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2025-02-11
In recent years, with the development of maxillofacial prosthodontics, the simulation of prostheses has become the goal of today's prosthodontics. Patients are no longer limited to the functional application of prostheses, but have further improved their requirements for aesthetics. Colorimeter is a tool that can quantify the color of the surface of an object. The objectivity and accuracy of the instrument's color measurement lay the foundation for its application in the field of prosthodontics. This article introduces the application of colorimeter in the field of oral prosthodontics.
According to the color representation method of the International Commission on Illumination, for any given object color, its characteristics can be expressed by tristimulus values X, Y, Z or X10, Y10, Z10 chromaticity coordinates. The observer can draw a tristimulus value curve based on the spectral tristimulus values. The X, Y, and Z curves represent the amount of red, green, and blue primary colors required to match the spectral stimulus values of each wavelength. In 1964, the X10, Y10, and 10 spectral tristimulus values were supplemented. Since the latter has a larger field of view, higher accuracy in color discrimination, and is in line with people's actual observation of color, it is widely used.
Color measuring instruments are tools that objectively measure color based on the visual characteristics of the human eye. There are many ways to classify color measuring instruments. They can be divided into spectroscopic type and photometric integration type according to the size of the spectral band of the receiver's instantaneous response; they can be divided into stable light source type and pulse light source type according to the characteristics of the bright light source; they can be divided into single-channel spectral scanning type and multi-channel spectral fixed type according to the arrangement of the receiver; they can be divided into non-compensated type and introduced compensation type according to the different drift processing methods; according to the structure, there are desktop fixed probes, desktop movable probes; there are also pocket-sized and portable classification methods. Here, this article only discusses the two most commonly used categories, namely spectroscopic color measuring instruments and photoelectric integration color measuring instruments.
1. Spectrophotometric colorimeter
Also known as spectral photometric colorimetric instrument or spectrophotometric colorimetric instrument. This type of instrument does not directly measure the three stimulus values of the color itself, but measures the spectral reflection or transmission characteristics of the object, that is, the spectral radiance factor or spectral transmittance of the object is measured, and then the standard illuminant and standard observer recommended by the International Commission on Illumination are selected to calculate the three stimulus values of the color, chromaticity coordinates and reflection spectrum in the visible light band through the integrating sphere. Spectral photometric colorimetric instruments are mainly composed of two parts: a monochromator and a detector. The monochromator plays a role in splitting light, and there are two types: a prism monochromator and a diffraction grating monochromator. Spectrophotometric colorimetric instruments are the mainstream equipment in color measurement, with high measurement accuracy. Traditional spectrophotometric colorimetric instruments are complex in design, have many parts, are large in size, not durable, have unreliable data, and are more expensive than other types of products. This greatly limits its use and is generally only suitable for laboratories. However, with the continuous advancement of technology, the existing spectrophotometers are small, simple, lightweight, inexpensive, and have unique features and excellent performance. This also provides a guarantee for color measurement in the oral field.
2. Photoelectric integral color measurement instrument
Also known as photometric integration colorimetric instrument. This type of instrument simulates the tristimulus value characteristics of the human eye and directly measures the tristimulus values of color using the photoelectric integration effect. This type of instrument uses color filters to filter the spectral response of the photodetector used to make it consistent with the International Commission on Illumination standard observer; at the same time, the illumination source is also filtered to make it consistent with the relative spectral power distribution of the standard illuminant. Photoelectric integration colorimetric instruments use photoelectric integration elements with specific spectral sensitivity to calculate the tristimulus values or chromaticity coordinates of the object color based on the instrument response value proportional to the color. The main purpose of this instrument is often to compare the difference between two similar colors. In a geometric sense, it is to measure and express the "distance" between adjacent color points in the color space (color set), that is, the degree of difference between the two colors must have the highest possible degree of conformity with the difference in subjective perception. The overall optical conditions of the photoelectric integration instrument should meet the Luther conditions, but in actual color filter correction, it is impossible for researchers to make the instrument completely meet the Luther conditions, and can only meet them approximately. The degree of approximation determines the accuracy of the instrument. Photoelectric integrator instruments have errors in their measurement principles, so their accuracy is naturally not as good as that of spectrometers.
1. Measurement of natural tooth color
As patients' requirements for the beauty of dentures continue to increase, domestic and foreign scholars have conducted a lot of research on the color of natural teeth. Studies have shown that the color parameters of natural teeth decrease in brightness and turn yellow with age, but the red-green phase changes are not completely consistent in different parts of different teeth. Due to the use of color measuring instruments in tooth color measurement, people not only obtain accurate values of chromaticity that cannot be achieved by the naked eye, but also summarize the distribution law and related factors of tooth color through statistics of values, which provides guidance for color comparison in future clinical work; in addition, it also finds out the shortcomings of existing color plates and restorative materials, which points out the direction for the future production of more comprehensive and authoritative color plates and restorative materials with better simulated colors.
2. Measurement of gum color
With the research on dentures, the color of gums has also received increasing attention. Domestic and foreign scholars have successively applied different methods to test the color of gums. Initially, people's research methods on gum color mainly relied on naked eye observation, but this method has a certain degree of subjectivity and the description of color is not accurate enough. With the continuous development of colorimetry and the emergence of a large number of color measuring instruments, people began to use color measuring instruments to measure the color of gums. This measurement method is more objective and accurate than the value obtained by naked eye observation. Although the colorimetric value obtained by photographing the gums with a camera and then processing them is objective, there will definitely be deviations in the colorimetric values of photos taken by cameras of different brands and in different environmental backgrounds. In view of the above reasons, using a color measuring instrument to collect the color of gums is the most feasible and reliable method.
3. Measurement of maxillofacial skin color
Defects in maxillofacial soft tissues caused by maxillofacial tumors, trauma, etc. can cause great distress to patients. In the past, there were few studies on the color of oral and maxillofacial soft tissues, so the simulation of prosthetic restorations was poor. This made it necessary to establish a database of normal maxillofacial skin color and produce prosthetics with better simulation in color. The use of colorimetric instruments to collect data values of maxillofacial skin color can objectively and directly reflect the color of people's skin, laying the foundation for the development of prosthetic materials suitable for the Chinese population.
