Crown lengthening

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Joined: Tue Nov 14, 2017 12:16 pm

Crown lengthening

Post by jgold1981 » Sun Nov 19, 2017 10:17 am


I had some follow up questions about restoring my root-canal-treated molar. The tooth in question (#14) has an MO silver filling that extends in one spot almost to the bone, in violation of biologic width. Although it was irritated when I first got the filling 2.5 years ago, it's gotten better and doesn't hurt or bleed as long as I floss carefully. When I've gone for my check-ups, the hygienists haven't detected any super-deep pockets around the tooth. I have had the same experience with a similar filling violating biologic width on tooth #3 for the last nine years - i.e. some discomfort that has gotten better over the years The only time I feel any pain near either tooth is if a dentist sticks an explorer in one small spot to make the point that the biologic width is violated ;). The bone hasn't seemed to have been subject to any uncontrollable resorption process.

When I consulted a prosthodontist about restoring #14 with cuspal coverage after my RCT is complete (he recommended an onlay because of the large amount of remaining tooth structure), he tried to persuade me to get crown lengthening first because of the BW violation. I'm a little skeptical. First, my gums were already very receded before treatment, and I'm concerned that taking away more bone will jeopardize my ability to get an implant if I ever lose the tooth (I think I just barely have 1 cm of bone between the tooth and the sinus; the tips of the roots in fact stick into the sinus cavity). Second, while the current situation is not ideal, it hasn't resulted in massive unpredictable bone loss or pain. Also, if BW is really a problem, wouldn't the bone recede on its own over time?

Is there a reason to think that replacing the silver amalgam with a cast gold restoration will make the situation worse if I don't get crown lengthening? Also, why isn't orthodontic extrusion a viable alternative to crown lengthening? The prosthodontist said it's expensive and takes a long time to accomplish. Isn't that still better if it leaves more bone, and a more favorable crown-to-root ratio?

Lastly, does having the margin so far below the gumline create difficulty in getting a good impression for a cast restoration? Can that be addressed by removing some of the soft gum tissue (which I understand will grow back afterwards)?


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Re: Crown lengthening

Post by sbornfeld » Sun Nov 19, 2017 4:38 pm

You are really asking me to second-guess your dentist and prosthodontist although they have seen you and I have not. Therefore you've got to understand that I can answer only in a general way, and I'm at a severe disadvantage with respect to a professional opinion compared to the dentists who've examined and treated you. So I'll advise you to take what I say as merely my opinion based upon the information that you've posted.
I have been guilty of violating the biologic width on many occasions (please don't tell my parole officer). It is NOT a non-issue, but how big an issue it is depends upon the presence of periodontal disease and oral hygiene. Sometimes you get away with it, and sometimes you don't. Most of the time when I extend a restoration deeply under the gumline it's because I'm doing a large filling and trying to avoid doing a crown. If a crown or other cast restoration is being made, there is usually more margin at or near the gumline. So respecting the biologic width is more important in these cases.
Insurance pretty uniformly does NOT have a benefit for crown lengthening. The reasons for this are lost in history. In my opinion it's only to save money, but the materials given to patients definitely give many the impression that this is a frivolous procedure only done to generate a fee. This is definitely NOT the case. Furthermore, I refer patients to the periodontist for crown lengthening, so the recommendation comes from someone other than the operator. But not infrequently, I'll get resistance from the patient. In that case I will proceed with the restoration, so long as the patient has been properly informed.
In answer to your other questions: yes, sometimes the gum will recede in response to injury, obviating the need for the crown lengthening. Sometimes you get a more or less stable periodontal pocket. If it's considered serious enough, periodontal surgery can be done later. The downside of this is that the margin of the crown may be exposed. This may not be important in the presence of good oral hygiene and in an area that is not esthetically critical.
If you are doing a crown lengthening procedure that involves removal of bone, one must keep in mind whether there is sufficient remaining bone for adequate periodontal support. I find that since periodontists started placing implants, there is less tendency to retain periodontally-questionable teeth. In any case, I am not going to argue the case with a periodontist or a prosthodontist. They know how much bone you need. But as a practical matter, it is tough to get a periodontist to sign off on crown lengthening a tooth with short roots.
I don't know how to answer you with regard to orthodontic extrusion. The textbook says that when you extrude the tooth, the bone extrudes with it. So in the past year I treated a patient with a broken-down lower incisor, and his periodontist recommended rapid extrusion. I was told that if the extrusion is rapid, the bone DOESN'T follow. (What I THOUGHT was: if the extrusion is "rapid" enough, it becomes an EXTRACTION). In any case (and I won't go into the minutia of actually doing this on a root broken down to the gumline;) suffice it to say I felt I was doing frontier dentistry. We maybe got an extra millimeter of exposed root, but mostly the bone extruded with the tooth.
Yes, having a margin deep under the gumline certainly does make obtaining an adequate impression more challenging. Yes, it CAN be addressed by removing soft tissue, but you can see that this becomes a little bit like doing a crown lengthening on the cheap.
Finally, I'd say that undergoing the amount of dentistry you have with this tooth, I certainly hope it has a good medium-to-long-term prognosis. Assuming that, I wouldn't worry too much about losing the tooth and getting an implant. If you truly have only a centimeter of bone overlying your sinus, you will almost certainly need sinus surgery in order to place an implant there--whether you have crown lengthening or not.
Steven Bornfeld, DDS
Brooklyn, NY

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Re: Crown lengthening

Post by jgold1981 » Mon Nov 20, 2017 12:48 pm

Dr. Bornfeld,

Thank you so much for your detailed and thoughtful response! It's definitely not an issue of money for me, just weighing the dental health benefits and downsides of removing bone from the affected tooth as well as adjacent teeth. My understanding is that while it promotes gum health not to have the margin under the gum, it's also better for teeth to have more bone around them, and to have a smaller crown-to-root ratio. At my age (mid-30's), I also think it's likely my gums will recede some more with time even if I continue taking good care of them, and given the recession that occurred earlier in my life, my teeth are already somewhat exposed. In fact, I think that some of the problems I've had with decay close to the gumline on the two teeth I mentioned have to do with the fact that the way teeth narrow towards the gums, combined with receded gums, makes it easier for food to get trapped between teeth when there's less gum tissue around.

It sounds like I've been lucky to date in not having the width violations result in major issues (I am maniacal about flossing around the affected teeth!) and may have what you describe as "stable" pockets around the affected teeth. If the onlay margin turns out to be more irritating, it seems based on your post that I can just get CL done later (I'm not concerned about the aesthetics as the gingival margin can't be seen from the cheek side). I'll give it some more thought, but at the moment I'm inclined to see how bad (or not) things get without CL and get it done later if it does turn out to have been necessary.


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Re: Crown lengthening

Post by jgold1981 » Mon Nov 20, 2017 1:26 pm

I forgot to add - in terms of biocompatibility, would a cast metal onlay be expected to be more or less irritating to the gum than the amalgam filling that's currently there?

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