title: Effects of temperature on composite resin shrinkage.
abstract: OBJECTIVE
  To determine whether temperature affects the polymerization shrinkage of composite resin.
  
  
  METHODS
  Volumetric shrinkage of a microfill composite was measured using a video-imaging device. The material was cooled to 4 degrees C or heated to 37 degrees C, 54 degrees C, or 68 degrees C. Room-temperature (20 degrees C) composite was used as the control. The composite was light activated using a quartz-tungsten-halogen curing device. Polymerization shrinkage was recorded at 1-minute intervals for 10 minutes after the beginning of photoinitiation. The data were subjected to ANOVA, Fisher's PLSD test, and linear regression analysis (alpha = 0.05).
  
  
  RESULTS
  Volumetric shrinkage ranged from 0.2% to 4.7%. Shrinkage of the composite at 37 degrees C was similar to that at room temperature. Preheating the composite to 54 degrees C or 68 degrees C significantly increased shrinkage. The apparent polymerization shrinkage of the refrigerated composite was significantly less than that of the control, although this might have been an artifact of the test method. Regression analysis revealed a strong correlation between temperature and volumetric shrinkage.
  
  
  CONCLUSIONS
  Preheating composite to relatively high temperatures (54 degrees C or 68 degrees C) to increase its flow and adaptation causes an increase in volumetric shrinkage. At body temperature, composite shrinkage is similar to that at room temperature.
authors.affiliation: Department of Operative Dentistry, University of North Carolina, Chapel Hill, NC 27599-7450, USA. rick_walter@dentistry.unc.edu
authors.forename: Ricardo
authors.initials: R
authors.lastname: Walter
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Swift
authors.forename: Huma
authors.initials: H
authors.lastname: Sheikh
authors.forename: Jack L
authors.initials: JL
authors.lastname: Ferracane
mesh_terms: D055598:Chemical Phenomena; D003080:Cold Temperature; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental / Q000145:classification; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D058105:Polymerization; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014741:Video Recording
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C039734:Durafill