title: Influence of metal surface finishing on porcelain porosity and beam failure loads at the metal-ceramic interface.
abstract: BACKGROUND
  Investigators suggest that metals should be finished in 1 direction before porcelain application to minimize metal irregularities and trapped contaminants. These irregularities are thought to be focal points for porosity and crack propagation.
  
  
  OBJECTIVE
  This study investigated the influence of metal finishing and sandblasting on (1) porosity production at the porcelain-metal interface, and (2) porcelain-metal beam failure load.
  
  
  METHODS
  Eighty cast metal samples were divided into 4 test groups: (A) bidirectional finish/sandblasting; (B) unidirectional finish/sandblasting (C) bidirectional finish only; and (D) unidirectional finish only. The porcelain applied was 1.5 mm thick. Samples were sectioned longitudinally. Half of the samples were subjected to a 3-point flexural test. The remaining samples were sectioned into 4 slices and were examined with a light microscope (x500). Number and diameter of porosities at the metal-porcelain interface were recorded.
  
  
  RESULTS
  Mean loads at failure (lbs) were as follows: A, 11.1 +/- 1.3 (5.03 +/- 0.58 Kg); B, 11.2 +/- 1.7 (5. 08 +/- 0.77 Kg); C, 4.0 +/- 1.8 (1.81 +/- 0.81 Kg); and D, 5.0 +/- 2. 1 (2.26 +/- 0.95 Kg). Groups A and B were significantly different from groups C and D (P<.0001). Nonsandblasted samples (C and D) exhibited a separation at the ceramometal interface, which prevented quantification of porosity size and number. Average interface porosity sizes (microm) (A, 8.99 +/- 1.92; B, 10.03 +/- 1.86) showed no significant difference. The mean interface porosity number (A, 62. 3 +/- 16.02; B, 67.4 +/- 10.01) showed no significant difference.
  
  
  CONCLUSIONS
  Direction of metal finishing did not affect the porosity number and size at the ceramometal interface or the beam failure loads. Sandblasting increased the beam failure loads. Nonsandblasted samples showed detachment of the porcelain from the metal.
authors.affiliation: University of Rochester Eastman Dental Center, Rochester, NY 14620, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: Hofstede
authors.forename: C
authors.initials: C
authors.lastname: Ercoli
authors.forename: G N
authors.initials: GN
authors.lastname: Graser
authors.forename: R H
authors.initials: RH
authors.lastname: Tallents
authors.forename: M E
authors.initials: ME
authors.lastname: Moss
authors.forename: D T
authors.initials: DT
authors.lastname: Zero
mesh_terms: D000537:Aluminum Oxide; D000704:Analysis of Variance; D003775:Dental Polishing / Q000379:methods*; D003776:Dental Porcelain / Q000737:chemistry*; D019544:Equipment Failure Analysis; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D016062:Porosity; D018709:Statistics, Nonparametric; D013499:Surface Properties
chemical_list: D016876:Metal Ceramic Alloys; D003776:Dental Porcelain; D000537:Aluminum Oxide