title: Assessment of polymerization contraction stress of three composite resins.
abstract: OBJECTIVE
  The purpose of this study was to measure the development of contraction stress of three composite resin restorative materials during photo-polymerization: a micro-hybrid composite (Filtek Z250, 3M ESPE, St. Paul, MN, USA); a nano-filled composite (Filtek Supreme, 3M ESPE, St. Paul, MN, USA); and a low-shrinkage composite (AElite LS, Bisco Inc., Schaumburg, IL, USA).
  
  
  METHODS
  Curing shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen-curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40 s. The contraction force (N) generated during polymerization was continuously recorded for 150 s after photo-initiation. Contraction stress (MPa) was calculated at 20, 40, 60 and 150 s. Data were statistically analyzed.
  
  
  RESULTS
  The low-shrinkage composite AElite LS exhibited the lowest stress values compared to other materials (p<0.05). Statistical analysis did not show significant differences between Filtek Z250 and Filtek Supreme.
  
  
  CONCLUSIONS
  The low-shrinkage composite showed lower contraction stress than micro-hybrid and nano-filled composite. Ideally, non-shrinking resins would represent the ultimate solution to overcome polymerization contraction and stress-related problems.
authors.affiliation: Department of Biomedicine, Division of Dentistry and Biomaterials, University of Trieste, Via Stuparich 1, I-34129 Trieste, Italy.
authors.forename: Milena
authors.initials: M
authors.lastname: Cadenaro
authors.forename: Matteo
authors.initials: M
authors.lastname: Biasotto
authors.forename: Nicola
authors.initials: N
authors.lastname: Scuor
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Breschi
authors.forename: Carel L
authors.initials: CL
authors.lastname: Davidson
authors.forename: Roberto
authors.initials: R
authors.lastname: Di Lenarda
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D008027:Light; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D013314:Stress, Mechanical; D013696:Temperature; D013997:Time Factors
chemical_list: C485363:Aelite LS; D003188:Composite Resins; D003764:Dental Materials; C474035:Filtek Supreme; C444701:Filtek Z250; D011108:Polymers