title: The effect of photopolymerization on the degree of conversion, polymerization kinetic, biaxial flexure strength, and modulus of self-adhesive resin cements.
abstract: BACKGROUND
  Understanding the effect of the degree of conversion on the mechanical properties of auto- and dual-polymerizing self-adhesive resin cements leads to a better estimation of their performance in different clinical scenarios.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the effect of photopolymerization on the degree of conversion (DC) and polymerization kinetic of 4 dual-polymerized resin cements, 20 minutes after mixing, and its effects on the mechanical properties (biaxial flexural strength [FS] and modulus [FM]) after short-term aging.
  
  
  METHODS
  Conventional (RelyX ARC and Clearfil Esthetic Cement) and self-adhesive resin cements (RelyX Unicem and Clearfil SA Cement) were applied to a Fourier infrared spectrometer to assess the DC (n=5) under the following 3 polymerization conditions: direct light exposure (dual-polymerizing mode), exposure through the prepolymerized disk, or autopolymerizing. The polymerization kinetic was recorded for 20 minutes. Then, disk-shaped specimens (n=11) were prepared to evaluate the effect of polymerization on the FS and FM in both extreme polymerization conditions (dual-polymerizing or autopolymerizing). Data were statistically analyzed by 2-way repeated measure ANOVA (DC) and by 2-way ANOVA (FS and FM), followed by the Tukey-Kramer post hoc test (α=.05).
  
  
  RESULTS
  Autopolymerizing groups exhibited reduced DC means, whereas intermediate values were observed when resin cements were polymerized through the disk. All groups exhibited higher DC at the end of 20 minutes. The polymerization kinetic revealed a rising curve, and materials, when directly photopolymerized, reached a plateau immediately after light exposure. Regarding the flexural biaxial testing, most of the resin cements were affected by polymerization mode and differences among groups were product dependent.
  
  
  CONCLUSIONS
  The resin cements achieved immediate higher DC and mechanical properties when photopolymerized. The total absence of photoactivation may still impair their mechanical properties even after short-term aging.
authors.affiliation: Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil. Electronic address: traguiar@gmail.com.
authors.forename: Thaiane R
authors.initials: TR
authors.lastname: Aguiar
authors.affiliation: Graduate student, Department of Operative Dentistry, University of Guarulhos, Guarulhos, Brazil.
authors.forename: Michele
authors.initials: M
authors.lastname: de Oliveira
authors.affiliation: Assistant Professor, Department of Operative Dentistry, Ponta Grossa State University, Ponta Grossa, Brazil.
authors.forename: César A G
authors.initials: CA
authors.lastname: Arrais
authors.affiliation: Associate Professor, Department of Social Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil.
authors.forename: Glaucia M B
authors.initials: GM
authors.lastname: Ambrosano
authors.affiliation: Professor, Department of Oral Rehabilitation, Georgia Regents University, College of Dental Medicine, Augusta, Ga.
authors.forename: Frederick
authors.initials: F
authors.lastname: Rueggeberg
authors.affiliation: Associate Professor, Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Giannini
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D055117:Curing Lights, Dental / Q000145:classification; D003624:Darkness; D055119:Elastic Modulus; D005898:Glass / Q000737:chemistry; D006801:Humans; D008027:Light; D008422:Materials Testing; D018583:Pliability; D011092:Polyethylene Glycols / Q000737:chemistry; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry; D011829:Radiation Dosage; D019279:Resin Cements / Q000737:chemistry / Q000528:radiation effects*; D055116:Self-Curing of Dental Resins / Q000295:instrumentation / Q000379:methods; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: C581302:Clearfil SA; D003188:Composite Resins; D011109:Polymethacrylic Acids; C483701:Rely X Unicem; C462240:RelyX ARC; D019279:Resin Cements; C477352:Sinfony composite resin; C530542:clearfil esthetic cement; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate