title: Vertical and horizontal polymerization shrinkage in composite restorations.
abstract: OBJECTIVE
  Polymerization shrinkage developed in vertical and horizontal directions after light activation of light-curing composite restorative materials. The purpose of this study was to examine the effects of vertical and horizontal polymerization shrinkage on: (a) dimensional changes of resin composites in tooth cavities; (b) shear bond strengths to enamel and dentin; and (c) marginal gap width in a non-reacting Teflon mold.
  
  
  METHODS
  Vertical and horizontal polymerization shrinkage in tooth cavities were measured immediately (3 min) after light activation. With the same time lapse, shear bond strengths to enamel and dentin and marginal gap widths in Teflon mold were also measured.
  
  
  RESULTS
  There was a significant correlation between vertical and horizontal polymerization shrinkage (r=0.647, p=0.043) in the tooth cavity. Composite materials which produced small vertical shrinkage also produced smaller horizontal shrinkage. Composite materials which produced small vertical shrinkage in the tooth cavity exhibited greater shear bond strengths to both enamel (r=-0.697, p=0.025) and dentin (r=-0.752, p=0.012). Composite materials which produced smaller horizontal shrinkage produced smaller marginal gap widths in the Teflon mold (r=0.829, p=0.003). No relationships were observed between horizontal shrinkage in the tooth cavity and shear bond strengths to both enamel and dentin (p>0.05).
  
  
  CONCLUSIONS
  During the early stage of setting (<3 min) in tooth cavities, the vertical shrinkage of light-activated composite restorative materials was correlated with horizontal shrinkage.
authors.affiliation: Department of Biomaterials, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8525, Japan. Electronic address: mirie@md.okayama-u.ac.jp.
authors.forename: Masao
authors.initials: M
authors.lastname: Irie
authors.affiliation: Department of Biomaterials, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8525, Japan.
authors.forename: Jiro
authors.initials: J
authors.lastname: Tanaka
authors.affiliation: Occlusion and Removable Prosthodontics, Okayama University Hospital, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8525, Japan.
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Maruo
authors.affiliation: Occlusion and Removable Prosthodontics, Okayama University Hospital, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8525, Japan.
authors.forename: Goro
authors.initials: G
authors.lastname: Nishigawa
mesh_terms: D003188:Composite Resins; D003793:Dental Restoration, Permanent; D006801:Humans; D066298:In Vitro Techniques; D008422:Materials Testing; D058105:Polymerization
chemical_list: D003188:Composite Resins
keywords: Bond strength; Composite restoration; Light curing; Polymerization shrinkage