Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrophotometer
Patent
1987-08-13
1989-06-06
Evans, F. L.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrophotometer
356323, 356328, 433 26, G01J 342, G01J 336
Patent
active
048366749
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and to apparatus for determining the color to be given to an object, in particular a ental prosthesis, on the basis of the color of another object, in particular the adjacent teeth in the mouth of the patient.
BACKGROUND OF THE INVENTION
It is essential for a dental prosthesis (e.g. a crown, a bridge, an implant, etc.,) to be as close as possible in color to the adjacent teeth.
At present, the color of a dental prosthesis is determined at sight, in general by a dentist comparing color samples with the teeth of the patient. This procedure gives results that necessarily depend on the dentist's capacity to distinguish between colors which are very similar, which is sufficient reason for results that are not always very satisfactory.
It may also happen that a prosthesis color selected in this way is very close to the color of the adjacent teeth so long as the teeth are illuminated by a light source giving a generally uniform spectrum, but that the prosthesis color appears quite different when the teeth are illuminated by a light source such as a fluorescent tube which radiates a spectrum concentrated in a few lines (a phenomenon sometimes known as metamerism).
Colorimeters exist which measure the color of an object by using filters to determine the tristimulus values X, Y, and Z of the object's color, thereby enabling said color to be reproduced by mixing three primary colors. However, a knowledge of the tristimulus values applicable for any given illumination is not sufficient for specifying the values under different illumination. Thus, in order to obtain good results using colorimeters it is necessary to take a large number of color measurments under different lighting conditions, which is a considerable problem.
The invention seeks to mitigate this problem.
An aim of the invention is to provide a method and apparatus for determining the apparent colors of an object corresponding to various different types of illumination, on the basic of a single measurement performed under unspecialized illumination.
Another aim of the invention is to provide a method and apparatus of the above-mentioned type suitable for performing such measurements on objects which are difficult of access, such as a person's teeth.
SUMMARY OF THE INVENTION
The present invention provides a method of determining the color, in particular of a dental prosthesis, with reference to the color of an identical object such as adjacent teeth in the mouth of a patient, the method consisting in: picking up color information in situ by means of one or more optical fibers suitable for being inserted into the mouth of the patient to pick up light reflected from a tooth adjacent to the emplacement for the prosthesis; in transmitting the reflected light by optical fiber to a spectrocolorimeter; and in determining the diffuse spectral reflectance D(.lambda.) of the tooth, and then in calculating the various apparent colorations of the tooth corresponding to different types of light by which it may be illuminated, in order to define the prosthesis color having the best possible match from the esthetic point of view with the adjacent teeth.
After being suitably sampled, the diffuse spectral reflectance of the illuminated tooth can be used to calculate the tristimulus values of the tooth's coloration under any possible type of illumination; and in practice this is done for standardized types of light source representative of various possible types of illumination (e.g. an equal energy source, C.I.E. standard illuminants, a spectrum line source, etc.).
The invention thus makes it possible to obtain the tristimulus values of the apparent colors of a tooth under different types of illumination from a single measurement, and thereby makes it possible to select a prosthesis color with tristimulus values that are as close as possible to those of the apparent colors of the tooth.
Diffuse spectral reflectance measurements may be performed, and the apparent colors may be determined for several of the patient's teeth and for sev
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patent: 4375919 (1983-03-01), Busch
patent: 4654794 (1987-03-01), O'Brien
Lequime Michel
Millet Jocelyn
Bertin & Cie
Evans F. L.
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