title: Degree of conversion of three composite materials employed in the adhesive cementation of indirect restorations: a micro-Raman analysis.
abstract: OBJECTIVE
  Adhesive luting of indirect restorations can be carried out employing dual- or light-curing materials. This in vitro study evaluated the degree of conversion (DC) of the materials employed in this procedure, seeking how the combination of time and power of curing applied during polymerisation, as well as the temperature of the light-curing composite, influenced the DC.
  
  
  METHODS
  One hundred and eighty onlays of different thicknesses (2 mm, 3 mm, 4 mm) were luted with three different composites: two dual-curing cements (Variolink II and Calibra) and a light-curing composite (Venus). The same halogen lamp was used with three different modalities selected to provide a constant quantity of energy. The time/power combinations tested were 400 mW/cm(2) for 120 s, 800 mW/cm(2) for 60s and 1200 mW/cm(2) for 40 s. The light-curing composite was employed at room temperature and after preheating at 54 degrees C. Each sample was examined in three positions using the Micro-Raman Dilor HR LabRam spectrometer to evaluate the polymer conversion degree. The data were analysed using analysis of variance and the Student-Newman-Keuls test (p=0.05).
  
  
  RESULTS
  The dual-curing materials showed average conversion percentages close to 64%, although onlays thickness clearly influence the degree of conversion, the light-curing composite showed satisfactory results only when onlays thickness was thin, however preheating significantly improved the performance of the light-curing composite under onlays of great thickness.
  
  
  CONCLUSIONS
  Optimal luting of indirect restorations is clearly dependent from light source power, irradiation time and dual-cure luting cement or light-curing composite chosen. It should be calibrated for each material to acquire high DCs. Preheating of light-curing only composites allows for the materials to reach optimal conversion degrees.
authors.affiliation: Department of Dental Materials and Restorative Dentistry, University of Siena, Italy.
authors.forename: Pier Antonio
authors.initials: PA
authors.lastname: Acquaviva
authors.forename: Francesca
authors.initials: F
authors.lastname: Cerutti
authors.forename: Gianmaria
authors.initials: G
authors.lastname: Adami
authors.forename: Massimo
authors.initials: M
authors.lastname: Gagliani
authors.forename: Marco
authors.initials: M
authors.lastname: Ferrari
authors.forename: Enrico
authors.initials: E
authors.lastname: Gherlone
authors.forename: Antonio
authors.initials: A
authors.lastname: Cerutti
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D001840:Dental Bonding / Q000379:methods*; D018772:Dental Marginal Adaptation; D007284:Inlays / Q000379:methods*; D019279:Resin Cements / Q000737:chemistry* / Q000528:radiation effects; D013059:Spectrum Analysis, Raman
chemical_list: C433205:Calibra; D003188:Composite Resins; D019279:Resin Cements; C488393:Venus (composite resin); C103502:Variolink