Primary bar blockout for processing Locator retained overdenture

[Jmichael]

Hi, just a real basic question about blocking out an implant retained primary bar with Locator abutments before making my processing model in preparation for processing a Locator retained lower overdenture. In addition to the usual all-around-the-bar blockout, I'm wondering it it's best to also lightly blockout the top of the primary bar to keep the overdenture acrylic from sitting directly on it. I'm thinking that without blocking out the top of the bar, the overdenture becomes rigid and possibly more prone to stress fractures, while blocking out on top of the bar and keeping the acrylic off of it allows for the Locator retained overdenture to have some slight resiliency. In other words, the Locator attachments in the overdenture would engage female Locator abutments on the primary bar, and the acrylic would not be in direct contact with the top of the bar (or any other portion of the bar).
I'm of the opinion that a light blockout on top of the bar would be best, but I am interested in everyone's opinion. I suppose that it can be done either way. I saw this pic on Preat's Locator bar web page, it appears that they leave the top of the bar exposed prior to processing:

 

[droberts]

Hi, just a real basic question about blocking out an implant retained primary bar with Locator abutments before making my processing model in preparation for processing a Locator retained lower overdenture. In addition to the usual all-around-the-bar blockout, I'm wondering it it's best to also lightly blockout the top of the primary bar to keep the overdenture acrylic from sitting directly on it. I'm thinking that without blocking out the top of the bar, the overdenture becomes rigid and possibly more prone to stress fractures, while blocking out on top of the bar and keeping the acrylic off of it allows for the Locator retained overdenture to have some slight resiliency. In other words, the Locator attachments in the overdenture would engage female Locator abutments on the primary bar, and the acrylic would not be in direct contact with the top of the bar (or any other portion of the bar).
I'm of the opinion that a light blockout on top of the bar would be best, but I am interested in everyone's opinion. I suppose that it can be done either way. I saw this pic on Preat's Locator bar web page, it appears that they leave the top of the bar exposed prior to processing:

Here is a technique you may want to consider.

1. Block bar out with wax. Thin film of wax on top of bar, very thin filling screw access holes.
2. Place Locator impression coping on females.
3. Duplicate full cast / bar using silicone.
4. Place analogs in impression coping and pour up.
5. Transfer the duplicate cast to the articulator and transfer the set-up.
6. Process as you would a normal denture.
This technique allows the preservation of the master cast, fitting denture to the master cast to check any occlusal adjustments.
Note: You may need to relieve deep under cuts to fit denture to master cast.
This process has worked very well with consistent results time after time.

 

[Jmichael]

Thanks DRoberts, that was my exact plan for making a processing model. In fact, I separated it from the silicone mould earlier today, none of the 4 impression copings were retained in the duplicating silicone (and of course there is no getting them back in place in the silicone). I have popped them off of the Locator abutments and lightly lubed the female locator abuts with vaseline, hoping that they will come off more readily in my next attempt. Thinking about running a loop of clasp wire around the 4 of them to add more retention in the silicone.

 

[AJEL]

Exactly ad Robert described I do not use the copings as the silicone will hold the analog normally just fine.
The other thing that this technique does is to remove an expensive bar from processing and chance for damage.
The only other thing I have done is instead of a thin film of wax I use a thin electric tape nicely warmed over the bar to keep an exact even thickness, I have also in the past had bertram cast a over structure like a table cloth on a table for the denture to be processed over, cost around $150. but for heavy denture biters has been a lifesaver.

 

[DMC]

Scan working model with bar?

Reproduce by milling or printing and add spacer/blockout digitally.

Process...

That would be my first idea in 2013 for this mission.

Ajel, you pay $150 for a spacer? WOW.

You must be rich. I'll scan/print you a spacer for $20 LOL

How would you ruin one of the hardest metals on the planet by processing plastic on it?

It can take 1500C or higher, and I can't see any stone or plastic messing up a bar?


What am I missing here? (something I am sure?)

 

[Jmichael]

Exactly ad Robert described I do not use the copings as the silicone will hold the analog normally just fine.

Thanks for your advice on the secondary bar. I have been debating whether to make a mesh inner frame or a thin solid bar encompassing the primary bar as you described. I am leaning toward the cast mesh inner frame.
Just wondering tho, when you say that you do not use the impression copings when duping the model, how are you placing the Locator analogs?

 

[Jmichael]

Scan working model with bar?

Reproduce by milling or printing and add spacer/blockout digitally.

Process...

That would be my first idea in 2013 for this mission.

Ajel, you pay $150 for a spacer? WOW.

You must be rich. I'll scan/print you a spacer for $20 LOL

How would you ruin one of the hardest metals on the planet by processing plastic on it?

It can take 1500C or higher, and I can't see any stone or plastic messing up a bar?


What am I missing here? (something I am sure?)

No scanner, doing this the old fashioned way.
The secondary casting is not a spacer, it's purpose is to strengthen the Locator retained overdenture.
As far as damaging the primary bar during processing, if acrylic were to get under it or locked to it due to some blockout error (it's possible) you might run into a problem recovering the primary bar without some damage. Also, the master model with it's analog implant sites would be destroyed, it's best to preserve that model for future use (rebasing, replacing worn teeth, ect).

 

[AJEL]

Thanks for your advice on the secondary bar. I have been debating whether to make a mesh inner frame or a thin solid bar encompassing the primary bar as you described. I am leaning toward the cast mesh inner frame.
Just wondering tho, when you say that you do not use the impression copings when duping the model, how are you placing the Locator analogs?

I have found over tha past few years that the model analogues will tend to just hold fine if the impression is acurage, again it does not work with hydrocoloid but does for silicone or a silicone layer with hydrocoloid. try a St george silicone over your blockout and put the analogues in the little putty matrix to check me out.

 

[rhicks3302]

I believe the attachments are for retention, not support. The bar needs to provide the support. I like some sort of acrylic or metal stops on the bar. A thin amount of block-out on top of the bar is ok if you have a resilient attachment, i.e., o-ring, ERA (yuck) and I guess some would consider a Locator a resilient attachment. Hader clips, OT Strategy or Bredent SG all need the surrounding bar to bear the occlusal load or they are prone to ineffectiveness or failure.

 

[AJEL]

ricks

I believe the attachments are for retention, not support. The bar needs to provide the support. I like some sort of acrylic or metal stops on the bar. A thin amount of block-out on top of the bar is ok if you have a resilient attachment, i.e., o-ring, ERA (yuck) and I guess some would consider a Locator a resilient attachment. Hader clips, OT Strategy or Bredent SG all need the surrounding bar to bear the occlusal load or they are prone to ineffectivenessor failure.

Bredent, Hader, I still go with t tape spacerTmall taobao agent - Sienke PVC insulation tape electrical tape lengthened super thin super strong adhesive Gaffer tape - Tmall,TaoBao Agent,Tmall English Taobao, Tmall Outlet - Products Online from China taobao at passtao.com, the Hader almost needs a smidgen play to properly engage (check what the green blockout processing piece does) The only bars that work without a tiny play are all on 4. (I agree with the ERA comment but I have one now with 4 mini era's on it) Anyone remember the slant lock?

 

[Jmichael]

I believe the attachments are for retention, not support. The bar needs to provide the support. I like some sort of acrylic or metal stops on the bar. A thin amount of block-out on top of the bar is ok if you have a resilient attachment, i.e., o-ring, ERA (yuck) and I guess some would consider a Locator a resilient attachment. Hader clips, OT Strategy or Bredent SG all need the surrounding bar to bear the occlusal load or they are prone to ineffectiveness or failure.

Thanks for your thoughts on this, your thinking makes sense to me. Regarding Hader bars, here's an image from Preat's Hader Bar instructional page, they recommend blocking out the entire bar, leaving only the spacers & clips:

And, as you can see below in this image from Preat's Locator bar info page, they do the opposite on a Locator bar, leaving the top of the bar exposed:

 

[rhicks3302]

The two implant Hader bar that they show is designed to be mainly tissue supported. I don't see too many two-implant bars anymore. Most two-implant treatment plans are attachments directly to the implants. The bar-supported treatment plans that I was referring to are generally 4 or more implants. I'm pretty sure Tom Bormes from Preat would tell you the same thing.

 

[Jmichael]

Thanks. I plan to call them tomorrow and see what they recommend. This bar of mine is a 3 implant bar.

 

[AJEL]

scot

Ajel, you pay $150 for a spacer? WOW.

You must be rich. I'll scan/print you a spacer for $20 LOL

How would you ruin one of the hardest metals on the planet by processing plastic on it?

would that be milled with attachment housings & full coverage over the bar down to the tissue so that the PMMA can be processed to it with retention loops? for $20.?
If a bar is sort of torked out of a processed denture because the blockout didn't quite do it they don't generally set passively on implants especially from 3 to 13 position long bars. If it didn't sit passively would you re mill the bar N/C as it is so strong?
If I was rich I wouldn't be working Saturday & Sunday, just making ends almost meet these last few years.