Aesthetic dentistry imposes several demands on the artistic abilities of the dentist and the technician, therefore knowledge of the underlying scientific principles of color is essential.
“Color is the result of the physical modification of light by colorants
as observed by the human eye and interpreted by the brain”
Color combination not only improves aesthetics but also makes the restoration appear natural and attractive. Color cannot be perceived without light, which is a form of electromagnetic energy visible to the eye.
Perception of color
As light enters the eye through the cornea and lens, an image is focused on the retina. The amount of light entering the eye is controlled by the iris, which dilates or constricts depending on the level of illumination. The retinal rods and cons can adjust the variation of light intensity.
Quality of Light
The quality of light source is the most influential factor when determining tooth shade.
The ideal light source is natural light, occurring around mid-day for accurate color comparison.
The time of the day, month and weather conditions affect the color of sunlight. If the light source changes, then the light reflected from an object changes too; in that case, a different color is perceived. The absence of ideal conditions has led to the use of artificial lighting for color matching. The light source that approximates standard daylight is ideal for shade matching.
Three dimensions of color
Color is usually described according to the Munsell color space in terms of hue, value, and chroma.
Hue is the attribute of a color that enables the clinician to distinguish between different families of color, whereas value indicates the lightness of a color. Chroma is the degree of color saturation.
When color is determined using the Munsell system, value is determined first followed by chroma. Hue is determined last by matching with shade tabs of the value and chroma already determined.
Properties of Colour
Human teeth are characterized by varying degrees of translucency, which can be defined as the gradient between transparent and opaque.
With increased translucency, light is able to pass the surface and is scattered within the restoration.
Fluorescence is the absorption of light by a material and the spontaneous emission of light in a longer wavelength. In a natural tooth, it primarily occurs in the dentin because of the higher amount of organic material.
Opalescence is the phenomenon in which a material appears to be of one color when light is reflected from it and of another color when light is transmitted through it.
The change in color perception of two objects under different lights is called metamerism.
Measurement of Colour
• Manual method: Shade guides
Tabs of similar hue are clustered into letter groups while chroma is designated with numerical values (1-4).
• Instrumental method: Colorimeters, Spectrophotometers and Spectroradiometer.
Shade Selection is a procedure which provide patients an aesthetic restoration that harmoniously blends to the patient’s existing dentition. Clinicians often lend up with compromised restoration because they encounter difficulty in interpreting a multi-layered structure of varying thickness, opacities and optical surface characteristics.
• Early shade guides were derived from tooth colors that were considered pleasing rather than from the distribution of shades found in the general population.
• Clark introduced a custom shade guide in 1931 based on visual assessment of human teeth, recorded in Munsell Hue, Value and Chroma.
• A new generation of shade guides has been developed to address these deficiencies.
• Shofu offered the Natural Color Concept while Vita introduced a 3-dimensional shade guide system (Vita 3D-Master).
Guidelines for Visual Shade Matching
- Shade Matching should be made under balanced lighting and in an appropriate shade-matching environment (with grey colour wall/ cabinets).
- Remove bright colours from field of view that influences the shade matching e.g. makeup, tinted eye glasses, lipstick and bright clothes.
- The teeth to be matched should be clean. If necessary, stains should be removed by prophylaxis.
- Evaluate shade under multiple light sources to avoid problem of metamerism (e.g. natural daylight and fluorescent light).
- Shade matching should be made at the beginning of a patient’s visit. Tooth colour increases in value when the teeth are dry.
- The patient should be viewed at eye level so that the most colour-sensitive part of the retina is used.
- A viewing working distance is approximately 25 cm.
- Shade matching should be made quickly (less than 5 seconds), with the shade tab placed directly next to the tooth being matched. The dentist should be aware of the eye fatigue, particularly if very bright fiber optic illumination has been used.
- The dentist can rest eyes between viewing by focusing on a neutral gray surface before a matching, to balance all the colour sensors of the retina.
Limitations of shade guides
• Does not cover the complete color space of natural teeth color.
• Shades are not systematic in their color space.
• Lack of consistency among the individual dentist in matching colors.
• None of the commercially available shade guides are identical.
• Quality control issues regarding color mismatches of shade tab and porcelain batches from the same manufacturer.
• Limitations of the instrumental method
• Translucency mapping is inadequate.
• Positioning of the probe or mouth piece seems to be critical to the repeatability of the measurement.
• Limited area is measured.
• Designed to measure flat surfaces.
• Prone to edge loss effects
• Cosmetic and bright colored clothes should be removed.
… OTHER Limitations of shade guides
- Fail to account for the variability found in natural teeth, e.g. fluorescence, opalescence, translucency, enamel thickness, and objectivity.
- Effects of surface texture on light reflection.
However, there are special lights that are colour corrected to emit light with a more uniform distribution of colour that can be utilized, e.g. Optilume TrueShade.
Instruments Used for Shade Selection
A trichromatic colorimetric measurement tool that provides an objective assessment of color characteristics from light passing through the primary filters of red, green and blue. It simulates the way the human eye perceives color.
– Detector, signal conditioner and software
– 3 or 4 photo-diodes with filters
3 principle elements: a standard light source “D65”
– Means to direct the light source to an object and receive the light reflected or otherwise returned from the object.
– Determines the intensity of received light as a function of wavelength.
– Provide most accurate color measurements.
Note: [D65] is intended to represent average daylight and has a correlated colour temperature of approximately 6500 K.
Shade Guides with Technology
Vita EasyShade® V
The VITA Easyshade V digital spectrophotometer was developed for precise, fast and reliable shade determination of natural teeth and ceramic restorations.
•First system to combine digital color imaging and colorimetric analysis
• Handheld device with fiber optic cable, halogen light source
• Image recorded on flash card hence no computer required
• ShadeScan software for shade and translucency mapping in basic Vitapan classical shades
The digital shade matching technology that allows totally accurate evaluation of spectral data, unaffected by light sources in the surgery or other ambient light.
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