title: Determining the direction of shrinkage in dental composites by changes in surface contour for different bonding configurations.
abstract: OBJECTIVE
  To determine if polymerization shrinkage of a light-cured composite is directed toward the light source, and if a relationship exists between C-factor and magnitude of deflection.
  
  
  METHODS
  Either a self-cured composite or light-cured composite each was placed in an experimental model of composite cured in a glass ring. Changing the surface area prepared for bonding within the cavity preparation produced three different C-factors (the ratio of bonded to unbonded surface areas): 0, 1.9, and 4.8. Profilometer tracings were obtained, and the largest deviation from the height of the glass ring was reported. An uncured control sample also was evaluated and showed a linear tracing with fluctuations of less than 0.5 micron. The specimens were then cut in half and examined by scanning electron microscope.
  
  
  RESULTS
  The top (unbonded) surface exhibited a concave shrinkage profile with the greatest deflection at the center. The magnitude of deflection at the center increased as the cavity's C-factor increased from 31 microns (C = 0) to 57 microns (C = 4.8). The bottom (unbonded) surface, similarly formed a concave surface. When the composite was bonded to the glass, fractures in the glass wall near the glass-composite interface were observed.
authors.affiliation: Bisco Inc., 1100 West Irving Park Road, Schaumburg, IL 60193, USA. Byoung_In_Suh@bisco.com
authors.forename: B I
authors.initials: BI
authors.lastname: Suh
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D003799:Dental Stress Analysis; D008027:Light; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011108:Polymers / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013499:Surface Properties
chemical_list: C098721:Aelitefil; D003188:Composite Resins; D011108:Polymers; D012821:Silanes; C078905:Bisfil; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide