title: Alternative photoinitiator system reduces the rate of stress development without compromising the final properties of the dental composite.
abstract: OBJECTIVE
  Stress development during the polymerization process continues to be a major factor that limits predictability and longevity of resin composite restorations. This study evaluated the effect of the photoinitiator type on the maximum rate of polymerization (R(p)(max)), stress development (final stress and maximum rate, R(stress)(max)), degree of conversion (DC) and cross-link density (CLD) of materials containing camphorquinone (CQ), phenylpropanedione (PPD) or CQ/PPD.
  
  
  METHODS
  R(p)(max) was evaluated via differential scanning calorimetry (DSC). Contraction force measurement was assessed with a single cantilever device for 5min. The samples were subsequently tested by infrared spectroscopy (FTIR) to evaluate the DC. After, samples were soaked in ethanol to evaluate the swelling coefficient (alpha) as a way to estimate the CLD. The results were analyzed by one-way ANOVA and Tukey's test (p=0.05).
  
  
  RESULTS
  CQ showed the highest R(p)(max) and R(stress)(max). PPD produced the lowest DC and the highest alpha. The mixture CQ/PPD produced statistically lower R(p)(max) and R(stress)(max) than CQ alone, but similar DC and CLD.
  
  
  CONCLUSIONS
  CQ/PPD reduced the R(p)(max) and R(stress)(max) without a reduction in DC and CLD. Therefore, the use of alternative photoinitiator systems could be a promising way to reduce the stress developed during the composite's polymerization without affecting the final properties.
authors.affiliation: Dental School, The University of Passo Fundo, PO Box 611/613, Campus I, BR 285, Km 171, Passo Fundo, RS 99001-970, Brazil. schneider@fop.unicamp.br
authors.forename: Luis Felipe J
authors.initials: LF
authors.lastname: Schneider
authors.forename: Simonides
authors.initials: S
authors.lastname: Consani
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Sakaguchi
authors.forename: Jack L
authors.initials: JL
authors.lastname: Ferracane
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate; D047188:Chalcones; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects*; D055117:Curing Lights, Dental; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D044367:Phase Transition; D055668:Photochemical Processes; D011092:Polyethylene Glycols; D011109:Polymethacrylic Acids; D013729:Terpenes
chemical_list: D047188:Chalcones; D003188:Composite Resins; D011109:Polymethacrylic Acids; D013729:Terpenes; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C048339:camphoroquinone; C100349:1-phenyl-1,2-propanedione