October 2024
The patient initially presented on 03.07.23 for evaluation and retrieval of a fractured abutment screw from reportedly an Astra 4.2 EV implant in the #3 site. I stated “reportedly”, as this implant turned out to be a 4.8 EV implant that was restored with 4.2 EV components. Hindsight is often 20/20, so a look back is an interesting experience, with some excellent lessons to be learned. This iatrogenic error started with restoration of this implant as a 4.2 EV, I believe because that was the data received from the dentist who placed the implant in Victoria, BC. I do not have the correspondence that was shared between them, but we do have initial referral sheets, both clearly state this was a 4.2EV implant. That data, plus the initial radiograph from the restoring and referring doctor, led my search for the reason for this repeated failure, completely in the wrong direction.
Referral slip of the implant information from the implant placement Dr.(Top) and the restoring and referring Dr.(Bottom)
The case had a very stormy initial history with early screw loosening and then fracture of the abutment screw, which precipitated the referral to my practice. With a total mindset that this implant was a 4.2 EV, I was looking for “why” this restoration had behaved so uncharacteristic for an Astra conical implant, with multiple early screw loosening and then the screw fracture. Screw loosening and fracture are symptomatic of the same mechanical issue, occurring on just a different point on the failure curve. Screw problems occur when the abutment screw is not protected by joint stability, allowing the loss of screw preload and then progressing toward total joint failure.
The first issue to address was to recover the fractured abutment screw successfully. This screw fragment presented as a non-mobile, Type II case where the screw fracture resided above the first implant thread but could not be recovered with non-rotary instruments. The case then required a precision, concentric mobilization technique to safely recover the fragment. This was accomplished with a custom drill guide and custom drills. A .8mm bore was concentrically placed and a .8mm screw extractor was used to dislodge and back out the fragment. The tissue was very inflamed, so the implant was internally cleaned, and a healing abutment placed. The etiology of the failure pointed at the conical connection not engaging to protect the screw. Therefore, the thought was possibly tissue trapped in the conical interface had prevented the proper engagement of the 11 degree conical walls. However, this tissue issue was very uncharacteristic for an Astra case, as one of the routine findings is the very healthy tissue around the implant, making the restorative steps routinely easy. The patient returned on 4.20.23 with improved tissue, but not as healthy as normally would occur for an Astra EV with a healing abutment in place. The area was cleaned, and a new abutment screw was ordered. Then on 5.03.23 the abutment and crown were delivered back with the new abutment screw, taking care to make sure the implant interface was clean, and the screw was properly torqued. Clinically, the crown seated WNL, with contacts and occlusion.
On 05.31.23 the patient reappeared thinking the crown was loose again, but clinically all appeared tight and solid. The screw was rechecked and found to be fully torqued at 25Ncm. Thinking we had resolved the case, we were totally surprised to learn from the patient that the restoration had again become loose, this time over the Thanksgiving break. He had another dentist recover the crown and place a healing abutment. He was seen again in our office on 01.23.24, and we were back to square one with inflamed tissue and no idea as to the reason for his repeated restorative failures. The tissue was cleaned again, and a slightly larger healing abutment was placed to prep the tissue to a more appropriate size. The thought was still centered on the conical interface as somehow being at the root of the problem, so he was reappointed to recheck the continuity of the conical connection in three weeks. On 02.07.24 the healing abutment was recovered with the tissue again better, but not totally healed up to usual Astra tissue standards. With the healing abutment torqued to 25 Ncm, a radiograph was taken and there appeared to be a space in the conical connection. Still thinking there was a conical connection issue, Dykem bluing was used to witness the conical connection. Comparing the recovered crown with a new 4.2 Atlantis abutment, there was a better witness when the 4.2 abutment seated on a 4.2 analog, but there was some witness with the existing restoration into the implant. There was still no clear conclusion as to why this problem was reoccurring and persistent.
The problem was eventually resolved, sort of “via the back door”. After grinding on the issue mentally for a while, and after seeing two subsequent cases in which wrong components had been placed into another implant brand, I reviewed the case and realized this case was probably restored with the wrong components from the start, suspecting this implant was a 4.8 EV and not a 4.2 EV. All the findings seemed to point to that conclusion, even the non-mobile screw fragment made sense as a 4.2EV abutment screw is a M1.8x.35 screw and the 4.8EV uses an M2x.40 which has a different thread pitch. This would create the binding and cross threading of the screw the more the screw was torqued in. In other words, total torque applied to deliver the screw would be mostly thread torque with very little preload on the screw. So, on 07.23.24 a call was placed to the patient and as this thought was about to be shared, he told me that the original implant placing Dr. had re-restored the case and all was good now. I asked what components were used and he was informed he had used 4.8 components. Finally, the “why” question was answered. This was a pure, iatrogenically created case, due to receipt of wrong information, leading to failure to understand the problem early in the process. However, it is still hard to understand how the case was built using all of the wrong components, without some sense that something was misfitting, whether it was a transfer coping not seating or a screw that was resistant to seating, secondary to a mismatch in thread pitch. This was a very interesting complication scenario, but a very frustrating case for all involved.
After seeing several of these cases in the last six months, where wrong components have been used, I now realize and consider iatrogenic construction as my #1 issue when I see early failure cases where the mechanics have failed very early in function. It might not be easy to spot exactly what issue it is, as in this case, but I think there will be one to find. Why? There simply is not enough time for loading cycles and excessive loading issues to act on the mechanical system to create the failure in a properly assembled construction. What time frame does this span? I would think weeks to months in function and not years.
This case seems to point directly at Occam’s Rasor, “the simplest explanation is often the closest to the truth”. CAM