Optics: measuring and testing – By shade or color – Trichromatic examination
Reexamination Certificate
1999-08-02
2003-02-25
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By shade or color
Trichromatic examination
C356S425000, C433S029000
Reexamination Certificate
active
06525819
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to devices and methods for the measurement of the color and reflectance of a tooth. The invention also provides for selecting a color and reflectance for a dental prosthesis which most closely matches that of the natural tooth.
BACKGROUND OF THE INVENTION
The conventional method of determining a color to use in the manufacture of a dental prosthesis is to use a number of comparison samples. The samples are held up to the patient's teeth surrounding the location where the prosthesis will be placed and the sample most closely matching the color of the teeth is chosen by visual observation. The difficulty in obtaining the optimum color match by this method is due to several factors which include the color and intensity of the light illuminating the comparison, the experience and visual acuity of the person making the comparison, and the use of a limited number of samples.
A standard, unambiguous system for measuring tooth colors is needed. Such a system should provide for accurate and repeatable color measurements in different environments such as various dentists' offices and manufacturers' laboratories. High-resolution color measurement data can then be provided to prosthesis manufacturers to ensure an optimum color match between a prosthesis and its surrounding natural teeth.
A number of previous inventions useful for measuring tooth colors have been patented. Some describe apparatuses for making color measurements and others describe methods for making measurements and using the results in the manufacture of artificial teeth. Several such inventions are briefly described in the following paragraphs.
U.S. Pat. No. 5,690,486, teaches a device for detecting the color of a damaged tooth and determining a color-matched restorative material. It describes the use of multiple LEDs for successively emitting light of different colors toward a target and a light sensor for receiving light reflected from the target, all contained within a hand-held, battery powered device. The device uses a fiber optic wand to convey light between the device and the tooth.
U.S. Pat. No. 5,739,915 describes as prior art a document-scanning system having a set of RGB light sources, a self-focus lens array (SLA) comprising a single row of rod lenses, and a single-row photosensor array. In operation, the light sources of each color are sequentially illuminated and light reflected from the document is focused by the lens onto the photosensor array. A set of electrical signals corresponding to each element of the array is produced by the array for each of the RGB colors. The RGB signals are then combined for subsequent color reproduction.
U.S. Pat. No. 5,838,451 discloses an apparatus for the measurement of spectral reflectance or spectral absorbance of an object or a material. The reflectance apparatus comprises multiple LEDs surrounding a photosensor, all mounted on a common substrate, and a lens for coupling light to and from the object.
U.S. Pat. No. 5,844,680 also discloses an apparatus for measuring and analyzing spectral radiation. It discloses three embodiments comprising: (1) multiple LED light sources with a single sensor, (2) a single light source with multiple sensors, and (3) multiple sources and sensors.
U.S. Pat. No. 5,851,113 discloses a system comprising a probe containing a plurality of optical fibers connected to a color measurement system. The patent describes various means of color measurement, including multicolored light sources (red, green, blue=RGB), and various analysis techniques.
U.S. Pat. No. RE 31,290 describes an imaging system comprising a rectangular photosensor array and a lens contained in a small probe connected to the system by a fiber optic bundle. Three light sources produce red, green, and blue light in sequence. Light is conducted from the sources through the fiber optics to the probe tip and reflected from the object of interest back through the lens to the array in the probe.
U.S. Pat. No. 5,766,006 teaches a system comprising an intraoral camera connected to a shade analyzer subsystem. The patent discloses a camera comprising either a single or a triple charge coupled device (CCD) array for capturing an image of the tooth in three (RGB) colors.
U.S. Pat. No. 5,760,929 discloses an image processing apparatus for discriminating colors and color patterns or boundaries in an RGB image signal and for generating signals indicating the color boundaries.
U.S. Pat. No. 3,986,777 describes a tristimulus colorimeter which measures the red, green and blue light reflected from a sample. The sample is illuminated through a probe by a light source having a satisfactory uniform distribution of light over the visible spectrum. Light reflected from the sample through the probe passes through a rotating color filter wheel, which is synchronized with a digital voltmeter, to a photosensitive diode.
U.S. Pat. No. 4,096,217 describes a method of using a tristimulus colorimeter in making artificial teeth.
Each of the preceding examples describes technology, apparatuses or methods for making color measurements or comparisons. However, none of them describes the invention of a small, hand-held and inexpensive colorimeter which can permit an operator unskilled in color analysis to quickly and objectively make consistent color measurements and comparisons.
An object of the present invention is to provide a high-resolution colorimeter system, utilizing solid-state opto-electronic technology, for measuring and characterizing tooth and prosthesis colors.
BRIEF SUMMARY OF THE INVENTION
The invention is a colorimeter especially suited for dental applications comprising a hand-held probe, similar in size to a dental drill, attached by an electrical cable to a small display module.
The colorimeter provides the capability for measuring the colors of a number of points along a line on the surface of an object such as a tooth. A measurement is made while placing the tip of the probe against, or in close proximity to, the surface of the object. The display module to which the probe attaches contains a microprocessor and provides a control, display and data interface to the operator. The display module can be adapted for fastening to the wrist of the operator thereby leaving both hands free to manipulate the probe and other tools. The colorimeter is particularly well suited for measuring the color of teeth in a dentist's office in preparation for making dental prostheses which accurately match the color of natural teeth. The colorimeter generates from a single measurement an array of color data points measured along a line on the surface of an object. From those data points, the processor can perform statistical analysis yielding a single color value, generate and display a color profile along a line, compare measured values with a preloaded table of values, or upload color data to a remote location for laboratory or manufacturing purposes. The colorimeter can also use variations in the color values measured along a line to identify boundaries of areas on a surface. For example, the color profile can be used to identify the gum line on a tooth.
As used herein, the term “color value” means any representation of a measured color. For example, it can be a single number or a symbol, or it can be a group of numbers or symbols such as three RGB ratios, a set of tristimulus values, or a set of statistical parameters representing a vector. A color value can also be represented by the result of a comparison of measured color values to stored color values.
The probe comprises multiple light emitting diodes (LEDs) for successively emitting light of different colors toward a surface, a linear array of light sensors for receiving light reflected from the surface, and a lens for directing light from the target to the array, all contained within the probe itself.
The LEDs are arranged in a line near the probe tip and coupled to the target via a light pipe. The LEDs emit preferably three—red, green and blue (RGB)—primary colors. The three colo
Delawter S. Brett
Emerson Gary
Franklin Brian
Wagner Gregg A.
Evans F. L.
LeBoeuf, Lamb, Greene & MacRae, L.L.P.
PocketSpec Technologies Inc.
Stanley Elizabeth
Strong Gayle L.
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