title: The effect of extended aging on the optical properties of different zirconia materials.
abstract: OBJECTIVE
  The purpose of this study was to determine if the optical properties of zirconia and glass-ceramic (e.max) were affected by low-temperature degradation (aging).
  
  
  METHODS
  Experiment samples were fabricated with seven zirconia brands (n=10): Zenostar, Zirlux, Katana, Bruxzir, DD-BioZX2, DD-cubeX2, NexxZr; and e.max were used as a control. This resulted in a total of 80 samples in the experiment. The L*, a* and b* were measured for each sample, and then the optical properties including translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP) were calculated. The samples were aged (20, 40, 60, 80, 100h), and the optical properties were calculated after each interval.
  
  
  RESULTS
  Most zirconia brands had lower L*, higher a*, higher b* with increased aging, which visually corresponds to darker, redder, and more yellow. Aging also increased CR, lowered TP, and lowered OP. e.max was also affected by aging but still had the highest TP (23.9±2.8), L* (81.7±3.4), and lowest CR (0.41±0.05) compared to any zirconia. The Zenostar had the closest TP (24.1±0.4), and L* (90.2±0.5) values to e.max before aging. However, after 100h of aging, the DD-cubeX2was least effected and had the highest TP (22.2±0.6) and lowest CR (0.43±0.01) compared with other zirconia samples and highest OP (11.3±0.2) of all ceramic samples.
  
  
  CONCLUSIONS
  The optical properties of zirconia and e.max materials were affected by aging with the effects increasing with time. The magnitude of change was affected by seven brands of dental zirconia.
authors.affiliation: Department of Prosthetic Dental Sciences, College of Dentistry, Taibah University, Medina, Saudi Arabia; Department of Materials Science and Engineering, School of Engineering, The University of Alabama at Birmingham, United States. Electronic address: drtariq05@gmail.com.
authors.forename: Tariq F
authors.initials: TF
authors.lastname: Alghazzawi
mesh_terms: D002516:Ceramics; D003116:Color; D003764:Dental Materials; D000068897:Iridescence; D008027:Light; D008422:Materials Testing; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D015040:Zirconium
chemical_list: D003764:Dental Materials; C023506:Glass ceramics; D015040:Zirconium; C028541:zirconium oxide
keywords: Aging; Contrast ratio; Low-temperature degradation; Opalescence; Optical properties; Translucency; Zirconia