title: Temperature-dependence of creep behaviour of dental resin-composites.
abstract: OBJECTIVE
  To determine the effect of temperature, over a clinically relevant range, on the creep behaviour of a set of conventional and flowable resin-composites including two subgroups having the same resin matrix and varied filler loading.
  
  
  METHODS
  Eight dental resin-composites: four flowable and four conventional were investigated. Stainless steel split moulds (4 mm × 6 mm) were used to prepare cylindrical specimens for creep examination. Specimens were irradiated in the moulds in layers of 2mm thickness (40s each), as well as from the radial direction after removal from the moulds, using a light-curing unit with irradiance of 650 mW/cm(2). A total of 15 specimens from each material were prepared and divided into three groups (n=5) according to the temperature; Group I: (23°C), Group II: (37°C) and Group III: (45°C). Each specimen was loaded (20 MPa) for 2h and unloaded for 2h. Creep was measured continuously over the loading and unloading periods.
  
  
  RESULTS
  At higher temperatures greater creep and permanent set were recorded. The lowest mean creep occurred with GS and GH resin-composites. Percentage of creep recovery decreased at higher temperatures. At 23°C, the materials exhibited comparable creep. At 37°C and 45°C, however, there was a greater variation between materials. For all resin-composites, there was a strong linear correlation with temperature for both creep and permanent set.
  
  
  CONCLUSIONS
  Creep parameters of resin-composites are sensitive to temperature increase from 23 to 45°C, as can occur intra-orally. For a given resin matrix, creep decreased with higher filler loading.
authors.affiliation: School of Dentistry and Photon Science Institute, University of Manchester, UK. drelsafti@yahoo.com
authors.forename: S
authors.initials: S
authors.lastname: El-Safty
authors.forename: N
authors.initials: N
authors.lastname: Silikas
authors.forename: D C
authors.initials: DC
authors.lastname: Watts
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D006358:Hot Temperature; D016014:Linear Models; D008422:Materials Testing; D014783:Viscosity
chemical_list: D003188:Composite Resins; C509998:Grandio; C488393:Venus (composite resin); C527485:estelite flow quick