Implant Bridge Noob Question (hexed vs non-hexed)

[HonestAbe]

I feel like I'm thinking about time zones or some other abstract but simple thing that I just can't wrap my head around. Had a case yesterday where I was told to pick out abutments for a screw retained implant bridge, like 19-21 (19/20 abutments with 21 cantilever). I chose two stock abutments that were non-hexed because I thought that those were the correct choice for screw retained implant bridges and the senior tech told me to switch it to hexed.

He's tried explaining it to me but there's something about it that I'm just not understanding, hoping hearing it some other ways might jog that last switch in my brain so I can understand why and when to use non-hexed.

I guess the essence of my question is, WHEN do I want to use non-hexed implant abutments for bridges. Is it solely determined by screw vs cement retained?

 

[npdynamite]

If it is a screw retained bridge then you are correct, you should be using a non engaging abutment. If it is cement retained you would need engaging abutments.

The only thing that throws me off in what you wrote is "stock abutments" just because they seem so uncommon these days and are typically used with cement retained bridges. So to ensure we are on the same page in terms of screw retained, is this bridge being cemented to the abutments in the lab, or will it be cemented in the mouth and the lab is just adding screw holes just in case of it needing to be retrieved in the future?

 

[Brett Hansen CDT]

Non hexed abutments are used for screw retained bridges. Hexed abutments "could" work if the implants are "very" parallel, but using hexed abutments adds complexity and could cause problems without adding any benefit.

I have one doc that continues to send in stock abutments. I modify those and use them to do screw retained crowns as long as the path of insertion into the implant is relatively parallel with the adjacent teeth contacts. After designing the crown, I put a hole through the crown that roughly lines up with the path of insertion into the abutment screw channel.

Cantilevers on implants "should" be avoided if possible. It raises the risks of the implant not surviving long term. Implants like forces along the vertical axis of the implant. It's possible the senior tech might want to use hexed abutments due to the fact you are creating a cantilever bridge. I still wouldn't but that might be their thinking.

There are no 100%'s in implant dentistry. There are too many variables involved. As techs, we should be informing our doctors of any issues we see with a restoration they prescribe that may lower the survivability of the prosthesis long term. We should also keep in mind that we can do tens of thousands of restorations with a 99% success rate, but in the case of that 1% failure, it's a 100% failure for that specific patient.

 

[rkm rdt]

100% certain I will never use a stock abutment ever.

 

[HonestAbe]

If it is a screw retained bridge then you are correct, you should be using a non engaging abutment. If it is cement retained you would need engaging abutments.

The only thing that throws me off in what you wrote is "stock abutments" just because they seem so uncommon these days and are typically used with cement retained bridges. So to ensure we are on the same page in terms of screw retained, is this bridge being cemented to the abutments in the lab, or will it be cemented in the mouth and the lab is just adding screw holes just in case of it needing to be retrieved in the future?

I just asked and this one is going to be cemented in the lab. We are going to use stock abutments as that's what the doctor requested though we might have to modify them some. I haven't done the cementing part of the process yet, I've been only on the scanning/design/milling side of things so I'm going to try and sit in on that and learn.

Hypothetically, if it was going to be cemented in the mouth, then the anti-rotation is used right? The idea being if the impression and model are accurate that everything should match up and the doctor can replicate the position of the abutment that the lab model had?

 

[TheLabGuy]

Whenenver I have a screw-retained bridge...i usually leave one abutment hexed and the other one non-hexed. I just look down at the implant analogs and see which one is parrallel to the proximal contacts, that's the one I leave hexed, the other one will be non-hexed.

 

[Brett Hansen CDT]

I just asked and this one is going to be cemented in the lab. We are going to use stock abutments as that's what the doctor requested though we might have to modify them some. I haven't done the cementing part of the process yet, I've been only on the scanning/design/milling side of things so I'm going to try and sit in on that and learn.

Hypothetically, if it was going to be cemented in the mouth, then the anti-rotation is used right? The idea being if the impression and model are accurate that everything should match up and the doctor can replicate the position of the abutment that the lab model had?

Yes, if this was a cement retained bridge, then "hexed" abutments are the way to go. If it is screw retained, then you would use non-engaging or "non hexed" abutments.

 

[Brett Hansen CDT]

Whenenver I have a screw-retained bridge...i usually leave one abutment hexed and the other one non-hexed. I just look down at the implant analogs and see which one is parrallel to the proximal contacts, that's the one I leave hexed, the other one will be non-hexed.

I was going to add in my first post that I know some techs do it this way.

 

[npdynamite]

Ok, so if you are going to be doing the cementing in lab then generally you would use non engaging abutments because there is any difference in parallelism then the bridge may not seat if they are hexed.

I also am familiar with and have done things as LabGuy just said using one hexed and one not

 

[HonestAbe]

Just got parts in for another screw retained bridge. This time both are custom abutments, and both are hexed. Does something about it being a custom vs stock abutment change things? I asked another experienced tech here and got the same feedback about doing both non-hexed, or one of each as TheLabGuy and others said.

Dentistry was a mistake, let's go back to extracting everything!

 

[Brett Hansen CDT]

Just got parts in for another screw retained bridge. This time both are custom abutments, and both are hexed. Does something about it being a custom vs stock abutment change things? I asked another experienced tech here and got the same feedback about doing both non-hexed, or one of each as TheLabGuy and others said.

Dentistry was a mistake, let's go back to extracting everything!

Is the doctor having the abutments fabricated and then sent to your lab? I am not aware of anyone making custom abutments with a non engaging interface. I have been begging Atlantis for this for years. I use DESS for my non engaging ti bases when I need to fabricate a screw retained bridge.

 

[TheLabGuy]

Is the doctor having the abutments fabricated and then sent to your lab? I am not aware of anyone making custom abutments with a non engaging interface. I have been begging Atlantis for this for years. I use DESS for my non engaging ti bases when I need to fabricate a screw retained bridge.

I'm curious, why don't you just polish the hex off?

 

[Brett Hansen CDT]

I'm curious, why don't you just polish the hex off?

I've done this a couple of times, but only after informing the doctor and getting their permission. The two cases I can remember doing this on were abutments they sent me to use. I already have fought the battle against Straumann in my area and won. If I were to manually adjust an Atlantis abutment in their implant and something went wrong, then they would have ammo to try and trash my lab as they have done in the past.

 

[HonestAbe]

Is the doctor having the abutments fabricated and then sent to your lab? I am not aware of anyone making custom abutments with a non engaging interface. I have been begging Atlantis for this for years. I use DESS for my non engaging ti bases when I need to fabricate a screw retained bridge.

This other case I'm talking about were custom straumen abutments that we ordered based on the doc's scan.

I feel like maybe I should try a make a flow chart or something to see this visually.

If I understand correctly, a screw-retained implant bridge on custom abutments be hexed because that's the only way they're offered, but if it's on stock abutments the generally accepted practice is to do both non-hexed, or one hexed/one non-hexed?

 

[Brett Hansen CDT]

Here is how I restore most implant cases:

Single Unit Screw Retained Case: Scan for Atlantis Custom Base(engaging)
Multi Unit Screw Retained Case where the implants will be bridged: Order non-engaging Ti bases(usually Dess)
Single Unit Cemented Case: Scan for Atlantis Custom Abutment(engaging)
Multi Unit Cement Retained Case: Scan for multiple engaging Atlantis Custom Abutments

You can substitute Straumann, or Nobel, or whichever implant company for Atlantis if you want to go that route but the process is the same. The only issue I have run into with Ti-bases is the width of the Ti base under the tissue. When you add in the thickness of the restoration material, it can be hard for the doctor to insert if the tissue hasn't been contoured(it almost never is). I just make sure I talk with the doc about that first before going that route.

 

[npdynamite]

Allow me to further confuse things. Unfortunately in the world of custom abutments and all the weird specific things doctors want such as a screw retained bridge but specifically using custom abutments rather than Ti bases, you can run into things that don't specifically have a solution. While it has been mentioned that nothing in dental is 100%, I would look at screw retained bridges requiring at least one of the abutments to be non-indexed. The exception, which was noted earlier is very uncommon. So, with your indexed custom abutments the only way to properly proceed is to cut the indexing off of one. Some platforms are better than others for this and different people have different views on whether this should be done. I should also note, I think trucrown might mill non indexed custom abutments? it definitely is not common.

It seems to me that part of your difficulty is having a doctor provide parts without understanding, which parts are needed, so you will probably have to have a conversation there. I would try to just provide you with the scans so that you can ensure all parts will work with the planned final solution. I believe Dess and truabutment make some good nonengaging components that you could potentially use. Dess's libaries will even allow you to work from a Straumann scan body

 

[sidesh0wb0b]

it all depends upon the fixtures being parallel. if they are, then engaging abutments will work just fine. if not, then like @TheLabGuy said, one engaging works and one nonengaging.
worst case, if you use two engaging abutments and path of insert is an issue, you can (carefully) remove the engaging portion on many systems and end up with a non engaging. i agree completely with @npdynamite above. there are many options out there, dess is one of them. open implants is another, and imagine usa, and more.

 

[Contraluz]

look down at the implant analogs and see which one is parallel to the proximal contacts, that's the one

This is important, especially if the paths of insertion are very divergent.
But, and if possible, I keep the mesial implant engaging. It gets more complicated to find the path of insertion, the further back you go.

A lot of good things have been said here.

 

[Pronto]

My experience with stock abutments are they work about 5% of the time unmodified. I hate modifying them so we charge well to do that. We used to do custom cast abutments but most of them have gone by the wayside with digital designed abutments. We used to use Atlantis but are now designing them ourselves on 3Shape and saving a lot of money and time, plus we get what we want for a design. Going back to the engaging/ unengaged issue, if they were not parallel we would do engaging custom cast abutments and use a surveyor. We also did one engaging and nonengaging in certain situations.

 

[KentPWalton]

I'm curious, why don't you just polish the hex off?

When you adjust the abutment below the margin of the stock component, you then void the warranty of the part. The part was not intended for the hex to be polished off. That is why implant companies offer non-engaging solutions.