ASTM E2466-06

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Designation: E2466 – 06
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. A number 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
still camera, DSC, by broadband measurement of the reflectance of teeth.The illumination angle is 45
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.
NOTE 1—This procedure may not be applicable for all types of dental
1. Scope
work.
1.1 This test method covers the procedure, instrumental
1.7 The apparatus, measurement procedure, data analysis
requirements, standardization procedures, material standards,
technique are generic, so that a specific apparatus, measure-
measurement procedures, and parameters necessary to make
ment procedure, or data analysis technique may not be ex-
precise measurements of in-vivo tooth color and tooth white-
cluded.
ness. In particular it is meant to measure the color of teeth in
1.8 The values stated in SI units are to be regarded as the
selected human subjects.
standard. The values given in parentheses are for information
1.2 Digital images are used to evaluate tooth color of both
only.
posterior and anterior dentition (teeth). All other non-relevant
1.9 This standard does not purport to address all of the
parts, such as gums, spaces, etc., must be separated from the
safety concerns, if any, associated with its use. It is the
measurementandtheanalysis.Alllocalizeddiscoloration;such
responsibility of the user of this standard to establish appro-
as stains, inclusions, etc., may be separated from the measure-
priate safety and health practices and to determine the
ment and the analysis.
applicability of regulatory limitations prior to use.
1.3 Thebroadbandreflectancefactorsofteetharemeasured.
The colorimetric measurement is performed with a digital still
2. Referenced Documents
camera while using an illuminator(s) that provides controlled
2.1 ASTM Standards:
illumination on the teeth. The measured data from a digital
D2244 Practice for Calculation of Color Tolerances and
image are captured using a DSC. This test method is particu-
Color Differences from Instrumentally Measured Color
larly useful for the gamut of tooth color which is:
Coordinates
1.3.1 CIE L* from 55 to 95,
E179 Guide for Selection of Geometric Conditions for
1.3.2 CIE a* from 3 to 12,
Measurement of Reflection andTransmission Properties of
1.3.3 CIE b* from 8 to 25 units.
Materials
1.4 The wavelengths for this test method include that
E284 Terminology of Appearance
portion of the visible spectrum from 400 to 700 nm.
E308 Practice for Computing the Colors of Objects by
1.5 Data acquired using this test method is for comparative
Using the CIE System
purposes used during clinical trials or other types of research.
E313 Practice for Calculating Yellowness and Whiteness
1.6 This test method is designed to encompass natural teeth,
Indices from Instrumentally Measured Color Coordinates
artificial teeth, restorations, and shade guides.
E1345 Practice for Reducing the Effect of Variability of
This test method is under the jurisdiction of ASTM Committee E12 on Color
and Appearance and is the direct responsibility of Subcommittee E12.06 on Image For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Based Color Measurement. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Jan. 15, 2006. Published March 2006. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
E2466-06. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2466 – 06
Color Measurement by Use of Multiple Measurements 3.2.12 posterior teeth, n—posterior teeth are the large teeth
E1767 Practice for Specifying the Geometries of Observa- in the back of the mouth.
tion and Measurement to Characterize the Appearance of 3.2.13 spatial whitening response, n—the evaluation of
Materials color or color change used to determine unit dosing.
2.2 ISO Publications:
4. Summary of Test Method
ISO 17321-1, Colour characterization of digital still cam-
eras (DSCs) – Part 1: Stimuli, metrology, and test proce-
4.1 Thistestmethoddescribestheproceduresforbroadband
dures
reflectance measurement of teeth, in-vivo and in-vitro. The
2.3 ISCC Publications:
standardization of the instrumentation used to measure a
Technical Report 2003-1 Guide to Material Standards and
subject’s teeth is defined. The basis for the selection of
Their Use in Color Measurement
specimens and the measurement protocol given.The data from
the reflectance measurements are converted to colorimetric
3. Terminology
values. The results are reported in terms of CIE tristimulus
3.1 Terms and definitions in Terminology E284 are appli-
values, other colorimetric coordinate system values, and colo-
cable to this test method.
rimetric indices.
3.2 Definitions—Terms included in this section are peculiar
to this standard.
5. Significance and Use
3.2.1 angle of incidence, n—u and optional u , the polar
1 2
5.1 The light reflected from the facial anterior teeth can be
angle between the central ray of the illuminator(s), I and I ,
1 2
used to calculate color coordinates. Monitored over time,
and the Z axis which is normal to the camera. See Fig. A1.1.
changes in color can be observed. These data reveal informa-
3.2.2 anterior teeth, n—anterior teeth are the six upper and
tion about the efficacy of a product, treatment study, or
six lower front teeth; the anterior teeth consist of incisors and
epidemiology of tooth color. For example, clinical studies of
cuspids (canines).
consumer tooth whitening systems evaluate the efficacy of
3.2.3 bit depth, n—the number of digital bits used to store
manufacturers’ products.
information contained in each pixel.
5.2 The change in color of the facial surfaces of anterior
3.2.3.1 Discussion—The higher the depth, the more colors
teeth can be used to optimize the efficacy of tooth whitening
are in an image. With 8 bit-per-channel color, there are a total
systems. For example, the data can provide the answer the
of 256 bits available for color representation in each of the R,
question: “What is the optimum percentage of whitening agent
G, B channels. RGB 8 bit-per-channel color is sometimes
in a consumer tooth whitening system?”
called “24 bit color.”
5.3 This procedure is suitable for use in research and
3.2.4 canine, n—the third tooth from the center of the
development, marketing studies, comparative product analy-
mouth towards the back of the mouth; these are the front teeth
ses, and clinical trials.
that have one rounded or pointed edge used for biting.
5.4 Prior research shows that a popular visual assessment
3.2.5 facial surfaces, n—of or toward the face, used to
method of determining tooth color, changes in tooth color, and
designate the side of the tooth that is facing away from the
whiteness among clinicians yields less than desirable results
tongue side.
(1-4). These assessment tools are designated “shade guides.”
3.2.6 in-vitro, adj or adv—in an artificial environment
They consist of tooth-shaped, synthetic objects in the form of
outside of the human body.
teethallofslightlydifferentcolorsordifferentshadesfromone
3.2.7 in-vivo, adj or adv—within a living body; that is,
another. A “shade” is generally regarded as a color slightly
measurements made of a living tooth in a living body.
different from a reference color (on a comparative basis). The
3.2.8 maxillary anterior teeth, n—the four front upper
colors of the synthetic teeth in these “shade guides” do not
incisors and the canine teeth. See Fig. A1.5.
progress linearly as observed visually or logically in a CIE
3.2.9 native digital still camera spectral response function,
colorimetriccoordinatesystem, andtheyaremetamerictoreal
n—thefunctionrelatingsceneradiancetoimageintensityofan
teeth.
imaging system is called the digital still camera spectral
5.5 Translucency—Human teeth are translucent and the
response function.
degree of translucency varies widely between subjects. How-
3.2.10 polarization, n—the orientation of the vibration pat-
ever, translucency does not vary over the short term and is not
tern of light waves in a singular plane.
therefore a consideration in this test method.
3.2.11 polarizer filter, n—a component that blocks one of
the two planes of vibration of an electromagnetic wave,
6. Interferences
producing linearly polarized light.
6.1 Ifthestandardlaboratoryconditionslistedin6.2change
3.2.11.1 Discussion—A polarizing filter can be used in
during the test or from test to test by an appreciable amount,
sunglasses to reduce glare.
these conditions may cause interferences, and the accuracy and
precision requirements of this test method may not be
Available from International Imaging Industry Association (I3A), 701
Westchester Avenue, Suite 317W, White Plains, NY 10604, 914-285-4933,
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. Dental_tables/Colorshadguid.html.
E2466 – 06
achieved. In some cases these effects may only be observed beams located at 45° relative to the normal of the sample plane
during the performance of the test. are required to examine posterior teeth (on each side of the
6.2 Factors Effecting Test Results—The following factors mouth) and to achieve the uniformity requirements.
are known to affect the test results. 7.3.3 Position—Typically the Source Illumination Assem-
6.2.1 Environmental:
blies are in a fixed position relative to the sample (Subject)
6.2.1.1 Extraneous Radiation—Extraneous light from other holder and the DSC. Therefore, small variations in u are
sources and near-infrared (NIR) radiations must be shielded
minimized. The angle u is the subtended angle between the
from the test apparatus. Source Illumination Assembly Units and the DSC. Refer to
6.2.1.2 Vibrations—Mechanical oscillations that cause
Fig. A1.1.
components of the apparatus to move independently from one 7.3.4 Source Optical Elements—The optical elements must
another may cause errors in test results.
condition the radiation from the source so that it is spatially
6.2.1.3 Thermal Changes—Temperature changes occurring uniform within 610 %. The distance, d, from the DSC to the
during a test or differences in temperature between testing
sample plane must be selected to maintain the uniformity
locations may affect the reflectance factor of the standardiza- requirements. Refer to Fig. A1.6.
tion, calibration, and verification plaques, and the apparatus
7.3.5 Spectral Power Distribution—The exact spectral na-
spectral response function.
ture of the illuminator is immaterial for the measurement of
6.2.1.4 Power Input Fluctuations—Large changes in the
teeth and non-fluorescent specimens so long as the source is
line frequency or supply voltage may cause the apparatus to
stable with time and has adequate energy at all wavelengths in
report erroneous results.
theregionrequiredformeasurement.AnapproximationtoD50
6.2.2 Retractors—Thesurfacefinishoftheretractorsaffects
provides an equal energy spectrum over the area of interest for
the experimental test results. It has been determined that a
DSCs. Commonly used light sources include incandescent
neutral (clear) finish on the surface of the retractors may
lamps, either operated without filters or filtered to simulate
introduce a bias into the test results.
standard illuminants, flashed or continuous-wave xenon-arc
6.3 Standardization—The system must allow for successful
lamps and discrete pseudo-monochromatic sources, such as
standardization.
light emitting diodes (LEDs).
6.4 Equipment Operation—If the system cannot be stan-
7.3.6 Polarization—The linear polarizer provides and con-
dardized, a series of checks must be performed (lighting,
trols the polarization state of the incident light. This polarizer
camera, etc.) to identify the reason. The component of the
on the illuminators plus a cross polarizer filter on the lens
system in error will be adjusted or replaced to bring the system
system of the DSC eliminates glare caused by reflection of the
back into calibration.
subject’s teeth during imaging. Wavelength range, extinction
6.5 Controlling Factors:
ratio, transmittance, and beam deviation are important param-
6.5.1 These interferences may be eliminated and problems
eters and must be selected.
avoided by controlling and regulating each factor within the
7.3.7 Heat Rejection Filters—These filters remove undes-
constraints of the allowable experimental error.The values and
ired near-infrared (NIR) radiation including heat that adversely
limitsforthesefactorsaretypicallydeterminedexperimentally.
affects the subject and provide spectral shaping of the spectral
power distribution of the source illumination.
7. Apparatus
7.3.8 Selective Blue Filters—These filters condition the
7.1 General—The components described in this section are
spectral power distribution of the illumination so that the
described generically. The intention is not to exclude any
spectral power distribution is similar to an approximate equal
component from being used, or to exclude any type of
energy spectrum, such as illuminant D50.
instrument that may be available commercially. Between 4 and
7.4 Sample Plane Holder—The sample plane holder pro-
6 different components or component assemblies are required
vides a secure mount so that it positions the subjects incisors
to accomplish the measurement.
normal to the Z axis and centered along the X andYaxes.This
7.2 Geometry—The geometry of the system is 45:0 as
must be done so that the teeth are presented to the DSC in a
describedinPracticeE1767andGuideE179.TheDSCSystem
repeatable and reproducible manner. The sample mount must
Geometry (Coordinate System) and Angular Conve
...