title: Effect of light curing protocol on degree of conversion of composites.
abstract: OBJECTIVE
  To evaluate the degree of conversion (DC) of two light-cured composites with different protocols of light curing.
  
  
  METHODS
  One hundred and ninety two specimens (n = 8) were prepared (5 mm × 2 mm) according to experimental groups: two composite resins (Filtek Supreme and four seasons); three light curing protocols [20 s with the tip of the light curing unit (LCU) device touching composite surface (C); 20 s with the tip of the LCU at 8 mm distant from composite surface (D); and tip of the LCU at 8 mm distant from composite surface and polymerization time required to obtain a radiant exposure of 16 J/cm(2) (DS)]. Four LCUs (Bluephase 16i, Ultralume LED 5, XL 3000 and Optilux 501C) were used. DC of the bottom and top surface of specimens were measured using a FTIR spectrometer. Data were statistically analyzed by 3-way split splot ANOVA and Tukey's test (alpha = 0.05).
  
  
  RESULTS
  The results showed that DC of the top surface was higher than the bottom at all experimental conditions (p < 0.0001). Overall, the curing at 8 mm of distance did not affect conversion rate on the top surface (p > 0.05), but bottom surfaces showed DC reduction (p < 0.05). The highest monomer conversion values were observed for C and DS situations.
  
  
  CONCLUSIONS
  The distance between the LCU and material surface and radiant exposure can affect the DC. Polymerization at distance should be performed with curing units with higher light power and/or extended exposure time.
authors.affiliation: Department of Restorative Dentistry.
authors.forename: Anderson
authors.initials: A
authors.lastname: Catelan
authors.forename: Maria do Carmo Aguiar Jordão
authors.initials: Mdo C
authors.lastname: Mainardi
authors.forename: Giulliana Panfiglio
authors.initials: GP
authors.lastname: Soares
authors.forename: Adriano Fonseca
authors.initials: AF
authors.lastname: de Lima
authors.forename: Gláucia Maria Bovi
authors.initials: GM
authors.lastname: Ambrosano
authors.forename: Débora Alves Nunes Leite
authors.initials: DA
authors.lastname: Lima
authors.forename: Giselle Maria
authors.initials: GM
authors.lastname: Marchi
authors.forename: Flávio Henrique Baggio
authors.initials: FH
authors.lastname: Aguiar
mesh_terms: D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D055117:Curing Lights, Dental / Q000145:classification; D003764:Dental Materials / Q000737:chemistry / Q000528:radiation effects*; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation / Q000379:methods*; D008422:Materials Testing; D058105:Polymerization; D011897:Random Allocation; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C474035:Filtek Supreme; C111840:flowable hybrid composite
keywords: composite resin; degree of conversion; polymerization