title: The effect of soft-start polymerization by second generation LEDs on the degree of conversion of resin composite.
abstract: Fourier-Transform (FT)--Raman spectroscopy was used to evaluate in vitro the degree of conversion (DC) of Charisma dental composite cured by three different light curing units (LCUs) using soft-start and normal protocols. Eighty circular blocks of resin (7 mm in diameter x 2.5 mm thick) were prepared and cured using the following sources: halogen light (Degulux soft-start, n = 20, G1-G2), low power light emitting diode (LED) with transparent polymer tip (LD13, n = 20, G3-G4) and fiber optic tip (LD13, n = 20, G5-G6) and, finally, high power LED (Radii, n = 20, G7-G8). The top and bottom surfaces of the blocks were analyzed by FT-Raman spectroscopy. The respective DCs were estimated calculating the peak height ratio of the aliphatic C=C (1640 cm(-1)) and aromatic C=C (1610 cm(-1)) Raman modes. The DC at the surfaces ranged between 50% and 60% for the top and 46% and 58% for the bottom. The halogen light and high power LED LCUs with the soft-start and normal protocols produced the highest DC values of dental composite at both surfaces (p < 0.001). Curing by low power LED in the soft-start protocol did not produce adequate DC at the depth of 2.5 mm. The type of LCU light guide tip did not present a significant statistical difference in the final DC of the dental composite (p > 0.05).
authors.affiliation: Discipline of Restorative and Operative Dentistry, School of Dentistry, University of Vale do Paraíba, São José dos Campos, SP, Brazil.
authors.forename: L E S
authors.initials: LE
authors.lastname: Soares
authors.forename: P C S
authors.initials: PC
authors.lastname: Liporoni
authors.forename: A A
authors.initials: AA
authors.lastname: Martin
mesh_terms: D002244:Carbon / Q000737:chemistry / Q000528:radiation effects; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D003764:Dental Materials / Q000737:chemistry / Q000528:radiation effects*; D004867:Equipment Design; D005336:Fiber Optic Technology / Q000295:instrumentation; D006801:Humans; D008029:Lighting / Q000295:instrumentation*; D008422:Materials Testing; D055100:Optical Fibers; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013499:Surface Properties; D013997:Time Factors
chemical_list: C084111:Charisma composite resin; D003188:Composite Resins; D003764:Dental Materials; D011108:Polymers; D002244:Carbon