Crowns

A full crown is a casing that goes around the entire part of the tooth that is visible covering all of it from the biting surface right down to the gum line. 

The rule of thumb we use to decide if a tooth needs a crown is: If there is more filling material than remaining tooth structure holding this filling material then we seriously recommend placing a crown over it – the 50/50 rule. 

Before a crown can be placed the tooth has to be made smaller so the casing can be fit over it so that it will fit in with the teeth on either side as well as with the tooth above. After the tooth is made smaller a mold is taken and a temporary crown is placed over the tooth. The mold goes to a dental technician who pours plaster into the mold to create a copy of the teeth. The copy of the prepared tooth is then used to fabricate a crown out of 20 carat gold, or creates a gold core of 20 carat gold and fuses porcelain to it (pfm – porcelain fuse to metal), or makes it entirely of porcelain or zirconia.

Present costs for a single crown are around $1,100. Included in this is the dental technician charge, often referred to as the lab cost, which is around $400.

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Crown type used depends on the location of the crown in the mouth,
although there are those that like to flash some gold

Teeth are small structures formed mainly from calcium. They are the hardest things in the human body.  But they are also brittle and do some flexing when put under loads. When we chew they can be subjected to forces of 500 pounds per square inch and more (3,500 kilopascals for those of you who are metric).  This is hard enough on any tooth, never mind the repaired teeth. If a tooth has been damaged and has had parts of it replaced by filling materials there is less of it to resist these pressures. Plus the remaining tooth structure will flex differently than the filling material it is supporting.  A crown that covers the entire tooth and then some resists these forces and holds the tooth together.

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Crowns are expensive but long lasting
The average length of a crown preparation appointment is one hour. Then there is a custom fabrication of the crown using expensive materials by a third party who has very specialized skills.  A full gold crown will usually need a week to be fabricated. A white crown will usually take two weeks. The patient then has to come back usually for a half hour appointment to have the crown cemented.

Crowns are very long lasting 
If a crown has a good foundation cemented it can last for decades. It can lengthen the life of a tooth indefinitely whereas without one a heavily filled tooth will be at much higher risk of fracturing and being lost or needing a root canal. The other problem with heavily fractured teeth is that they always break on the weekend or when you are travelling away from home.

Crown Failure
The weak spots for a crown are the margins which is the outside edge of it where it joins with the tooth. There is always a microscopic gap. This is not an issue unless the mouth is exposed to too much sugar or the mouth becomes excessively dry to reduced saliva production due to medications or saliva gland cancer. This microscopic gap/margin becomes vulnerable to bacteria populating this area and eventually tunneling under the crown and destroying the tooth below. Once the bacteria have invaded the tooth under the crown they will do a lot of damage very quickly. A loose crown needs immediate attention.

Clenchers and Grinders are always terrifying for us dentists. They can destroy our best repairs in short periods of time. 

NOTE: Teeth that need crowns have often been subjected to a certain amount of trauma due to bacteria invading and the dentist removing and replacing the damaged tooth with filling material. This may have happened several times before the crown treatment is done. The pulp inside the tooth may have been compromised by these repeated incursions and the crown treatment may be the final straw to shove it over the edge. A root canal might be required after all this.  This however, is unpredictable.

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