January 2025
This case presented on referral from an oral surgeon for retrieval of a fractured Straumann abutment from a Straumann RC implant in the #14 site. This implant was placed in February of 2013 and restored in June of 2013 with a Straumann abutment. This implant had been in function without issue until January of 2025 when the crown suddenly displaced. He had no awareness of the restoration becoming loose prior to the crown displacement. The restoring dentist had uncovered the implant top, but there was no definitive evidence of a prior recovery attempt. The abutment had fractured obliquely below the implant top, and the abutment screw fragment was blocking the through bore.
When both the abutment and abutment screw are fractured with the fragments both in place in the implant, it does present a recovery dilemma, as each is blocking the retrieval of the other. If possible, it is usually easier to clear the through bore first by either moving or preferably retrieving the abutment screw first, then addressing the abutment fragment second. The plan in this case was to retrieve the abutment screw, as the screw did have some mobility, but unfortunately, only for about 30 degrees of rotation. It seemed the fracture zone had created a metal bur that would snag into the side wall of the through bore.
To gain additional rotational torque on the screw fragment, a micro slot was placed in the screw fragment top and with a small custom slot driver the screw was then rotated up enough to clear the implant threads. However, it could not be delivered out of the abutment fragment, as it needed to be pulled up with simultaneous rotation. The thought at that point was that there could be an internally threaded through bore, which would require the screw threads to pass through to deliver the screw fragment. To accomplish this, a .6mm custom drill was used to place a .6mm bore into the screw fragment to a depth of about 2-3mm. A custom .6mm screw extractor was then placed into the bore to engage the screw fragment. Rotation with a straight up distraction motion was used and the screw fragment was delivered. There were no internal threads found in the abutment, so the challenge was just gaining the ability to apply enough upward pressure. Once the through bore was clear, a modified red stripe screw extractor (Ankylos, Dentsply Implants) was engaged, and the abutment fragment was “wobbled” out. Following cleaning of the implant, the implant was examined under the microscope at 25x and found to be free of any structural defect visible at that level of inspection.
The interesting aspect of this case is it again points out abutment failures occur as a combination of strength of the implant pillar and the amount of force and loading cycles working on it. The force side of the equation is most often blamed for 100% of the failure, as in bruxism and clenching. However, when I do not see evidence of pathway wear, I would think much of the occlusal loading would be transferred by the millions of load cycles incurred in mastication. Obviously, occlusal bite force can be a factor, with a wide range of maximum posterior bite force. Also, other factors, such as tooth migration over time can allow an implant to become more of a centric interference. It can be very convenient to dismiss, or overlook, the mechanical issues that seem to be present in an almost predictable way, that contribute to the numerous abutment fracture cases I see.
Occlusal force is magnified by off axis or torsional loading, where the force is compounded by the leverage arm present. The leverage arm is the magnifying destructive force in the equation. In replacing a molar, it is impossible to avoid torsional loading with the larger size of the occlusal table relative to the smaller diameter of the implant. Therefore, the implant pillar mechanics has to be robust enough to resist this force over millions of loading cycles. Typically, I see fractures propagate through the abutment cross section at the implant top, when the implant to abutment connection is stable. This cross-sectional size is critical with smaller diameters breaking more than larger ones. When the cross-sectional area in this zone drops below 7-8 sq.mm, abutment fractures seem to occur more readily, as in this case, where the fracture zone measured 4.88sq.mm. Systems that “gang” smaller diameter interfaces into larger diameter implants seem to be very prone to this problem. This practice is widely done in many current implant designs, for numerous reasons. We currently have many redacted cases posted on our website mastrovichdental.com and will soon be posting a deeper dive into this topic of abutment fractures as a function of abutment size at the implant top.
For additional information regarding these procedures, there are additional case studies posted on our website.
Charlie Mastrovich, DDS
