title: Influence of photoinitiator type on the rate of polymerization, degree of conversion, hardness and yellowing of dental resin composites.
abstract: OBJECTIVE
  To evaluate the degree of conversion (DC), maximum rate of polymerization (Rpmax), Knoop hardness (KHN) and yellowing (b-value) of resin composites formulated with phenylpropanedione (PPD), camphorquinone (CQ), or CQ/PPD at different concentrations. The hypotheses tested were (i) PPD or CQ/PPD would produce less Rpmax and yellowing than CQ alone without affecting DC and KHN, and (ii) Rpmax, DC, and KHN would be directly related to the absorbed power density (PDabs).
  
  
  METHODS
  CQ/amine, PPD/amine and CQ/PPD/amine were used at low, intermediate and high concentrations in experimental composites. Photoinitiator absorption and halogen-light emission were measured using a spectrophotometer, Rp with differential scanning calorimetry (DSC), DC with DSC and FTIR, KHN with Knoop indentation; and color with a chromameter. The results were analyzed with two-way analysis of variance (ANOVA)/Student-Newman-Keul's test (p<0.05). Correlation tests were carried out between PDabs and each of DC, Rpmax and KHN.
  
  
  RESULTS
  The PDabs increased with photoinitiator concentration and PPD samples had the lowest values. In general, maximum DC was comparable at intermediate concentration, while Rpmax and KHN required higher concentrations. DC was similar for all photoinitiators, but Rpmax was lower with PPD and CQ/PPD. PPD produced the lowest KHN. Yellowing increased with photoinitiator concentration. PPD did not reduce yellowing at intermediate and/or high concentrations, compared to CQ-formulations. PDabs showed significant correlations with DC, Rpmax and KHN.
  
  
  CONCLUSIONS
  PPD or CQ/PPD reduced Rpmax in experimental composites without affecting the DC. The use of PPD did not reduce yellowing, but reduced KHN. DC, Rpmax and KHN were dependent on PDabs.
authors.affiliation: Dental Materials Division, Piracicaba Dental School, University of Campinas, Piracicaba, SP, Brazil. felipefop@gmail.com
authors.forename: Luis Felipe J
authors.initials: LF
authors.lastname: Schneider
authors.forename: Carmem S C
authors.initials: CS
authors.lastname: Pfeifer
authors.forename: Simonides
authors.initials: S
authors.lastname: Consani
authors.forename: Scott A
authors.initials: SA
authors.lastname: Prahl
authors.forename: Jack L
authors.initials: JL
authors.lastname: Ferracane
mesh_terms: D010129:4-Aminobenzoic Acid / Q000737:chemistry / Q000528:radiation effects; D000042:Absorption; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D002152:Calorimetry, Differential Scanning; D047188:Chalcones / Q000737:chemistry / Q000528:radiation effects; D003116:Color; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D011092:Polyethylene Glycols / Q000737:chemistry / Q000528:radiation effects; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013729:Terpenes / Q000737:chemistry / Q000528:radiation effects; D062366:para-Aminobenzoates
chemical_list: D047188:Chalcones; D003188:Composite Resins; D003764:Dental Materials; D011108:Polymers; D011109:Polymethacrylic Acids; D013729:Terpenes; C523330:ethyl 4-N,N-dimethylaminobenzoate; D062366:para-Aminobenzoates; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C048339:camphoroquinone; D010129:4-Aminobenzoic Acid; C100349:1-phenyl-1,2-propanedione