title: The effect of resin composite pre-heating on monomer conversion and polymerization shrinkage.
abstract: OBJECTIVE
  To determine monomer conversion and polymerization shrinkage of a resin composite after different pre-heating procedures and storage intervals.
  
  
  METHODS
  For a commercial resin-based composite the immediate (5 min) and final (24h) degree of conversion was measured on top and bottom surfaces utilizing FTIR spectroscopy. Composite pre-heating temperatures were selected between 10 and 68 degrees C. Polymerization shrinkage was measured according to Archimedes' principles of buoyancy after 5 min at respective pre-heating temperatures and after 24h dark and wet storage at 37 degrees C. Intra-cavity temperature development was monitored using a K-type thermocouple.
  
  
  RESULTS
  No significant increase in immediate as well as in final degree of conversion were measured from composite pre-heating at 68 degrees C compared to 54 and 39 degrees C. Linear correlations were detected immediately after photo-polymerization and on the top surface after 24h storage. Polymerization shrinkage as a function of pre-heating temperatures exhibited a linear correlation after 5 min, but no statistically different behavior after 24h.
  
  
  CONCLUSIONS
  Pre-heating of resin composites does not increase degree of conversion over time. It can be clinically beneficial, due to a superior marginal adaptation. This advantageous effect of reduced material paste viscosity has to be clinically addressed, since temperature rapidly drops to the physiological level upon removal from the pre-heating device.
authors.affiliation: Dental Clinic 1 - Operative Dentistry and Periodontology, University of Erlangen-Nuremberg, Glueckstr. 11, D-91054 Erlangen, Germany. lohbauer@dent.uni-erlangen.de
authors.forename: Ulrich
authors.initials: U
authors.lastname: Lohbauer
authors.forename: Spiros
authors.initials: S
authors.lastname: Zinelis
authors.forename: Christos
authors.initials: C
authors.lastname: Rahiotis
authors.forename: Anselm
authors.initials: A
authors.lastname: Petschelt
authors.forename: George
authors.initials: G
authors.lastname: Eliades
mesh_terms: D001831:Body Temperature; D003188:Composite Resins / Q000737:chemistry; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D003804:Dentin; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D044367:Phase Transition; D044366:Transition Temperature; D014783:Viscosity
chemical_list: D003188:Composite Resins; C501891:Tetric EvoCeram