title: Polymerization kinetics of dental adhesives cured with LED: correlation between extent of conversion and permeability.
abstract: OBJECTIVE
  The aim of this study was to analyze the polymerization kinetics of different adhesive films in relation to their permeability after exposure to different LED curing units.
  
  
  METHODS
  One adhesive from each class was analyzed: a three-step etch-and-rinse (OptiBond FL; Sybron-Kerr), a two-step etch-and-rinse (One-Step, Bisco), a two-step self-etch (Clearfil Protect Bond, Kuraray) and a one-step self-etch adhesive (Xeno III; Dentsply DeTrey). Adhesive films were prepared and cured with SmartLite IQ (Dentsply) or L.E. Demetron I (Demetron Kerr) up to complete curing. Polymerization kinetic curves of the tested adhesives were obtained with differential scanning calorimetry (DSC). In particular, total reaction time and extent of polymerization (Ep) at 20, 40 or 60s were compared. Permeability of the adhesive films was evaluated on flat dentin surfaces of human extracted teeth connected to a permeability device and statistically analyzed.
  
  
  RESULTS
  Total reaction time differed among the adhesives tested: OptiBond FL<Clearfil Protect Bond<One-Step<Xeno III with both curing units (p<0.05). At 20s OptiBond FL showed the highest Ep, while the lowest values were obtained with One-Step and Xeno III (p<0.05). E(p) increased when curing time was prolonged (40 and 60s) for all adhesives tested (p<0.05), however, on simplified adhesives, incomplete polymerization took place even after prolonged exposure intervals. An inverse correlation was found between Ep of the adhesives and their permeability using LED curing units.
  
  
  CONCLUSIONS
  This study supports the hypothesis that, longer curing times than those recommended by the respective manufacturer decrease permeability of the bonded interfaces.
authors.affiliation: Department of Biomedicine, Unit of Dental Sciences and Biomaterials, University of Trieste, Via Stuparich 1, I-34129 Trieste, Italy. lbreschi@units.it
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Breschi
authors.forename: Milena
authors.initials: M
authors.lastname: Cadenaro
authors.forename: Francesca
authors.initials: F
authors.lastname: Antoniolli
authors.forename: Salvatore
authors.initials: S
authors.lastname: Sauro
authors.forename: Matteo
authors.initials: M
authors.lastname: Biasotto
authors.forename: Carlo
authors.initials: C
authors.lastname: Prati
authors.forename: Franklin R
authors.initials: FR
authors.lastname: Tay
authors.forename: Roberto
authors.initials: R
authors.lastname: Di Lenarda
mesh_terms: D000269:Adhesives / Q000737:chemistry* / Q000528:radiation effects; D000328:Adult; D002152:Calorimetry, Differential Scanning; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D003806:Dentin Permeability; D017220:Dentin-Bonding Agents / Q000737:chemistry* / Q000528:radiation effects; D004867:Equipment Design; D006801:Humans; D007700:Kinetics; D008029:Lighting / Q000295:instrumentation*; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D008875:Middle Aged; D010539:Permeability; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D019279:Resin Cements / Q000737:chemistry / Q000528:radiation effects; D013997:Time Factors
chemical_list: D000269:Adhesives; C103506:Bis-GMA, BPDM, HEMA dental-bonding resin; C503075:Clearfil Protect Bond; D003764:Dental Materials; D017220:Dentin-Bonding Agents; D008689:Methacrylates; C469607:OptiBond FL; D011108:Polymers; D019279:Resin Cements; C487957:Xeno III