title: Effects of radiant exposure values using second and third generation light curing units on the degree of conversion of a lucirin-based resin composite.
abstract: OBJECTIVE
  Using Fourier transform infrared analysis (FTIR) in vitro, the effects of varying radiant exposure (RE) values generated by second and third generation LED LCUs on the degree of conversion (DC) and maximum rate of polymerization (Rpmax) of an experimental Lucirin TPO-based RC were evaluated.
  
  
  METHODS
  1 mm or 2 mm thick silicon molds were positioned on a horizontal attenuated total reflectance (ATR) unit attached to an infrared spectroscope. The RC was inserted into the molds and exposed to varying REs (18, 36 and 56 J/cm2) using second (Radii Plus, SDI) and third generation LED LCUs (Bluephase G2/Ivoclar Vivadent) or a quartz tungsten based LCU (Optilux 501/SDS Kerr). FTIR spectra (n=7) were recorded for 10 min (1 spectrum/s, 16 scans/spectrum, resolution 4 cm-1) immediately after their application to the ATR. The DC was calculated using standard techniques for observing changes in aliphatic to aromatic peak ratios both prior to, and 10 min after curing, as well as during each 1 second interval. DC and Rpmax data were analyzed using 3-way ANOVA and Tukey's post-hoc test (p=0.05).
  
  
  RESULTS
  No significant difference in DC or Rpmax was observed between the 1 mm or 2 mm thick specimens when RE values were delivered by Optilux 501 or when the 1 mm thick composites were exposed to light emitted by Bluephase G2, which in turn promoted a lower DC when 18 J/cm2 (13 s) were delivered to the 2 mm thick specimens. Radii Plus promoted DC and Rpmax values close to zero under most conditions, while the delivery of 56 J/cm2 (40 s) resulted in low DC values.
  
  
  CONCLUSIONS
  The third generation LCU provided an optimal polymerization of Lucirin TPO-based RC under most tested conditions, whereas the second generation LED-curing unit was useless regardless of the RE.
authors.affiliation: Universidade Guarulhos, Centro de Pós Graduação e Pesquisa, Guarulhos, SP, Brasil.
authors.forename: Kelly Antonieta Oliveira Rodrigues de Faria
authors.initials: KA
authors.lastname: Cardoso
authors.affiliation: Universidade Estadual de Ponta Grossa, Departamento de Odontologia, Ponta Grossa, PR, Brasil.
authors.forename: Driellen Christine
authors.initials: DC
authors.lastname: Zarpellon
authors.affiliation: Universidade Guarulhos, Centro de Pós Graduação e Pesquisa, Guarulhos, SP, Brasil.
authors.forename: Camila Ferreira Leite
authors.initials: CF
authors.lastname: Madruga
authors.affiliation: Universidade Guarulhos, Centro de Pós Graduação e Pesquisa, Guarulhos, SP, Brasil.
authors.forename: José Augusto
authors.initials: JA
authors.lastname: Rodrigues
authors.affiliation: Universidade Estadual de Ponta Grossa, Departamento de Odontologia, Ponta Grossa, PR, Brasil.
authors.forename: Cesar Augusto Galvão
authors.initials: CA
authors.lastname: Arrais
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000528:radiation effects*; D055117:Curing Lights, Dental; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D044367:Phase Transition; D010720:Phosphines / Q000528:radiation effects*; D058567:Photoinitiators, Dental / Q000737:chemistry; D058105:Polymerization / Q000528:radiation effects; D011829:Radiation Dosage; D012016:Reference Values; D015203:Reproducibility of Results; D017550:Spectroscopy, Fourier Transform Infrared; D013997:Time Factors
chemical_list: C520678:(2,4,6-trimethylbenzoyl) diphenylphosphine oxide; D003188:Composite Resins; D010720:Phosphines; D058567:Photoinitiators, Dental