title: Light transmission through porcelain.
abstract: OBJECTIVE
  This study evaluates the effect of shade and thickness of porcelain in light transmission.
  
  
  METHODS
  One hundred and twenty-eight disks of Duceram porcelain were made to combine four different thicknesses (1.5; 2.0; 3.0; 4.0 mm) and eight shades (A(1); A(4); B(1); B(4); C(1); C(4); D(2); D(4)). A digital power meter (Newport Optical Power Meter was used to measure light transmission. The porcelain transmission coefficient was calculated using Lambert-Beer law, t(c)=Ce(-alphad), where t(c) is the transmission coefficient, C the contribution factor of the reflection coefficient, e a constant, alpha the absorption coefficient and d is the sample thickness.
  
  
  RESULTS
  The transmission coefficients did not vary statistically in relation to the two visible light-curing units studied. From all the samples, the colors A(1) and D(2), thickness 1.5 mm, presented the highest percentages of transmission (8%) and the shades, A(4), B(4) and C(4), thickness 4 mm, the lowest (0.5%). The relationship between the Naperian logarithm of the transmission coefficient and the samples thickness followed the Lambert-Beer law. The linear adjustment of the experimental points of the two variables, showed the absorption coefficient (alpha) and the constant value related to the reflection (C) of each porcelain shade. The reflection coefficient values of all shades did not vary statistically among themselves.
  
  
  CONCLUSIONS
  For most shades there was a significant decrease in light transmission as the sample porcelain thickness increased. For the same thickness most shades presented statistical difference between the transmission coefficients. However, the larger the thickness, the higher the number of shades which, statistically, showed no difference.
authors.affiliation: Department of Restorative Dentistry, Federal University of Minas Gerais, Belo Horizonte, Brazil. rogelit@terra.com.br
authors.forename: Rogéli T R C
authors.initials: RT
authors.lastname: Peixoto
authors.forename: Vanessa Maria F
authors.initials: VM
authors.lastname: Paulinelli
authors.forename: Herbert H
authors.initials: HH
authors.lastname: Sander
authors.forename: Marcos D
authors.initials: MD
authors.lastname: Lanza
authors.forename: Luiz Alberto
authors.initials: LA
authors.lastname: Cury
authors.forename: Luiz Thadeu A
authors.initials: LT
authors.lastname: Poletto
mesh_terms: D000042:Absorption; D003776:Dental Porcelain; D008027:Light; D010783:Photometry; D012542:Scattering, Radiation
chemical_list: C095718:Duceram; D003776:Dental Porcelain