A Comparative Study of the Effect of two Bonding Agents on the Shear Bond Strength of the Repaired Composite Restorations

Statement of Problem: One of the major problems in old composite filling reconstruction is creating powerful bond strength between the existing composite and the new composite filling. Furthermore, complete exchange of the old composite filling may jeopardize the tooth structure. In this situation, repairing the previous composite filling is more practical and the risk of pulp involvement may be decreased. No study has been done on the comparison of G-Bond and other bodings effects with or without silane usage except the manufacturer's claims. The aim of this study was to evaluate the effect of two different bonding agents on the shear bond strength of the existing composite and the new composite filling with or without silane usage.Methods and Material: In this experimental and in vitro study, 50 cylindrical composite blocks were prepared. Ten samples were used as control group in the size of 5×6 mm (one piece composite). The remaining 40 samples as the case groups were made in the size of 5×3 mm. The samples were stored in distilled water at 37oc for 2 weeks. The surface of all the samples were roughened, etched and cleaned. These 40 samples were divided into 4 equal groups based on the bonding procedure and silane usage. The groups were Clearfil S3 bond and silane (group A), Clearfill S3 Bond only (group B), G Bond and silane (group C), and G Bond only (group D). Then, the samples were stored in distilled water for another 2 weeks. The specimens were loaded to failure in shear mode with a crosshead speed of 0.5 mm/min until fracture. Shear bond strengths were analyzed with one way analysis of ANOVA. Shear bond strength was significantly different in the 5 groups. Shear bond strength in the control group was 34.24 Mega pascal, being significantly higher than that in the other 4 groups. The averages of the shear bond strength, were 25.88, 23.14, 21.19 and 17.20 for group A, B, C and D respectively. The results showed a statistically significant difference between the 4 groups and the control group. The results of this study indicate that composite cohesive strength (control group) had the highest strength, whereas there was no statistical difference among the other groups.