October, 2002

Dear Dr. Mady: I recently had a root canal done on one of my teeth and my dentist said that I will need a post and crown. What is a post for and is it really needed?- Dennis G.

Dear Dennis: After any tooth has had root canal therapy performed on it, it usually will require some sort of dental restorative treatment, for strength and longevity. Many teeth that require root canal treatment already have large fillings or portions of the tooth missing. This may have been caused by decay or damage, but regardless, a tooth in this position will need to be fully functional again.

Once a tooth has had endodontic therapy, it is weakened from the roots being reamed out and actually becomes brittle. To strengthen the tooth, your dentist will recommend a crown or a one in combination with a post. A post is a pin-like rod that is usually fabricated from titanium or precious metal or a composite fibre material. It is placed down into the root(s) after the root has been prepared and is then seated and cemented into position. Then your dentist can build up the tooth with some sort of filling or core material and the crown can later be placed over this post and core. A post can even be created from cast metal and made in conjunction with the crown or even as part of it.

A root-canaled tooth with a post can be compared with a house being built on sand. If the foundation is sand, as soon as a storm passes through, the house will wash away. If a root canal is performed and any significant tooth structure is gone from your tooth, it will not withstand the test of time, even if a crown is placed. The post is basically the foundation in this case. Posts are usually only placed in those teeth which have extensive portions of their natural tooth structure missing. This may be the case for you.

The greater the amount of tooth that can extend into the center of the cap or crown, the better the prognosis will be. In cases where there is not much clinical crown remaining, the post acts as an anchor for the filling material to assist in retention of the final crown.

The process is fairly simple. Your dentist will simply remove a portion of the gutta percha (rubber-like root canal filling material) from the root(s) of the tooth and try to leave approximately five mm in the root to keep the seal at the root apex intact. The inside of the root is shaped so it eventually has parallel walls (tapered walls in the case of cast post), then the post is secured in place with a dental cement. Your dentist will then evaluate your specific situation to help him determine which type of core material to use around the top of the post. After the crown prep is completed an impression is taken that will be used by a lab technician to fabricate a metal, porcelain fused to metal, or all-ceramic crown. If a cast post is used, an impression will be taken for it at the same time. This crown will bring the tooth back to a size and shape more similar to what it originally was.

The final crown will not only strengthen and protect the tooth, but will considerably improve the esthetics of the tooth. Also it seals up all the margins of the tooth on solid tooth structure and not on filling material, when cemented in place. It prevents bacteria from invading the inner aspects of the tooth, so it can also be described as a barrier. It sounds like your dentist has given you an excellent treatment option for the situation at hand.

This column is reprinted with the permission of the author and The Windsor Star. "Ask the Dentist" is written by Windsor dentist (and ECDS member), Dr. David Mady Jr.. The column appears the first Thursday of each month in the Windsor Star. Readers with questions can write to "Ask The Dentist", c/o The Windsor Star, 167 Ferry St., Windsor Ontario, N9A 4M5



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