title: Effect of glaze thickness on the fracture toughness and hardness of alumina-reinforced porcelain.
abstract: BACKGROUND
  Although porcelain is the most esthetic restorative material available, it is subject to fracture during function. Glazing reduces the size of flaws in the surface of the porcelain and increases its resistance to crack propagation, but the optimum thickness of this glazed layer has not been determined.
  
  
  OBJECTIVE
  This study compared the fracture toughness (Kc ) and Vickers hardness number (VHN) of an alumina-reinforced porcelain at different thicknesses of glaze.
  
  
  METHODS
  Disks of feldspathic porcelain reinforced with 2% aluminum oxide were prepared and glazed for 0, 30, 60, 90, and 120 seconds. Fracture toughness and Vickers microhardness were determined with a microindentation technique. Thickness of the glazed layers was measured with a SEM.
  
  
  RESULTS
  Mean Vickers hardness number and fracture toughness values both decreased significantly with glazing times from 0 to 60 seconds, and increased significantly with glazing times from 60 to 120 seconds (P <.001, ANOVA). SEM examination revealed an increase in glazed layer thickness with increased glazing time.
  
  
  CONCLUSIONS
  Minimal and maximum thicknesses of glaze layers on alumina-reinforced porcelain resulted in a surface that was harder and more resistant to fracture than moderate glaze thicknesses.
authors.affiliation: Goldschleger School of Dental Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: H
authors.initials: H
authors.lastname: Baharav
authors.forename: B Z
authors.initials: BZ
authors.lastname: Laufer
authors.forename: R
authors.initials: R
authors.lastname: Pilo
authors.forename: H S
authors.initials: HS
authors.lastname: Cardash
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D000538:Aluminum Silicates / Q000737:chemistry; D000704:Analysis of Variance; D003776:Dental Porcelain / Q000737:chemistry*; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D017680:Potassium Compounds / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors
chemical_list: D000538:Aluminum Silicates; D017680:Potassium Compounds; D003776:Dental Porcelain; C016447:feldspar; D000537:Aluminum Oxide