Dental crowns have been a mainstay in dentistry for the last hundred years. In order for a crown to stay on (retention) it needs to have sufficient height of the remaining tooth structure to cement to. In addition, technologies of the past only involved porcelain fused to a metal substructure. While this technique is still used today, obtaining an acceptable aesthetic outcome involves placing the margins of the crown under the gum tissue. Anytime we place a margin of a restoration “under” the gums, we invite other problems. These include but are not limited to:
- Swollen gums
- Bleeding gums
- “Bluish” gums
- Difficulty in cleaning the interface between the crown and the tooth
- Extreme difficulty in accessing the fit of the crown under the gum
- Decay in and around the margin of the tooth.
With the advent of the newer bonded ceramic (porcelain like) restorations we are able to do two things. First, we are able to effectively place a bonded “onlay” on the tooth. An onlay allows us to remove less… and in certain cases, substantially less… tooth structure. We are able to “tooth bank” this remaining tooth structure that can be made available at a later date… hopefully years from now. The second advantage is the newer alumina and zirconia crowns have “more” translucency (but not as much as all porcelain) than the metal substructure found in the porcelain fused to metal crowns.
Significance of a non-metal substructure for dental crowns
The significant nature of a non-metal substructure is two fold. First, is the obvious lack of a dark metal color or edge to the crown. The second and just as important is the “translucency” that a non-metal substructure provides. A metal substructure with porcelain bonded on top blocks the flow of light through the tooth. The tooth acts like a fiber optic unit and some light naturally goes through the tooth. This effect makes the tooth look vital and life-like. When you completely block out the light, the underlying root surface looks gray. While the margin on the porcelain fused to metal crown is made entirely of porcelain (in some instances) that interface still looks gray due to the lack of translucency.
Bonded restoration and porcelain -like” substructures are allowing dentist to provide much more natural looking restorations and is some instances, allow us to remove less tooth structure. A small metal margin is esthetically acceptable on a tooth way back in your mouth but… as you move forward… aesthetics become a greater and greater concern. Bonded restorations help us solve or mitigate some of these problems.