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Solving Common Problems with Science: Implant Abutment Screw Loosening

Video highlights

  • Common reasons for screw loosening
  • Understand how screws work
  • Considerations regarding facial change and development
  • Correct usage of torque limiting tools
  • Practical tips and habits to avoid screw loosening

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Anonymous
02.04.2023 | 12:28

What is if the abutment-diameter is bigger than the previous gingiva-former?? Then proper gingiva-forming is even more mportant?

I experience often that i can screwca crown a lot deeper when waiting these 10minutes ... Maybe thats my insufficient gingiva-forming in advance then?

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I experience often that i can screwca crown a lot deeper when waiting these 10minutes ... Maybe thats my insufficient gingiva-forming in advance then?

Profile picture for user drsvoboda

It can be very difficult to verify that you have optimized the fit of the implant-abutment connection clinically. Being able to screw the abutment-crown complex deeper is a sign that it is not down all the way. However, even if the abutment-crown complex does not appear to go down further, this is not a verification that the fit is optimized. The contacts with adjacent teeth may be preventing it from seating properly,  and/or the bone or gingival may be preventing its seating. With multiple teeth prosthetics where the abutments are already embedded in the prosthesis, the abutment connectors are often aligned in non-optimal 3-D positions that prevent them from seating. This is often the case with multiple unit prosthetics installed by the screw-in technique. 

Certainly the simplest clinical condition is when abutments are installed without the prosthesis attached  ... and indeed ... if the abutment does not slip right into place ... the dentist should be prepared to expose the implant top, remove any tissue impediments and verify the seating of the abutment visually.  This would be the best we can do to mitigate the negative effects of the implant-abutment misfit. Of course ... also pay close attention to all the important information provided by Dr. Wadwhani. 

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Profile picture for user drsvoboda
02.04.2023 | 17:24

Why do you assume that an optimized fit of components when it is difficult to achieve clinically?

Besides the problem of non-optimal parts there are the root causes of misfits that must be mentioned. Prosthesis Dimensional Error contributes to the misalignment of parts when the connectors embedded in the prosthesis have smaller tolerances for error than the prosthesis. Incongruent Paths of Insertion when the paths of insertion determined by adjacent teeth is incongruent with those determined by the implant and abutment-crown complex. Resistance to Displacement by adjacent hard and soft tissues that can prevent the abutment from seating into the implant. What do you think? 

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Besides the problem of non-optimal parts there are the root causes of misfits that must be mentioned. Prosthesis Dimensional Error contributes to the misalignment of parts when the connectors embedded in the prosthesis have smaller tolerances for error than the prosthesis. Incongruent Paths of Insertion when the paths of insertion determined by adjacent teeth is incongruent with those determined by the implant and abutment-crown complex. Resistance to Displacement by adjacent hard and soft tissues that can prevent the abutment from seating into the implant. What do you think? 

Profile picture for user cpkw1

You are correct

abutment positioning and resistance from both hard and soft tissue will affect the way an abutment will seat into or onto the implant fixture.

it is imperative that the clinician understand path of insertion and gingival tissue resistance and displacement effect.

If the periimplantitis tissues are too tight then the abutment and abutment restoration complex may not seat fully.

this places extra stress on the screw and leads to premature failure.

path of insertion is also critical- (even though teeth have been shown to move laterally by upto 150 microns from studies on tooth wedging) the guiding path can prevent seating of the abutment.

this should always be critically accessed both clinically and during the laboratory procedures with accommodations being made where necessary!

thank you for your great questions!

 

 

 

Profile picture for user drsvoboda

I believe that understanding the root causes of mechanical misfit connections is key to reducing treatment complications … like screw loosening and implant breakage .. related to fixed prosthetics. Misfit connections are less stable than optimized connections and are also a known risk factor for peri-implantitis. Knowledge about the mechanisms by which dentists cause them does not appear to be common. I have published a concise explanation of their root causes “Slides 38-43 in my presentation “Making Fixed Prosthesis Installation Safer … “ under articles at www.ReverseMargin.com” 
I look forward to your comments. :-) 

 

Profile picture for user drsvoboda

Dear Dr. Wadhwani, Thank you for your answers. You mentioned Path of Insertion. Indeed, even for a single tooth there are multiple Paths of Insertion to consider. There is the path of insertion determined by the adjacent teeth and other tissues, the path of insertion determined by the implant and its screw channel, and the path of insertion determined by the abutment connector and its abutment screw.

The problems is, to get an optimized implant-abutment fit with the current screw-in system (where the abutment has been incorporated into the crown on a dental model) it would be nearly impossible to align all these paths of insertion within the tolerance of their connecting parts ... if those tolerances were plus/minus 5 microns - 1/20 the diameter of a hair. It would be difficult to adjust contacts at that tolerance with a rotary instrument while holding the crown complex in one's hand. If the mesial and distal contact were slightly off ... that would likely result in a misfit as it would not allow the abutment to seat optimally. This certainly could lead to all the problems you mention including peri-implant disease. 

Now with multiple units, well I can say that is really impossible as it is not even possible to align implants within such a narrow tolerance and the model error would even make the other paths of insertion even more difficult to align. This is a BIG problem. The only solution I see is for the manufacturers to make the fit of connectors sloppier (ie larger tolerances). However larger tolerances would be expected to behave more like misfit joints, as they would leave more space for pathogens to breed and be looser than parts with tighter tolerances.  

Why don't the implant manufacturers publish the tolerances of their parts to help dentists choose what is best for their patients? Why don't they reveal this common problem of misfit parts to dentists that is related to the screw-in system that they promote? Without that information ... how can clinicians use their ingenuity begin to address the implant-abutment and abutment-prosthetic connector misfit problem and its consequences?  I look forward to your comments. 

Profile picture for user drsvoboda

Dr. Wadhwani, Regarding the comment that natural teeth can move150 microns laterally. I assume you mean that adjacent teeth can move 150 microns to compensate for expected Prosthesis Dimensional Error and Incongruent Paths of Insertion. While it is possible for some teeth, especially those that have lost some support I am not sure we can depend on adjacent teeth to properly compensate for the above problems and Resistance to Displacement by adjacent tissues. I know that gingiva can be very difficult to displace when it is thinner and up against bone or adjacent hard tissues. I know that implant retained adjacent crowns are very difficult to displace and teeth that are contacting other teeth are difficult to displace. Indeed I would say that it is usually not that easy to predict whether we have successfully displaced adjacent teeth and other tissue and adjusted contacts sufficiently to ensure an optimized fit of the implant-abutment junction when installing the crown or bridge onto teeth or dental implants. 

Indeed, I do believe that the dentists' best chance to optimize the implant-abutment connection is when there is no tooth attached to the abutment. The attached tooth adds to the complexity by needing  contact adjustment and it obscures the dentist's vision.  Also if the abutment is free to align itself with the implant, it has the the best chance to do so optimally. This problem is of course multiplied with multiple units. What do you think?