"effect of various surface treatment on repair strength of composite resin "

statement of problem: in some clinical situations, repair of composite restorations is treatment of choice. improving the bond strength between one new and old composite usually requires increased surface roughness to promote mechanical interlocking since chemical bonding might not be adequate. similarly, the treatment of a laboratory fabricated resin composite restoration involves the same procedures, and there is a need to create the strongest possible bond of a resin cement to a previously polymerized composite. purpose: the aim of this study was to evaluate the effect of various surface treatments on the shear bond strength of repaired to aged composite resin. materials and methods: eighty four cylindrical specimens of a composite resin were fabricated and stored in distilled water for 100 days prior to surface treatment. surface treatment of old composite was done in 6 groups as follow: 1- air abrasion with cojet sand particles with micoretcher  silane  dentin bonding agent 2- air abrasion with 50µm al2o3 particles phosphoric acid silane dentin bonding agent 3- air abrasion with 50µm al2o3 particles  phosphoric acid  dentin bonding agent 4- diamond bur  phosphoric acid  silane  dentin bonding agent 5- diamond bur  phosphoric acid  dentin bonding agent 6- diamond bur  phosphoric acid  composite activator  dentin bonding agent then fresh composite resin was bonded to treated surfaces. twelve specimens were also fabricated as control group with the same diameter but with the height twice as much as other specimens. all of the specimens were thermocycled prior to testing for shear bond strength. the bond strength data were analyzed statistically using one way anova test, t test and duncan's grouping test. results: one-way anova indicated no significant difference between 7 groups (p=0.059). one-way anova indicated significant difference between the three diamond bur groups (p=0.036). silane had a significant effect on the repair bond strength of diamond bur/silane group. there was no significant difference in the bond strength diamond bur/composite activator group and diamond bur/no silane group. silane had no significant effect on the repair bond strength of air abrasion group. the lowest bond strength was for diamond bur/ composite activator group. conclusion: the best surface treatment for repair of an aged composite restoration could be used of diamond bur with silane, air abrasion with or without silane or ceramic deposition with cojet sand system. silanation is a necessary step in the repair of composite resin with the use of diamond bur but not with the use of air abrasion.