rely-X U 200 (3M ESPE) and Panavia SA (Kuraray) were modified by addition of 0.5 and 1 wt% GA. For each group 10 specimens with 0.5mm thickness and 7mm diameter were prepared. Vickers hardness was measured at the surfaces of each resin disc with three randomized indentations. Biaxial flexure strength was measured by placing each specimen into a custom-made testing jig on a universal testing machine at 1.27mm/min until failure. RCs without GA were used for control. Data were analyzed using ANOVA and Tukeys HSD.
Results: Vickers hardness values ranged from 41.6 to 58.6 for Rely-X and 27.2 to 33.6 for Panavia. Biaxial flexure strength values ranged from 76.53 to 109.78MPa for Rely-X and from 73.37 to 108.27MPa for Panavia. GA addition significantly lowered the Vickers hardness values for Rely-X (p<0.05) whereas for Panavia only 0.5% addition of GA resulted with a significant decrease (p<0.05). Addition of GA reduced biaxial strength values significantly for both of the RCs (p<0.05).
Conclusions: Addition of 0.5 and 1 wt% GA for improving the durability of resin-dentin bonds adversely affected the mechanical properties of RCs tested.