title: Effect of various veneering techniques on mechanical strength of computer-controlled zirconia framework designs.
abstract: OBJECTIVE
  The objectives of this study were to evaluate the fracture resistance (FR), flexural strength (FS), and shear bond strength (SBS) of zirconia framework material veneered with different methods and to assess the stress distributions using finite element analysis (FEA).
  
  
  METHODS
  Zirconia frameworks fabricated in the forms of crowns for FR, bars for FS, and disks for SBS (N = 90, n = 10) were veneered with either (a) file splitting (CAD-on) (CD), (b) layering (L), or (c) overpressing (P) methods. For crown specimens, stainless steel dies (N = 30; 1 mm chamfer) were scanned using the labside contrast spray. A bilayered design was produced for CD, whereas a reduced design (1 mm) was used for L and P to support the veneer by computer-aided design and manufacturing. For bar (1.5 × 5 × 25 mm(3) ) and disk (2.5 mm diameter, 2.5 mm height) specimens, zirconia blocks were sectioned under water cooling with a low-speed diamond saw and sintered. To prepare the suprastructures in the appropriate shapes for the three mechanical tests, nano-fluorapatite ceramic was layered and fired for L, fluorapatite-ceramic was pressed for P, and the milled lithium-disilicate ceramics were fused with zirconia by a thixotropic glass ceramic for CD and then sintered for crystallization of veneering ceramic. Crowns were then cemented to the metal dies. All specimens were stored at 37°C, 100% humidity for 48 hours. Mechanical tests were performed, and data were statistically analyzed (ANOVA, Tukey's, α = 0.05). Stereomicroscopy and scanning electron microscopy (SEM) were used to evaluate the failure modes and surface structure. FEA modeling of the crowns was obtained.
  
  
  RESULTS
  Mean FR values (N ± SD) of CD (4408 ± 608) and L (4323 ± 462) were higher than P (2507 ± 594) (p < 0.05). Mean FS values (MPa ± SD) of CD (583 ± 63) and P (566 ± 54) were higher than L (428 ± 41) (p < 0.05). Mean SBS values (MPa ± SD) of CD (49 ± 6) (p < 0.05) were higher than L (28 ± 5) and P (30 ± 8). For crown restorations, while cohesive failures within ceramic and zirconia were seen in CD, cohesive failures within ceramic were found in both L and P. Results were verified by FEA.
  
  
  CONCLUSIONS
  The file splitting technique showed higher bonding values in all mechanical tests, whereas a layering technique increased the FR when an anatomical core design was employed.
  
  
  CONCLUSIONS
  File splitting (CAD-on) or layering veneering ceramic on zirconia with a reduced framework design may reduce ceramic chipping.
authors.affiliation: Department of Prosthodontics, Ege University, School of Dentistry, Izmir, Turkey.
authors.forename: Burcu
authors.initials: B
authors.lastname: Kanat
authors.forename: Erhan M
authors.initials: EM
authors.lastname: Cömlekoğlu
authors.forename: Mine
authors.initials: M
authors.lastname: Dündar-Çömlekoğlu
authors.forename: Bilge
authors.initials: B
authors.lastname: Hakan Sen
authors.forename: Mutlu
authors.initials: M
authors.lastname: Ozcan
authors.forename: Mehmet
authors.initials: M
authors.lastname: Ali Güngör
mesh_terms: D001031:Apatites / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry; D017076:Computer-Aided Design; D003442:Crowns; D001840:Dental Bonding; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D003801:Dental Veneers; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006801:Humans; D006813:Humidity; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D001031:Apatites; D003764:Dental Materials; C493120:lithia disilicate; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; C023506:Glass ceramics; D015040:Zirconium; C025105:fluorapatite; C028541:zirconium oxide
keywords: CAD/CAM; file splitting; finite element analysis; flexural strength; fracture resistance; shear bond strength