title: Shear bond strength comparison between conventional porcelain fused to metal and new functionally graded dental restorations after thermal-mechanical cycling.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effect of thermo-mechanical cycling on the metal-ceramic bond strength of conventional porcelain fused to metal restorations (PFM) and new functionally graded metal-ceramic dental restorations (FGMR).
  
  
  METHODS
  Two types of specimens were produced: PFM and FGMR specimens. PFM specimens were produced by conventional PFM technique. FGMR specimens were hot pressed and prepared with a metal/ceramic composite interlayer (50 M, vol%) at the metal-ceramic interface. They were manufactured and standardized in cylindrical format and then submitted to thermal (3000, 6000 and 12,000 cycles; between 5 °C and 60 °C; dwell time: 30s) and mechanical (25,000, 50,000 and 100,000 cycles under a load of 50 N; 1.6 Hz) cycling. The shear bond strength tests were performed in a universal testing machine (crosshead speed: 0.5mm/min), using a special device to concentrate the tension at the metal-ceramic interface and the load was applied until fracture. The metal-ceramic interfaces were examined with SEM/EDS prior to and after shear tests. The Young's modulus and hardness were measured across the interfaces of both types of specimens using nanoindentation tests. Data was analyzed with Shapiro-Wilk test to test the assumption of normality. The 2-way ANOVA was used to compare shear bond strength results (p<0.05).
  
  
  RESULTS
  FGMR specimens showed significantly (p<0.001) higher shear bond strength results than PFM specimens, irrespective of fatigue conditions. Fatigue conditions significantly (p<0.05) affected the shear bond strength results. The analysis of surface fracture revealed adhesive fracture type for PFM specimens and mixed fracture type for FGMR specimens. Nanoindentation tests showed differences in mechanical properties measured across the metal-ceramic interface for the two types of specimens, namely Young's Modulus and hardness.
  
  
  CONCLUSIONS
  This study showed significantly better performance of the new functionally graded restorations relative to conventional PFM restorations, under fatigue testing conditions and for the materials tested.
authors.affiliation: Center for Mechanical and Materials Technologies, University of Minho, Campus de Azurém, Guimarães 4800-058, Portugal. brunohenriques@dem.uminho.pt
authors.forename: B
authors.initials: B
authors.lastname: Henriques
authors.forename: S
authors.initials: S
authors.lastname: Gonçalves
authors.forename: D
authors.initials: D
authors.lastname: Soares
authors.forename: F S
authors.initials: FS
authors.lastname: Silva
mesh_terms: D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D058250:Dental Restoration Repair; D008422:Materials Testing; D055595:Mechanical Phenomena; D008670:Metals / Q000737:chemistry*; D033081:Shear Strength; D013696:Temperature
chemical_list: D008670:Metals; D003776:Dental Porcelain