4-unit, 2-implant cement-retained bridge... Engaging or non-engaging abutments?

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ddsTech

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Hey everyone,

I've restored a lot of single unit implant cases for my doctors, but not implant bridges until recently. This is an anterior case with 2 Atlantis custom abutments on an Astra Tech TX 4.0mm platform. The implants are divergent and flared. The bridge will be cemented, but will have angulated screw channel access holes in case the screws come loose. The implant screw channels would exit through the incisal edges without the angled channels.

Different reputable sources say either that you always want to use all non-engaging abutments on implant-supported bridgework, or you can use one non-engaging and one engaging, or leave them both engaging. Very confusing..... What has been your experience over the years with this issue? I'm wondering if I should cut off the engaging elements or leave them on?

Mark
 
KTR

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When the bridge is not screw retained, you have to choose engaging for both because the doctor could never get them locked down in the exact position you have on the model. Especially if they are angled.
 
Sda36

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Hey everyone,

I've restored a lot of single unit implant cases for my doctors, but not implant bridges until recently. This is an anterior case with 2 Atlantis custom abutments on an Astra Tech TX 4.0mm platform. The implants are divergent and flared. The bridge will be cemented, but will have angulated screw channel access holes in case the screws come loose. The implant screw channels would exit through the incisal edges without the angled channels.

Different reputable sources say either that you always want to use all non-engaging abutments on implant-supported bridgework, or you can use one non-engaging and one engaging, or leave them both engaging. Very confusing..... What has been your experience over the years with this issue? I'm wondering if I should cut off the engaging elements or leave them on?

Mark
Hi Mark, my understanding is that leaving engaging can be problematic at delivery especially divergent ones. I try to leave one engaging ( implant likely to have most functional load) and then cut off the other. Reason being is to reduce load on screws more. I've done a fair bit of these and have tried to follow this plan and to date, no issues..."where some wood dammit" Hope I didn't just jynx myself
Hope this makes sense and all the best on your case. Happy Holidays Mark!
 
Sda36

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Hi Mark, my understanding is that leaving engaging can be problematic at delivery especially divergent ones. I try to leave one engaging ( implant likely to have most functional load) and then cut off the other. Reason being is to reduce load on screws more. I've done a fair bit of these and have tried to follow this plan and to date, no issues..."where some wood dammit" Hope I didn't just jynx myself
Hope this makes sense and all the best on your case. Happy Holidays Mark!

P.S you can also try just reducing the hex with a rubber wheel but with really divergent ones you need complete removal of the hex or Dr. is going to have a real problem getting it home. Try for yourself on model with soft tissue in place to get an idea.
 
Contraluz

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The bridge will be cemented, but will have angulated screw channel access holes in case the screws come loose.
If that is the case, and one ore both screws come loose, it may still be problematic to get the bridge off, depending the angulation.

Multi abutment screw retained restorations are usually done with non engaging abutment interfaces, since they are cemented prior to insertion. More extensive cement retained bridge work is oftentimes cemented with temp cement, due to the option to have it retrievable.

KTR and Sda36 have both good points regarding the situation.
 
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Your question is about draw.
If you have 2 divergent implants and plan to make a cemented FPD, just create 2 engaging custom abutments, make them parallel with a draw path of insertion. Your Dr can use the FPD as a jig to position the abutments, then torque and cement. Abutment screw loosening does not happen in my world: straumann BL implants with straumann genuine cust abutments and torqued to spec. Inexperienced Drs often don't torque the abut screw to spec , they strip the head for some stupid reasons and don't achieve spec torque and then the abut screw becomes loose...
 
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I appreciate everyone's input on this. All good responses. Thanks very much!

The concept of non-engaging abutments reducing the load on the screws, as Sda36 mentioned, is what keeps me coming back to this idea of cutting off the engaging element. If the bridge is cemented though, doesn't this already minimize that strain on the implants and screws as long as the bridge fits passively? I'm thinking that the screw strain issue is a much bigger factor for screw-retained restorations. If everything isn't perfect with a screw-retained bridge, something has to break, remodel or orthodontically move to relieve that strain. Not so with a cemented bridge that fits passively, correct?

KTR - valid point about trouble aligning the abutments properly without the engaging elements. If I did remove them, DrG's suggestion of using the FPD as the seating jig should be accurate enough to align them correctly, I would think?

Keith Goldstein, I love the concept of the Angled screw channel ti bases non engaging you mentioned. It would solve many issues I'm seeing in cases. Question.... is the bond strength of the bridge to the Ti base great enough to support tall restorations? If a bridge or crown is 10mm in height, is the cement bond enough to hold the restoration in place?

DrG, that's exactly how I'm doing the case. The Atlantis abutments are done, with draw like a traditional FPD case. Unfortunately, we've had some screw loosening issues in the past, so the Dr. wants access to the screws.

As Contraluz mentioned in his post, regarding larger cases, Dr. Carl Misch talks a lot about using "soft access" cements that make these cemented bridges "removable" without cutting screw access channels in the restoration. Bosworth Super EBA zinc oxide eugenol cement is an example of a "soft access" cement he uses. Another one is a polycarboxylate cement, Duralon. He gives different indications for each. I'd love to know how difficult it is to remove an implant-supported FPD cemented with these cements. If I read Dr. Misch correctly, this is his preferred was to go over screw-retained restorations.
 
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Tibase design has improved. Some have pre-sandblasted retention form (like Dess) and it is probably a very good idea as you will avoid blasting the smooth collar. Tibase are now available in multiple retention heights in an attempt to address the lack of pure mechanical retention forms we had. The bonding of the prosthesis to the tibase is technique sensitive....I see, hear too many debonding
 
Jason D

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I don’t really understand this question… If they are a custom abutments with cemented restorations you need to use engaging abutments

using non-engaging abutments just creates an assortment of possible issues including seating issues, screw loosening and fracture...
 
Sda36

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I appreciate everyone's input on this. All good responses. Thanks very much!

The concept of non-engaging abutments reducing the load on the screws, as Sda36 mentioned, is what keeps me coming back to this idea of cutting off the engaging element. If the bridge is cemented though, doesn't this already minimize that strain on the implants and screws as long as the bridge fits passively? I'm thinking that the screw strain issue is a much bigger factor for screw-retained restorations. If everything isn't perfect with a screw-retained bridge, something has to break, remodel or orthodontically move to relieve that strain. Not so with a cemented bridge that fits passively, correct?

KTR - valid point about trouble aligning the abutments properly without the engaging elements. If I did remove them, DrG's suggestion of using the FPD as the seating jig should be accurate enough to align them correctly, I would think?

Keith Goldstein, I love the concept of the Angled screw channel ti bases non engaging you mentioned. It would solve many issues I'm seeing in cases. Question.... is the bond strength of the bridge to the Ti base great enough to support tall restorations? If a bridge or crown is 10mm in height, is the cement bond enough to hold the restoration in place?

DrG, that's exactly how I'm doing the case. The Atlantis abutments are done, with draw like a traditional FPD case. Unfortunately, we've had some screw loosening issues in the past, so the Dr. wants access to the screws.

As Contraluz mentioned in his post, regarding larger cases, Dr. Carl Misch talks a lot about using "soft access" cements that make these cemented bridges "removable" without cutting screw access channels in the restoration. Bosworth Super EBA zinc oxide eugenol cement is an example of a "soft access" cement he uses. Another one is a polycarboxylate cement, Duralon. He gives different indications for each. I'd love to know how difficult it is to remove an implant-supported FPD cemented with these cements. If I read Dr. Misch correctly, this is his preferred was to go over screw-retained restorations.
Hi, to be clear, I suggested you keep the abutment with most possible load- engaged.
 
Sda36

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I appreciate everyone's input on this. All good responses. Thanks very much!

The concept of non-engaging abutments reducing the load on the screws, as Sda36 mentioned, is what keeps me coming back to this idea of cutting off the engaging element. If the bridge is cemented though, doesn't this already minimize that strain on the implants and screws as long as the bridge fits passively? I'm thinking that the screw strain issue is a much bigger factor for screw-retained restorations. If everything isn't perfect with a screw-retained bridge, something has to break, remodel or orthodontically move to relieve that strain. Not so with a cemented bridge that fits passively, correct?

KTR - valid point about trouble aligning the abutments properly without the engaging elements. If I did remove them, DrG's suggestion of using the FPD as the seating jig should be accurate enough to align them correctly, I would think?

Keith Goldstein, I love the concept of the Angled screw channel ti bases non engaging you mentioned. It would solve many issues I'm seeing in cases. Question.... is the bond strength of the bridge to the Ti base great enough to support tall restorations? If a bridge or crown is 10mm in height, is the cement bond enough to hold the restoration in place?

DrG, that's exactly how I'm doing the case. The Atlantis abutments are done, with draw like a traditional FPD case. Unfortunately, we've had some screw loosening issues in the past, so the Dr. wants access to the screws.

As Contraluz mentioned in his post, regarding larger cases, Dr. Carl Misch talks a lot about using "soft access" cements that make these cemented bridges "removable" without cutting screw access channels in the restoration. Bosworth Super EBA zinc oxide eugenol cement is an example of a "soft access" cement he uses. Another one is a polycarboxylate cement, Duralon. He gives different indications for each. I'd love to know how difficult it is to remove an implant-supported FPD cemented with these cements. If I read Dr. Misch correctly, this is his preferred was to go over screw-retained restorations.


This is a method first proposed by Dr. Harold Shavell of Chicago. Using Duralon, which is tough stuff for sure, he would Vaseline the preps and the the resultant adheshion would be in the temps themselves,not bonded to the preps.
 
PDC

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I appreciate everyone's input on this. All good responses. Thanks very much!

The concept of non-engaging abutments reducing the load on the screws, as Sda36 mentioned, is what keeps me coming back to this idea of cutting off the engaging element. If the bridge is cemented though, doesn't this already minimize that strain on restorations.

I really don’t understand your logic here. There is no reason to use non engaging abutments. You can design the abutments to be paralleI and achieve a passive fit with the bridge eliminating worries about broken screws.

Engaging abutments will provide a more secure abutment. Reason being is that you have more surface area “engaged” at the abutment interface thus providing more stability.

lf screw torque protocols are followed then you shouldn’t have any screw breakage issues. Give the doctor an insertion guide as insurance if need be.
 
JMN

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Hey everyone,

I've restored a lot of single unit implant cases for my doctors, but not implant bridges until recently. This is an anterior case with 2 Atlantis custom abutments on an Astra Tech TX 4.0mm platform. The implants are divergent and flared. The bridge will be cemented, but will have angulated screw channel access holes in case the screws come loose. The implant screw channels would exit through the incisal edges without the angled channels.

Different reputable sources say either that you always want to use all non-engaging abutments on implant-supported bridgework, or you can use one non-engaging and one engaging, or leave them both engaging. Very confusing..... What has been your experience over the years with this issue? I'm wondering if I should cut off the engaging elements or leave them on?

Mark
You are overcomplicating things and needlessly scarring yourself.
This bridge will be no different than a tooth borne bridge. With the exception that formthe first time in your life your bridge preps are almost exactly what and how you want them shaped if you did it instead of the doctor because you are doing the preps.

You are making custom abutments to create a path of draw/path of insertion.
In understanding when to engage or not to engage the anti-rotational features you only need to know if the abutments will be seated as individuals, not all at once. OR if they will be seated all at once.

If they are to be placed one at a time, you want engaging to prevent micro-rotation and eventual screw loosening among other things.

If the abutments are joined together and being seated as one unit and not individually you do not need tomengage the anti-rotational features as the abutment being a non-indivduated part of a non separable whole will prevent rotation of all the abutments which are part of that (sub)structure.

You *may* use one or two engaging abutments in places where all non-engaging would be fine, but it is increasing the chance that they will not all seat uniformly or even at all. An engaging abutment will require the entire restoration to be inserted following the path of insertion of that engaging abutment, which as you know allows quite little if any deviation of direction.




Yes you can use all engaging on a 7 implant screw retained bridge. But you better have the most awesome oral surgeon in history getting those implants sunk perfectly parrallel. You can use all nin-engaging on a cement retained bridge, but you'll need to produce and provide a setaing jig to let the placement dentist get them in the proper rotational timing so that the bridge will seat. It is best, however, to always use engaging when seating abutments as individuals and non-engaging when seating as a group. Much less headaches for all involved.


I hope that made sense, and helps you get a better understanding of reasons for the should/shouldn't/may/can confusion.
 
Contraluz

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Unfortunately, we've had some screw loosening
If I may, Is there a pattern in the brand, or implant platform, in which you have experienced screw loosening?
 
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We arent just considering making the preps parallel so the bridge will draw. The engaging portion of abutments must be able to draw also. If there are multiple implants and one is not close to parallel with the others, imagine screwing long engageing abutments like conical Straumann. Cement the bridge on to it, remove the screws and it wont draw off the model. This is what the OP is considering, I believe.
Like SDa36 was saying, you may need to rubber wheel some of the engagement down on a couple. For the Doctor to get them seated accurately though, thats a trick if too much is removed and resulting in non-engagement. The Doctor hasnt thought this through.
 
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I don’t really understand this question…
I really don’t understand your logic here.
You are overcomplicating things and needlessly scarring yourself.
I do a lot of reading, and if any of the reputable sources I read had stated the issue as plainly as what you guys have explained, I wouldn't have needed to ask the question. Based on all of your posts, it makes sense to me now and I was over-complicating things. Thanks very much for taking the time to make it clear. Seeing the color pictures of failed implant bridges makes me want to do everything right.

Your question is about draw.
We arent just considering making the preps parallel so the bridge will draw. The engaging portion of abutments must be able to draw also.
Right. I just need to make sure the Dr knows that the bridge and abutments won't be retrievable as one unit once it's cemented in place (with the engaging elements left on). The screw access holes could be confusing, though. It will have the appearance of being screw-retained.

If I may, Is there a pattern in the brand, or implant platform, in which you have experienced screw loosening?
That's a tricky one and I'd rather not name names because I can't be 100% sure that operator error isn't a factor. I've had 4 single-unit implant cases where the screws either wouldn't engage at all or came loose within a few days.
 
JMN

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Right. I just need to make sure the Dr knows that the bridge and abutments won't be retrievable as one unit once it's cemented in place (with the engaging elements left on). The screw access holes could be confusing, though. It will have the appearance of being screw-retained.
The term that has come about for cemented crowns or bridges with screw access holes for the abutment screw is 'screwmented'.

Sometimes it means a crown cemented outside the mouth to the abutment (to reduce cement getting in to the implant/human interface point and reduce chances of peri-implantitis) OR for a situation like you are making with a crown/bridge that has screw access holes but cannot be placed/drawn as one device.


Nobody knew all this stuff without asking. Never keep a question to yourself. We all had to learn from someone and that (and terrible jokes) is what this place is about.

Real glad you got your answers.
 
JMN

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Right. I just need to make sure the Dr knows that the bridge and abutments won't be retrievable as one unit once it's cemented in place (with the engaging elements left on). The screw access holes could be confusing, though. It will have the appearance of being screw-retained.
One thought that you may or may not know.

When a dentist takes a xray of the restoration they will be able to see that it is engaging or not engaging.

Titanium is not totally radio-opque, so the engaging or non-engaging base of the abutment will be known to them by looking at the xray and will not have to guess or rely on thier chart notes to know even if the patient changes dentists.
 
rkm rdt

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I leave one engaging and one with the hex removed.
Always a custom abutment.
 
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