title: Human perception of dental porcelain translucency correlated to spectrophotometric measurements.
abstract: OBJECTIVE
  This study evaluated the relationship between instrumental measurements and subjective visual assessment of differences in dental porcelain translucency.
  
  
  METHODS
  Unshaded feldspathic porcelain was used with controlled amounts of tin oxide to create two groups of 12-mm diameter disks with incremental changes in opacity. Contrast ratio (CR = Yb/Yw) was determined with a spectrophotometer, and used as a measure of porcelain translucency (Group A = 0.20 to 0.40; Group B = 0.6-0.8). Within each group, there were 14 specimens with 11 CRs. Three observer groups (first year dental students, residents, faculty with >10 years of shade matching experience) were recruited to assess the translucency between porcelain disks under two lighting conditions (reflected light, transmitted light). Each subject's ability to distinguish between specimens of differing translucency was determined. Descriptive statistics and three-way ANOVA followed by a post-hoc Tukey-Kramer test were used to evaluate the translucency perception threshold (TPT) of subjects (alpha= 0.05).
  
  
  RESULTS
  The overall mean TPT (DeltaC) was 0.07, while 50% of the subjects could perceive a 0.06 CR difference between porcelain specimens. Three-way ANOVA revealed a significant difference in translucency perception among the observer groups (p < 0.0001), whereas the main effects for porcelain opacity (p= 0.3038) and lighting condition (p= 0.0645) were not significant, and no significant interactions were found. Post-hoc Tukey-Kramer test indicated that the mean TPT observed in the faculty group (DeltaC = 0.04) was significantly lower than those observed in student (DeltaC = 0.09) and resident groups (DeltaC = 0.08), while there was no significant difference between students and residents.
  
  
  CONCLUSIONS
  The overall mean TPT of all subjects was 0.07, and 50% of the study population perceived a 0.06 CR difference in translucency. Increased shade matching experience (> or =10 years) significantly improved the ability to perceive differences in translucency; however, neither the viewing condition nor porcelain opacity affected the perceived translucency threshold.
authors.affiliation: Department of Dentistry, Shin Kong Wu Ho-Su Memorial Hospital, Shihlin District, Taipei, Taiwan. prostholiu@hotmail.com
authors.forename: Min-Chieh
authors.initials: MC
authors.lastname: Liu
authors.forename: Steven A
authors.initials: SA
authors.lastname: Aquilino
authors.forename: Peter S
authors.initials: PS
authors.lastname: Lund
authors.forename: Marcos A
authors.initials: MA
authors.lastname: Vargas
authors.forename: Ana M
authors.initials: AM
authors.lastname: Diaz-Arnold
authors.forename: David G
authors.initials: DG
authors.lastname: Gratton
authors.forename: Fang
authors.initials: F
authors.lastname: Qian
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D003775:Dental Polishing; D003776:Dental Porcelain / Q000737:chemistry*; D004056:Differential Threshold / Q000502:physiology; D005179:Faculty, Dental; D006801:Humans; D007396:Internship and Residency; D008027:Light; D017680:Potassium Compounds / Q000737:chemistry; D013053:Spectrophotometry; D013335:Students, Dental; D013499:Surface Properties; D017971:Tin Compounds / Q000737:chemistry; D014796:Visual Perception / Q000502:physiology*
chemical_list: D000538:Aluminum Silicates; D017680:Potassium Compounds; D017971:Tin Compounds; D003776:Dental Porcelain; C016447:feldspar; C045358:stannic oxide