title: Comparison of an absolute and surrogate measure of relative translucency in dental ceramics.
abstract: OBJECTIVE
  The objective was to compare absolute translucency with a frequently used surrogate measure of relative translucency (contrast ratio) from 14 all-ceramic materials having a wide range of translucencies.
  
  
  METHODS
  Standardized disks were fabricated from fourteen ceramics, varying both thickness (0. 3mm, 0.5 mm, 1.0 mm, and 1.5 mm) and chroma (high and low). Absolute translucency (percent transmission) was measured using a spectroradiometer with an integrating sphere. Relative translucency was measured using a spectrophotometer as contrast ratio (contrast ratio; ratio of L* values recorded on black and white backgrounds). Non-linear regression was used to compare measurements of absolute versus relative values for each of the spectrophotometers.
  
  
  RESULTS
  Contrast ratio was not able to characterize translucency across the range of materials studied and became less sensitive with increasing opacity. A non-linear correlation was found between percent transmission and contrast ratio down to 50% transmission (r(2)=0.97) and contrast ratio was insensitive to transmission differences below 50% transmission.
  
  
  CONCLUSIONS
  Contrast ratio is not a direct measure of translucency and cannot be used below 50% transmission.
authors.affiliation: Department of Reconstructive Sciences, University of Connecticut School of Dental Medicine, Farmington, CT 06030-1615, USA.
authors.forename: Lisa S
authors.initials: LS
authors.lastname: Spink
authors.forename: Patchanee
authors.initials: P
authors.lastname: Rungruanganut
authors.forename: Spiro
authors.initials: S
authors.lastname: Megremis
authors.forename: J Robert
authors.initials: JR
authors.lastname: Kelly
mesh_terms: D000465:Algorithms; D000537:Aluminum Oxide / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D006801:Humans; D008027:Light; D008277:Magnesium Oxide / Q000737:chemistry; D008422:Materials Testing; D011874:Radiometry / Q000295:instrumentation; D013053:Spectrophotometry / Q000295:instrumentation; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; C520133:IPS e.max CAD LT; C508050:IPS e.max Press; C075815:IPS-Empress ceramic; C483026:In-Ceram Alumina; C485633:In-Ceram Zirconia; C493120:lithia disilicate; C111130:spinell; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D008277:Magnesium Oxide; D015019:Yttrium; C023506:Glass ceramics; D015040:Zirconium; D000537:Aluminum Oxide