title: Fracture resistance of metal ceramic restorations with two different margin designs after exposure to masticatory simulation.
abstract: BACKGROUND
  Although the esthetic outcome of a collarless metal ceramic restoration is superior to that of a restoration with a metal margin, its mechanical strength has not been evaluated.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate and compare the fracture resistance of metal ceramic restorations with metal margins to that of metal ceramic restorations with circumferential porcelain margins, after exposure to masticatory simulation.
  
  
  METHODS
  Twenty-four metal ceramic restorations were fabricated and paired with 24 cobalt-chrome tooth analogs. Twelve of the specimens had metal margins, while the remainder had circumferential porcelain margins. The restorations were cemented on the metal tooth analogs with a resin-modified glass ionomer luting agent (FujiCEM). All specimens were subjected to cyclic loading by a texture analyzer. A total of 600,000 loading cycles in an aqueous environment was performed, with a minimum load of 0 N and a maximum load of 200 N. Controlled loads were then applied to the teeth until fracture, using a stainless steel rod with a 2-mm-wide, rounded end, mounted in a universal testing machine. The specimens were examined under a stereomicroscope to determine failure mode. Descriptive statistics and the independent t test (alpha=.05) were used to determine the effect of failure loads among the tested groups.
  
  
  RESULTS
  The independent t test revealed statistically significant differences among the 2 tested groups (P<.001). The 2 groups presented different failure modes. Metal ceramic restorations with metal margins presented cohesive failures starting from the point of load application. Metal ceramic restorations with circumferential porcelain margins demonstrated a combination of adhesive and cohesive failures, starting from the point of load application and extending to the highest point of the proximal margins.
  
  
  CONCLUSIONS
  Metal ceramic restorations with metal margins required significantly greater loads (P<.001) to fracture than metal ceramic restorations with circumferential porcelain margins. (J Prosthet Dent 2009;102:172-178).
authors.affiliation: Department of Prosthodontics and Operative Dentistry, Division of Graduate and Postgraduate Prosthodontics; private practice, Thessaloniki, Greece. kmichalakis@the.forthnet.gr
authors.forename: Konstantinos X
authors.initials: KX
authors.lastname: Michalakis
authors.forename: Athanasios
authors.initials: A
authors.lastname: Stratos
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hirayama
authors.forename: Kiho
authors.initials: K
authors.lastname: Kang
authors.forename: Foteini
authors.initials: F
authors.lastname: Touloumi
authors.forename: Yukio
authors.initials: Y
authors.lastname: Oishi
mesh_terms: D001732:Bite Force; D019245:Compressive Strength; D003442:Crowns; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000295:instrumentation / Q000379:methods; D003799:Dental Stress Analysis; D004955:Esthetics, Dental; D006801:Humans; D008409:Mastication; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D013314:Stress, Mechanical; D016474:Weight-Bearing
chemical_list: D016876:Metal Ceramic Alloys