title: Effect of water temperature on the fit of provisional crown margins during polymerization.
abstract: BACKGROUND
  When fabricating a provisional crown with the direct technique, dentists are concerned with margin discrepancies that result from polymerization shrinkage.
  
  
  OBJECTIVE
  This in vitro study examined the effect of water temperature on the fit of provisional crown margins during resin polymerization.
  
  
  METHODS
  The experiment was designed to simulate a direct technique to fabricate provisional crowns. After mixing autopolymerizing methyl methacrylate resin, the material was placed in a preformed polycarbonate crown. The crown was seated on a prepared premolar-shaped die with a shoulder margin. After 1 minute and 50 seconds, the crown was removed and polymerization was continued under the following conditions: 20 degrees C air, and water at 0 degrees C, 10 degrees C, 20 degrees C, 30 degrees C, 40 degrees C, 60 degrees C, and 80 degrees C. Six minutes after polymerization, the crown was trimmed and reseated on the die. Discrepancy of crown margin was measured with a 3-dimensional digitizer.
  
  
  RESULTS
  Margin discrepancy varied with the condition during resin-polymerization (ANOVA, P <.001). The crowns polymerized in 20 degrees C and 30 degrees C water revealed the best margin fit, showing 3 times more accurate margin fit than those polymerized in 20 degrees C air (Bonferroni/Dunn procedure, P <.01).
  
  
  CONCLUSIONS
  Conditions during resin polymerization were significant factors that affected margin fit of provisional crowns using the direct technique. Water temperatures of 20 degrees C and 30 degrees C produced the best fit at the margin of the provisional crown.
authors.affiliation: Faculty of Dentistry, Kyushu University, Fukuoka, Japan and GC Dental Products, Kasugai, Japan. tack@dent.kyushu-u.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Ogawa
authors.forename: S
authors.initials: S
authors.lastname: Aizawa
authors.forename: M
authors.initials: M
authors.lastname: Tanaka
authors.forename: S
authors.initials: S
authors.lastname: Matsuya
authors.forename: A
authors.initials: A
authors.lastname: Hasegawa
authors.forename: K
authors.initials: K
authors.lastname: Koyano
mesh_terms: D000704:Analysis of Variance; D003442:Crowns; D018772:Dental Marginal Adaptation; D003794:Dental Restoration, Temporary / Q000379:methods*; D008768:Methylmethacrylates / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D008768:Methylmethacrylates; D011108:Polymers; D014867:Water