Tips on Making Single Unit Temporary Crown on Teeth with Reduced Periodontium

As a prosthodontist, I make temporary crowns all the time. I make single units, quadrant splinted crowns and full mouth temporary crowns all the time.  The nature of my work requires me to make them quickly and predictably.  I make so many of them I can probably do them in my sleep now.  In any case, I would like to share with you a particular scenario of making single unit crowns where I used to sweat all the time.

In the early years of my career, whenever I find myself doing a crown where there has been a history of gingival recession and bone loss exposing the roots of the abutment as well as the adjacent teeth, my temporary crown would always be stuck and I had trouble getting a good margin surrounding the tooth.  I would waste so much time redoing the temporary only to find myself stuck with the same problem.  Now, I see the potential problem in advance and take steps to avoid these problems.  I want to share these tips with you so to minimize your frustration.

In general, teeth that had a reduced periodontium will typically have the following clinical features:

  • Long clinical crown height
  • Multiple Interproximal black triangles
  • Exposed interproximal root concavity

 

Common Challenges in These Cases:

I find myself that because of the long clinical crown height, the preps are often very retentive.  The interproximal black triangles alongside with the adjacent root concavity mean that I have extra acrylic interproximally that can often get stuck into the undercuts upon removing the temporary crown. My temporary crown usually will break half way through especially interproximally.   For these reasons, here are my tips

Tip 1:

Modifying your matrix:

First of all, there are countless ways for one to prepare the matrix for your temporary crown.  You can make a putty matrix on the tooth engaging at least one tooth mesial and one tooth distal to the tooth.  You can take a sectional impression of the quadrant using fast setting PVS material.  You can make a vacuum formed matrix of the required area.  Or you can make a block temp and carve out your anatomy chairside.  There are pros and cons for each technique.  For me, I usually make a sectional impression using bite registration material of the required area.  I use bite registration material because of its fast setting nature.  But in theory, you can use any regular impression material that you see fit.

   

You will notice that because of the history of gingival recession and bone loss, the impression will usually have many interproximal tags of materials.

   

So in the past, I would remove these tags of materials (both circled in blue and pink) because they sometimes can prevent me from seating the sectional impression back in the mouth accurately, I would snip them right off using a hemostat or a cotton plier. In this example, if I am doing a crown on tooth 16, the areas where I circled in pink are ones I definitely would remove.  The ones I circled in blue now I would sometimes leave them in.  By leaving the interproximal tags intact circled in blue, I may have less acrylic stuck interproximally upon removal.  But I still run the risk that temporary may break interproximally.  It just means I have less bulk of acrylic to deal with.

Tip #2
Expect the Temporary to Break Interproximally. Then use a matrix band to block out the root concavity and repair your margin interproximally or other areas as required

In the past, I would keep making a temporary crown until I get one that would not break.  I would have my wishful thinking that I can wiggle it off while it is still in the rubbery stage.  But more often it would still break. So now, I expect it to break and expect to repair the margin.  But once it breaks, I placed a matrix band on the tooth distal and mesial to the prep so I can flow some resin interproximally to pick up the margin without getting it stuck into the root concavity on the adjacent teeth.

  

Once I have the margin picked up interproximally, I can reline and/or repair the margin as I see fit to improve the fit of the temporary.  This time I add a little bit at a time so I don’t get too much stuck interproximally again.

Another way of avoiding the temporary to get stuck inteproximally is to use the block temporary technique. In this technique, you make a block of PMMS (Polymethyl methacrylate e.g Jet) and apply it to the tooth while it is in a rubbery stage and have the patient bite into the material.  While it is setting in the rubbery stage, you will remove and adapt it to the tooth back and forth until it is set.  Once it is completely set, you can then carve the block of acrylic freehand and to make it look like a tooth.  This method may have a lower risk of getting the temporary stuck because you can literally mold the interproximal area while it is rubbery.  However, this technique does require a lot of time and skill and with the expected polymerization shrinkage, you are bound to reline the temporary crown to obtain your ideal margin.  In some schools, they don’t even teach this technique.

Tip #3: Thicken up your temporary prior to trimming

Finally, my last tip does not apply specifically to the clinical situation of long teeth with black triangles.  But rather, it applies  to all my temporary restorations. Normally, once I have my temporary removed from the tooth, prior to trimming the excess, I would evaluate the temporary and add flowable resin to areas that are thin or areas that have voids.  Typically, common areas that may be thin are closer to the margin.  So rather than trimming my temporary to margin at this point which may get too thin and fracture off,  I add flowable resin to these areas to thicken it up.  This will create more bulk around the margin so upon trimming that area, it will have less risk of fracture.  This may also minimize the multiple attempt to add, to repair and to trim the margin to get your perfect temporary crown.

That’s it!  I hope you find these tips useful.  If you have any great tips to share, please let me know.  Learning through your own mistakes can be a valuable lesson but if anyone can offer these tips to me early on, it would save me so much time and frustration of figuring what to do to avoid these problems repeatedly. Thank you for reading.

Please check out my other posts too.