title: Photoinitiator content in restorative composites: influence on degree of conversion, reaction kinetics, volumetric shrinkage and polymerization stress.
abstract: OBJECTIVE
  To determine the influence of rate of polymerization, degree of conversion and volumetric shrinkage on stress development by varying the amount of photoinitiators in a model composite.
  
  
  METHODS
  Volumetric shrinkage (with a mercury dilatometer), degree of conversion, maximum rate of reaction (RPmax) (with differential scanning calorimetry) and polymerization stress (with a controlled compliance device) were evaluated. Bis-GMA/TEGDMA (equal mass ratios) were mixed with a tertiary amine (EDMAB) and camphorquinone, respectively, in three concentrations (wt%): high = 0.8/1.6; intermediate = 0.4/0.8 and low = 0.2/0.4. 80 wt% filler was added. Composites were photoactivated (400 mW/cm2 x 40 seconds; radiant exposure = l6 J/cm2). A fourth experimental group was included in which the low concentration formulation was exposed for 80 seconds (32 J/cm2).
  
  
  RESULTS
  For the same radiant exposure, conversion, RPmax and stress increased with photoinitiator concentration (P < 0.001). When the low concentration group exposed to 32 J/cm2 was compared with the high and intermediate groups (exposed to 16 J/cm2), RPmax still increased with the photoinitiator concentration between all levels (P < 0.001) but conversion and stress did not vary (P > 0.05). Shrinkage did not vary regardless of the photoinitiator concentration or radiant exposure. For the photoinitiator concentrations used in this study. Polymerization stress was influenced by conversion but not by rate of reaction.
authors.affiliation: Department of Biomaterials and Oral Biochemistry, School of Dentistry, University of São Paulo, Brazil. pfeifercs@gmail.com
authors.forename: Carmem S
authors.initials: CS
authors.lastname: Pfeifer
authors.forename: Jack L
authors.initials: JL
authors.lastname: Ferracane
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Sakaguchi
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Braga
mesh_terms: D010129:4-Aminobenzoic Acid / Q000737:chemistry; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D055598:Chemical Phenomena; D002626:Chemistry, Pharmaceutical; D003187:Compliance; D003188:Composite Resins / Q000737:chemistry*; D055117:Curing Lights, Dental; D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008422:Materials Testing; D055668:Photochemical Processes; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D011829:Radiation Dosage; D013314:Stress, Mechanical; D013499:Surface Properties; D013729:Terpenes / Q000737:chemistry; D013997:Time Factors; D062366:para-Aminobenzoates
chemical_list: 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