One of dentistry’s biggest challenges is matching the color of a single central incisor (aka your front tooth) so that your new crown looks natural. To understand why requires a little background on light and color.
As you may recall from high school science class, light carries color to our eyes. All the colors we see are the result of light either being reflected or absorbed by whatever object we’re looking at. All light contains every visible color in the spectrum, but we can’t see light at all until it is reflected off of an object. When light hits an object, some colors are absorbed into it. Those not absorbed are reflected back to our eyes as color.
Every material reflects light differently. Wood and metal, for example, absorb different amounts of light, so it’s a challenge to make one look like the other. Sometimes, under the right circumstances we can pull off an illusion that makes wood look like metal. In dentistry, we are always trying to create the illusion that dental materials such as porcelain, composites and acrylics are actually enamel, dentin and everything else that exists in natural teeth.
Color has three components: Hue, Chroma and Value:
• Hue is the color itself, such as red, green or yellow
• Chroma is the strength of the color
• Value is the degree of brightness or darkness (the amount of white or black)
In matching the shade of natural teeth, the most important component of color is Value. This is because our jaws are in the shape of an arch. The base of the arch is in the back of the mouth and the highpoint is in the front of the mouth. The midline, usually located between the central incisors, is the middle of the arch. Typically, this corresponds to the middle of your face.
As you can imagine, the farther a tooth is from the midline, the less its surface will be visible and the less light it will absorb. If the Value is matched very closely, the Hue and Chroma will blend under limited lighting, making it relatively easy to match the shade in the back of your mouth (the posterior) than it is in the front (the anterior) or what is referred to as the “aesthetic zone” that comprises your front six teeth.
In the aesthetic zone, Hue and Chroma take on a more important role, but once
again, Value (how bright the tooth looks) is still the top consideration. Because your teeth are all usually in the same color range (Hue), if the Chroma is close enough, the Value will cause our eyes to perceive the teeth to match. Even normal, natural teeth may vary in shade, but the Value causes our eyes to see them as the same.
In reality, however, no two eyes see any color exactly the same – not even your own two eyes! Try this experiment: Take a solid colored object and look at it in a lot of light. Then close your right eye and note the color. Now, open your right eye and close your left eye. Try this back and forth quickly a few times and observe that the color will look slightly different to each eye.
When observing a color, our brains actually merge the images produced in each eye so that what we see is an average. Next, try looking at the same object in very low light. The difference between the eyes will be less or not at all. If you can get the light low enough, you will still be able to see the object, but not the color. At some point, without sufficient light, we are only able to see in black and white.
In dentistry, this use of Value to blend to the human eye will work in almost every situation – except at the midline. That location is the spot where the most light is visible and where our brains will interpret the color most critically.
This explains why even the most skilled dentists and dental technicians can get a shade match on a single central incisor to look indistinguishable from a natural tooth in artificial light, but not in sunlight. Or why they can achieve a match in sunlight but not in incandescent light. Or in incandescent light not in florescent light. We can pull off the illusion, but not in every kind of light.
There are a few options available for matching the shade of single central incisors. One is to match the type of light in which the patient is most often seen. Depending on the amount of translucency in the adjacent central incisor, the choice of restorative material can be critical in obtaining a match. But the surefire way to obtain a match that will create the illusion in every kind of light is to include the adjacent central incisor and restore both with the same materials.
While the science of light and color is far too complex to describe in a single blog post, I hope that this explanation leads to a better understanding of what goes into creating the illusion of a natural tooth.