As you know, dental schools at best might devote only a few hours to colour science; at worst, they completely ignore it.
As early as 1931, E. B. Clark wrote of this in his article The Colour Problem in Dentistry. During the following seventy years, many articles have been authored by leading clinicians and colour researchers who spoke of clinical dentists’ lack of knowledge on shade matching.
Many practitioners experience counter-productive frustration, due to lack of education in this area, when attempting the colour matching of restorations.
It is unfortunate, but just as true, that many practitioners also don’t understand the science of human colour perception. Achieving a colour match is a major component in ensuring that the patient is pleased with the outcome of the restoration procedure.
Let us talk about the basics. The human eye has two structures, rods and cones, and these receive the visible light wavelengths. Simply put, rods perceive brightness or intensity and cones perceive colour. This information is then interpreted by the brain that then creates the appropriate perception.
As we know, colour is perceived differently by different people and can be affected by such factors as age, gender, fatigue, diet, colour-blindness and lighting conditions, for example. One’s individual experiences can also affect the way in which colour is perceived.
Another important component of shade matching is translucency. This relates to the degree of light which is transmitted as opposed to that which is absorbed. When translucency is associated with opacity, defined as light being reflected or absorbed, we have the components of colour most associated with the natural character that defines a patient-pleasing dental restoration.
There is an optical phenomenon, metamerism, which causes two objects to appear to match under one type of lighting source and condition and to appear quite different under another. Modern biomimetic materials act to reduce the effects of metamerism, by emulating the colour of natural teeth.
One more important consideration in shade selection is contrast. In the usual environment of the dental clinic there are many contrasting colours found; on the walls, bibs, and so on. The ability of the clinician to accurately assess the colour of a restorative material can even be effected by inflamed gingival tissues.
As an aid to the clinician, standard shade guides were developed and are quite useful in deriving a general value. They should not, however, be implicitly relied upon when selecting a direct composite. All of today’s manufacturers exert great effort to match, but the inevitability of variation in each restoration militates against a simple singular shade selection approach.
Other tools, like electronic shade meters, while of some value in shade matching, generally leave out other critical colour components such as translucency and opacity, for example. Other factors the clinician must consider include the size of preparation, colour condition of the underlying natural tooth, and adjacent tooth colour, to mention but a few.
It is may be concluded, then, that to optimize the aesthetic outcome of restorations a successful clinician must understand how colour science and environmental conditions effect that outcome.
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