title: Post-curing conversion kinetics as functions of the irradiation time and increment thickness.
abstract: OBJECTIVE
  This study evaluated the variation of conversion degree (DC) in the 12 hours following initial photoactivation of a low-shrinkage composite resin (Venus Diamond).
  
  
  METHODS
  The conversion degree was monitored for 12 hours using Attenuated Total Reflection (ATR) F-TIR Spectroscopy. The composite was placed in 1 or 2 mm rings and cured for 10 or 20 seconds with a LED lamp. ATR spectra were acquired from the bottom surface of each sample immediately after the initial photoactivation (P=0), 30 minutes (P=0.5) and 12 hours after photoactivation (P=12) in order to obtain the DC progression during the post-curing period. Interactions between thickness (T), irradiation time (I) and post-curing (P) on the DC were calculated through ANOVA testing.
  
  
  RESULTS
  All the first order interactions were statistically significant, with the exception of the T-P interaction. Furthermore, the shift from P=0 to P=0.5 had a statistically higher influence than the shift from P=0.5 to P=12. The post-curing period played a fundamental role in reaching higher DC values with the low-shrinkage composite resin tested in this study. Moreover, both the irradiation time and the composite thickness strongly influenced the DC.
  
  
  CONCLUSIONS
  Increased irradiation time may be useful in obtaining a high conversion degree (DC) with a low-shrinkage nano-hybrid composite resin, particularly with 2 mm composite layers.
authors.affiliation: Department of Surgical Sciences, Dental School Lingotto, University of Turin, Turin, Italy. nicola.scotti@unito.it
authors.forename: Nicola
authors.initials: N
authors.lastname: Scotti
authors.forename: Alberto
authors.initials: A
authors.lastname: Venturello
authors.forename: Francesco Andrea Coero
authors.initials: FA
authors.lastname: Borga
authors.forename: Damiano
authors.initials: D
authors.lastname: Pasqualini
authors.forename: Davide Salvatore
authors.initials: DS
authors.lastname: Paolino
authors.forename: Francesco
authors.initials: F
authors.lastname: Geobaldo
authors.forename: Elio
authors.initials: E
authors.lastname: Berutti
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D055117:Curing Lights, Dental; D006801:Humans; D008422:Materials Testing; D053761:Nanocomposites / Q000737:chemistry / Q000528:radiation effects*; D044367:Phase Transition; D058105:Polymerization / Q000528:radiation effects; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors
chemical_list: D003188:Composite Resins; C488393:Venus (composite resin)