Basic principles and techniques in colorimetry

Basic principles and techniques in colorimetry

1. Introduction :

With the evolution of cosmetic dentistry, the patient’s complaints, the practitioner is faced with the challenge of reproducing a natural appearance of his restorations for this the choice of color is fundamental to achieve the integration of the latter

2. Definition of color:

Color is a visual perception of the spectral distribution of visible light. Its description is made according to different approaches (artistic, physical, physiological, etc.). It is a sensation that originates from the stimulation of specialized photoreceptors, the cones and rods, located on the retina.

3. Basic color parameters:

The color is defined by three parameters:

• the hue (or chromatic tone),
• saturation
• the brightness .

1. The shade:

Hue or chromatic tone is the quality by which we distinguish one color family from another

It represents the wavelength that is mostly reflected by an object.

It corresponds to different colored sensations such as blue, green, red, yellow, etc.

2. Saturation:
   • Saturation is the quality by which we distinguish a bright color from a pale color, it is the quantity of pigment contained in a color (we speak of color intensity)
   • It represents the density or intensity of a color
   • Saturation generally increases from the free edge to the neck of the teeth although the brightness is almost identical
3. Brightness:

Brightness is the quality by which we distinguish a light color from a dark color.

• Black has zero brightness and white has maximum brightness.
• Brightness is easily appreciated by removing the chromaticity of the colors

4. Additional color settings
   1. Opalescence

Opalescence is the optical property of dental hard tissues characterizing their ability to selectively transmit certain lengths of white light and reflect others.

2. Fluorescence:

Optical property of dental hard tissues characterizing the capacity to absorb light photons to re-emit them with a different wavelength upon returning to the initial energy state

Fluorescence makes teeth appear brighter in daylight

3. Translucency:

To define translucency, we must also define opacity and transparency.

• Transparency : A material is transparent if it allows the passage of light rays.
• Opacity : A material is opaque if it does not allow light rays to pass through it, so nothing can be perceived through it.
• Translucency : a material is translucent if it also lets light rays pass through but it diffuses most of these rays: we can see an object through it but we cannot distinguish it perfectly.

4. Pearlescent effect:

The pearly effect is a surface effect that some young teeth exhibit. It is shiny, slightly metallic, comparable to the iridescent reflections of aragonite crystals and certain mollusk shells.

5. Surface condition:

The surface microgeography of natural teeth directly influences color perception because it conditions the percentage of reflected light flux compared to the percentage of light flux transmitted or absorbed by the tooth

• The rougher the surface of a tooth (young tooth, little worn), the more light is reflected and then results in a shiny and bright surface condition.
• On the other hand, the smoother a tooth is (old tooth, worn by abrasion and/or erosion), the more the incident ray gives rise to a single reflected ray, which reduces the brightness of the tooth.

6. Characterization:

The characterizations represent particular and punctual colored aspects

5. Optical properties of the tooth

• The color of the natural tooth will be determined by the three types of tissue that compose it: enamel, dentin and cementum.
• It is the location and composition of these tissues that will define the optical behavior of the tooth.
• Enamel is a translucent tissue. It is largely responsible for the brightness of the tooth.
• Dentin is more opaque , it will determine the shade and saturation of the tooth.
• When we observe a wear section of a tooth, we notice that the tooth is more saturated in the center and lighter towards the outside.
• The transparent layer is always located as a sub-layer under the surface enamel. It acts as a conductor of light. The light circulates under the enamel.

6. Determination and transmission of color:
   1. Visual survey:

Visual sampling involves comparing the tooth adjacent to the restoration to different shade samples until the closest match is found. The protocol for choosing the final color varies depending on the brand and shade guide used.

The choice of shade should ideally be made in conditions of natural light, ideally that of the sun between noon and 3 o’clock with a northern exposure and approximately 3/5 of scattered white clouds, the latter are difficult to obtain in the dental office, hence the use of assisted visual survey

2. Assisted visual survey:

To improve the accuracy and reliability of visual surveys, some manufacturers have developed assistance tools:

• Calibrated lamps : provide a calibrated and continuous light source.
• Camera.

3. Instrumental survey:

In order to limit the subjectivity and imprecision of simple or assisted visual surveys, different tools can be used ( ). These are colorimeters and spectrophotometers , an intraoral optical camera and photographic analysis software.

The performance of these systems can be evaluated according to three criteria:

• precision , which is the ability to give measurements free from accidental errors. It defines the dispersion of results. A high-fidelity device gives reproducible measurements but which may be far from the true value;
• accuracy , which is the ability to give results that are not tainted by error. A highly accurate device gives measurements close to the true value but which may be dispersed between them (poor fidelity);
• accuracy, which is the ability to give measurements that are both faithful (close to each other) and accurate (close to the true value). This is the main quality sought.

Colorimeters are the first instrumental systems for determining color to have been used in dentistry. The spectral analysis of light reflection is done through three filters (red, green and blue) which allow a color to be defined by its trichromatic coordinates.

These colorimeters can be used in the office to determine the color of teeth or in the laboratory to check the color of prostheses.

The same applies to spectrophotometers, which carry out a spectral measurement of the luminous flux transmitted or reflected under their own light source which is a visible polychromatic incident light.

The measurement is made using optical fibers, through a central spot that must be positioned properly on the dental surface to be analyzed. The tool is ergonomic, and its use is simple and quick. Its fidelity (96.4%) and accuracy (92.6%) are high, which is not the case with all systems.

Conclusion : Knowledge of fundamental color parameters and tools

enabling it to be determined allows the practitioner to obtain aesthetic restorations which are as close as possible to the appearance of natural teeth .

Annexes:

Shade selection sites: http://www.scadent.org/news/free-color-training http://www.toothguide.de/default.aspx

Basic principles and techniques in colorimetry

  Wisdom teeth can cause infections if not removed in time.
Dental crowns protect teeth weakened by cavities or fractures.
Inflamed gums can be a sign of gingivitis or periodontitis.
Clear aligners discreetly and comfortably correct teeth.
Modern dental fillings use biocompatible and aesthetic materials.
Interdental brushes remove food debris between teeth.
Adequate hydration helps maintain healthy saliva, which is essential for dental health.

Basic principles and techniques in colorimetry