A Fractured Abutment Screw Case Initially Attempted With a Generic Recovery Kit and No Microscopic Visualization – 0035

This is the first case, in a series of four, that involve progressively more difficult, immobile screw recovery. All of the cases in this series have the common issue of a previously failed recovery attempt, or multiple attempts, that were complicated by the use of various ineffective recovery tools and protocols. This series highlights how these tools and techniques created additional difficulties and complications, and how they violated the basic principles developed and followed in this practice, that encourage predictable results. The procedural and tooling inadequacies include (1) a lack of microscope visualization to properly diagnose and progressively track a case into a successful outcome, (2) not starting the recovery with conservative instrumentation, until proving the case will require a more aggressive approach to resolve, (3) then, when progression to rotary instrumentation is deemed necessary, not having the precision tools and techniques to safely resolve the case.

This first case illustrates what can happen when a fractured abutment screw recovery is attempted without proper magnification, and the use of rotary recovery tools that were not guided with sufficient precision to avoid implant damage. The eventual outcome was good, but the recovery, described below, became more complicated and less predictable due to the prior misguided retrieval attempt.

The patient was treated in my office in November of 2024 after her initial recovery attempt was unsuccessful elsewhere. This case involved a Straumann BL RC 4.1 implant placed in January of 2022 in the #19 site along with a Straumann BL RC 4.8 in the #18 site. Post integration, both implants were restored and in function, but when #19 was retrieved to modify a tight contact, a new abutment screw fractured while the restoration was being delivered. The restoring dentist referred the case to the periodontist who had placed the implants and recovery of the screw fragment was attempted. This procedure involved use of a recovery kit from US Dental Depot, which in all aspects seems to be identical to the NeoBiotech SR kit.

Due to multiple eccentric drilling efforts, in the prior recovery effort, I was highly suspicious the kit tooling was not adaquate to produce consistant concentric drilling on this fractured Strumann RC implant abutment screw. This has yet to be confirmed in my lab with the actual tooling from the kit, as it was not present at the recovery appointment. I did have the chance to evaluate the kit, but it was in connection with a previous case which involved a different implant system. That case will be reviewed as the third case in this series, along with the basics of achieving precision guidance from a drill system and the reason a drill might not start or stay concentric.

As can be appreciated in the above two preop photographs taken before any recovery attempts in our office, the screw fragment now presented as locked, non-mobile and in need of mobilization to be retrieved. These two eccentric drilling attempts can be easily visualized at 9:00 and 1:00 in the above right photograph.

At this point, the plan was to center drill the screw fragment and apply a screw extractor in the hope it would provide enough torque to overcome the thread distortions created by the two previous eccentric efforts.

The goal in recovering a non-mobile screw fragment is to do so without injuring the implant. The safest approach is to work concentrically in the screw fragment, which is furthest away from the implant and implant threads. To apply additional torque to the fragment, a concentric bore is made into the fragment so various recovery instruments can engage or lock into the fragment. To predictably drill a concentric bore, a precision guidance system needs to be established to guide the drill, along with the means to follow the process with a clinical microscope, making sure the boring process has not deviated off course and into the implant. In this case, the previous recovery effort did involve using a guidance system, but the above photograph clearly shows the instruments and procedures were inadequate to start and stay concentric. The variability between the two drilling efforts is remarkably independent and divergent. Additionally, as a microscope was not used, on that prior effort, visualization was not adequate to understand what was happening and definitely not soon enough to avoid implant damage.

The treatment approach used to resolve this case
The first step to get on track with this recovery was to set up a precision custom drill guide and confirm it was doing what it was set up to do: keep the drilling effort concentric and on target. The setup entailed using a clear, light cured ortho resin (Orthocril LC) to secure the guide to the adjacent teeth, creating a removable, but very secure and repeatably stable guide. This is important, as the drilling process produces metal fragments that need to be cleared along with intermittent checks on the drilling process using magnification. Most available guide systems incorporate a handle system, which is intended to help control and stabilize the guide cylinder. Unfortunately, they often do not provide a stable and secure attachment to many implant interfaces, due to two factors: (1) various implant to abutment interfaces do not achieve the same stability and (2) they cannot resist the amount of torque a handle can exert. Experience has proven resin is significantly superior, as the additional time invested to set it up can easily be recovered by the additional precision it provides during the procedure. With guide stability established, a custom left hand spotting drill was used to confirm the drilling process was starting the bore concentrically. A spotting drill is designed to seek center and is more accurate than starting with the usual twist drill, which can “wander” as it attempts to start the drilling process. Once the center was confirmed microscopically, then a custom left hand .8mm drill was used to drill about 3mm into fragment. With the .8mm bore completed, a 1mm drill was used to slightly enlarge the top 1mm so a .8mm screw extractor could engage more positively. Using the screw extractor by hand, the fragment was then mobilized and retrieved. As the top implant threads had been altered by the previous dentist’s eccentric recovery effort, two M1.6x.35 metric taps were used to clean and verify that the threads were clear. The first tap used was a plug tap, as plug taps have 3-5 tapered threads at the end and are easier to “clock” into the existing implant threads. Once the plug tap bottomed out in the implant, the tap was switched to a bottoming tap, which has only 1-2 tapered threads at the end, that allow the tap to verify the bottom threads in the implant.

Fortunately, the previous eccentric drilling efforts were terminated before significant damage to the implant threads were done. However, drilling into the implant threads virtually assured the fragment would be locked and not be recovered without progressing to techniques to increase rotational torque, or as will be reviewed in the following cases, a total drill out protocol. Because the recovery was completed without any further implant damage, the threads on the implant remained sufficient for screw stability, so the prognosis for this implant was unchanged by this fractured screw event.

For additional information regarding these procedures, there are additional case studies posted on our website.

Charlie Mastrovich, DDS