Accidental Iatrogenic Placement of Four Trilobe Locator Abutments into Nobel Conical implants

05.14.24

The patient presented for retrieval of two fractured Locator abutments in two Nobel conical implants in the #27 and #30 sites. These implants were placed on 10.13.2022. The Locator stabilized mandibular overdenture was delivered in October of 2023. When the Locator abutments fractured, he initially presented to his restorative dentist who then referred him to the surgeon who placed the implants. When the surgeon’s retrieval attempt was unsuccessful, he then referred the patient to our practice. Prior to the appointment, we requested the specific implant sizes from the surgeon’s office as they had listed them correctly as Nobel Active implants but had not indicated the sizes. In the panoramic radiograph, they appeared to be two different diameters. They did respond to our email stating both were Nobel RP conical connection 4.3 implants. I had gone into this detail because it turned out the #27 implant had a M1.6 screw thread, which is consistent with the NP interface. So, it was possibly just a clerical error, by Dr. Cho’s office, that then created some confusion during the recovery appointment. If not, the record should be evaluated.

Reviewing the panoramic radiograph prior to the appointment and realizing these abutments had failed sequentially and were only in function for a short time, I was thinking there was a strong possibility there was an iatrogenic component involved with the mechanism of failure. This became evident very quickly in the appointment, as the abutment in the #22 implant was quite loose and was recovered easily. This abutment did not fit a Nobel conical analog but was a perfect fit in a Nobel Trilobe implant analog. I had seen this error once before when another Nobel conical mandibular implant case had fractured two Locator abutments with only two weeks of function. Although the two fractured abutments were not available at this appointment, I now was suspicious that all four of the abutments had Trilobe interfaces and that was the mechanism of failure.

Attention was first given to #27, and after exposing the implant top the screw fragment presented as a type IV case where the fragment is below the first implant thread and non-mobile. There was clear evidence of a prior recovery attempt. As the fragment was not mobile, a concentric mobilization technique was initiated first, in the hopes of avoiding a complete drill out.

Custom precision drill guides were stabilized with light cured orthodontic resin, and a custom spot drill was used to initiate the drilling process and confirm a concentric starting point. Once this was established, a .8mm custom left hand drill was used to create a bore completely though this short fragment. When in the process of enlarging the bore with a 1.1mm drill in preparation for using a screw extractor, the fragment was dislodged and was recovered. The implant was then cleaned and an M1.6x.35 bottoming tap was used to verify the integrity of the threads. The slight implant damage described below will be of no consequence in the future prognosis of this implant.

Attention was then turned to #30 and the same process was used as described above.

As with #27, the implant was cleaned and an M2.0x.4 bottoming tap was used to verify the integrity of the threads.

As all three of the recovered abutments were Trilobe, it was assumed the last remaining one in #19 was as well. To avoid another fractured abutment necessitating another screw recovery, this abutment was retrieved and was later used to create the photographs below. As there were no healing abutments, silicone was placed into all of the tissue tunnels, and he was directed to return to his restorative dentist to place either healing abutments or new appropriate Locator abutments for these Nobel conical implants.

The following photographs show the problem of placing a Trilobe Locator into a Nobel conical connection implant.?CAM

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