title: Mapping camphorquinone consumption, conversion and mechanical properties in methacrylates with systematically varied CQ/amine compositions.
abstract: OBJECTIVE
  To evaluate conversion, bulk mechanical properties and camphorquinone (CQ) consumption in methacrylate resins, comprising a range of overall initiator concentrations and CQ/amine ratios.
  
  
  METHODS
  BisGMA (Bisphenol-A glycidyl dimethacrylate), TEGDMA (triethyleneglycol dimethacrylate) and UDMA (urethane dimethacrylate) were mixed at a 1:1:1 molar ratio. CQ was used as the visible light photosensitizer, in combination with EDMAB (Ethyl p-dimethylamino benzoate), at 3:1, 2:1, 1:1, 1:2 and 1:3 weight ratios, at 0.5, 1.0, 1.5, 2.0 and 3.0 wt% overall initiator concentration. Butylhydroxytoluene was added at 0.05 wt% as an inhibitor. Unfilled resins were photoactivated with a dental light source (VIP Jr, Bisco) for 60 s at 600 mW/cm(2). Flexural strength/modulus were assessed in 2×1×10 mm bars, tested in three-point bending. Degree of conversion was assessed at the bottom of the same specimens using FT-RAMAN. CQ consumption was measured using a UV-vis spectrometer. Data were analyzed with two-way ANOVA/Tukey test (α=5%).
  
  
  RESULTS
  Lower conversion and inferior mechanical properties were observed with lower overall initiator concentrations and higher amine/CQ ratios. The lowest overall initiator concentration (0.5%) presented the statistically lowest conversion/properties results, except for the 1:3 amine/CQ ratio. For overall concentrations equal or greater to 1.5%, the amine/CQ ratio did not influence conversion or mechanical properties. CQ consumption was less efficient for the highest overall initiator concentrations and lower amine/CQ ratios.
  
  
  CONCLUSIONS
  Above 1.5 wt% overall initiator concentration, the conversion and general mechanical properties were independent of the initiator concentration. Therefore, there seems to be no benefit to increasing the initiator concentration above that level. At higher camphorquinone concentrations, light transmission and photosensitizer consumption becomes impaired, which could lead to decreased depth of cure and yellowing of the restoration.
authors.affiliation: University of São Paulo, School of Dentistry, Biomaterials and Oral Biochemistry Department, São Paulo, SP, Brazil.
authors.forename: T
authors.initials: T
authors.lastname: Guimarães
authors.affiliation: Fluminense Federal University, School of Dentistry, Restorative Dentistry Department, Niterói, RJ, Brazil; Veiga de Almeida University, School of Dentistry, Oral Rehabilitation Area, Rio de Janeiro, RJ, Brazil.
authors.forename: L F
authors.initials: LF
authors.lastname: Schneider
authors.affiliation: University of São Paulo, School of Dentistry, Biomaterials and Oral Biochemistry Department, São Paulo, SP, Brazil.
authors.forename: R R
authors.initials: RR
authors.lastname: Braga
authors.affiliation: Oregon Health and Science University, School of Dentistry, Biomaterials and Biomechanics, Portland, OR, USA. Electronic address: pfeiferc@ohsu.edu.
authors.forename: C S
authors.initials: CS
authors.lastname: Pfeifer
mesh_terms: D000588:Amines / Q000032:analysis*; D002164:Camphor / Q000031:analogs & derivatives* / Q000737:chemistry; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000588:Amines; D008689:Methacrylates; D002164:Camphor; C553149:camphorquinone
keywords: Amine; Camphorquinone; Degree of conversion; Methacrylates; Photopolymerization