broken/excess margins on crown temporaries

[accu94672]

I'm having an extremely tough time understanding how to make acceptable margins for my crown provisonals ( 3-units ). I usually end up with broken margins and was never able to fix any of them in my practicals. ( I once even thought my margins were perfect but only to have an instructor pull out my typodont from my mannikin, turn the typodont upside down, and show me broken/excess margins that I never even knew existed.-- so I guess I don't even know how to check for bad margins either) By the way, I'm using PVS for making my temporaries and my crown preparations are almost always good.

So I'm wondering if anyone here is sympathetic enough to explain to me the optimal procedures for doing crown margins. ( and/or provide me with any helpful links/text from your dental school that explains crown margins )

I wholeheartedly admit that my questions/problems are somewhat elementary and ridiculous but I have another provisionals practical in about like 10 days and there's no one I can ask about this. ( Technically, I already failed this prostho class because I failed so many of its previous practicals. This next practical I'm taking is like the ultimate remedial practical where I have one last chance at a C. If I fail this for real, my gpa will become really low and will add to the burdens of one other lab class that I failed two months ago. )

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[45540]

What type of margin are you using? I assume it's a shoulder since it's used as an abutment for the bridge. Let me try to find some notes.

 

[accu94672]

What type of margin are you using? I assume it's a shoulder since it's used as an abutment for the bridge. Let me try to find some notes.

shoulder with bevel

 

[lnn2]

Sorry to hear that. You're not the only one with the problem. It seems like you still have the same problem. I'll see if I can find any pics.
http://forums.studentdoctor.net/showthread.php?t=167653

 

[Sterichind69]

Honestly, I had problems with the margins too. See if you can use a light cure resin to paint on the margins of your temp. We use to use it for the practicals. If you can't use the light cured resin, make you original 3-unit temp, close the margins flush with your finish line. Then after you get those closed margins, add acrylic to the outside of those margins to reinforce them so they don't fracture. Plus, stop using the shoulder with the bevel for this typodont crap. The moment I stopped using the bevel I got rid of that thin acrylic margin and got a flush margin with a plain shoulder. The boards allow a strict shoulder.

Hope this helps.

 

[Energon]

Rest assured OP your question is not silly in any way. Yes it would really help if you could tell me what kind of material you are using for your temp. We use jet acrylic which is probably the worst kind.

Anyways here is my advice to you:
1. Make sure you have a good matrix fitting the original tooth well.
2. Wait long enough for the material to harden (if you are not using a light cured material).
3. Take your esthetic trimming burrs and make sure you contour the margins when the temp is on the tooth itself (in clinic, you will have to use a lot of water and take breaks frequently or else you will fry the pulp)
4. Also, if you break a portion of the margin during the contouring process, there are better ways to fix it.

If you give me a better idea of what material you are using, i can be a lot more helpful.

 

[DcS]

As someone else mentioned, flowable composite or normal composite works very well for margin repair. Make sure to put some vasoline on the tooth or it usually sticks to the tooth and breaks off. I'm not sure if you are allowed to use that.


Rest assured that on a patient temps are MUCH easier compared with lab. At least that is my experience so far (and many of my classmates).

As far as trimming it in mouth, I would not advise that. You should have no problem in clinic w/ a patient taking it out and trimming it. There is no way to safeguard you will not go through the temp and ruin a good margin, especially if you already have final impressions.

 

[ItsGavinC]

I posted a similar horror story last fall when I was doing FPDs. In my post, I noted that I was using a PMMA material (such as Jet). The responses were all unanimous: Jet is horrible.

Everybody recommended a bis-acryl material, like Integrity from Dentsply Caulk. Although my preclinical instructors didn't have any, I was able to get some on my own through other channels, and the stuff is AMAZING.

It makes ALL the difference in my temporaries. I've gone from working for 1.5 hours on margins to working for 5-10 minutes TOPS.

This isn't an exaggeration. The stuff is just better and the syringe dispenser makes a world of difference.

 

[Gutta Percha]

Why are you using a shoulder with a bevel? Pick the type of margin you want to use and prep it. Shoulders with bevels are very difficult to do correctly in real situations and are a waste of time b/c the margins are usually short, but closed. I recommend a chamfer. As far as temps go, ask the person grading you if he does all his temps himself. If not, then ask if he checks his DA's temps this well. Somethings in dental school are a learning experience and have nothing to do with dentistry.

 

[accu94672]

I have to do a provisional on shoulders/bevels because, for the practical, we will be given prepped teeth that have shoulders/bevels. Also, I am using Duralay as my acrylic and PVS as my matrix. I use vaseline to lubricate my teeth.

I also just thought of some specific questions.

1. When I realize that I have broken margins, do I fix it by adding acrylic on the prep's shoulder/bevel area and then put my temp on top of it and wait? Or do I put my temp back in the PVS, add some acrylic around the PVS's margins and then put it back on the prep and wait? For fixing broken margins, how runny or doughy is the acrylic supposed to be? ( is it supposed to be the same as when I originally did my temp ? )

2. There are some instances when my margins actually do cover the bevels. But when I hold my prep upside down with the temp still on it, I see open margins between the prep and the temp. What should I do?

3. Is it still considered an open or excess margin if my temp covers all the prep way down to the gingival? Or does it absolutely have to end on the bevel?

4. I have a problem with detecting open/excess margins with the typodont inside the mannikin. I usually use an explorer for this and I sometimes end up not finding some open margins, especially the interproximal ones. What should I do? This is a true story: we never learned about margins; the prof just said 'no open or excess margins.' Everyone already knew what to do except for me, and I never missed or slept thru a lab class.

5. What do you recommend for trimming excess margins?


Your responses would be greatly appreciated. I really have no one to ask because this prostho class is now officially over except for the remedial practical coming up.

 

[SPBest]

2. There are some instances when my margins actually do cover the bevels. But when I hold my prep upside down with the temp still on it, I see open margins between the prep and the temp. What should I do?

I just thought of two things as you mentioned this problem. Excessive monomer will cause more shrinkage as the acrylic sets up, this will cause it to "suck-back" from the margin. Secondly, don't press the matrix down too hard. The excess pressure will cause the matrix to flare out on the buccal and lingual.

Hope this helps.