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How Whitening Works

Course Number: 657

The Basics: How we see color

To understand the principles behind oxidative whitening we must first consider the fundamentals of color vision2 – shown below (Figure 1) with the observation of a red apple.

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Figure 1.

Light (from sunlight, fluorescent or incandescent light bulbs etc.) projects on an object. This light contains a variety of wavelengths. Some light is absorbed by the object and some light is reflected. We see the reflected light. Reflected light is processed by the retina, which transmits the signals of the reflected light to the brain. Human beings see light as three sets of colors and combinations of colors – Yellow - Blue - Red –which are a collection of color families defined as the hue. The intensity of the color we see is defined as Chroma and is demonstrated by the shift from pink to crimson. Lastly, the colors we see are described in terms of lightness –a parameter defined as the value – which ranges from 0 (totally black) to 100 (totally white).

We must also consider that observed tooth color can also be affected by additional optical phenomena. This includes metamerism (color appears different in different conditions of light), opalescence (observed shifts in reflected and absorbed light based on wavelength), fluorescence (absorption of light and chemiluminescent transmittance of light at a longer wavelength) and translucence (the diffusion of light into a material to variable depths – and reflection back to the observer with variable scattering). An example of these phenomena acting in concert to affect tooth color is the bright white appearance of teeth in the blue light in a discotheque. Importantly, tooth color is also influenced by the background against which it is observed – this is a phenomena well known to those in artistic fields as simultaneous contrast. Simultaneous contrast is the reason some patients’ teeth appear whiter against different backgrounds of skin tone, gingival color or make up (e.g., red lipstick).

Figure 2 below shows examples of simultaneous contrast for a number of different color combinations. The insert block of color is exactly the same in each quadrant – but appear different.

Figure 2 - Simultaneous Contrast

With respect to tooth color, this means that skin tone and color of gingiva can have an impact on shades associated with teeth by professionals and individual patients.2-4