Monday, May 9, 2016

Complications in Implant Dentistry


Case # 18   “My Implant Crown Never Felt Tight Like the Others”

Patient has a tissue level Straumann implant that is placed and allowed to integrate for 8 weeks. Impressions are made for a screw retained crown. The crown is delivered by an exceptionally skilled and experienced referral and torqued to 32 N/cm.  Shortly after this time the patient notes some movement in the crown; having other implants he questions this.  The abutment screw is retorqued; it is tight but still has some side to side movement, although almost clinically unperceivable. There was no pain on torquing the screw.  He lives with this for a year and notes it is slowly getting more mobility.

He presents to our office for evaluation.  First step is PA radiograph and CBCT that look fine.  Next is clinical exam and there is a rotational movement from left to right very minimally when the crown is grasped between the fingers.  It is barely perceivable but is present. On percussion the crown sounds solid

Diagnosis would include implant loosing integration.  Loose abutment screw and or loose crown.  Each interface must be checked systematically.  Since this is a screw retained crown that eliminates the need for drilling through the crown to access the prosthetic screw to remove it. It also eliminates the possibility of the cement union failing.  Although on a side note for the future there are many lab techniques using milled restorations that are advocating cementation of a crown to an abutment to create a screw retained restoration, only time will tell if this interface will weaken in some cases. In this case it was a cast UCLA type abutment.

The composite was removed a small cotton pellet was removed and the screw was reversed.  The screw was very tight and required a torque wrench to counter torque.  It caused no pain or distress to the patient when this was done. The area was irrigated after the crown was removed; a small amount of metal particulate consistent with a grinding movement of the crown was evident in the implant body.

To test the implant it was percussed and sounded solid an implant mount was placed and the implant was torqued and counter torqued with no pain or movement...  It was determined the implant was solid.  There was some debris in the implant consistent with the friction from abutment mobility.  

So next the internal integrity of the implant was tested to make sure the abutment had not degraded the internal connection. This was done by the placement of a transfer type impression coping it was place and tightened and attempts were made to rotate it. There was no movement.  This confirmed the implant internal connection was not damaged or rounded by the crown movement.  So continuing in a bottom to top analysis. The abutment was tested.

The abutment was tested by placing the screw retained crown on a brand new implant analog.  The model and original analog was not used since these sometimes become accidently modified in the lab setting.  It was noted that the crown ucla abutment did not fit flush to the implant analog.  There was a gap caused by a small hang up on the buccal where the porcelain extended to the metal junction. When the crown was placed on the analog mounted in the model as supplied by the lab it sat flush.   This was removed carefully under magnification incrementally until the crown fit snuggly on the new implant analog.  At this time the restoration was transferred to the mouth and fit snuggly with no rotational mobility.  A new abutment screw was placed and torqued to 32 N/cm, contacts and occlusion were tested Teflon tape and composite were used to seal the access hole.

A good example of a common problem that does occur in implant dentistry and why it is important to have a supply of impression copings and analogs as well as abutment screws always in stock so the this type of diagnosis can be made and corrected for the patient.


No comments:

Post a Comment