title: The effect of clinically relevant thermocycling on the flexural properties of endodontic post materials.
abstract: OBJECTIVE
  It is suggested that fibre-reinforced composite (FRC) posts have lower elastic moduli than metal posts and this will reduce the incidence of root fracture. However, the mechanical properties may be altered in the oral environment. The aims of this study were to determine the effect on the flexural properties of FRC and metal post materials produced by: (1) a thermocycling regime which was clinically relevant and representative of that which would occur during 1 year in the mouth and (2) storage for 1 year at body temperature.
  
  
  METHODS
  Nine FRC and two metal post material samples were sealed in polythene sleeves and thermocycled between 10 degrees C and 50 degrees C for 10,000 cycles. Additional samples were stored dry at 37 degrees C for 1 year. The flexural strength and moduli were determined by three-point bending and compared with untreated control samples.
  
  
  RESULTS
  Thermocycling and storage at 37 degrees C for 1 year decreased the mean flexural modulus of all materials. This was statistically significant for 8 of 11 materials after thermocycling, and 4 of 11 materials after storage at 37 degrees C (p<0.05). Thermocycling and storage at 37 degrees C produced a non-significant increase in yield strength for both metal post materials. Thermocycling significantly increased the flexural strength of Postec while it decreased for the other FRC materials. Storage at 37 degrees C increased the flexural strength of three FRC materials (significantly for Postec) while it was decreased among the other materials.
  
  
  CONCLUSIONS
  Although some of the changes noticed in flexural properties were statistically significant, it is doubtful that they are of sufficient magnitude to affect clinical performance.
authors.affiliation: University of Birmingham, School of Dentistry, St Chads Queensway, Birmingham B4 6NN, UK. d.a.stewardson@bham.ac.uk <d.a.stewardson@bham.ac.uk>
authors.forename: Dominic A
authors.initials: DA
authors.lastname: Stewardson
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Shortall
authors.forename: Peter M
authors.initials: PM
authors.lastname: Marquis
mesh_terms: D002244:Carbon; D000077482:Carbon Fiber; D003188:Composite Resins; D003722:Dental Alloys; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D005898:Glass; D006358:Hot Temperature; D008422:Materials Testing; D018583:Pliability; D011176:Post and Core Technique; D013997:Time Factors
chemical_list: D000077482:Carbon Fiber; D003188:Composite Resins; D003722:Dental Alloys; C009753:fiberglass; D002244:Carbon