Cosmetic Dentistry Blog Cosmetic and General Dentistry Questions Answered

June 20, 2019

My crown on my front tooth isn’t staying on


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Dr. Hall,
I read your last answer about the crown not staying on. I have a root canal in tooth # 10 (upper left lateral incisor). The crown stayed on for about ten years. Then, about 1 1/2 years ago, my dentist replaced it. During the time since the new crown was placed, it has come off several times and been recemented. It never has felt really secure. Do you think there is hope for the crown to stay on if re-cemented? There isn’t really much to cement it to.
Thanks, Evelyn from California
 
Evelyn,

There should be a way to get this crown to stay on better. The problem is probably in the design of the crown preparation, and not in the strength of the cement or bonding material. If that’s true, it would mean you need a new crown for this to stay on. That’s just a guess. But let me give you an explanation of what can be done when a tooth has had a root canal treatment and there isn’t much tooth left to hold on to.

I wrote in an earlier post that the main reason crowns come off is that they aren’t prepared with proper retention form. Now, if there isn’t much tooth structure left, it isn’t possible to properly prepare the tooth. So what I would do to improve the retention would be to cement a fiberglass post deep into the canal. It needs to be a post with some flexibility to it, or under the stress of oral function the post could fracture the tooth root. I would then bond to the tooth and the post some core material.

Here are photographs of a case of a crown on a front tooth in a situation like this, courtesy of the dental journal Dentistry Today.
close-up photo of a broken down lateral incisor tooth with a fiberglass post fitted into the root canal spaceIn this first photograph, some of the root canal filling material has been removed and a fiberglass post is fitted into the canal. The post needs to go deeply into the tooth, but not so far as to require removal of all of the root canal filling material. About 2/3 of the length of the tooth would be good.

A close-up photograph of the same lateral incisor, with core material added and the core trimmed into a crown preparation.Then the post is bonded into the canal and a core material is built up. Composite is usually used for both the bonding of the post into the canal and the core. That composite is then shaped into a conventional crown preparation as shown here.

Built up like this, the tooth should be able to retain a crown easily. I will note that there has to be some tooth structure remaining. The amount of tooth remaining in this case is about the minimum amount needed. If a front tooth, say, is broken off level with the gums, and the retention has to come completely from the post, it won’t work. Normal oral function will create twisting stresses on the post and will eventually dislodge it.

I hope this is helpful.
Dr. Hall

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About David A. Hall

Dr. David Hall was one of the first 40 accredited cosmetic dentists in the world. He practiced cosmetic dentistry in Iowa, and in 1990 earned his accreditation with the American Academy of Cosmetic Dentistry. He is now president of Infinity Dental Web, a company in Mesa, Arizona that does complete Internet marketing for dentists.

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