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.

December 9, 2016

Should my dentist grind on my porcelain crowns?


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Dr. Hall,
Earlier this year I got porcelain crowns on my 2 front teeth. One came loose and fell off. I had it “cemented” back on at the dentist & she ground down the porcelain to correct the bite after it was placed. Less than a week later the back side of my crown broke off where the bite adjustment had been made. What do you suggest? Should porcelain crowns ever be ground on or does this weaken them?
– Cheri from Minnesota

Cheri,
When you get a new porcelain crown, it isn’t uncommon for the dentist to have to adjust the crown to your bite, which is done by grinding on it some.
Having said that, something isn’t right about your experience here. Here are the three things that trouble me:

• First of all, one of the crowns came loose. This isn’t something that should be happening to a permanently cemented crown. Something wasn’t done right for a new crown to be falling off that soon.
• Second, the bite should have been adjusted when the crown was first placed. This is strange that the bite has to be adjusted after it is recemented. Something went wrong in the recementation process. The recemented crown must not have gotten back on straight for it to require new adjustments.
• And third, of course, you had the back of the crown break off. This wouldn’t happen unless the porcelain was ground so much as to be dangerously thin.

The fix is to have this crown replaced. But I would go somewhere else for this. I have real concerns about your current dentist being able to get this right. Oh, and she should compensate you for having to do this.

– Dr. Hall

For information on why crowns fall off, please see my earlier post, “The main reason your crown probably fell off.”

Do you have a comment or a question or anything else to add? We’d love to hear from you. Enter your comment below.

Click here to ask Dr. Hall a question of your own.

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.

August 11, 2016

This dentist does a really fast crown preparation


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Hi Dr. Hall,
Should I consider leaving my current dentist? When I first met my dentist, I was amazed a how incredibly fast he could trim down a tooth for a crown. It seemed like less than ten seconds. However it now seems as though he shaved some teeth down too far. Two of his crowns have fallen out twice, and there does not seem to be much tooth left to hold them. Could it be that he was working too fast and took too much off of the existing teeth?
I am not planning on suing but I cannot afford to lose any more teeth to his crown work, and cannot afford implants at the moment. Should I seek out a different dentist? Is there any guarantee with a crown?
– Marcos from New Jersey

Marcos,
While there is not really a guarantee with a crown, there is a concept in dental care called the standard of care–a minimum standard that an average dentist should provide his or her patients. There may be situations where there simply isn’t much tooth left to hold the crown on, so even a dentist who is doing everything right could have problems with an occasional crown staying on. But if there are recurring problems with crowns from a particular dentist with crowns falling off, that could indicate a breach of the standard of care and the dentist could be liable.

I realize that you don’t want to sue, and I’m not suggesting that. But knowing the dentist’s liability can be used to give you a bargaining position to get things fixed correctly without having to pay another dentist to do this over.

You say that two crowns have fallen off twice, and that you could see there wasn’t much tooth left on these teeth. While I don’t know the history of these teeth, that, together with your description of how little time this dentist spent on the crown preparations, suggests to me that the teeth were prepared with too much taper. I refer you to my earlier post on this subject, The Main Reason Your Crown Probably Fell Off, where I explain the role of taper.

In over 20 years of dental practice and placing many hundreds of crowns, I never had a crown that I placed fall off. I say that not to brag but to make the point that if a tooth is properly prepared and a crown properly cemented, it will stay on. Yes, it takes more time and trouble to prepare a tooth precisely so the crown stays on, and it is also more time and trouble to seat and cement a crown with an ideal preparation, which is why most dentists compromise on the ideal preparation a little bit. It sounds like your dentist compromises a lot in the interests of speed.

So to get to the point. Yes, if I were you, I’d find a dentist who does crowns that stay on. And then I would get these two teeth fixed with crowns that stay on. It may be necessary to have new crowns made. Even if a tooth is over-prepared, there are ways to modify the preparation, either with retentive grooves, or with a buildup and possibly the use of pins, so that a crown will stay on better. Or, depending on the material in the crown, it may be possible with bonding technology to get a poorly prepared crown to stay on. I would find a dentist who can take care of this for you, and ask that dentist to help you get some type of refund, even if it’s a partial refund, from your current dentist.

– Dr. Hall

Do you have a comment or a question or anything else to add? We’d love to hear from you. Enter your comment below.

Click here to ask Dr. Hall a question of your own.

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.

July 9, 2016

Why does my crown keep falling off?


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Dr. Hall,
I have had a crown put on by a dentist and it was done same day. No temporary. Not sure what type of material he used for the crown. It fell out three times in less than a year. I went to a different dentist on the fourth time it fell out and he replaced the setting with a new one stating the other dentist didn’t create a good setting. This new crown is Zirconia Porcelain and it has fallen out twice in a month. He is suggesting a full porcelain crown on the same setting as he states the cement is adhering to my tooth but not the crown. He says the all porcelain has a more rough underside to adhere to the cement better. Any suggestions on what my next move should be?
– Stephanie from North Carolina

Stephanie,
Your same-day crown was a CEREC crown or a similar type that is milled by a computer in the dental office while you wait. But when properly prepared and bonded on, it will stay on permanently. It’s not the material your crown is made of. Gold crowns, porcelain crowns, CEREC crowns, zirconia crowns–all of them can be made to stay on solidly, permanently. I have most of those types of crowns in my own mouth and they stay on just fine.

There are two main factors for retention of a dental crown–the bonding strength of the cement, and the shape of the tooth preparation. Of those two, the shape of the tooth preparation is far more important. If the tooth is prepared with only a slight taper, a crown can be cemented with a very weak cement and it will still stay on. If it is prepared with a lot of taper, some of the strongest cements will not hold it on.

I’m not saying that getting a good bond between the crown and your tooth wouldn’t solve your problem. The strength of the cement is a factor. And I know very little about your tooth and the techniques these dentists used. But I do know that a tooth prepared with good retention form will not have a crown falling off three times in less than a year, regardless of the cement used. So even though I know very little about your tooth, I’m pretty confident that it was prepared with inadequate retention form.

So what should your next move be? I would find a dentist who knows how to do crowns that stay on. In 23 years of dental practice, I never had a crown fall off of any that I did for my patients, so I know it can be done.

For further understanding of this principle, of creating a crown that stays on, see my blog post from about nine months ago, “The main reason your crown probably fell off.”

I hope this is helpful.
Dr. Hall

Do you have a comment or a question or anything else to add? We’d love to hear from you. Enter your comment below.

Click here to ask Dr. Hall a question of your own.

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.

October 8, 2015

The main reason your crown probably fell off

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I happened across a website the other day, Oral Answers, that had a post, “Six Reasons Why Your Crown Fell Off.” As I read it, in my mind it highlighted the difference between this website and other dental websites. The dentist writing this gave six “politically correct” possible answers that pretty nearly absolve dentists of any responsibility in this mishap and skirt the main cause.

The author of the website appears to be a nice guy. He is a dentist and identifies himself only as Tom. And it’s not that the information is incorrect, it’s just sanitized. It seems to adhere to the philosophy I’ve had preached at me from other dentists, that we professionals need to stick together and defend each other. And so Tom, rather than frankly explain what he was taught in dental school about crowns falling off, instead tries to portray dentists as nearly infallible.

For me, I can’t bring myself to do that. I need to tell it like it is and let the chips fall where they may. My professional duty, as I see it, isn’t to make other dentists look good but to help the patient.

Here are the six reasons Tom gives, with my comments on each one. Again, they’re all true. It’s just that he leaves off the main reason, which is what he and I were taught in dental school. So after I list his six reasons, I’ll let you in on a dental school lecture about the main reason crowns actually come off.

1 – The tooth underneath the crown got decayed.
This will definitely cause the crown to come off. However, if you are having regular checkups, your dentist will spot this decay well before it is extensive enough to cause the crown to fall off.

2 – The cement holding the crown on wasn’t strong enough. This could be due to contamination of the cement while it was being prepared or any number of other reasons. If this is the case, your dentist can usually re-cement the crown back onto your tooth.
This is the closest he comes to faulting the dentist. But he presents this as so easy to fix that it makes the dental mistake easy to forgive. In reality, I would attribute this cause to fewer than 1% of crowns falling off. I don’t think I ever saw a case like this in my practice.

3 – You ate too many chewy foods.
I was never taught in dental school to advise my patients with permanently cemented crowns not to eat chewy or sticky foods, and I never told them that. I will add that in 23 years of practice, I never had a crown that I put on just fall off, and my patients ate jelly bellies, taffy, whatever. I also have eight crowns myself and don’t observe any diet restrictions because of them. But if you do have a borderline crown or a temporary crown, yes, sticky foods will give you problems.

4 – The crown broke.
Again, this will do it, but it rarely happens. I’m trying to remember if I ever saw a broken crown in my practice. I may have seen one or two over my 23 years. In the old days, some pure porcelain crowns would break if they were used too far back in the mouth.

5 – You abused your crown.
He mentions grinding your teeth or using your teeth as tools. Yes, he is correct, this will stress your crown, but if the crown is done well it won’t be enough to loosen it so that it comes off.

6 – There wasn’t enough tooth structure to hold onto the crown.
Here he’s getting close to the main reason that crowns come off. This happens most often with short teeth. However, we dentists are taught how to address short teeth and get a crown to stay on. There are retentive grooves and other preparation features we can put into the crown preparation to deal with a short tooth.

The Main Reason

Keeping a crown from falling out

Now let’s go to our dental school training. Here are a couple of slides from a dental school lecture. Dr. Al Amri is teaching his students crown retention and resistance forms, the two principles involved in crown preparation that keep the crown on the tooth.

He explains to the students that the greater the taper in the crown preparation, the less likely the crown is to stay on. In his graph, which I have enlarged below, he teaches that by tightening up the taper,Taper the prep to keep the crown from falling off the dentist can increase the retention dramatically.

This seems like a simple solution and you may wonder, then, why every dentist doesn’t just prepare the teeth with minimum taper. There are a couple of reasons. First, to prepare a tooth with minimum taper requires a lot of precision. What if the dentist is off just a little bit? He or she could end up with what is called an undercut. I’ve illustrated that in this small diagram below. crown retention graph In an undercut, the tooth preparation is narrower crown-retention-graph-edited at the bottom than at the top. Having even the slightest undercut makes it impossible to make a crown to fit—it simply won’t slide on the tooth. If there is a small undercut in just one small part of the preparation, the crown won’t work. And the less taper there is in the crown, the more time and effort it takes to tell if you have an undercut.

The second reason is that the tighter taper makes it harder to seat the crown. The tighter taper, which makes it hard to dislodge the crown once it’s on, makes it harder to get on during the seating appointment. Any irregularity in the surface of the tooth or the internal surface of the crown needs to be resolved. There is less room for error.

A dentist can avoid these issues by simply creating more taper in the crown. And some dentists do just that. They may not be intentionally taking shortcuts—they may just lack confidence in their ability to create a perfect crown, so they just shoot for acceptable, with the result that they have some crowns that end up falling off. In my practice, I always prepared crowns with as little taper as I possibly could, and in 23 years I never had a crown fall off. However, I did see crowns done by other dentists that did come off, and most often these were crowns with inadequate retention form—too much taper.

We dentists, when we talk among ourselves, will talk about this issue of crown retention, and we fully understand that we are pretty much in control. But many dentists, when they are talking to patients, don’t feel the inclination to be quite so honest, for fear it will tarnish the profession. That’s their mindset. But it’s not mine.

Do you have a comment? We’d love to hear from you. Enter your comment below.

Click here to ask Dr. Hall a question of your own.

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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