Retightening of abutment screws: does it help?
One of the most serious and prevalent problems associated with the restorative aspect of dental implants is loosening and fracturing of screws. Different techniques have been suggested to help prevent this complication. 1,2,3 A recent study examined the effect of different torque application techniques (torqued, retorqued once, and retorqued twice) on the removal torque of implant-supported fixed complete dental prostheses.
The conclusion:
Retightening abutment screws once after the initial torquing could enhance the removal torque of the screw. Care must be taken when retorquing the screws more than once, as this may inversely affect the removal torque.1
Which technique do you use? Do you retorque twice in your practice?
1\. Int J Oral Maxillofac Implants. 2017 Mar/Apr. [The Effect of Torque Application Technique on Screw Preload of Implant-Supported Prostheses](https://www.ncbi.nlm.nih.gov/pubmed/27632154) Al-Otaibi HN 2\. Winker S, Ring K, Ring JD, Boberick KG. Implant screw mechanics and the settling effect: an overview. J Oral Implantol. 2003;29:242“245. (in this study the authors recommend that: “Implant screws should be retightened 10 minutes after the initial torque application as a routine clinical procedure to help compensate for the settling effect.” 3\. Siamos G, Winkler S, Boberick KG. The relationship between implant preload and screw loosening on implant-supported restorations. J Oral Implantol. 2002;28:67“73.4 Comments on Retightening of abutment screws: does it help?
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Geoff
4/25/2017
It used to be suggested to torque once and then wait for several minutes to give the threads time to "relax" and then torque again. Read an article a couple of years ago in which they studied the relaxation over time (sorry, don't remember the article). They said the vast majority of the relaxation happens in the first ten seconds. So I torque once again after ten seconds.
Mark Bornfeld DDS
4/25/2017
It bears mentioning that the dependent variable in the aforementioned study ("removal torque") is really a surrogate for resistance to loosening. Although it makes intuitive sense that removal torque may be inversely related to probability of loosening, that would be an assumption. It may even be that repetition of torqueing may contribute to metallurgical strain, ultimately increasing risk of screw fracture. I await an in-vivo randomized controlled trial, with reasonable statistical power, that measures what matters-- directly.
Alejandro Berg
4/27/2017
Having done a masters thesis on this subject I think I cans share some light into this matter. There are several assumptions about screws but basically when you tighten a screw, due to the mismmatch of the thread and the implant inner thread( and please don´t believe in the " we make perfect matching parts" crap because that is by today industry standards a total imposibility) you will get some contact between a small piece of one or two threads and that is it. You may want to believe in graphite or other covers but they are not really effective, they are some type of compensation in order to get some similar grip as you would with a deformable gold screw, remember that today´s titanium screws are made of grade 4/5 or 23, and that means small to none deformation at 40ncm. So, retightening.... what happens when a screw gets loose? or better yet why a screw gets loose? there are several possibilities as to why but the most common is poor fitting of the abutment (Fully castable abutments are the N°1 seller in the world and they are, for lack of a technical word; crap). Poor fitting can also be achieved by overcasting CrCo Abutments or Ti abutments, specially if its a direct crown with several porcelain cookings.Please also there are companies that have negative camber, 1 degree or so, remember that friction is not seal. There is another very common reason, the crown does not go all the way in due to over contour or excesive contact pressure( mesial or distal). What happens to the screw when it gets loose, part of the time it gets small fractures right where it was in contact with the inner thread of the implant and becomes useless, other time it gets deformed and what i call pre breaking stage, useless anyway. So if retightening is needed, a reason must be found and the screw replaced for a new one at the very least.
Have a great day.
Kenneth Szurgot
5/7/2017
Alejandro
I agree that excessive pressure from the contacts is a big problem along with open embrasures between natural teeth-implant contact. This is minimized with a cement down restoration since there will be inaccuracy in the crown abutment interface. With screwed down restorations all that stress from a divergent contact will now be on the screw. This can cause plastic deformation of the screw threads
I have not found an adequate method of paralleling these contacts. Have you come across anyone who has a solution?
Is your research published?
