A crown (or cap) improves the strength and appearance of a tooth.
Why might I need a crown?
- Improve the appearance of a discolored or heavily restored tooth
- Strengthen a tooth at risk of fracture due to large fillings or trauma
- Repair teeth that are unrestorable by other means
Fillings restore the appearance of your tooth after a cavity or break. What they can't do is restore the original strength of the tooth. The job of a filling is to fill a gap and to look good doing it.
Teeth with large fillings are weakened and at risk of fracture. New fillings are adjusted out of the direct bite. The biting force is now transferred onto the remaining tooth. If the bite force is large enough and the remaining tooth small enough, fractures will occur from overloading.
This becomes a risk when
- The filling is greater than half the width of a tooth
- A cusp (the tall part of the tooth) has been removed
- A cavity at the gum line has undermined the tooth above it.
A Crown holds the entire top part of the tooth together, so that it cannot split under force. Another version of this is an onlay, which covers the biting surface without covering the sides of the tooth. The onlay still prevents fracture but has a more conservative preparation technique. More remaining natural tooth is always a good thing, and onlays are often a better solution.
That's a Crown in a nutshell, but read on if you want to learn more
How long will a crown last?
- The average lifespan is about 12 years. Failure of the actual crown is rare. The most common causes of crown failure are new cavities, pulpal disease (root canal or extraction) and gum disease. If well cared for there is no reason a crown should not last decades.
How is the crown prepared ?
- In the first appointment the dentist removes a thin layer from all around the tooth to make space for the crown. Crowns are done on teeth that have large fillings or fractures, which means much of what is removed is old filling material
- An impression of the tooth is made and sent to our lab, where the crown is made. In the meantime we cement on a temporary crown.
- When the new crown arrives, we carefully remove the temporary crown and permanently cement your new crown.
What is a crown or onlay made of?
Many materials are available, these 4 types of crown/onlay are used most often here at Pottsville Beach Dental.
- Bonded Porcelain ( EMAX or Lithium Disilicate)
- Milled Porcelain (Zirconia)
- Porcelain fused to metal
- Full gold
Bonded Porcelain (EMAX)
EMAX crowns and onlays have excellent esthetics. Done well they are indiscernable from natural teeth. EMAX is 3-5x stronger than traditional porclelains. The main advantage is the ability to bond the EMAX to the tooth, which further enhances the strength. One of the problems with older types of porcelain is their abrasiveness. Some types of porcelain can literally wear through the opposite tooth. The abrasiveness of EMAX is less than PFM or traditional crowns, but more than gold or zirconia. Although EMAX is extremely strong for a porcelain, it is not as strong as gold or zirconia.
Milled Porcelain (Zirconia)
Milled crowns offer good esthetics, but the crown is cut from a solid block of zirconia, resulting in fewer options for shading and color matching. It is the strongest porcelain, with a flexural strength 2.5X that of EMAX. The abrasiveness is more similar to natural tooth than EMAX but still more than Gold. The bond of Zirconia to tooth is less reliable than EMAX, and more akin to gold or PFM.
Porclelain Fused to Metal (PFM)
PFM crowns offer good esthetics, but PFM crowns can appear opaque because light does not shine through like all porcelain or natural teeth. The strength and fit are very good, but the abrasiveness is quite high. Zirconia is generally a better aesthetic choice, and the usual reason for using PFM is to match existing PFM crowns to create a uniform appearance.
Gold crowns are the strongest available material and require less removal of tooth structure. They are suitable for someone who wants a very durable restoration and is not concerned with aesthetics. The fit of a gold crown or onlay also tends to be superior to porcelain.