Tooth colour: a review of the literature

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Abstract

Objectives. To review current knowledge with respect to tooth colour and its measurement.

Methods. ‘Medline’ database for the period 1966 to the present day and ‘ISI Web of Science’ database for the period 1974 to the present day were searched electronically with key words tooth, teeth, colour and color.

Conclusions. The colour and appearance of teeth is a complex phenomenon, with many factors such as lighting conditions, translucency, opacity, light scattering, gloss and the human eye and brain influencing the overall perception of tooth colour. The measurement of tooth colour is possible via a number of methods including visual assessment with shade guides, spectrophotometry, colourimetry and computer analysis of digital images. These methods have successfully been used to measure longitudinal tooth colour changes when the dentition has undergone tooth whitening procedures.

Introduction

A smile has been said to be one of the most important interactive communication skills of a person.1 The ultimate objective of aesthetics in dentistry is to create a beautiful smile, with teeth of pleasing inherent proportions to one another, and a pleasing tooth arrangement in harmony with the gingiva, lips and face of the patient.2 In addition, the aesthetics of any restoration needs to consider the parameters of surface form, translucency and colour.2., 3., 4., 5. Patients and consumers now demand not only a healthy mouth but also a perfect smile. Indeed, it has been reported in the UK that 28% of adults are dissatisfied with the appearance of their teeth6 and in the USA that 34% of an adult population are dissatisfied with their current tooth colour.7

The colour of the teeth is determined by the combined effects of intrinsic and extrinsic colourations.8 Intrinsic tooth colour is associated with the light scattering and absorption properties of the enamel and dentine.9 Extrinsic colour is associated with the absorption of materials (e.g. tea, red wine, chlorhexidine, iron salts) onto the surface of enamel, and in particular the pellicle coating, and which ultimately cause extrinsic stain.10 The many factors associated with tooth discolouration and staining, both intrinsic and extrinsic, have recently been extensively reviewed.8

Since the extrinsic stains are on the tooth surface, these can be thoroughly removed by the abrasive action of a dental prophylaxis11 and controlled by the regular use of an effective toothpaste.12 There are many treatment methods and materials available to enhance the intrinsic colour of the teeth. Night guard vital bleaching, introduced in 1989 is one such technique,13 where a carbamide peroxide gel is held against the anterior teeth with a custom fitted gum shield in order to lighten the colour of the teeth. Today, tooth whitening continues to be ever more popular, either through professionally applied products14., 15., 16. or through mass market consumer products.17., 18.

With this increase of interest in tooth whitening, this paper aims to review current knowledge with respect to tooth colour.

Section snippets

Colour and colour space

The phenomenon of colour is a psychophysical response to the physical interaction of light energy with an object, and the subjective experience of an individual observer.19 Three factors can influence the perception of colour, namely, the light source, the object being viewed and the observer viewing the object. The light source can emit radiant energy of a range of wavelengths and this is characterised by the relative amount of energy emitted at each wavelength in the visible spectrum. The

Optical properties of teeth

The colour of a tooth is determined by a combination of its optical properties. When light encounters a tooth, four phenomena associated with the interactions of the tooth with the light flux can be described:23 (1) specular transmission of the light through the tooth, (2) specular reflection at the surface, (3) diffuse light reflection at the surface and (4) absorption and scattering of light within the dental tissues. Tooth colour has been shown to result from the volume scattering of light,

Measurement of tooth colour

Many methods are currently used to assess tooth colour. These range from visual subjective comparisons using paper, coloured porcelain or acrylic resin shade guides to instrumental objective measurements using spectrophotometers, colourimeters and image analysis techniques.

Visual colour determination, by comparison of the tooth with standard colour tooth shade guides, is the most frequently applied method in dentistry.24 It is a subjective process whereby the tooth and the shade guide are

Tooth colour distribution

The range of colour and distribution of colour in different regions of the tooth have been described by a number of investigators. In general, the maxillary anterior teeth are slightly more yellow than mandibular anterior teeth,40 and the maxillary central incisors are higher in value than the lateral incisors and canines.40., 64., 67., 87.

There are no significant differences in tooth colour between males and females according to a number of studies involving natural teeth.67., 23. In contrast,

Tooth colour perception and appearance

In contemporary dentistry, the needs of patients are considered in terms of function and dental appearance. The appearance of the teeth is related to both cultural factors and individual preferences, i.e. the viewer's perception of a visual experience can be pleasant or unpleasant, and what is considered ‘beautiful’ in one culture may be ‘ugly’ in another.3 The most common associations with facial attraction are the eyes and mouth.92 The oral region plays an important role when an individual

Conclusions

The colour and appearance of teeth is a complex phenomena, with many factors such as lighting conditions, translucency, opacity, light scattering, gloss and the human eye and brain influencing the overall perception of tooth colour. The measurement of tooth colour is possible via a number of methods including visual assessment with shade guides, spectrophotometry, colourimetry and computer analysis of digital images. Each method has its own limitations and set of advantages and disadvantages.

Acknowledgments

The author would like to thank Mike McGrady of 4-Front Research, Capenhurst for his help in the preparation of the manuscript.

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