title: Effects of aqueous and acid-based coloring liquids on the hardness of zirconia restorations.
abstract: BACKGROUND
  The effects of the application of aqueous coloring liquids on the mechanical properties of zirconia have not yet been investigated.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the effects of 3 different coloring techniques and the number of coloring liquid applications on the hardness of zirconia.
  
  
  METHODS
  Eighty specimens were divided into 8 groups (n=10); nonshaded zirconia, preshaded zirconia, acid-based coloring liquid zirconia, and aqueous coloring liquid zirconia (1, 3, 6). Vickers hardness was measured. Data were analyzed via 1-way and 2-way ANOVAs. Multiple comparisons were performed using a Scheffé test (α=.05).
  
  
  RESULTS
  Statistically significant differences in hardness were found between acid-based coloring liquid zirconia and aqueous coloring liquid zirconia (P<.001). Increasing the number of coloring liquid applications decreased the hardness value of acid-based coloring liquid zirconia (P<.001) but had no effect on the hardness of aqueous coloring liquid zirconia (P>.05).
  
  
  CONCLUSIONS
  Within the limitations of this study, the hardness of zirconia was influenced to differing degrees depending on coloring technique. The number of coloring liquid applications affected the hardness of zirconia colored with the acid-based coloring liquid but not the hardness of zirconia colored with the aqueous coloring liquid.
authors.affiliation: Lecturer, Department of Dental Laboratory Science, College of Health Sciences, Catholic University of Pusan, Busan, Republic of Korea.
authors.forename: Ji-Young
authors.initials: JY
authors.lastname: Nam
authors.affiliation: Associate Professor, Department of Dental Laboratory Science, College of Health Sciences, Catholic University of Pusan, Busan, Republic of Korea. Electronic address: mgpark@cup.ac.kr.
authors.forename: Mi-Gyoung
authors.initials: MG
authors.lastname: Park
mesh_terms: D000143:Acids; D003116:Color; D006244:Hardness; D066298:In Vitro Techniques; D008422:Materials Testing; D013499:Surface Properties; D014867:Water; D015040:Zirconium / Q000737:chemistry*
chemical_list: D000143:Acids; D014867:Water; D015040:Zirconium; C028541:zirconium oxide