Acrylic Teeth dislodge from hybrid prosthesis: anybody else have this problem?

I have been having a problem with acrylic denture teeth becoming dislodged from fixed-detachable prostheses [hybrid prostheses].  Is there a particular metal framework design that someone could describe that would not result in the teeth being dislodged?  Is there a minimum acrylic thickness that should be present under and around the denture teeth?  Can anything be done to increase the retention of the denture teeth?  Anybody else having this problem?



25 thoughts on: Acrylic Teeth dislodge from hybrid prosthesis: anybody else have this problem?

  1. LC says:

    There are multiple variables that go in to teeth dislodging from a hybrid prosthesis.

    1) Occlusion: the occlusion has to match the opposing arch, so it is different depending on the patient’s existing scenario. You should not be attempting to recreate standard 3-point occlusion in any hybrid case. Typically you’re looking at either lingualized occlusion on hybrid/denture or hybrid/hybrid cases or you’re looking for fast posterior disclusion with anterior guidance on hybrid/fixed or hybrid/natural cases.

    2) Acrylic/tooth bond: in hybrids the rules are the same as in dentures in regards to materials. The more tooth to acrylic interface you can have the better. We have produced a huge variety of bar designs ranging from 3/4 TI wrap-arounds with TI lingual and tissue sides to bar patterns that were full acrylic wrap-arounds with individual diatoric retention “rods” for each tooth to our current method – minimal TI bar with more room for acrylic. The latter works the best and has less shear/breakage.

    3) Intra-oral space: this goes back to design of prosthesis. If sufficient vertical dimension between the arches has not been established then the prosthesis becomes “slim” and there is a significant increase in breakage. this is why it is so important to reduce bone when choosing a hybrid for the final prosthesis.

    4) Bar design: the bar should be in a position in relation to the occlusal table so as to be “under” the primary force. In other words, if the patient bites in their “I’m going to crunch this piece of candy” position the force of the bite should be directionally over the bar support. Having the bar too far buccal or lingual to the bite force can cause shearing.

    Source: lab tech who has produced literally thousands of these cases.

    • Kelly Loyd CDT,BS,TE says:

      suggest you try Prettau Zirconia Bridges. No metal bar, no stainning, highly resistant to chipping and fracturing, works with all major implant brands, wear prototype to verify function, esthetics prior to final restoration, 12mm occl spacing, no more acrylic fractures, denture teeth popping out not to mention denture teeth wear, and the smells, 5 yr warranty. Company manufacturer of the Prettau Zirconia is Zirkonzahn. If that existing hybrid in you practice is experiencing constant maintenance and you want to flip it…call me.

  2. CRS says:

    I’m going to go out on a limb here, sometimes some bone needs to be reduced to allow room for the framework and if the bite is collapsed this will also decrease the intra-arch distance. I think the lab can tell you the parameters for acrylic and technical spec. I’m wondering if the patient parameters re being considered. Do you have a friendly prostodontist to evaluate the situation. Usually the teeth popping off is due to an occlusal or intra-arch issue. Just some thought to get the discussion going. Thanks for reading!

    • Charles Schlesinger says:

      LC nailed the high points.
      In my experiences, it has been not enough interarch distance. A milled bar needs between 17-20mm of space between the crest and the incisal edges. If this space is not provided, the lab must decrease the thickness of acrylic and/or shave down the backs and necks of the teeth- this results in a weaker structure overall.

      I believe the biggest culprit in broken teeth is lack of proprioception. A patient with hybrids is going to gnash their teeth and likely use higher forces than their own natural teeth with PDLs would allow. For this reason occlusion is very important.

  3. Richard Waghalter, DDS says:

    I had one problem case like this. The lab made the framework too thick and not enough room for the teeth, The teeth were shells occlusal and buccal. I agree with LC.
    I have switched labs and am making the patient a full zirconium denture. wioth the old lab I had them make a new framework but it was too big too. I am tired of having to re-do teeth each time he comes in every 3 wks.

    • LC says:

      Different materials do solve some of the problems, but if you are creating screw-retained hybrids in conjunctions with a surgical procedure like All-On-4 it changes the price structure and therefore the accessibility of the product/process to many patients.

      I think that the issue is not with the material so much as the fact that not all the requirement of the procedure leading up to the final prosthesis have been met. Once we get to that point we’re back to the good ol’ Internal Dental Lab motto “Make It Work”

  4. RZ says:

    I have also had similar problems in a few cases. I think the main factors here are relatively big mastication forces and at the same time lack of control of the chewing cycle.
    It has been shown that the forces and the efficacyof chewing with implant supported (not tissue supported) overdentures and hybrid dentures is close to that of chewing with natural teeth. But since the receptors from the periodontal ligaments are missing, the control of chewing is not as good. And even if you make perfect occlusion, there will occasionally be contacts, which will overload the acrylic (or composite) teeth. Especially if you have this type of dentures in both the upper and lower jaw. The control of chewing is better if there are some natural teeth present, and the forces are lower if you have a conventional denture in the opposing arch.
    I think this is why it is wise to try to keep some natural teeth, which can support an overdenture together with strategic implants. And when we are planing two hybrid or implant supported dentures in an edentolous patient, we should explain in advance, that some teeth may brake or fall out, and we might have to make some repairs.

    • Dan says:

      I totally agree with RZ. The main issue with these screw retained restorations is the capability of the patient to bite with between 80 to 90 percent of the force they had when they had natural teeth. We fabricate our hybrid bars with individual pins going into every anterior tooth and still I have seen few hybrids either ours or some other lab’s that doesn’t come back to fix a tooth that broke every few months. It is the nature of these cases. It’s only acrylic and some will break sooner or later. And, if they don’t the teeth will be worn down to a flat piece of acrylic sooner than later, for the same reasons. Just like patients need to be recalled periodically to clean under those bars, some teeth will break occasionally. And it doesn’t matter whether you use premium teeth or not. And if you think that using hybrid composite teeth will be better, think again. Composite teeth are more brittle and they break even easier.

  5. Richard Hughes, DDS, FAAID, FAAIP, DABOI says:

    I have had this problem with bar restained overdentures and even a bar breaking. Occlusal parafunction, lack of proprioception and interocclusal space are all issues. I n my cases there was enough interocclusal space and material bulk. Occlusal parafunction and lack of proprioception were the issues. The patients were not removing said prosthesis as recommended for sleeping. Once they did so the breakage stopped. All of the docs posting comments make valid points.

  6. mwjohnson dds, ms says:

    tooth fracture is one of the most frustrating things of a hybrid restoration. You did not specify if it was max. or mand. so I’ll address both. I’m a prosthodontist, been making hybrids for 23 years. If they oppose a max. denture there’s usually no problem. It’s when they start opposing a natural dentition that we run into trouble. The maxillary hybrids should have a slight horizontal open bite so the occlusal forces are on the posteriors. As the posterior teeth wear, the occlusion will shift to the anteriors and the forces are facial, trying to break the teeth out… and they do! The stronger the denture tooth (Ivoclar phonares 2 are composite hybrid teeth) the less wear and the longer the anterior teeth will stay in. I have made gold linguals to try and keep 6-11 in the hybrids. I am now using more sophisticated materials (like the author above with the Zirconium, except I am using Bredent composite denture veneers bonded to a titanium framework) to combat the breakage.

    If the breakage is in the mandible then it’s usually that the posterior teeth are wearing or the patient is biting something very hard or parafunctioning. Again, the breakage is usually against a natural dentition maxilla which delivers at least twice the force as that of a maxillary denture.

    • sharon goodwin says:

      I like the sound of using composite denture veneers onto the framework! Thank you for sharing this info..Can you get away with less space requirements for this? In your experience what is the minimal space requirement form the ridge crest to the incisal edges for your hybrids you make? Which lab makes your hybrids with the Bredent teeth? Thank you very much for your information.

  7. Michael Tischler, DDS says:

    Any hybrid screw retained bridge is susceptible to chipping and a disassociation of the acrylic to the underlying bar. The screw holes are one of the weakest points. An overdenture also has this inherent susceptibility being acrylic. In my opinion the best answer to both of these prosthetic solutions is a monolithic zirconia screw retained bridge. The benefit of YTZ Zirconia is that the high modulus of elasticity creates a rigid framework that stabilizes the implants, doesn’t fracture when there is sufficient prosthetic height, and doesn’t chip or stain. The prosthetic height needed is less than acrylic metal supported comparisons. 12mm or more, not 15mm-20mm. The screw holes are not susceptible to fracture either.

  8. Dr M C says:

    Good topic! I’ve had similar problems and my experience with these problems tells me that a)the area around the abutments on the denture is very weak and as acrylic has more flex it tends to fracture at these points and b) the patient puts much more force as compared to conventional complete dentures. So the solution is to re enforce the dentures with a framework that runs along the ridge and loops around the abutments both labially and lingually with continuity from one side to the other. The metal framework is more like a bar of atleast 2mm thickness. Please give feedback to improve

  9. M J Olim, DDS says:

    These patients have become edentulous for a variety of reasons and chief among them in my opinion is bruxism and clenching. We can replace their natural teeth with implant supported prostheses but for many these parafunctional habits continue and breakage will occur. The patient should be made aware of this. If I make two opposing fixed detacheables it will happen! I caution them about it and document it so when the time comes to do the repair they here my” I told you so”. I also like to encourage them to have a spare set so things can be repaired well at the lab. Obviously a bruxism appliance should also be given.

  10. CRS says:

    Excellent discussion, would it be prudent to have a recall protocol on theses cases regarding occlusal wear and hygiene since there is no PDL and proprioception? I think that if these prosthesis have a weak point such as teeth popping off that is preferable o losing an implant. This is the stuff that is not discussed and routine revision and maintenance of the prosthesis seems to be key points. I’m very impressed since I do not restore and this is very helpful in treatment planning.

  11. Mark Huels, CDT, MICOI says:

    A lot of good points discussed here. When I read the question of teeth “popping out” I pictured a clean separation from the acrylic with no fracture involved. If that is the case then it is a technique issue with the lab. A lot of labs use fluid resin for these which results in a much weaker bond between the teeth and processed acrylic. Also at issue is the boil out. I intentionally do not have a large boil out tank so I can use clean water with each case. This problem can and should be avoided! If the problem is fractured teeth refer to the answers above.

  12. Dr. Alex Zavyalov says:

    The description of the case does not contain any space parameters and probably the dentist does not create enough room for this restoration. Dr. DiTolla has pointed on it many times. Many of GP do not know some important dental technical/material properties and cannot foresee pure technical complications.

  13. JS says:

    I was thinking this discussion would be a prequel to tonight’s webinar on the Prettau Zirconia Screw Retained Implant Bridge. I will be watching the webinar and it advertises to correct all of the concerns of breakage in the traditional acrylic hybrids listed above. But I am wondering what the feedback is from actual users (not the guy who developed the technology and is now selling it) as to any other problems that might arise with it. For example, as CRS said earlier, I would rather the hybrid fail than the implants that support it.

    • Michael Tischler, DDS says:

      JS,

      Yes the webinar tonight will address the shortcomings of acrylic. I certainly didn;t invent this prosthesis, but do believe in it. On our lab website is a JOMI article showing 100% success with Prettau with 3 implants supporting full arches.
      With respect to implant stress, YTZ zirconia actually wears teeth less than feldspathic porcelain and the stress is no different than porcelain on implants that have worked for many years. All this without the chipping and staining.

  14. CRS says:

    I know you guys are tired of hearing this, and I might be a rare specialist who likes to help, but it is always helpful to have a specialist for back up and advice with practical experience, it is just another weapon in our arsenal . I love asking my restorative docs on their ends how to do things and I have learned a lot from this blog with its mixed bag of treating practitioners! Laboratories are excellent sources, literature searches,courses etc how we learn. We don’t know what we don’t know and if there is a problem at least in my state you will be held to the standard of a specialist. And yes there are a lot of specialists who are not helpful an judgmental I think this blog s great since the posters put themselves out there! Thanks for reading lets me careful out there!

  15. Dr Aurangabad India says:

    This is the best discussion on this site so far. Very practical &useful for all those who do hybrid fixed prosthesis. If someone has not encountered this problem means he/she has not done enough work
    I gave occlusal splint ( one like bleaching trays) to one of my young patient with bruxism & the problem is stopped.
    All other points raised by all the doctors & labs in above discussion are worth remembering . Thanks for good inputs.

  16. Roger B Galburt,, DDS says:

    Here at Tufts University Implant Center we recently did a pilot study on one aspect of this problem. We have tested the bond between different qualities of acrylic teeth to the base material. We have found that the lower cost denture teeth bond at a higher bond strength than do the more expensive cost teeth. This is probably due to the hardness of the denture tooth acrylic. We will be continuing this research going forward.

  17. Bhavin Changela DDS says:

    Thank you all of you sharing your knowledge. I have similar problem where I have restored upper hybrid with opposing natural teeth. Patient broke both canines couple of times and one time acrylic from #6 to #11. Now I am adding some mess for support so let’s see how well it retained.

    • Michael Tischler says:

      The Prettau Zirconia Bridge resolves this problem from happening.
      We only need 12mm of prosthetic space. There just needs to be enough alveoloplasty done.
      In our office we have done over 100 arches with great success and our lab is creating this for dentists from all over the US and Canada.
      Our in lab course (www.zrcourse.com) is being given November 8th and 9th in Woodstock, NY
      It is very valuable since we share a wealth of knowledge from our experience with cases examples.

      Michael Tischler, DDS

Comments are closed.

Posted in Clinical Questions.
Bookmark Acrylic Teeth dislodge from hybrid prosthesis: anybody else have this problem?