The dentist and dental patient will need to reach a consensus regarding the color change that the new porcelain veneers will be expected to make. More than likely this topic was at the top of the patient's questions list that they brought with them to their initial consultation appointment and has already been discussed. If so what is needed now is for the dentist to collect and record tooth shade information so they can communicate to the dental laboratory the color change that is sought.
Before we continue we should explain some of the optical properties associated with teeth and how these properties help to generate what people consider a normal tooth appearance. Teeth are not solid enamel but instead a tooth's enamel is just an outer encasement. When light strikes a tooth it penetrates into the tooth's translucent enamel layer and is then reflected back out when it strikes the more opaque tooth structure that lies underneath (tooth dentin). It is this manner of handling light that gives a tooth its characteristic luster.
The glass-like nature of porcelain veneers allows them to mimic this same type of light handling effect. Because a porcelain veneer is translucent light can pass through it just like it does with tooth enamel. This light will then be reflected back out when it strikes the opaque layer of cement that lies underneath the veneer. The net effect is that the porcelain veneer generates a lustrous enamel-like appearance.
In comparison dental veneers that are created using dental bonding (dental composite) will not generate an enamel-like luster to the same degree. This is because dental bonding is only semi-translucent. When light strikes dental bonding a great portion of it will be reflected directly off the bonding's surface. There is less internal penetration and reflection of light, and therefore a less lustrous appearance is created.
The dentist will want the porcelain veneer to generate as much translucency effect as is possible (so it looks life-like and natural), yet be opaque enough to adequately mask the color of the tooth structure that lies underneath (so a color change can be insured).
The dentist will relay information to the dental laboratory technician about that color that is the end goal of the dental treatment. They will also need to provide the dental technician with a shade value representing the color of the tooth structure that will lie underneath the veneer and needs to be masked. The degree of difference between these two colors will allow the dental technician to gauge what amount of veneer opaqueness will be required to accomplish the desired color change.
We're getting a little ahead of ourselves here but there is yet another factor that will play a significant role in the final color of a porcelain veneer. This factor is the shade of the cement that is used to bond the veneer into place.
As we stated previously, light will pass into and through a porcelain veneer and then be reflected off the more opaque cement layer that lies underneath it. When light strikes the cement certain portions of the light's spectrum (certain wavelengths of the light) will be absorbed. Those portions of the light's spectrum that have not been absorbed by the cement will be reflected back out of the veneer and constitutes that light that our eyes see and interpret as being the tooth's color. (This is the normal way physics operates and it why we see different objects as being different colors.)
So when a dentist places a porcelain veneer, no matter what shade the veneer is, the dentist has a very good chance of being able to tweak its precise final coloration by way of changing the shade of cement (assuming that the veneer itself is not too opaque). And in fact evaluating the way
different shades of cement can affect the color of a veneer can be an important part of the try-in phase of placing porcelain veneers.