[Prosthetics]  Interesting All-on-4 restorative failure....

Hello guys!


Here's an interesting restorative failure I've seen recently.  Of all the arches I've done, this is the first failure I've seen other than the odd tooth breakage.  Thought I'd share to see what you others have seen.....   Panorex is from delivery appointment in August.  Pa's from today.  See below.


Delivered final acrylic hybrid in August, always check for passive bar fit and check occlusion carefully while fabricating and delivering....  She returned 3 weeks ago with the unit completely out of her mouth!  She fractured all 4 screws!   Needless to say I was a bit shocked.....  She had felt some kind of 'crack/noise" and called in to let my staff know (FIRST lesson to learn, let your new front desk staff know that you want to know if an all-on-4 patient calls in......  arghhhh) Anyways, I didn't hear about it, they booked her in a few days later.  By that time the rest had broken off.  Crazy.


So I swapped out the multiunits and redeliverd the appliance with new screws.  Very obviously she had completely ground down the occlusion on the acrylic teeth (you see her opposing is heavily restored implants/PFM.     It was amazing the wear she had done in such little time to the acrylic. Seeing this, my initial thought was she ground down so much that she was hitting very heavily on the distal extension, creating such forces that she borke the screws due to a 'diving board' effect.   I was in a bit of a pinch for time so I adjusted the bite back to ideal removing the distal contacts, made her a bruxism guard to reduce some of the wear, and thought I'd check it again in a few weeks to see what the wear patterns were like after a few weeks.   I discussed the idea of either redoing in porcelain or at least redoing the posterior teeth in Zirconia or Emax, after we revaluated the wear.  My local lab here in the interior has a way to make the teeth Zr instead of Acrylic, i'm not sure how the bond would be though..... any thoughts?    


So she returned today and teeth were still in.... but when i went to check the screws she had broke off 3 of 4 screws, only #45 was still intact!  She felt a similar "crunch" chen she bit something on the weekend.   So that got me thinking perhaps its a bar issue.  I tried the one screw passive test and looks as though the #35 is open as you see in the PA.    Having said that I wanted to screw the 35 instead of the 45 to compare seat, but I couldn't get the screw out of the MUA and didn't have another in stock (this was end of the day today.....)


So I am planning to reimpress and remake the bar.  I am going to double check the passiveness of the bar by grinding the tissue contact away just to make sure its not being held up on bone or tissue.....    Any thoughts as to what else might have caused this?  Always good to get some other opinions on these unique situations!




So a couple of quick question for those who care to share their thoughts.....


1)  any tips on getting broken screws out of multiunits?   (I got lucky and had the exact size in stock so I could just swap the abutments out, which I think is smart to replace them after screw breakage anyways..... any thoughts?)  But in a pinch if I hadn't had them in stock I would have loved to have been able to get the screws out.


2) at delivery of final prosthesis (or bar try-in I suppose), do you rely on panorex to confirm seat?  I find the panorex causes some overlap and is hard to tell often.  To be honest I generally just visually inspect but also confirm bar fit with panorex.  Haven't had any issues.... until now!


2)  Do you agree this is a bar issue?  Could it have been affected at processing if it was passive at try-in?  I can defenitely get all 4 screws tightened.


3) as a learning case, perhaps your feedback on A04 opposing a heavily restored arch?   (Mark, I know your last course I was at you mentioned you were often doing porcelain on max and acrylic on mand, mind you those were upper lower cases, so this case is different in that her upper arch was as was, I didn't set it up..)   Perhaps I should have pushed harder for porcelain occlusion....


Thanks!  Hope you are all well and hope this is a case we can learn from!



by Sean Bicknell at Wed, Oct 28, 2015 3:16 AM

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Ho-Young Chung Replied at Sun, Nov 1, 2015 3:27 AM

Hi Sean, I'm not an expert on fixed cases but I'll put in my two cents for what it's worth. I agree with you that the bar has too much cantilever. I would take a final abutment level impression. Have the lab make a verification jig then resplint it in the mouth then try it in again on the master model without the soft tissue and do the one screw passivity test. The 35 part of the bar doesn't look like it is passive as per your observation. I'll bet that it won't be passive on your new master model either. I could be wrong here but if you go zirconia on the bottom, you may start seeing porcelain chipping from the upper crowns. The other faculty members can give you more insight. Ho-Young

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Madeson Basie Replied at Thu, Oct 29, 2015 5:19 PM

You say she ground down the acrylic teeth. What are the chances she has Sleep Apnea ? And has there been a loss of vertical dimension pre-op?

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Sean Bicknell Replied at Wed, Oct 28, 2015 3:20 AM

My other thought is perhaps I've over extended the bar in the 4th quad, will defenitely shoren that if we go to remake.....