title: Influence of shade and irradiation time on the hardness of composite resins.
abstract: This study tested the following hypotheses: 1. increasing light irradiation time (IT) produces greater values of superficial hardness on different depths (0 and 3 mm); and 2. a dark shade composite (A3) needs longer IT than a light shade composite (A1) to produce similar hardness. Disk-shaped specimens (n=24 per shade) were fabricated using a 3-mm-thick increment of composite resin (Z100). Specimens were randomly assigned to 3 groups (n=8) according to the IT (400 mW/cm2) at the upper (U) surface: A1-10 and A3-10: 10 s; A1-20 and A3-20: 20 s; A1-40 and A3-40: 40 s. Specimens were stored in black lightproof containers at 37 masculineC for 24 h before indentation in a hardness tester. Three Vickers indentations were performed on the U and lower (L) surfaces of each specimen. The indent diagonals were measured and the hardness value calculated. The results were analyzed statistically by ANOVA and Tukey's test (alpha=0.05). Statistically significant differences were found between U and L surfaces of each composite shade-IT combination (p=0.0001) and among the ITs of same shade-surface combination (p=0.0001), except between groups A1-20U and A1-40U, confirming the study hypothesis 1 and partially rejecting the hypothesis 2.
authors.affiliation: Faculdade de Odontologia, School of Dentistry, University of Passo Fundo, Passo Fundo, RS, Brazil. dbona@upf.br
authors.forename: Alvaro
authors.initials: A
authors.lastname: Della Bona
authors.forename: Vinícius
authors.initials: V
authors.lastname: Rosa
authors.forename: Dileta
authors.initials: D
authors.lastname: Cecchetti
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D055117:Curing Lights, Dental / Q000145:classification; D006244:Hardness / Q000528:radiation effects*; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D017797:Prosthesis Coloring; D018709:Statistics, Nonparametric
chemical_list: D003188:Composite Resins