title: Translucent zirconia in the ceramic scenario for monolithic restorations: A flexural strength and translucency comparison test.
abstract: OBJECTIVE
  To compare three different compositions of Yttria-Tetragonal Zirconia Polycrystal (Y-TZP) ceramic and a lithium disilicate ceramic in terms of flexural strength and translucency.
  
  
  METHODS
  Three zirconia materials of different composition and translucency, Aadva ST [ST], Aadva EI [EI] and Aadva NT [NT](GC Tech, Leuven, Belgium) were cut with a slow speed diamond saw into beams and tabs in order to obtain, after sintering, dimensions of 1.2×4.0×15.0mm and 15.0×15.0×1.0mm respectively. Blocks of IPS e.max CAD LT were cut and crystallized in the same shapes and dimensions and used as a reference group [LD]. Beams (n=15) were tested in a universal testing machine for three-point bending strength. Critical fracture load was recorded in N, flexural strength (σ in MPa), Weibull modulus (m) and Weibull characteristic strength (σ0in MPa) were then calculated. Tabs (n=10) were measured with a spectrophotometer equipped with an integrating sphere. Contrast Ratios were calculated as CR=Yb/Yw. SEM of thermally etched samples coupled with lineal line analysis (n=6) was used to measure the tested zirconia grain size. Data were statistically analyzed.
  
  
  RESULTS
  Differences in translucency, flexural strength and grain size were found to be statistically significant. CR increased and flexural strength decreased in the following order ST(σ 1215±190MPa, CR 0.74±0.01)>EI(σ 983±182MPa, CR 0.69±0.01)>NT(σ 539±66MPa, CR 0.65±0.01)>LD (σ 377±39Mpa, CR 0.56±0.02). The average grain size was different for the three zirconia samples with NT(558±38nm)>ST(445±34nm)>EI(284±11nm).
  
  
  CONCLUSIONS
  The zirconia composition heavily influenced both the flexural strength and the translucency. Different percentages of Yittria and Alumina result in new materials with intermediate properties in between the conventional zirconia and lithium disilicate. Clinical indications for Zirconia Aadva NT should be limited up to three-unit span bridges.
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, 53100, Italy. Electronic address: m.carrabba@yahoo.it.
authors.forename: Michele
authors.initials: M
authors.lastname: Carrabba
authors.affiliation: Biomaterials and Tissue Engineering Research Group, School of Dentistry, University of Leeds, Leeds, LS2 9LU, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Keeling
authors.affiliation: Biomaterials and Tissue Engineering Research Group, School of Dentistry, University of Leeds, Leeds, LS2 9LU, UK.
authors.forename: Aziz
authors.initials: A
authors.lastname: Aziz
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, 53100, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vichi
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, 53100, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Fabian Fonzar
authors.affiliation: Biomaterials and Tissue Engineering Research Group, School of Dentistry, University of Leeds, Leeds, LS2 9LU, UK.
authors.forename: David
authors.initials: D
authors.lastname: Wood
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, 53100, Italy; Biomaterials and Tissue Engineering Research Group, School of Dentistry, University of Leeds, Leeds, LS2 9LU, UK.
authors.forename: Marco
authors.initials: M
authors.lastname: Ferrari
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D003764:Dental Materials; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006801:Humans; D008422:Materials Testing; D008962:Models, Theoretical; D013314:Stress, Mechanical; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; C520133:IPS e.max CAD LT; C493120:lithia disilicate; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide; C091417:yttria
keywords: Contrast ratio; Flexural strength; Grain size; Lithium disilicate; Monolithic restoration; Translucency; Translucent zirconia; Y-TZP