title: Correlation between polymerization shrinkage and marginal fit of temporary crowns.
abstract: OBJECTIVE
  During polymerization, temporary c&b materials (t-c&b) undergo shrinkage which may lead to marginal inaccuracies of the temporary restoration. The degree of correlation between these two factors is still unknown. Hence, the objective of this study was to determine the polymerization shrinkage of t-c&bs and to evaluate, to which degree the shrinkage is correlated to the width of the marginal gap.
  
  
  METHODS
  Six different t-c&bs (2 monomethacrylates and 4 dimethacrylates) were used to fabricate temporary crowns (n = 12) on two prepared teeth (stainless steel) of different diameters (5 and 7 mm). The crown diameters and marginal discrepancy were measured at various storage times after mixing (10, 30, 60 min) using a travelling microscope. In addition, the shrinkage (bonded-disk method) and content of inorganic filler (ashing method) were recorded. The statistical analysis was carried out using parametric tests, the F-test and Pearson's correlation (p = 0.05).
  
  
  RESULTS
  The marginal discrepancies increased as a function of increasing storage time (10 min: 0.162-0.218 mm; 60 min: 0.271-0.521 mm). Lower values were recorded for monomethacrylates than for the dimethacrylates (greatest changes recorded during the first 30 min). The shrinkage values recorded 10 min after mixing varied between 3.25 and 4.10%. There was no significant relationship between the width of the marginal gap and shrinkage (p > 0.05).
  
  
  CONCLUSIONS
  Shrinkage values are not suitable to predict the marginal accuracy of a temporary restoration. At least 30 min should elapse between fabricating and trimming temporary crowns to avoid further inaccuracies.
authors: Department of Prosthetic Dentistry, Justus-Liebig-University, Giessen, Germany. markus.balkenhol@dentist.med.uni-giessen.de
authors: Markus
authors: M
authors: Balkenhol
authors: Michael
authors: M
authors: Knapp
authors: Paul
authors: P
authors: Ferger
authors: Ulrich
authors: U
authors: Heun
authors: Bernd
authors: B
authors: Wöstmann
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003442:Crowns; D018772:Dental Marginal Adaptation; D003794:Dental Restoration, Temporary; D003799:Dental Stress Analysis; D003833:Denture, Partial, Temporary; D008689:Methacrylates / Q000737:chemistry; D044367:Phase Transition
chemical_list: D003188:Composite Resins; D008689:Methacrylates