title: Flexural strength and failure modes of layered ceramic structures.
abstract: OBJECTIVE
  To evaluate the effect of the specimen design on the flexural strength (σ(f)) and failure mode of ceramic structures, testing the hypothesis that the ceramic material under tension controls the mechanical performance of the structure.
  
  
  METHODS
  Three ceramics used as framework materials for fixed partial dentures (YZ--Vita In-Ceram YZ; IZ--Vita In-Ceram Zirconia; AL--Vita In-Ceram AL) and two veneering porcelains (VM7 and VM9) were studied. Bar-shaped specimens were produced in three different designs (n=10): monolithic, two layers (porcelain-framework) and three layers (TRI) (porcelain-framework-porcelain). Specimens were tested for three-point flexural strength at 1MPa/s in 37°C artificial saliva. For bi-layered design, the specimens were tested in both conditions: with porcelain (PT) or framework ceramic (FT) layer under tension. Fracture surfaces were analyzed using stereomicroscope and scanning electron microscopy (SEM). Young's modulus (E) and Poisson's ratio (ν) were determined using ultrasonic pulse-echo method. Results were statistically analyzed by Kruskal-Wallis and Student-Newman-Keuls tests.
  
  
  RESULTS
  Except for VM7 and VM9, significant differences were observed for E values among the materials. YZ showed the highest ν value followed by IZ and AL. YZ presented the highest σ(f). There was no statistical difference in the σ(f) value between IZ and IZ-FT and between AL and AL-FT. σ(f) values for YZ-PT, IZ-PT, IZ-TRI, AL-PT, AL-TRI were similar to the results obtained for VM7 and VM9. Two types of fracture mode were identified: total and partial failure.
  
  
  CONCLUSIONS
  The mechanical performance of the specimens was determined by the material under tension during testing, confirming the study hypothesis.
authors: Department of Restorative Dentistry, University of Passo Fundo, Passo Fundo, RS, Brazil.
authors: Márcia
authors: M
authors: Borba
authors: Maico D
authors: MD
authors: de Araújo
authors: Erick
authors: E
authors: de Lima
authors: Humberto N
authors: HN
authors: Yoshimura
authors: Paulo F
authors: PF
authors: Cesar
authors: Jason A
authors: JA
authors: Griggs
authors: Alvaro
authors: A
authors: Della Bona
mesh_terms: D000465:Algorithms; D000537:Aluminum Oxide / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D003775:Dental Polishing; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D055119:Elastic Modulus; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D017680:Potassium Compounds / Q000737:chemistry; D012464:Saliva, Artificial / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014465:Ultrasonics; D014618:Vacuum; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; C483026:In-Ceram Alumina; C485633:In-Ceram Zirconia; D017680:Potassium Compounds; D012464:Saliva, Artificial; C556625:VITA VM7; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; C016447:feldspar; C070870:In-Ceram; D015019:Yttrium; D015040:Zirconium; D000537:Aluminum Oxide