title: Indentation modulus and hardness of whisker-reinforced heat-cured dental resin composites.
abstract: OBJECTIVE
  Recent studies showed that ceramic whisker reinforcement imparted a two-fold increase in the strength of dental composites. The aim of this study was to investigate the indentation response and measure the elastic modulus, hardness, and brittleness of whisker-reinforced heat-cured resin composites as a function of filler level, heat-cure temperature, and heat-cure duration.
  
  
  METHODS
  Silica particles were fused onto silicon nitride whiskers to facilitate silanization and to roughen the whiskers for improved retention in matrix. Whisker filler mass fractions of 0, 20, 40, 60, 70, 74 and 79% were tested. Heat-cure temperature ranged from 100 to 180 degrees C, and duration from 10 min to 24 h. A nano-indentation system enabled the measurement of elastic modulus. Fracture toughness was measured and composite brittleness index was calculated. An inlay/onlay composite and a prosthetic composite were tested as controls.
  
  
  RESULTS
  Whisker filler level and heat-cure duration had significant effects on composite properties, while heat-cure temperature had non-significant effects. The whisker composite with 79% filler level had a modulus in GPa (mean (SD); n = 6) of 26.9 (1.0), significantly higher than 15.1 (0.2) of an inlay/onlay control, and 16.1 (0.3) of a prosthetic control (Tukey's multiple comparison test; family confidence coefficient = 0.95). The fracture toughness in MPa.m1/2 was 2.22 (0.26) for the whisker composite, higher than 0.95 (0.11) for inlay/onlay control, and (1.13 +/- 0.19) for prosthetic control. The brittleness index was (0.49 +/- 0.07) for whisker composite, lower than (1.02 +/- 0.12) for inlay/onlay control and (0.63 +/- 0.13) for prosthetic control.
  
  
  CONCLUSIONS
  Whisker filler level had a profound influence, heat-cure duration had significant effects, while temperature did not have significant effects, on the properties of whisker composite. The whisker composite had significantly higher elastic modulus and fracture toughness, and lower brittleness than the inlay/onlay and prosthetic controls.
authors.affiliation: Paffenbarger Research Center, American Dental Association Health Foundation, National Institute of Standards and Technology, Gaithersburg, MD 20899-8546, USA. hockin.xu@nist.gov
authors.forename: H H
authors.initials: HH
authors.lastname: Xu
authors.forename: D T
authors.initials: DT
authors.lastname: Smith
authors.forename: G E
authors.initials: GE
authors.lastname: Schumacher
authors.forename: F C
authors.initials: FC
authors.lastname: Eichmiller
authors.forename: J M
authors.initials: JM
authors.lastname: Antonucci
mesh_terms: D000704:Analysis of Variance; D002516:Ceramics / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry*; D016001:Confidence Intervals; D003764:Dental Materials / Q000737:chemistry*; D017266:Dental Prosthesis; D004548:Elasticity; D005899:Glass Ionomer Cements / Q000737:chemistry; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D007284:Inlays; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D012823:Silicate Cement / Q000737:chemistry; D017640:Silicates / Q000737:chemistry; D017655:Silicon Compounds / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors
chemical_list: D003188:Composite Resins; C069352:Concept resin; D003764:Dental Materials; D005899:Glass Ionomer Cements; D008689:Methacrylates; D011140:Polyurethanes; D012821:Silanes; D017640:Silicates; D017655:Silicon Compounds; C111282:dental polyglass; C029824:urethane dimethacrylate luting resin; D012823:Silicate Cement; D012822:Silicon Dioxide; C032734:silicon nitride