ASTM E2466-06(2011)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E2466 − 06 (Reapproved2011)
Standard Test Method for
Colorimetry of Teeth Using Digital Still Camera Technology
This standard is issued under the fixed designation E2466; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Tooth color is an important parameter used to ascertain certain medical and esthetic information.
CIE colorimetric values for the teeth are derived from the native RGB signals generated by a digital
stillcamera,DSC,bybroadbandmeasurementofthereflectanceofteeth.Theilluminationangleis45
degrees and CIELAB colorimetric coordinates are computed using equations contained in Practice
E308. This test method, E2466, specifies the procedure used for the measurement of tooth color
in-vivo and in-vitro with illumination at 45 degrees relative to the sample plane which is also the
normalofthemouth,underanapproximateequalenergyspectrum.Thistestmethodisappropriatefor
anterior and posterior teeth.
1. Scope 1.5 Data acquired using this test method is for comparative
purposes used during clinical trials or other types of research.
1.1 This test method covers the procedure, instrumental
1.6 Thistestmethodisdesignedtoencompassnaturalteeth,
requirements, standardization procedures, material standards,
artificial teeth, restorations, and shade guides.
measurement procedures, and parameters necessary to make
precise measurements of in-vivo tooth color and tooth white-
NOTE 1—This procedure may not be applicable for all types of dental
ness. In particular it is meant to measure the color of teeth in
work.
selected human subjects.
1.7 The apparatus, measurement procedure, data analysis
1.2 Digital images are used to evaluate tooth color of both technique are generic, so that a specific apparatus, measure-
posterior and anterior dentition (teeth). All other non-relevant ment procedure, or data analysis technique may not be ex-
parts, such as gums, spaces, etc., must be separated from the cluded.
measurementandtheanalysis.Alllocalizeddiscoloration;such
1.8 The values stated in SI units are to be regarded as the
as stains, inclusions, etc., may be separated from the measure-
standard. The values given in parentheses are for information
ment and the analysis.
only.
1.3 Thebroadbandreflectancefactorsofteetharemeasured.
1.9 This standard does not purport to address all of the
The colorimetric measurement is performed with a digital still
safety concerns, if any, associated with its use. It is the
camera while using an illuminator(s) that provides controlled
responsibility of the user of this standard to establish appro-
illumination on the teeth. The measured data from a digital
priate safety and health practices and to determine the
image are captured using a DSC. This test method is particu-
applicability of regulatory limitations prior to use.
larly useful for the gamut of tooth color which is:
2. Referenced Documents
1.3.1 CIE L* from 55 to 95,
1.3.2 CIE a* from 3 to 12, 2.1 ASTM Standards:
D2244Practice for Calculation of Color Tolerances and
1.3.3 CIE b* from 8 to 25 units.
Color Differences from Instrumentally Measured Color
1.4 The wavelengths for this test method include that
Coordinates
portion of the visible spectrum from 400 to 700 nm.
E179Guide for Selection of Geometric Conditions for
Measurement of Reflection and Transmission Properties
of Materials
This test method is under the jurisdiction of ASTM Committee E12 on Color
andAppearance and is the direct responsibility of Subcommittee E12.06 on Image
Based Color Measurement. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 1, 2011. Published June 2011. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2006. Last previous edition approved in 2006 as E2466– 06. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E2466-06R11. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2466 − 06 (2011)
E284Terminology of Appearance 3.2.10 polarization, n—the orientation of the vibration pat-
E308PracticeforComputingtheColorsofObjectsbyUsing tern of light waves in a singular plane.
the CIE System
3.2.11 polarizer filter, n—a component that blocks one of
E313Practice for Calculating Yellowness and Whiteness
the two planes of vibration of an electromagnetic wave,
Indices from Instrumentally Measured Color Coordinates
producing linearly polarized light.
E1345Practice for Reducing the Effect of Variability of
3.2.11.1 Discussion—A polarizing filter can be used in
Color Measurement by Use of Multiple Measurements
sunglasses to reduce glare.
E1767Practice for Specifying the Geometries of Observa-
3.2.12 posterior teeth, n—posterior teeth are the large teeth
tion and Measurement to Characterize the Appearance of
in the back of the mouth.
Materials
3.2.13 spatial whitening response, n—the evaluation of
2.2 ISO Publications:
color or color change used to determine unit dosing.
ISO 17321-1Colour characterization of digital still cameras
(DSCs) – Part 1: Stimuli, metrology, and test procedures
4 4. Summary of Test Method
2.3 ISCC Publications:
4.1 Thistestmethoddescribestheproceduresforbroadband
Technical Report 2003-1Guide to Material Standards and
reflectance measurement of teeth, in-vivo and in-vitro. The
Their Use in Color Measurement
standardization of the instrumentation used to measure a
3. Terminology
subject’s teeth is defined. The basis for the selection of
specimensandthemeasurementprotocolgiven.Thedatafrom
3.1 Terms and definitions in Terminology E284 are appli-
the reflectance measurements are converted to colorimetric
cable to this test method.
values. The results are reported in terms of CIE tristimulus
3.2 Definitions—Terms included in this section are peculiar
values, other colorimetric coordinate system values, and colo-
to this standard.
rimetric indices.
3.2.1 angle of incidence, n—θ and optional θ , the polar
1 2
angle between the central ray of the illuminator(s), I and I ,
1 2
5. Significance and Use
and the Z axis which is normal to the camera. See Fig. A1.1.
5.1 The light reflected from the facial anterior teeth can be
3.2.2 anterior teeth, n—anterior teeth are the six upper and
used to calculate color coordinates. Monitored over time,
six lower front teeth; the anterior teeth consist of incisors and
changes in color can be observed. These data reveal informa-
cuspids (canines).
tion about the efficacy of a product, treatment study, or
3.2.3 bit depth, n—the number of digital bits used to store
epidemiology of tooth color. For example, clinical studies of
information contained in each pixel.
consumer tooth whitening systems evaluate the efficacy of
3.2.3.1 Discussion—The higher the depth, the more colors
manufacturers’products.
are in an image. With 8 bit-per-channel color, there are a total
5.2 The change in color of the facial surfaces of anterior
of 256 bits available for color representation in each of the R,
teeth can be used to optimize the efficacy of tooth whitening
G, B channels. RGB 8 bit-per-channel color is sometimes
systems. For example, the data can provide the answer the
called “24 bit color.”
question:“Whatistheoptimumpercentageofwhiteningagent
3.2.4 canine,n—thethirdtoothfromthecenterofthemouth
in a consumer tooth whitening system?”
towards the back of the mouth; these are the front teeth that
5.3 This procedure is suitable for use in research and
have one rounded or pointed edge used for biting.
development, marketing studies, comparative product
3.2.5 facial surfaces, n—of or toward the face, used to
analyses, and clinical trials.
designate the side of the tooth that is facing away from the
5.4 Prior research shows that a popular visual assessment
tongue side.
method of determining tooth color, changes in tooth color, and
3.2.6 in-vitro, adj or adv—in an artificial environment
whiteness among clinicians yields less than desirable results
outside of the human body.
(1-4). These assessment tools are designated “shade guides.”
3.2.7 in-vivo, adj or adv—within a living body; that is,
They consist of tooth-shaped, synthetic objects in the form of
measurements made of a living tooth in a living body.
teethallofslightlydifferentcolorsordifferentshadesfromone
another. A “shade” is generally regarded as a color slightly
3.2.8 maxillary anterior teeth, n—the four front upper
different from a reference color (on a comparative basis). The
incisors and the canine teeth. See Fig. A1.5.
colors of the synthetic teeth in these “shade guides” do not
3.2.9 native digital still camera spectral response function,
progress linearly as observed visually or logically in a CIE
n—thefunctionrelatingsceneradiancetoimageintensityofan
colorimetriccoordinatesystem, andtheyaremetamerictoreal
imaging system is called the digital still camera spectral
teeth.
response function.
5.5 Translucency—Human teeth are translucent and the
degree of translucency varies widely between subjects.
Available from International Imaging Industry Association (I3A), 701
Westchester Avenue, Suite 317W, White Plains, NY 10604, 914-285-4933, http://
www.isotc42@i3a.org.
4 5
Available from ISCC, Inter-Society Color Council, 11491 Sunset Hills Rd., Available from University of Michigan, http://www.lib.umich.edu/dentlib/
Reston, Va, 20190, http://www.iscc.org. Dental_tables/Colorshadguid.html.
E2466 − 06 (2011)
However,translucencydoesnotvaryovertheshorttermandis 7.3.1 Source IlluminationAssembly—Containsthesourceof
not therefore a consideration in this test method. illumination and associated optics to produce irradiance, E,on
thesampleoveraspecifiedspotarea,designated A.Thesource
6. Interferences
is broadband and continuous in nature.Adiagrammatic repre-
6.1 Ifthestandardlaboratoryconditionslistedin6.2change
sentation of the components of a typical Source Illumination
during the test or from test to test by an appreciable amount,
Assembly Unit is shown in Fig. A1.3.
theseconditionsmaycauseinterferences,andtheaccuracyand
7.3.2 Source Beam(s)—Acollimated or slightly converging
precision requirements of this test method may not be
beam(s) focused on the sample plane. Since the shape and
achieved. In some cases these effects may only be observed
position of the specimens being measured vary widely, a small
during the performance of the test.
convergenceangleminimizeslocalvariationsinintensity.Two
beamslocatedat45°relativetothenormalofthesampleplane
6.2 Factors Effecting Test Results—The following factors
are required to examine posterior teeth (on each side of the
are known to affect the test results.
mouth) and to achieve the uniformity requirements.
6.2.1 Environmental:
7.3.3 Position—Typically the Source Illumination Assem-
6.2.1.1 Extraneous Radiation—Extraneous light from other
blies are in a fixed position relative to the sample (Subject)
sources and near-infrared (NIR) radiations must be shielded
holder and the DSC. Therefore, small variations in θ are
from the test apparatus.
minimized. The angle θ is the subtended angle between the
6.2.1.2 Vibrations—Mechanicaloscillationsthatcausecom-
Source Illumination Assembly Units and the DSC. Refer to
ponents of the apparatus to move independently from one
Fig. A1.1.
another may cause errors in test results.
7.3.4 Source Optical Elements—The optical elements must
6.2.1.3 Thermal Changes—Temperature changes occurring
condition the radiation from the source so that it is spatially
during a test or differences in temperature between testing
uniform within 610%. The distance, d, from the DSC to the
locations may affect the reflectance factor of the
standardization, calibration, and verification plaques, and the sample plane must be selected to maintain the uniformity
requirements. Refer to Fig. A1.6.
apparatus spectral response function.
6.2.1.4 Power Input Fluctuations—Large changes in the
7.3.5 Spectral Power Distribution—The exact spectral na-
line frequency or supply voltage may cause the apparatus to ture of the illuminator is immaterial for the measurement of
report erroneous results. teeth and non-fluorescent specimens so long as the source is
6.2.2 Retractors—Thesurfacefinishoftheretractorsaffects stable with time and has adequate energy at all wavelengths in
the experimental test results. It has been determined that a theregionrequiredformeasurement.AnapproximationtoD50
neutral (clear) finish on the surface of the retractors may provides an equal energy spectrum over the area of interest for
introduce a bias into the test results. DSCs. Commonly used light sources include incandescent
lamps, either operated without filters or filtered to simulate
6.3 Standardization—The system must allow for successful
standard illuminants, flashed or continuous-wave xenon-arc
standardization.
lamps and discrete pseudo-monochromatic sources, such as
6.4 Equipment Operation—If the system cannot be
light emitting diodes (LEDs).
standardized, a series of checks must be performed (lighting,
7.3.6 Polarization—The linear polarizer provides and con-
camera, etc.) to identify the reason. The component of the
trols the polarization state of the incident light. This polarizer
systeminerrorwillbeadjustedorreplacedtobringthesystem
on the illuminators plus a cross polarizer filter on the lens
back into calibration.
system of the DSC eliminates glare caused by reflection of the
6.5 Controlling Factors: subject’s teeth during imaging. Wavelength range, extinction
6.5.1 These interferences may be eliminated and problems ratio, transmittance, and beam deviation are important param-
avoided by controlling and regulating each factor within the eters and must be selected.
constraintsoftheallowableexperimentalerror.Thevaluesand
7.3.7 Heat Rejection Filters—These filters remove unde-
limitsforthesefactorsaretypicallydeterminedexperimentally.
sired near-infrared (NIR) radiation including heat that ad-
versely affects the subject and provide spectral shaping of the
7. Apparatus
spectral power distribution of the source illumination.
7.1 General—The components described in this section are
7.3.8 Selective Blue Filters—These filters condition the
described generically. The intention is not to exclude any
spectral power distribution of the illumination so that the
component from being used, or to exclude any type of
spectral power distribution is similar to an approximate equal
instrumentthatmaybeavailablecommercially.Between4and
energy
...