The patient presented on referral from Dr. B. for evaluation of an uncharacteristic screw loosening problem on three Dentsply EV implants. During her recent hygiene maintenance visit, in their office, she had related her frustration with the multiple times the screws had come loose, which generated the referral. Since Dr. Mc had placed the crowns, he related in a phone conversation, retightened the screws on the two-unit splint, #14-#15, 3 or four times since it was delivered approximately three years ago. Dr. Mc felt he had achieved a passive fit on the splint and had hypothesized the cause of the problem could be either excessive torsional loading on the joints resulting in the loose screws, possibly potentiated by a nocturnal bruxing habit. After gathering this information regarding her case history, it seemed this case would be a significant mechanical outlier as the #14 and #15 implants are 4.8mm and 5.4mm diameter implants respectfully, with both abutment to implant connections being quite robust, if the conical interfaces are engaged properly so the abutment screws are protected. Therefore, the first step was to evaluate her clinically, especially in regard to the fit of the conical connections and possibly evaluate the passive fit of the restoration. However, when she reported for this appointment, further questioning revealed #3 had loosen once and since this single unit had no possibility for an indexing issue secondary to splinting, the focus was dialed in the on conus fit issue. #14-15 was retrieved first by removing the abutment screws and it was readily apparent the conical connections had been altered in the fabrication or delivery of the prosthesis. As #3 was done concurrently with the #14-15 splint, #3 was retrieved in the same manner with the exact same findings. The implants were evaluated using 25x under the surgical microscope and at this level of examination found to be in good condition. The circumferential tissue adjacent to the implants was quite inflamed so healing abutments were placed which assured a good mechanical seal to support tissue recovery. The clinical situation was explained to the patient and she was relieved the implants seemed to be stable and only in need of replacement abutments and crowns. Uncertain as to her next step, she wanted to wait for this report so she could sort out the issue with Dr. Mc. The original restorations were retained in the office so the appropriate photography could be completed, and the report written. The following photos and explanations of the mechanics of the conical connection should make it very clear as to why these restorations were not successful. The restorations were built on cast-to abutments which provide a pre-machined interface for precision fit into the implant.
To provide the standard for evaluation, Dentsply provided a new identical cast-to component which was used in the following photographs.
With the understanding of what an unaltered new joint looks like, we can evaluate the #14-15 splint conical connections next. First the parts as recovered from both the buccal and lingual, indicated with Dykem and then after seating on the appropriate analog. Each interface was witnessed individually so maximum conus connection could be achieved without regard to any indexing issues.
The following photographs were taken in the same manner as the above photographs.
It is easy to see there is very little contact in the conus, just on a few remaining islands. The conical connection has been ground on, under contouring and eliminating the stability for the joint. Next, on #3, we will look at all four surfaces, but with only the recovered and witnessed views.
Just to be crystal clear, the above are cropped photographs of #3 mesial, above left and the Dentsply untouched interface. Comparing the two images, the amount of conus damage is substantial. Instead of a 11 degree positive angle, there is actually a hollow grind circumferentially. The indexing section has even been sandblasted.
There was no effort spent to verify the index of #14 and #15 as there was really no stability in either joint. With the amount of damage seen it was already a closed case for remaking the restorations. So why did the interfaces get mutalated to this extent? I could see where there might have been an attempt to improve the seating of the splint on the master cast to avoid cutting the casting and reindexing properly. #3 is basically unexplainable, other than a total disregard for the basics of good laboratory procedure.