title: Modulated photoactivation methods: Influence on contraction stress, degree of conversion and push-out bond strength of composite restoratives.
abstract: OBJECTIVE
  Verify the influence of curing methods on contraction stress, stress rate, and degree of conversion (DC) of a restorative composite and on bond strength of composite restoratives.
  
  
  METHODS
  For the stress test, composite (0.84 mm thick) was applied between two 5-mm diameter glass rods, mounted in a servohydraulic machine. Stress rate was taken by the value of stress/time at each second. DC was measured by micro-FTIR. Bond strength testing was performed using a push-out test. The C-factor in all tests was 3.0. Four curing methods were tested: continuous light (CL), soft-start (SS), and two pulse delay methods using different initial irradiances--150 mW/cm(2) (PD150) and 80 mW/cm(2) (PD80). Results were analyzed by ANOVA and Tukey's test (alpha=0.05).
  
  
  RESULTS
  Stress values ranged from 7.9 MPa (PD80) to 10.3 MPa (CL). No statistical difference was verified among CL, SS, and PD150. PD80 presented statistically lower stress values compared to CL and SS. CL presented the highest maximum stress rate, followed by SS, PD150 and PD80. Mean DC values ranged from 54.2% (PD150) to 55.9% (PD80), with no difference observed among the methods. For the bond strength test, values ranged from 26.4 MPa (CL) to 35.5 MPa (PD150). PD150 and PD80 were both statistically superior to SS and CL. SS presented statistically higher bond strength compared to CL.
  
  
  CONCLUSIONS
  Modulated curing methods were shown to be effective in reducing contraction stress rate and improving the strength of the bonded interface, and without compromising the DC of the restorative composite.
authors.affiliation: Department of Restorative Dentistry, Dental Materials Area, Piracicaba, School of Dentistry, UNICAMP Av. Limeira 901, Bairro Areião, CEP 13414-018, Piracicaba, São Paulo, Brazil. leonardogcunha@yahoo.com
authors.forename: Leonardo Goncalves
authors.initials: LG
authors.lastname: Cunha
authors.forename: Roberta Caroline Bruschi
authors.initials: RC
authors.lastname: Alonso
authors.forename: Carmem Silvia Costa
authors.initials: CS
authors.lastname: Pfeifer
authors.forename: Lourenço
authors.initials: L
authors.lastname: Correr-Sobrinho
authors.forename: Jack Liborio
authors.initials: JL
authors.lastname: Ferracane
authors.forename: Mário Alexandre Coelho
authors.initials: MA
authors.lastname: Sinhoreti
mesh_terms: D000818:Animals; D002417:Cattle; D003188:Composite Resins / Q000528:radiation effects*; D001840:Dental Bonding; D003748:Dental Equipment; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000379:methods*; D006244:Hardness; D008027:Light; D008422:Materials Testing; D044367:Phase Transition; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical
chemical_list: D003188:Composite Resins; C444701:Filtek Z250