Profilometeric and SEM evaluation of effect of polishing on surface roughness of two composites [silorane-based and methylmethacrylate-based] and a Glass ionomer

To evaluate the effect of polishing on surface roughness of silorane-based composite using profilometery and Scanning Election Microscopy [SEM] and compare it with that of a methylmethacrylate- based composite and a glass ionomer. In this study, 3 groups [n=28] were tested: specimens of two composites [Filtek P90 and Filtek P60] and a glass ionomer [Fuji IX] which were prepared in polyethylene molds [4 mm diameter x10 mm Height]. Half of the specimens in each group were finished with 180-grit silicon carbide paper and the remaining were finished with 180-grit, and subsequently polished with 250, 400, 800, 1000, 2000, and 2500-grit silicon carbide papers. The surface roughness was evaluated using a contact profilometer and then mean [R[a]] and maximum [R[max]] of surface roughness were recorded. Then, the surface of 4 specimens of each subgroup was observed under SEM. Statistical analysis was performed with T-test, ANOVA and Dunnett T3 tests. In all materials, Ra was different between polishing with 180 and 2500-grit silicon carbide papers. In 180-grit group, only Ra of Filtek P60 and Fuji IX showed significant difference [P=0.01]. In 2500-grit group, there was no significant difference between the Ra of Filtek P60 and Filtek P90 [P=0.56]. Polishing is recommended for the glass ionomer and posterior composite restorations

Comparison of polymerization shrinkage in methacrylate and silorane-based composites cured by different LEDs

Polymerization shrinkage in Methacrylate-based composite is one of the most important factors in composite restorations failure. Silorane-based composite is introduced to compensate this drawback and claimed to have low shrinkage. The aim of this study was to evaluate the polymerization shrinkage of these two composites. In this experimental study, 5 disk shape samples for each resin composites were placed in the centre of metallic ring bonded to microscopic glass slab. Top surface of ring was covered by a glass cover slip. Glass slab and sample were placed on a special LVDT holder in order to light cure from bottom surface and to measure the polymerization shrinkage. In this study, Deflecting Disk method and LVDT [linear variable differential transducer] was used for dimensional change measurement of resin composites. In this study, two LED curing units were used for composite polymerization. The mean of polymerization shrinkage in Z250 cured with LED and High Power LED was 11 15 +/- 0.08microm and 11.51 +/- 0.17microm, respectively [P=0.094], and in P90 cured with LED and High Power LED was 1.08 +/- 0.06microm and 1.16 +/- 0.12microm, respectively [P=0.019]. Silorane-based composite [P90] showed significantly less polymerization shrinkage than that of methacrylate-based composite [Z250]. For the two types of composite, there was no significant difference between the two curing units in polymerization shrinkage