title: Durability and Weibull Characteristics of Lithium Disilicate Crowns Bonded on Abutments with Knife-Edge and Large Chamfer Finish Lines after Cyclic Loading.
abstract: OBJECTIVE
  The aim of this study was to evaluate the durability of lithium disilicate crowns bonded on abutments prepared with two types of finish lines after long-term cyclic loading.
  
  
  METHODS
  Pressed lithium disilicate all-ceramic molar crowns were bonded (Variolink II) to epoxy abutments (height: 5.5 mm, Ø: 7.5 mm, conicity: 6°) (N = 20) with either knife-edge (KE) or large chamfer (LC) finish lines. Each assembly was submitted to cyclic loading (1,200,000×; 200 N; 1 Hz) in water and then tested until fracture in a universal testing machine (1 mm/min). Failure types were classified and further evaluated under stereomicroscope and SEM. The data (N) were analyzed using one-way ANOVA. Weibull distribution values including the Weibull modulus (m), characteristic strength (0), probability of failure at 5% (0.05), 1% (0.01), and correlation coefficient were calculated.
  
  
  RESULTS
  Type of finish line did not significantly influence the mean fracture strength of pressed ceramic crowns (KE: 1655 ± 353 N; LC: 1618 ± 263 N) (p = 0.7898). Weibull distribution presented lower shape value (m) of KE (m = 5.48; CI: 3.5 to 8.6) compared to LC (m = 7.68; CI: 5.2 to 11.3). Characteristic strengths (0) (KE: 1784.9 N; LC: 1712.1 N) were higher than probability of failure at 5% (0.05) (KE: 1038.1 N; LC: 1163.4 N) followed by 1% (0.01) (KE: 771 N; LC: 941.1 N), with a correlation coefficient of 0.966 for KE and 0.924 for LC. Type V failures (severe fracture of the crown and/or tooth) were more common in both groups. SEM findings showed that fractures occurred mainly from the cement/ceramic interface at the occlusal side of the crowns.
  
  
  CONCLUSIONS
  Lithium disilicate ceramic crowns bonded onto abutment teeth with KE preparation resulted in similar fracture strength to those bonded on abutments with LC finish line.
  
  
  CONCLUSIONS
  Pressed lithium disilicate ceramic crowns may not require invasive finish line preparations since finish line type did not impair the strength after aging conditions.
authors.affiliation: Private Practice, Riccione, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Cortellini
authors.affiliation: Dental Laboratory, Rimini, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Canale
authors.affiliation: Department of Dentistry, Division of Prosthodontics, Federal University of Rio Grande do Norte, Natal,, RN, Brazil.
authors.forename: Rodrigo O A
authors.initials: RO
authors.lastname: Souza
authors.affiliation: São Jose dos Campos Dental School, Department of Prosthodontics and Dental Materials, São Paulo State University, São José dos Campos, Brazil.
authors.forename: Fernanda
authors.initials: F
authors.lastname: Campos
authors.affiliation: São Jose dos Campos Dental School, Department of Prosthodontics and Dental Materials, São Paulo State University, São José dos Campos, Brazil.
authors.forename: Julia C
authors.initials: JC
authors.lastname: Lima
authors.affiliation: Dental Materials Unit, Center for Dental and Oral Medicine, Clinic for Fixed and Removable Prosthodontics and Dental Materials Science, University of Zurich, Zurich, Switzerland.
authors.forename: Mutlu
authors.initials: M
authors.lastname: Özcan
mesh_terms: D002516:Ceramics; D003442:Crowns; D003776:Dental Porcelain; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D008422:Materials Testing
chemical_list: C493120:lithia disilicate; D003776:Dental Porcelain
keywords: Crowns; cyclic loading; finish line; fracture strength; lithium disilicate ceramic; load-bearing capacity