1) Is it understood why the mechanics of the implant failed?
2) If the implant is clear of fractured components, will the case be stable if restored? If not, can the restorative design be altered to create stability?
If the above ‘why’ questions can not be answered positively, then even if the implant is cleared, the probability of a repeated mechanical failure is high. If the ‘why’ questions are answered positively, then progress into the ‘how’ questions (“how do I proceed?”).
Fractured Abutment Screw
If the problem is a fractured abutment screw, the basic algorithm, based on screw fragment position and mobility, should be followed.
Type I Case: screw fracture is above first implant thread and mobile
Type II Case: screw fracture is above first implant thread and is non-mobile
Type III Case: screw fracture is below first implant thread and mobile
Type IV Case: screw fracture is below first implant thread and is non-mobile
Mobile fragments can be attempted with non-rotary instruments, preferably under microscope level visualization. With a microscope and endodontic explorer, and / or modified endodontic spoon, a high percentage of cases can be recovered (approximately 70%). If the recovery is not successful, progression into a mobilization technique is necessary.
1) To keep the recovery percentage near or at 100%, mobilization techniques require the use of microscope guidance, along with precision drill guides, to keep the recovery effort concentric on the fragment and clear of the implant threads, which can complicate the case, making the recovery more difficult.
Therefore, the three levels of screw recovery are as follows:
A) Mobile – recovery with endodontic explorer and modified endodontic spoon, preferably under microscopic guidance
B) Non-mobile – center drilling the screw fragment and retrieving with a tapered left hand screw extractor of an appropriate diameter or fragment fork.
C) Non-mobile – if #2 does not retrieve the fragment, then a total drill out is necessary. Both level 2 and 3 require microscopic visualization and tracking throughout the procedure, to maintain implant safety, which ….
2) If the Case Type I procedure does not progress, the case should be referred if precision tooling and microscope visualization is not available.
As with fractured screws, retrieval of a fractured abutment presents with varying degrees of difficulty.
A fractured abutment can often be retrieved with a ‘wobbling’ tool inserted into the through-bore, once the abutment screw is retrieved (two piece abutment). The ‘wobbling’ tool must fit the through-bore with precision so the back-and-forth wobbling action transmits into the abutment interface to dislodge it. This technique works well with many abutment configurations, but will be less effective with taper fit designs with less than 16 degrees inclusive angle (8 degree taper).
The wobbling technique can be enhanced when a tapered screw retrieval tool is modified to engage the through-bore, resulting in a very positive transfer of energy into the interface. This can be very effective with two-piece titanium abutment fragments, but will not work with fractured zirconia abutments, as the zirconia is much harder and the tapered retrieval tool will not engage into the zirconia.
If ‘wobbling’ is not effective, some abutment fragments can be distracted by threading the through-bore and screwing in a bolt, which in turn is engaged by a distraction nut. Tightening the nut pulls up the bolt, which is attached to the abutment fragment. This technique is very effective in two-piece conical connections of less than 8 degree taper.
If distraction can not be used, then the abutment fragment must be drilled out freehand. This is a risky procedure, as the use of rotary instruments can not be precision guided, so microscopic visualization is imperative. Titanium solid abutments with less than 8 degree taper, and two-piece zirconia abutments, fall into this category and represent a difficult subset for IMR recoveries.