Figuring out if the Crown or Abutment is Loose: Techniques?

Dr. K. asks:
I have been doing cement retained crowns for the last 5 years. I use temporary cement to retain the crowns. Every now and then I have a patient come in with a loose crown. In almost all of these cases, it has been due to the abutment screw loosening. For molars and premolars I have been able to drill though the occlusal and access the abutment screw without any trouble. Occasionally I have had a crown where the cement was loose and the abutment was solid. For these cases I have been able to wiggle off the crowns. My problem is occasionally I have a case where I cannot figure out if the crown or the abutment is loose. Is there some technique for using radiographs to make this determination so I could be confident in my treatment?

8 thoughts on “Figuring out if the Crown or Abutment is Loose: Techniques?

  1. It’s good that temporary cement (or even a permanent cement with vaseline) is used. The crown should be removed completely and so should the abutment. At that point, you check to see if the implant is moving or not.

    Why does this keep happening? Perhaps the implant abutment isn’t torqued completely. For some implant systems between 32-35nm is needed for the torque. If it is less, there is a higher risk of abutment loosening. And in reality, you don’t want to keep retightening the abutment over and over again.

    What is another reason for abutment loosening? Bruxing. Try to make it a habit to fabricate a night guard for all of your patients who either need implants or extensive restorative treatment. Chances are, another dentist didn’t even talk about bruxing and grinding as a contributing factor to the patients’ dental conditions.

  2. Hello
    Standard protocol should be used while tightening the abutment screw. With this there won’t be any screw loosening. Also prosthetic part also lead to screw loosening. Everything should be considered prior to fabrication of prosthesis. If the single crown rotates then the reason is screw loosening.

  3. In sequence of the safety valve incorporated,in an aberrant contact,or occlusal loading, the cementation medium gives way,then the abutment screw loosens or fractures, and finally the implant fractures under stress. If you are getting repeated abutment screw loosening and/or crown debonding, apart from the torque on the screw, you must check for occlusal loading in all planes, especially excursive movements. If necessary, adjust,or even re-fabricate the crowns..best of luck..

  4. A loose screw always has a slight “rattling ” feeling when moving it .
    After tightenning the screw to the manufacturers torque doit a secdond time later and always keep cusps flatter to avoid lateral forces in parafunction.
    Peter

  5. Misch recommends tightening twice with 5 min interval to re-stretch the screw. I have not had any issues following this. I often feel the screw getting tighter using the same 35 n torque on the second attempt.

  6. There are several issues here that have a direct relationship to screw loosening. First is implant/abutment design. If you have a flat-to-flat connection (i.e. Nobel), the primary retentive device is the screw, not the abutment itself. Sheer forces tend to tilt the abutment off the table top resulting first in percolation of fluids/bioburden into the implant body and, ultimately, screws backing out of the connection. Short of changing your implant system, the best thing to do is as the previous poster suggested; torque at least twice leaving sufficient time for thread relaxation/deformity. You can also use a diamond coated screw (if it is available for your system) rather than the lab screw that comes with the case. These coated screws are far more resistant to backing out as they have an interference fit.
    The next alternative is to move to an implant design that has an interference fit built into the abutment. The screw merely serves as a device to drive the abutment into the implant body. This will not only eliminate screw loosening, but also dramatically reduce microleakage. And, finally, if you are using a system with this type of abutment connection, you can use a permanent cement to prevent cement washout and crown loosening.
    RJM

  7. Hi Robert,

    I agree with you 100% with your statements about the flat against flat connections vs conical connections. Unfortunately, I am not sure if the torquing multiple times or diamond coated screws will always help either because the problem is often not with the screw spinning out but actually elongating during mastication and once the screw elongates to the point that it has no friction anymore it is loose without ever spinning. The advantage of conical connections (or interference as you call them) is that there is minimal movement in the connection and the screw does not elongate. The best way to visualize that is by entering in google : “Zipprich and Implants” and see the videos that show how the abutments move under load. (I think that I can not insert outside links on this site).

    Best,

    Albert

  8. Tighten your screw 25 N to 30 N…you will rarly have a loose abutment..
    use your crown removal and hit the crwon ,,if it falls so it would be cement ;)
    usually loose cement fall down ; doesnt retain in its place..
    to avoid screw loosening in bridge try to tripod implant placement for more stability.

Comments are closed.