title: Effect of the photo-activation method on polymerization shrinkage of restorative composites.
abstract: This study measured the gap that resulted from polymerization shrinkage of seven restorative resin composites after curing by three different methods. Contraction behavior, according to the specimen region, was also characterized. The materials used for this study were Alert (Jeneric/Pentron, Wallingford, CT 06492, USA), Surefil (Dentsply Caulk, Milford, DE 19963, USA), P60 (3M Dental Products, St Paul, MN 55144, USA), Z250 (3M), Z100 (3M), Definite (Degussa-Hüls, Hanau, Germany) and Flow-it (Jeneric/Pentron). The composite was placed in a circular brass mold 7 mm in diameter and 2 mm in height. Photo-activation was performed by a) continuous light (500 mW/cm2) for 40 seconds; b) stepped light with low intensity (150 mW/cm2) for 10 seconds and high intensity (500 mW/cm2) for 30 seconds and c) intermittent light (450 mW/cm2) for 60 seconds. The top and bottom surfaces were then polished and after 24 +/- 1 hours, the contraction gap was measured by SEM at variable pressure (LEO 435 VP, Cambridge, England). Results were analyzed by ANOVA and the means compared by Tukey's test (5%). The results demonstrated 1) the continuous light method presented the greatest gap values (15.88 microm), while the other methods demonstrated lower polymerization shrinkage values (stepped light, 13.26 microm; intermittent light, 12.79 microm); 2) restorative composites shrunk more at the bottom surface (15.84 microm) than at the top surface (12.11 microm) and (3) the composites Alert (12.02 microm), Surefil (11.86 microm), Z250 (10.81 microm) and P60 (10.17 microm) presented the least contraction gaps, followed by Z100 (15.84 microm) and Definite (14.06 microm) and finally Flow-it (23.09 microm) low viscosity composite, which had the greatest mean value.
authors.affiliation: Department of Restorative Dentistry, Dental School of Piracicaba, UNICAMP, SP, Brazil.
authors.forename: A C
authors.initials: AC
authors.lastname: Obici
authors.forename: M A  C
authors.initials: MA
authors.lastname: Sinhoreti
authors.forename: M F
authors.initials: MF
authors.lastname: de Goes
authors.forename: S
authors.initials: S
authors.lastname: Consani
authors.forename: L C
authors.initials: LC
authors.lastname: Sobrinho
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003775:Dental Polishing; D003793:Dental Restoration, Permanent; D006801:Humans; D008027:Light; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D012822:Silicon Dioxide; D012833:Siloxanes / Q000737:chemistry; D013223:Statistics as Topic; D013499:Surface Properties; D013729:Terpenes / Q000737:chemistry; D013997:Time Factors; D014783:Viscosity; D015040:Zirconium
chemical_list: C406265:Alert composite resin; D003188:Composite Resins; C421785:Definite composite resin; C444701:Filtek Z250; C443708:P60 Condensible Resin Composite; D011108:Polymers; D012833:Siloxanes; C403464:SureFil packable composite; D013729:Terpenes; C083568:Z100 composite resin; C111840:flowable hybrid composite; D012822:Silicon Dioxide; D015040:Zirconium