title: Comparison of edge chipping resistance of PFM and veneered zirconia specimens.
abstract: OBJECTIVE
  To investigate the chipping resistance of veneered zirconia specimens and compare it to the chipping resistance of porcelain fused to metal (PFM) specimens.
  
  
  METHODS
  Veneered zirconia and PFM bar specimens were prepared in clinically relevant thicknesses. The specimen edges were chipped with different magnitude forces, producing chips of various sizes. The range of sizes included small chips that did not penetrate all the way through the veneers to the substrates, and also chips that were very large and reached the zirconia or metal substrates. The relationship between force magnitude and chip size (edge distance) was graphed. The resulting curves were compared for the veneered zirconia and PFM specimens. Knoop hardness vs. force graphs for the veneers and substrates were also obtained.
  
  
  RESULTS
  The zirconia and PFM veneer chipping data followed a power law (coefficient of determination, R(2)>0.93) as expected from the literature. The curves overlapped within the combined data scatter, indicating similar resistance to chipping. The chips made in both types of specimens detached and did not penetrate into the substrate when they reached the veneer/substrate intersections. The hardness-load curves for the veneers and substrates all exhibited an indentation size effect (ISE) at low loads. The Knoop hardness values with uncertainties of +/-one standard deviation at 4N loads for the metal, zirconia, and the metal and zirconia veneers are: (2.02+/-0.08, 12.01+/-0.39, 4.24+/-0.16 and 4.36+/-0.02GPa), respectively, with no statistically significant difference between the veneers (Tukey pairwise comparison at 0.95 family confidence).
  
  
  CONCLUSIONS
  This work indicates that a similar resistance to chipping might be expected for veneered zirconia and PFM restorations, in spite of the large difference in substrate hardness. Differences in susceptibility to chip spalling were not detected, but the chips in both specimen types detached off the sides in a similar manner instead of extending into the substrates.
authors.affiliation: American Dental Association Foundation, Paffenbarger Research Center, National Institute of Standards and Technology, Gaithersburg, MD, USA.
authors.forename: Janet B
authors.initials: JB
authors.lastname: Quinn
authors.forename: Veeraraghavan
authors.initials: V
authors.lastname: Sundar
authors.forename: Edward E
authors.initials: EE
authors.lastname: Parry
authors.forename: George D
authors.initials: GD
authors.lastname: Quinn
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing; D003776:Dental Porcelain / Q000737:chemistry*; D003801:Dental Veneers; D018130:Diamond / Q000737:chemistry; D006047:Gold Alloys / Q000737:chemistry; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D003764:Dental Materials; D006047:Gold Alloys; D016876:Metal Ceramic Alloys; D017680:Potassium Compounds; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; C016447:feldspar; D015019:Yttrium; D010165:Palladium; D018130:Diamond; C058233:Ceramco; D015040:Zirconium; C028541:zirconium oxide