title: Effect of the increase of energy density on Knoop hardness of dental composites light-cured by conventional QTH, LED and xenon plasma arc.
abstract: The aim of this study was to evaluate the effect of the increase of energy density on Knoop hardness of Z250 and Esthet-X composite resins. Cylindrical cavities (3 mm in diameter X 3 mm in depth) were prepared on the buccal surface of 144 bovine incisors. The composite resins were bulk-inserted and polymerized using different light-curing units and times: conventional QTH (quartz-tungsten-halogen; 700 mW/cm(2); 20 s, 30 s and 40 s); LED (light-emitting diode; 440 mW/cm(2); 20 s, 30 s and 40 s); PAC (xenon plasma arc; 1700 mW/cm(2); 3 s, 4.5 s and 6 s). The specimens were stored at 37 degrees C for 24 h prior to sectioning for Knoop hardness assessment. Three measurements were obtained for each depth: top surface, 1 mm and 2 mm. Data were analyzed statistically by ANOVA and Tukey's test (p<0.05). Regardless of the light source or energy density, Knoop hardness of Z250 was statistically significant higher than that of Esthet-X (p<0.05). Specimens cured with PAC had lower hardness than those cured with QTH and LED (p<0.05). Higher Knoop hardness was obtained when the energy density was increased for LED and PAC (p<0.05). No statistically significant differences (p>0.05) were found for QTH. Knoop hardness values decreased with the increase of depth. The increase of energy density produced composites with higher Knoop hardness means using LED and PAC.
authors.affiliation: Dental Materials Area, Faculty of Dentistry of Piracicaba, State University of Campinas (UNICAMP), Piracicaba, SP, Brazil.
authors.forename: Américo Bortolazzo
authors.initials: AB
authors.lastname: Correr
authors.forename: Mário Alexandre Coelho
authors.initials: MA
authors.lastname: Sinhoreti
authors.forename: Lourenço Correr
authors.initials: LC
authors.lastname: Sobrinho
authors.forename: Rubens Nisie
authors.initials: RN
authors.lastname: Tango
authors.forename: Luis Felipe Jochims
authors.initials: LF
authors.lastname: Schneider
authors.forename: Simonides
authors.initials: S
authors.lastname: Consani
mesh_terms: D000818:Animals; D002417:Cattle; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental / Q000145:classification*; D003737:Dental Cavity Preparation / Q000379:methods; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D006244:Hardness; D008027:Light; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C466112:Esthet-X; C444701:Filtek Z250; D011108:Polymers