title: Mechanical properties of zirconia after different surface treatments and repeated firings.
abstract: OBJECTIVE
  This study investigated the influence of surface conditioning procedures and repeated firings on monoclinic content and strength of zirconia before cementation.
  
  
  METHODS
  Sintered bar-shaped zirconia specimens were subjected to no surface treatment (control), air abrasion, or grinding (n=21). Their roughness was evaluated using a profilometer, and microscope analysis was performed on one specimen of each group. Then, 2 or 10 repeated firings (n=10) were executed, the monoclinic content of specimens was analyzed by X-ray diffraction, and a three-point flexural strength test was performed. Surface roughness values were compared using one-way analysis of variance (ANOVA) and Tukey honestly significant difference (HSD) tests, the monoclinic content values were tested using Kruskal-Wallis and Mann-Whitney U tests, and the flexural strength values were tested using two-way ANOVA and Tukey HSD tests (P=.05). Spearman's correlation test was performed to define relationships among measured parameters.
  
  
  RESULTS
  Surface-treated specimens were rougher than untreated specimens and had a higher monoclinic content (P<.005), and the relationship between roughness and monoclinic content was significant (P<.000). Neither surface treatment nor firing significantly affected the flexural strength, but Weibull analysis showed that for the air-abraded samples the characteristic strength was significantly lower after the 10(th) firing than after the 2(nd) firing.
  
  
  CONCLUSIONS
  After firing, a negligible amount of monoclinic content remained on the zirconia surfaces, and rougher surfaces had higher monoclinic contents than untreated surfaces. Multiple firings could be performed if necessary, but the fracture probability could increase after multiple firings for rougher surfaces.
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Istanbul Aydin University, Istanbul, Turkey.
authors.forename: Meryem Gülce
authors.initials: MG
authors.lastname: Subaşı
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Selcuk University, Konya, Turkey.
authors.forename: Necla
authors.initials: N
authors.lastname: Demir
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Bezmialem Vakif University, Istanbul, Turkey.
authors.forename: Özlem
authors.initials: Ö
authors.lastname: Kara
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Selcuk University, Konya, Turkey.
authors.forename: A Nilgun
authors.initials: AN
authors.lastname: Ozturk
authors.affiliation: Department of Chemical Engineering, Faculty of Engineering, Selcuk University, Konya, Turkey.
authors.forename: Faruk
authors.initials: F
authors.lastname: Özel
keywords: Ceramics; Flexural Strength; Surface Treatment; X-ray diffraction; Zirconium Oxide