Screw removal on screw-retained mandibular prosthesis: advice?

I am making a screw-retained mandibular prosthesis and we are utilizing an 8-year old Astra 3.5mm implant along with four new implants placed by my oral surgeon. I accessed the .050 hex very easily, but cannot get the screw loose. My drivers started twisting in the hex, so I stopped and sealed the opening. I ordered a Zimmer SRT ( screw removal tool) driver but have never used one before. I also have a call in to my oral surgeon to see if he has experience with this. I don’t mind taking this on again, but I am seeking any advise I can get on making this work. Can anyone offer tips on loosening the screw and the use of the SRT driver? Thank you! I am having an issue uploading a photo , but wanted to get this out. I will try to add the photo as a follow up.



7 thoughts on: Screw removal on screw-retained mandibular prosthesis: advice?

  1. Carlos Boudet, DDS, DICOI says:

    The Astra 3.5 takes a .050 driver, so if your driver is not damaged, take a good look at the screw head with magnification. The screw head hex must be damaged. Sometimes a Nobel driver will allow you to engage a damaged .050 hex better, try that and see if it works.

    Good luck!

  2. Guillermo Molina, DDS says:

    Look at the tip of your .050 driver to make sure it has all nice, sharp corners and angles. If not, then cut .5 to 1.0 mm off the tip in order to get better engagement of the driver into the screw. Also, push down on the driver as you turn it to help keep it positively seated inside the screw.

    Good Luck.

  3. Rob says:

    Hi,
    First check that the end of your screwdriver is not so worn that it will not engage a slightly distorted screw head.
    If the screw hex is only slightly damaged and the hex shape is still recognizable, and you have more than one hex driver, this might work. Carefully shave a tiny amount from the working end of the screwdriver. This creates a hex that is slightly greater than the .050 screwdriver that Carlos mentioned. (The screwdrivers taper outwards towards the handle.) It will go slightly further into the screw head with a little pressure. This may be enough to free the screw. The screw driver remains usable for further hex screws.
    But if it really won’t come out with the screwdriver, I’ve removed damaged screw heads using an end-cutting diamond. You match the end of the drill to the .050 hole and carefully drill down checking frequently and with loads of water coolant. It may eventually be possible to break the head off.
    Assuming that the threaded part of the screw is undamaged, you simply unscrew the remaining part from within the implant.

  4. Dr Dale Gerke, BDS, BScDent(Hons), PhD, MDS, FRACDS, MRACDS (Pros) says:

    There are many reasons why the screw might not unscrew. None are really important since your only objective is to remove it.
    The usual hex in the screw head is very similar to a Nobel, but there is a minor difference which (in this case) will probably not allow you to unscrew the screw (I suspect it will not fit closely enough to remove a tight screw).
    I presume you have good vision of the head. Sometimes practitioners use different head screws (eg universal head) made by non genuine suppliers. If it was a universal head, it can be very hard to differentiate if you cannot easily see it. So my first comment is to get good vision of the actual screw head.
    In my case (I inherit lots of patients with unknown implants and screws) I have about 30-40 different drivers which have been collected over 35 years. I simply try them individually until I find one that fits tightly enough to unscrew the screw. You probably do not have access to such a range of drivers but you might know a colleague who does. Perhaps borrow them.
    Alternatively, I mentioned a few weeks ago about an Astra or Nobel (both are similar) screw removal “bur” which is latch grip and fits in a slow hand piece and can be “pushed” onto the screw head and then run the hand piece in reverse. A reduction hand piece works best due to slower revs and more torque. However this method might not work since it is designed for broken screws and therefore there would usually be more surface area for the bur to “grab” onto. However it is cheap and easy to get one of these burs so it would be high on my agenda to try before I went too much further.
    The next step would be possibly a screw removal kit you mentioned. However these are expensive and not as easy to use as you might think.
    Therefore, if you have time and a lot of old high speed burs, you might like to try to cut off the top of the existing implant crown to expose the offending screw head. Once exposed, there are a variety of possibilities. You might like to “slot” the screw head (with a high speed bur – careful it is not as easy as it sounds) and use a slot driver (rather than a hex driver). Or if you create a “groove” around the head, and you can grasp the head, you might be able to grasp the head with any type of forceps you have available (eg root or artery forceps) and twist it loose.
    So you can see that there are many ways you could attempt to remove the screw. To some degree it is a little like extracting a root tip. You just have to think about different ways to get adequate access to the screw and try various instruments until you can get the right amount of purchase on it to remove it. I am sure you will find a way. We dentists are very inventive!

  5. Joseph Kim, DDS, JD says:

    If the screw is stripped, a reverse threaded, small abutment removal tip, can be used to engage the rounded off hex in the head of the screw. The AR mini tip by Hiossen fits perfectly into stripped 0.50 screws. Alternatively, just cut the head of the screw off with your highspeed handpiece, and remove the remnant screw with cotton forceps after removing the superstructure.

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