Long Span Implant Retained Bridges - Problem With Breaking

[JohnWilson]

Bernard thanks.
HI John,
I agree with many of your pros and cons, would love to discuss a little more.
1. Weight, we stopped providing conventional hybrid restoration in 1990 due to breakage of teeth and or acrylic. At that time we moved all these cases to porcelain to gold. Some patient with severe bone loss would require 22-23 mm of restorative material. I remember cases that had close to 3 ounces of gold in the casting. That said, we never ever had a patient comment on weight.
4. You're right about the best verification jigs having a possible discrepancy. That said, Isn't it more about tension on the implant-bone interface than the tension on the CAD base?

I hear you Bob, so glad the days of 65sf casted bars and substructures are a thing of the past. I always think of the one bar I did when we calculated the wax weight we needed to throw 3.6oz just for the pattern and then double that for the runner bar/sprue and button. I watched the casting tech do this one and I am sure having me watching made it even worse. Thank god for no splash and the thing worked but I always hoped for a better way.

As to the verification I mentioned, I noticed that when a verification jig gives a false reading its because the analog is often too LOW in the model and this allows the jig to seat in the mouth and unless the client is taking perfect radiographs at exactly a right angle to the fixture the film will look like everything is correct.

This leads to the screw constantly pulling and essentially extracting the cad base from the zirconia as its constantly under tension and is not bottomed out in the morse taper of the implant. This is when I see things start to go sour down the line.

 

[JohnWilson]

By the way John Wilson doing these cases with Ti bar and Zi top [davis bridge] you can reduce the the bulk greatly .I have done cases with only 6-7 mm in height in places the case is going strong for over 5 years now ,you can also save a lot of headaches on the really thick ones doing it this way.I actually charge less for zi ti because its more straight forward and a lot less manufacturing probs.

And you can fit the case in a much smaller disk as well I have a few in the lab that I am trying some interesting paths with right now.

 

[Labwa]

We are getting a little off topic but there are Interesting points everyone is bringing up and I think all interesting.
as a bit of background we do a heap of immediate AO4 using milled titanium frames in house Pressed with ivobase. We would like to think they are on the higher end of what is done in 48 hours post surgery but also up there with what would take 3-4 weeks (going to Nobel for frame) and we have had really good results over the last 4 years in terms of breakages (touch wood). To put a number on it we would be at less than 1 percent adjustment (mainly to tissue contacting areas) or repair of teeth which has been due to occlusion in most cases.
As the technology has become more accessible we are able and should be able to produce these types of restorations more efficiently to price them under zirconia as an option. Is it a final? Yes I think so. Are floating cast bars or PMMA's finals. No I don't think so.
We price the full zirconia arches above our hybrids based on the level of difficulty and cost of experience. I would be interested to understand if others see things differently.

 

[Affinity]

lachlan, you charge more for zr, but what is the difference in labor? It seems like it would be faster, labor-wise, to process a zr arch, as opposed to milling a bar, waxing up and cutting teeth, boilout, process, polish etc.

 

[Labwa]

Not at all I find Zirc full arches a lot more time consuming. I probably spend 50 percent less time on a hybrid than a full arch Zirc.

 

[BobCDT]

So many labs are doing the screw retained full denture tooth set-up for a try-in before going to a full zirconia case. If this is the workflow any of you use there are obvious labor savings to simply convert that to a hybrid.

 

[Smako]

First off, I want to start by saying how appreciative I am for the regular posters on this forum. I have for a long time been just a lurker, but have learned so much from the information you guys continue to provide online. I should definitely help and post more often. I just wanted to start off by thanking the regular guys that post on this sub like JohnWilson, Al., rkm_rdt, CatamountRob, Sideshowbob, Sevan, Bob-CDT, Travis, CoolHandLuke, zero_zero, JMN etc. I know I am missing a few, but please know your knowledge is appreciated.

The reason why I am writing today is that I have been having some major issues with long span zirconia bridges breaking. I am at a loss for what is causing it and was hoping maybe you guys can help shed some light. I took some time today to read through the Zirconia forum to see if anyone else has experienced similar issues, but it is hard to isolate what exactly is causing this.

Basically, the situation I am having is that doctors are sending me back broken bridges that are sectioned clean. I don't know what in my manufacturing process is causing them to do that. Some of these bridges cracked after just 2-3 weeks. I will detail my process as follows:

So we follow the basic protocol of verifying the cast with a series of jigs, verification bridges, etc. Our final master cast is verified using a stone jig, due to how brittle stone is. We noticed when we were using PMMA alone, there was still slight flex that would occur, that would cause the final zirconia prosthesis not to seat. Since then, we have been using gypsum stone verification jigs to make sure that the implant coordinates are properly recorded. If there is any variance at all, the stone will break, and we will correct the master cast.

After we have verified the master cast, design, aesthetics, etc. We then go to producing the final zirconia bridge off of the verified scans, etc. When producing the bridge, we almost always use a Roland DWX-50 with a set of CAP Ultra burs that are specifically used for small amounts of time, and only for these large bridges. After the bridge is milled, we will use a carbide bur to cut it out of the disk and shave down the sprues. To complete the removal of sprues, we will then use a bur made for smoothing zirconia to remove any last traces of the sprues.

After removing the sprues, we will stain the bridge using Zirkon Zahn stains. It then gets placed under a heat lamp for 40 min - 1 hour. After it is dried, we sinter using either a Sirona inFire Speed or a Sintra furnace. The zirconias we are using for these bridges are the Katana ML and DentalDirekt BioZX. The cycles used in either furnace are posted as images. When using the cycle for DDBioZX, we use the long program (3.2) and we have a max temp of 1530 degrees Celsius. When running the katana cycle, it recommends a max temp of 1500 degrees, but we run it at 1550 degrees Celsius. All of our furnaces are calibrated as well, so the units are getting to the proper temperature.

After the bridges come out of the furnace, we have a guy that finishes them. There is a bit of a language barrier but I spoke with him today on his finishing process. He is using an older porcelain oven with vacuum (NEY Centurion Q100) when applying glaze and finishing these bridges. He has a low temp of 1000 degrees Fahrenheit, and a high temp of 1680 degrees Fahrenheit. He cools for about 30 minutes and dries for 30 minutes. When he cools, he cools at a rate of 100 degrees Fahrenheit per minute. I think he may be cooling too rapidly, but don't know enough about the stain/glaze cycles to say otherwise. He also may run this cycle a number of times depending on how he finishes the case, how many times he has to glaze, etc. I don't know if this is where the integrity of the zirconia is being weakened to where it breaks intraorally. I have had close to 6 long span, monolithic implant bridges break like this on me and I have no idea what to do to resolve the issue going forward. I dont want to just keep milling the same thing and following the same procedure just to lead to a frustrated dentist, and an unhappy patient. If anyone has any advice, or suggestions at all it would be greatly appreciated. Thank you for taking the time to read my long post!

tl;dr:
Monolithic long span zirc bridges are breaking left and right. Following the same manufacturing protocol everyone else seems to use. CCan'tfigure out what in the manufacturing process is causing a defect in the zirconia for it to break like this. View attachment 26674 View attachment 26675 View attachment 26674 View attachment 26675 View attachment 26676 View attachment 26677 View attachment 26678

Good Evening. did you finally solve the problem? I have the same problem with the same furnace Sirona. On the last 2 bridges I had a break. but in the first jobs they didn't break. Thank you