title: Effect of different modes of light modulation on the bond strength and knoop hardness of a dental composite.
abstract: This study evaluated the bond strength and Knoop hardness of Z250 composite resin, light activated with XL2500 curing unit, using different protocols: continuous mode - high intensity (CH) (700 mW/cm(2)) for 20 s; continuous mode - low intensity (CL) (150 mW/cm(2)) for 20 s; and pulse-delay with 150 mW/cm(2) for 2(P2), 3(P3), 5(P5), 10(P10) or 15 s (P15), with a 1-min delay, followed by 700 mW/cm(2) for 20 s. For the push-out test (n=10), the bond strength values were obtained using a universal test machine at a crosshead speed of 0.5 mm/min. For Knoop hardness (n=5), the specimens were made using the same light-activation protocols. The hardness measurements were made with a hardness tester at six depths (top, 1, 2, 3, 4, and 5 mm). The data were subjected to ANOVA and Tukey's test at 5% significance level. For bond strength, CL and P5 presented significantly higher mean values (p<0.05) than the other groups. There was no statistically significant difference (p>0.05) between P2, P3, P10, P15 and CH. For Knoop hardness, CH and P15 presented the highest mean values from top surface up to 4 mm depth , while CL presented the lowest hardness mean values (p<0.05). From the depth of 3 mm to 5 mm, the mean values of all groups were significantly lower (p<0.05) than those recorded on top surface. In conclusion, for the pulse-delay method, the initial exposure time can influence bond strength and Knoop hardness of composites.
authors.affiliation: Dental Materials Area, Department of Restorative Dentistry, Dental School of Piracicaba, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Dalli'Magro
authors.forename: Mário Alexandre Coelho
authors.initials: MA
authors.lastname: Sinhoreti
authors.forename: Américo Bortolazzo
authors.initials: AB
authors.lastname: Correr
authors.forename: Rafael Leonardo Xediek
authors.initials: RL
authors.lastname: Consani
authors.forename: Eliseu Augusto
authors.initials: EA
authors.lastname: Sicoli
authors.forename: Marcio José
authors.initials: MJ
authors.lastname: Mendoça
authors.forename: Lourenço
authors.initials: L
authors.lastname: Correr-Sobrinho
mesh_terms: D003188:Composite Resins / Q000528:radiation effects*; D003793:Dental Restoration, Permanent / Q000379:methods; D003799:Dental Stress Analysis; D017220:Dentin-Bonding Agents / Q000528:radiation effects*; D006244:Hardness; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D044367:Phase Transition; D019279:Resin Cements / Q000528:radiation effects*; D013997:Time Factors
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; C444701:Filtek Z250; D019279:Resin Cements