title: Polymerization stress--is it clinically meaningful?
abstract: OBJECTIVE
  The objective of this article is to discuss the evidence for polymerization shrinkage and shrinkage stress of dental composite restoratives in terms of its potential relevance to the clinical situation
  
  
  METHODS
  Articles relating to the issue of polymerization contraction stress generation in dental composite materials, and the factors that influence it, were reviewed and included. Particular attention was paid to evidence derived from clinical studies. Articles were identified through PubMed and through the bibliographies of other articles.
  
  
  RESULTS
  There is extensive evidence for the presence of polymerization contraction stress in dental composites, as well as evidence for its deleterious effects, which include marginal leakage, gap formation, cuspal deflection, tooth cracking, reduced bond strength and lowered mechanical properties of the restorative. There is little, if any, direct evidence for the clinical effect of these contraction stresses. No study has directly established a link between these stresses and enhanced postoperative sensitivity or recurrent caries, for example. However, the concern over these stresses and the manner in which they influence the placement of current composite materials demonstrates that they are considered to be very important.
  
  
  CONCLUSIONS
  Though no direct evidence exists to prove that the generation of contraction stress in dental composite restorations causes reduced clinical longevity, the indirect evidence from numerous in vitro studies and the concern over controlling their effects proves that they are clinically relevant.
authors.affiliation: Department of Restorative Dentistry, Oregon Health & Science University, Portland, OR 97201, USA. Electronic address: ferracan@ohsu.edu.
authors.forename: Jack L
authors.initials: JL
authors.lastname: Ferracane
authors.affiliation: Department of Restorative Dentistry, Oregon Health & Science University, Portland, OR 97201, USA. Electronic address: hiltont@ohsu.edu.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Hilton
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003793:Dental Restoration, Permanent; D004548:Elasticity; D006244:Hardness; D008422:Materials Testing; D058105:Polymerization; D013718:Tensile Strength
chemical_list: D003188:Composite Resins
keywords: Clinical; Contraction stress; Dental composite; Polymerization shrinkage; Properties