July 2022
The patient presented on referral from Dr. S. for evaluation and implant mechanical rescue (IMR) to retrieve a fractured zirconia abutment from the 4.5×14 Ankylos CX implant in the #9 site. This fracture occurred secondary to a traumatic accident while using an exercise band failure as the patient was working out. The traumatic impact not only fractured the zirconia abutment on #9 but the #8 tooth as well. After having #8 stabilized with endodontic treatment, Dr. S. placed a post core and provisional.
As the implant was placed by Dr. K. about 8 years ago, he was referred there for recovery of the fractured zirconia abutment and abutment screw. Recovery of fractured zirconia abutments from Ankylos implants are almost always difficult and tricky due to the tight conical connection at 5.7 degrees and the hardness of the zirconia. Because the abutment screw is free floating (the through bore is smaller than the threads), this presents an additional roadblock to recovery. Evidently, the patient was seen for about 1.5 hours, and while not excessive in my experience, there was only partial recovery of the fractured components. On examination, it was clear while some of the conical portion of the zirconia abutment had been removed, so had some of the implant top. The decision was made to proceed with finishing the recovery as I felt the remaining portion of the conical connection was enough to provide a stable abutment to implant connection. As the area had been flapped the previous day the proximal sutures were left intact and only a small amount of tissue contouring was needed to provide adequate access to visualize the implant top. The site was photographed prior to proceeding with further recovery efforts. As the screw head had already been removed along with the top two thirds of the conical abutment, the bottom portion of the conical abutment was concentrically removed with a surgical length high speed round diamond under microscope visualization. This was done to the level of the indexing splines which start approximately 3mm below the top of the implant. At that time, the zirconia splines became visible, and several small chunks of zirconia were retrieved. With careful manipulation of the screw fragment with an endodontic explorer and modified endodontic spoon, the screw was mobilized and maneuvered so a surgical length ¼ round bur could be placed on the screw outside diameter (OD), in an open implant spline. Again, with microscope guidance, the screw fragment was recovered along with the remaining zirconia fragments. The implant was cleaned, and the supplied healing abutment was placed finger tight. The recovery was completed without further damage to the implant. The patient’s existing provisional was modified to fit the healing abutment contours and was recemented with Tempbond clear, as it appeared to be the cement that was previously used. The patient was dismissed to return to Dr. S. for continuation of his restorative treatment plan.
Due to the initial recovery effort, without a doubt, the implant top was altered and some of the conical connection was lost. I would think a custom titanium abutment would be preferable to zirconia. This abutment connection is small to begin with, 3.97sq mm at the implant top, and a strong argument can be made to avoid zirconia altogether in most if not all Ankylos applications. With the loss of approximately .5-.6mm of conical connection height this connection will become even smaller, and more prone to fracture. As stated earlier, I believe the stability of the abutment to implant connection will be stable in regard to abutment and screw stability, but that is due to the 5.7-degree conical interface and its ability to protect the screw. Use of a stronger abutment material that is more resistant to torsional loads might compensate for the decrease in surface area size. Caution should be taken to avoid non-OEM abutment components as several have larger through bore designs to avoid the laser assembled free floating screw design which will decrease the abutment strength even further. C.A.M.
