title: Effect of energy density and delay time on the degree of conversion and Knoop microhardness of a dual resin cement.
abstract: OBJECTIVE
  In the present study, we evaluated the influence of the photo-curing delay time and energy density on the degree of conversion and the Knoop microhardness of a resin cement.
  
  
  METHODS
  Seventy-eight samples were assigned to 13 groups (n = 6), one of which received no light curing (control). The samples were made of a dual-cured resin cement (RelyX ARC) with the aid of a Teflon matrix, submitted to one of the following energy densities (J/cm²): 7, 14, 20, and 28. Delay times were immediate (0), 1 min, or 2 min. After 24 h, the degree of conversion and microhardness were measured at three segments: cervical, medium, and apical. Data were submitted to three-way anova and Tukey's and Dunnett's tests, the latest of which was used to compare the control to the experimental groups.
  
  
  RESULTS
  No interaction was observed between delay time and energy density regarding the degree of conversion. The cervical segment showed the highest values, while the apical showed the lowest. Microhardness values concerning the cervical segment in all groups were statistically different from that obtained for the control.
  
  
  CONCLUSIONS
  A high-irradiance light-curing unit allows for a reduced irradiation exposure time with a short delay time, aimed at tooth restorations using a dual-cured resin cement.
authors: Piracicaba Dental School, University of Campinas, Piracicaba, Brazil.
authors: Maria do Carmo A J
authors: Mdo C
authors: Mainardi
authors: Maria Cecília C
authors: MC
authors: Giorgi
authors: Débora A N L
authors: DA
authors: Lima
authors: Giselle M
authors: GM
authors: Marchi
authors: Gláucia M
authors: GM
authors: Ambrosano
authors: Luiz A M S
authors: LA
authors: Paulillo
authors: Flávio H B
authors: FH
authors: Aguiar
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D055117:Curing Lights, Dental; D006244:Hardness; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000379:methods; D008422:Materials Testing; D011092:Polyethylene Glycols / Q000737:chemistry; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry; D011829:Radiation Dosage; D019279:Resin Cements / Q000737:chemistry*; D055116:Self-Curing of Dental Resins / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors
chemical_list: D011109:Polymethacrylic Acids; C462240:RelyX ARC; D019279:Resin Cements; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate
keywords: degree of conversion; hardness; polymerization; resin cement; root canal