ABSTRACT
When an amalgam restoration fails, the repair of existing amalgam restoration with fresh amalgam can be a practical alternative to the replacement of entire restoration. In most studies the bond strength of fresh amalgam to old amalgam is reported lower than the old amalgam itself. Therefore, the purpose of this study was to compare the effect of using adhesive system with surface irregularities and roughness on shear bond strength between fresh and set [old] amalgam. Fifty acrylic cylinders were made and a cavity preparation [6mm diameter by 2 mm high] was made in each cylinder. Forty cavities were filled with amalgam, level with cylinders surface and ten cylinders [control group =Group 1] were filled 5mm higher than the surface of cylinder using split die. After aging of all samples in water at 37°C for 14 days, the first 40 samples were divided into 4 groups and were repaired with fresh amalgam in the following manner. Group 2: with surface irregularities and roughness, group 3: using Panavia F, without surface irregularities and roughness, Group 4: using cement and surface irregularities and roughness, group 5: without cement and without surface irregularities and roughness. After storage in water at 37°C for 7 days, the shear bond strengths of groups were tested. Mean shear bond strengths and standard deviations [MPa] for groups were: in Group 1 [control]: 36 +/- 4.8, Group 2: 31.26 +/- 2.70, Group 3: 8.07 +/- 1.34, Group 4: 13.05 +/- 1.83 and in Group 5 no bond was seen. ANOVA revealed statistically significant difference among groups Duncan test indicated that there was a significant difference between each group with the other one. Results of this study didn't reveal any advantages for using Panavia F to increase the bond strength. According to the results obtained from making surface roughness and irregularities compared to the control group, this procedure can be suggested for repairing broken amalgam as an acceptable procedure