title: Effect of preheating on microhardness and viscosity of 4 resin composites.
abstract: OBJECTIVE
  This study was undertaken to determine the effect of temperature on the microhardness and viscosity of 4 resin composite materials.
  
  
  METHODS
  To investigate microhardness, samples of each of the 4 composite materials, prepared by standard insertion of resin into prefabricated moulds, were divided into 2 groups (n = 10 per group). On the first group, the resin composite materials were inserted into the moulds at room temperature and cured. On the second group, the resin composite materials were pre-heated in a heating device, inserted into the moulds and immediately cured. Microhardness after curing (both immediately and after 24 hours of storage) was determined (using a 300 g load applied for 10 seconds) and averaged for 5 randomly selected points on the top and bottom surfaces of each sample. To investigate viscosity, 0.5 g samples of room temperature or preheated resin composite (n = 15 per group) were placed under a 454 g load for 45 seconds before light-curing (40 seconds). After curing, each sample was photographed and the surface area calculated. Data were analyzed by t tests or one-way analysis of variance and Tukey's test.
  
  
  RESULTS
  Preheating the resin composites increased the microhardness and decreased the viscosity of the samples. Filtek Supreme Ultra resin composite had the highest mean microhardness, and Vit-l-escence resin composite had the lowest viscosity.
  
  
  CONCLUSIONS
  The effects of preheating resin composites may allow easier placement of restorations and greater monomer conversion.
authors.forename: Karen V
authors.initials: KV
authors.lastname: Ayub
authors.forename: Gildo C
authors.initials: GC
authors.lastname: Santos
authors.forename: Amin S
authors.initials: AS
authors.lastname: Rizkalla
authors.forename: Richard
authors.initials: R
authors.lastname: Bohay
authors.forename: Luis Fernando
authors.initials: LF
authors.lastname: Pegoraro
authors.forename: José H
authors.initials: JH
authors.lastname: Rubo
authors.affiliation: Schulich School of Medicine & Dentistry, Western University, London, ON.
authors.forename: M Jacinta M C
authors.initials: MJ
authors.lastname: Santos
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D006244:Hardness; D006358:Hot Temperature; D008029:Lighting / Q000295:instrumentation; D008422:Materials Testing; D013499:Surface Properties; D014783:Viscosity
chemical_list: D003188:Composite Resins; C543062:Filtek LS Low Shrink resin; C000590992:Filtek Supreme Ultra; C121818:Tetric ceram; C515948:Vit-l-escence Trans Ice