title: Mechanical properties of commercial high strength ceramic core materials.
abstract: OBJECTIVE
  The objective of the present study is to evaluate and compare the flexural strength, dynamic elastic moduli and true hardness (H(o)) values of commercial Vita In-Ceram alumina core and Vita In-Ceram matrix glass with the standard aluminous porcelain (Hi-Ceram and Vitadur), Vitadur N and Dicor glass and glass-ceramic.
  
  
  METHODS
  The flexural strength was evaluated (n=5) using 3-point loading and a servo hydraulic Instron testing machine at a cross head speed of 0.5 mm/min. The density of the specimens (n=3) was measured by means of the water displacement technique. Dynamic Young's shear and bulk moduli and Poisson's ratio (n=3) were measured using a non-destructive ultrasonic technique using 10 MHz lithium niobate crystals. The true hardness (n=3) was measured using a Knoop indenter and the fracture toughness (n=3) was determined using a Vickers indenter and a Tukon hardness tester. Statistical analysis of the data was conducted using ANOVA and a Student-Newman-Keuls (SNK) rank order multiple comparative test.
  
  
  RESULTS
  The SNK rank order test analysis of the mean flexural strength was able to separate five commercial core materials into three significant groups at p=0.05. Vita In-Ceram alumina and IPS Empress 2 exhibited significantly higher flexural strength than aluminous porcelains and IPS Empress at p=0.05. The dynamic elastic moduli and true hardness of Vita In-Ceram alumina core were significantly higher than the rest of the commercial ceramic core materials at p=0.05.
  
  
  CONCLUSIONS
  The ultrasonic test method is a valuable mechanical characterization tool and was able to statistically discriminate between the chemical and structural differences within dental ceramic materials. Significant correlation was obtained between the dynamic Young's modulus and true hardness, p=0.05.
authors.affiliation: Division of Biomaterials Science, School of Dentistry, Faculty of Medicine and Dentistry, The University of Western Ontario, N6A 5C1 London, Ont., Canada. arizkalla@eng.uwo.ca
authors.forename: A S
authors.initials: AS
authors.lastname: Rizkalla
authors.forename: D W
authors.initials: DW
authors.lastname: Jones
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D000704:Analysis of Variance; D002516:Ceramics; D003442:Crowns; D003776:Dental Porcelain / Q000737:chemistry; D003799:Dental Stress Analysis; D004548:Elasticity; D006244:Hardness; D008422:Materials Testing / Q000379:methods; D016876:Metal Ceramic Alloys / Q000737:chemistry; D018583:Pliability; D012044:Regression Analysis; D018709:Statistics, Nonparametric; D014465:Ultrasonics
chemical_list: C047475:Dicor ceramic; C062269:Hi Ceram; D016876:Metal Ceramic Alloys; C483703:Vitadur; D003776:Dental Porcelain; C070870:In-Ceram; C058236:Vitadur N; C023506:Glass ceramics; D000537:Aluminum Oxide