title: The effect of thermocycling on the fracture toughness and hardness of core buildup materials.
abstract: BACKGROUND
  Thermocycling has been shown to cause surface degradation of many dental materials, but its effect on the fracture toughness and hardness of direct core buildup materials is unknown.
  
  
  OBJECTIVE
  This study was designed to determine the effect of thermocycling on the fracture toughness and hardness of 5 core buildup materials.
  
  
  METHODS
  Fifteen specimens were prepared from each of the following materials: Fluorocore, VariGlass VLC, Valiant PhD, Vitremer, and Chelon-Silver. American Standard for Testing Materials guidelines for single-edge notch, bar-shaped specimens were used. Ten specimens of each material were thermocycled for 2000 cycles; the other 5 specimens were not thermocycled. All specimens were subjected to 3-point bending in a universal testing machine. The load at fracture was recorded, and the fracture toughness (K(IC)) was calculated. Barcol hardness values were also determined. Data were analyzed with 1-way analysis of variance and compared with the Tukey multiple range test (P<.05). Pearson's correlation coefficient was also calculated to measure the association between fracture toughness and hardness.
  
  
  RESULTS
  Fluorocore had the highest thermocycled mean K(IC) and Valiant PhD the highest non-thermocycled K(IC). Chelon-Silver demonstrated the lowest mean K(IC) both before and after thermocycling. One-way analysis of variance demonstrated significant differences between conditions, and the Tukey test showed significant differences (P<.05) between materials for both conditions. Most specimens also showed significant hardness differences between conditions. Pearson's correlation coefficient indicated only a mild-to-moderate correlation between hardness and fracture toughness.
  
  
  CONCLUSIONS
  Within the limitations of this study, the thermocycling process negatively affected the fracture toughness and hardness of the core buildup materials tested.
authors.affiliation: School of Dentistry, Marquette University, Milwaukee, WI 53201-6516, USA.
authors.forename: J I
authors.initials: JI
authors.lastname: Medina Tirado
authors.forename: W W
authors.initials: WW
authors.lastname: Nagy
authors.forename: V B
authors.initials: VB
authors.lastname: Dhuru
authors.forename: A J
authors.initials: AJ
authors.lastname: Ziebert
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000704:Analysis of Variance; D016722:Cermet Cements / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D016001:Confidence Intervals; D003722:Dental Alloys / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D005460:Fluorides, Topical / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D018583:Pliability; D011176:Post and Core Technique / Q000295:instrumentation*; D019279:Resin Cements / Q000737:chemistry; D018030:Silver Compounds / Q000737:chemistry; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D000180:Acrylic Resins; D016722:Cermet Cements; D003188:Composite Resins; D003722:Dental Alloys; D003764:Dental Materials; D005460:Fluorides, Topical; C074316:FluoroCore; D005899:Glass Ionomer Cements; D019279:Resin Cements; D018030:Silver Compounds; C081982:VariGlass VLC; C084550:Vitremer; C067445:Chelon Silver; C072894:Valiant PhD