ISO/TR 28642:2016

TECHNICAL ISO/TR
REPORT 28642
Second edition
2016-12-01
Dentistry — Guidance on colour
measurement
Médecine bucco-dentaire — Directives relatives au mesurage de la
couleur
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Visual and instrumental colour assessment . 3
4.1 Devices . 3
4.2 Setting . 4
4.2.1 llluminant . 4
4.2.2 Standard observer . 4
4.2.3 Geometric conditions . 4
4.2.4 Illuminance . 4
4.2.5 Visual angle of subtense . 4
4.2.6 Background. 4
4.2.7 Surround . 4
4.2.8 Additional/other considerations . 5
5 Observers . 5
5.1 Evaluation of colour competency of candidate for observer in studies on
acceptability or perceptibility in dentistry . 5
5.1.1 Ishihara colour blindness test . 5
5.1.2 Farnsworth-Munsell 100 hue test . . 5
5.1.3 Test for colour discrimination competency in dentistry . 5
5.2 Guidelines for observer selection for acceptability or perceptibility evaluation
in dentistry . 5
5.2.1 General tests . 5
5.2.2 Test for colour discrimination competency in dentistry . 5
5.2.3 Testing intervals for qualified observers . 6
6 Testing of acceptability and perceptibility thresholds . 6
6.1 Tissues and materials to be tested for perceptibility and acceptability thresholds . 6
6.2 Test methods . 6
6.2.1 Visual judgments . 6
6.2.2 Instrumental evaluation . 6
7 Application and interpretation . 6
7.1 Colour compatibility . 7
7.1.1 Colour compatibility between dental material and human tissues . 7
7.1.2 Colour compatibility between dental materials . 7
7.1.3 Coverage error of dental shade guides . 7
7.2 Colour stability . 7
7.2.1 Colour stability during fabrication/at placement . 7
[ ] 7
7.2.2 Colour stability after aging and staining 12 .
7.3 Colour interactions . 7
[ ][ ] 7
7.3.1 Colour shifting of aesthetic restorative materials 13 14 .
7.3.2 Masking potential of opaque materials . 8
8 Reporting of colour and colour difference assessment . 8
8.1 Illuminant . 8
8.2 Object . 8
8.3 Observer/instrument . 8
8.3.1 Observer . 8
8.3.2 Instrument . 9
Bibliography .10
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 106, Dentistry, Subcommittee SC 2, Prosthodontic
materials.
This second edition cancels and replaces the first edition (ISO/TR 28642:2011), which has been
technically revised.
iv © ISO 2016 – All rights reserved

Introduction
The colour appearance of teeth and other dentistry‑related tissues need to be matched and reproduced
in order to achieve acceptable aesthetics in an efficient manner. Three major groups of issues, related
to colour compatibility, colour stability and colour interactions, are identified and considered in this
document. Interpretation of colour differences associated with these three groups through 50:50 %
perceptibility and acceptability visual thresholds is suggested. Colour is a psychophysical phenomenon
that is assessed by both visual and instrumental methods. Other elements of appearance, including
gloss and translucency, affect aesthetics and may influence the characterization of colour appearance.
The International Commission on Illumination (CIE) colour difference formulae and resources, in
particular CIE Pub No 15.3, were used in this document.
TECHNICAL REPORT ISO/TR 28642:2016(E)
Dentistry — Guidance on colour measurement
1 Scope
This document identifies three types of topics related to shade conformity and interconvertibility
of monochromatic and polychromatic tissues and materials related to the discipline of dentistry; it
describes visual and instrumental methods for assessment of these topics.
This document suggests interpretation of the findings through colour difference thresholds and provides
guidelines for future standardization related to dental shade conformity and interconvertibility. It
also includes guidelines related to colour vision of persons undertaking visual colour assessments and
instructions for reporting of colour and colour difference assessments.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 1942, Dentistry — Vocabulary
ISO 11664-1, Colorimetry — Part 1: CIE standard colorimetric observers
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1942 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1
colour difference
single number or metric expressing the distance from complete match in colour or shade
Note 1 to entry: A colour distance metric defined by the International Commission on Illumination (CIE) is called
delta E (ΔE).
Note 2 to entry: Two formulae for calculating ΔE are recommended in this document: CIE 76 (denoted ΔE* ) and
ab
CIEDE2000 (denoted ΔE ).
3.2
50:50 % perceptibility threshold of colour difference
PT
difference in colour that can be detected by 50 % of observers under controlled conditions, with the
other 50 % of observers noticing no difference in colour between the compared objects
Note 1 to entry: A nearly perfect colour match in dentistry is a colour difference at or below the 50:50 %
perceptibility threshold.
3.3
50:50 % acceptability threshold of colour difference
AT
difference in colour that is considered acceptable by 50 % of observers under controlled conditions,
with the other 50 % of observers replacing or correcting the restoration
Note 1 to entry: An acceptable colour match in dentistry is a colour difference at or below the 50:50 %
acceptability threshold.
3.4
colour standards in dentistry
sets of polychromatic or monochromatic samples (tabs, chips, or patches), most frequently made of
dental ceramic or resin (tooth shade guides), or silicone elastomer (skin shade guides in maxillofacial
prosthodontics)
Note 1 to entry: The polychromatic and monochromatic samples are fabricated for the purposes of colour
matching hard and soft oral tissues, and human skin (see Reference [2]).
3.5
coverage error
index that describes the mean of minimal colour differences (ΔE* ) between the specimens of one set
min
(e.g. a shade guide) to each specimen of another set (e.g. natural teeth)
Note 1 to entry: The coverage error is calculated as the mean ΔE* for all best matches as follows:
min
ΣΔΕ *
min
Coverage error=
n
where n is the number of best matches.
Note 2 to entry: The smaller the coverage error, the higher the chances of successful shade matching.
3.6
tooth whitening
change in tooth colour caused by bleaching or stain‑removal agents and manifested by the increase in
the value of lightness and the decrease of chroma
3.7
colour shifting
change in perceived colour that is a sum of a blending effect and an effect of physical translucency
3.7.1
colour shifting due to blending
change in perceived colour of a material due to a change in surroundings
Note 1 to entry: Colour shifting due to blending is a psycho‑physical phenomenon and is not modelled by the
current CIELAB mathematical model; it is an optical illusion, visually perceptible, but not quantifiable or
measurable by any instrument.
3.7.2
colour shifting due to physical translucency
change in colour of translucent dental restorations caused by surroundings and background (underlying
layers of hard dental tissues or other restorative materials)
3.8
opacity
measure of the ability of a material to block the passage of light
Note 1 to entry: A material with high opacity is one with low translucency/transparency.
2 © ISO 2016 – All rights reserved

3.9
transparency
physical property of allowing the transmission of light through a material
Note 1 to entry: A material with high transparency is one with low opacity.
Note 2 to entry: Transparency is the extreme value of high translucency.
Note 3 to entry: A transparent material allows light to pass through undiminished, while a negligible portion of
the transmitted light is scattered.
3.10
translucency
ability of a material to allow light to pass through it
Note 1 to entry: A material with high translucency is one with low opacity.
Note 2 to entry: Translucent materials allow light to pass through only diffusely (they cannot be seen through
clearly).
3.11
gloss
capacity of a surface to reflect more light in some directions than in others
3.12
specular gloss
ratio of flux reflected in the specular direction to incident flux (i.e. the angle of the reflected light is
equal and opposite to the angle of the incident beam) for a specified angle of incidence, source, and
receptor angular aperture
Note 1 to entry: These reflections normally have the highest reflectances (see References [2] and [3]).
4 Visual and instrumental colour assessment
4.1 Devices
Frequently used devices for visual and instrumental colour assessment in dentistry are
spectrophotometers, spectroradiometers, colourimeters, imaging systems for traditional digital
imaging and spectral imaging, viewing booths, and different types of hand‑held shade matching lights.
Spectral measurement is pe
...