title: Effect of temperature on the degree of conversion and working time of dual-cured resin cements exposed to different curing conditions.
abstract: OBJECTIVE
  This study evaluated the degree of conversion (DC) and working time (WT) of two commercial, dual-cured resin cements polymerized at varying temperatures and under different curing-light accessible conditions, using Fourier transformed infrared analysis (FTIR).
  
  
  METHODS
  Calibra (Cal; Dentsply Caulk) and Variolink II (Ivoclar Vivadent) were tested at 25°C or preheated to 37°C or 50°C and applied to a similar-temperature surface of a horizontal attenuated-total-reflectance unit (ATR) attached to an infrared spectrometer. The products were polymerized using one of four conditions: direct light exposure only (600 mW/cm(2)) through a glass slide or through a 1.5- or 3.0-mm-thick ceramic disc (A2 shade, IPS e.max, Ivoclar Vivadent) or allowed to self-cure in the absence of light curing. FTIR spectra were recorded for 20 min (1 spectrum/s, 16 scans/spectrum, resolution 4 cm(-1)) immediately after application to the ATR. DC was calculated using standard techniques of observing changes in aliphatic-to-aromatic peak ratios precuring and 20-min postcuring as well as during each 1-second interval. Time-based monomer conversion analysis was used to determine WT at each temperature. DC and WT data (n=6) were analyzed by two-way analysis of variance and Tukey post hoc test (p=0.05).
  
  
  RESULTS
  Higher temperatures increased DC regardless of curing mode and product. For Calibra, only the 3-mm-thick ceramic group showed lower DC than the other groups at 25°C (p=0.01830), while no significant difference was observed among groups at 37°C and 50°C. For Variolink, the 3-mm-thick ceramic group showed lower DC than the 1-mm-thick group only at 25°C, while the self-cure group showed lower DC than the others at all temperatures (p=0.00001). WT decreased with increasing temperature: at 37°C near 70% reduction and at 50°C near 90% for both products, with WT reduction reaching clinically inappropriate times in some cases (p=0.00001).
  
  
  CONCLUSIONS
  Elevated temperature during polymerization of dual-cured cements increased DC. WT was reduced with elevated temperature, but the extent of reduction might not be clinically acceptable.
authors: Department of Operative Dentistry, University of Guarulhos, Guarulhos, Brazil.
authors: M
authors: M
authors: Oliveira
authors: P F
authors: PF
authors: Cesar
authors: M
authors: M
authors: Giannini
authors: F A
authors: FA
authors: Rueggeberg
authors: J
authors: J
authors: Rodrigues
authors: C A
authors: CA
authors: Arrais
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry; D055117:Curing Lights, Dental; D003764:Dental Materials / Q000737:chemistry; D005459:Fluorides / Q000737:chemistry; D005898:Glass / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry*; D055116:Self-Curing of Dental Resins; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D015018:Ytterbium / Q000737:chemistry
chemical_list: C433205:Calibra; D003764:Dental Materials; D008689:Methacrylates; D011109:Polymethacrylic Acids; D011140:Polyurethanes; D019279:Resin Cements; C029824:urethane dimethacrylate luting resin; C102799:ytterbium fluoride; C020946:triethylene glycol dimethacrylate; C103502:Variolink; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C023506:Glass ceramics; D015018:Ytterbium; D005459:Fluorides