Reconstruction of a three-dimensional optical model of tooth tissue
Quite often, we are faced with the problem of which restoration technique to choose for defects in the cutting edge of the frontal group of teeth. Of course, the type of restoration is dictated by the volume of the fraction. You can choose a direct or indirect recovery technique. But the problem lies not in the choice of design, but in the interpretation of color and the recreation of all elements of the tooth. Natural teeth have a very complex three-dimensional optical structure.It is almost impossible to recreate it in full.
Enamel and dentin tooth have different optical characteristics. Light transmission is one of the most important parameters. On how you managed to recreate a three-dimensional picture of the transparency and opacity zones of a natural tooth in your restoration, its integration with the remaining tissues of the patient’s tooth depends.
If your restoration is not sufficiently opaque, it will always have a gray tint, no matter what material you work on.
Sometimes, some dentists, when discussing some filling material, pronounce the phrase: “Yes! The material is not bad, it is well polished, but it is somehow gray! ”I can say with confidence: this is not a gray material, and the dentist simply did not understand the optical properties of the tooth material and tissues. No less disappointment can be experienced if the restoration is too opaque. Clear boundaries of the restoration are unlikely to please the patient.
The most translucent enamel. It covers the entire tooth and has the largest thickness in the incisal region and on the proximal surfaces. If you look closely, it is easy to see that the enamel is heterogeneous and has different light transmission in different areas. This is due to its structure. Transparent enamel prisms alternate with opaque interprism matter, and their spatial arrangement affects the refraction and diffusion of light passing through the enamel. Another factor affecting the light transmission of enamel is the degree of its mineralization: the higher the mineralization, the greater the light transmission, and vice versa.
As we know, a low degree of mineralization is characteristic of young teeth. The enamel of the teeth of young patients is characterized by the presence of a large number of different characteristics, usually white, this increases their brightness and reduces light transmission.
With age, the degree of mineralization of enamel increases, it becomes glassy with a gray or yellow tint. In addition, under the influence of the abrasion of the cutting edge of the enamel and further parts of the dentin, “enamel windows” appear, which visually give the teeth even greater light transmission.
The last factor affecting the light transmission of enamel is the microtexture of the teeth. In order to clearly demonstrate how the surface texture of enamel affects its optical properties, we took a small glass object. As you can see, it is transparent.
In order to create any irregularities on it, its surface was treated using a sandblasting machine with 50 micron aluminum oxide. The surface of the glass became opaque, and the light transmission of the glass decreased noticeably, but the brightness of the object itself increased, for our opinion it turned white, although the internal structure of the glass did not change.
Then we took a light source and directed it at the object. In the first case, light freely passes through the object. In the second case, the object partially absorbs light, partially reflects, partially transmits, but scatters most of the light.
See how the optical properties of glass fundamentally change, as soon as we change the smooth surface to a rough one. The same optical processes occur in tooth enamel. The enamel of the teeth of older people is thin, transparent, vitreous, it practically does not absorb (not to be confused with absorption) and does not scatter light, so it seems gray. Enamel of young teeth, by contrast, due to its texture, scatters and absorbs light well.
Another property of enamel is opalescence. The effect is named after the natural mineral opal. The optical property of this mineral is to reflect mainly short waves (blue) and transmit long waves (orange-red), so if the light falls on the opal and we see the reflected light, it looks like blue-blue, and if the light passes through the mineral, it looks like orange red.
As a rule, we can observe the effect of opalescence of enamel in places where the tooth enamel has the greatest thickness, that is, on the cutting edge.