Retrieval of a Defective Cement-Retained Implant Prosthesis
As the popularity of cement-retained implant prosthetics grows, so, too, does the need for retreatment. The predictable removal of cement-retained implant crowns has often proven difficult due to a multitude of variables, including locating the access and stripped screws. The techniques discussed in this article address these issues, thus simplifying the retreatment process.
A number of factors have converged to increase the volume of cement-retained implant prostheses. Chief among these factors are: a rise in gold alloy and laboratory costs,1,2 manufacturers’ attempts to simplify the prosthetic process, and demands of the general dentist to have implant treatment mimic standard fixed prosthetic protocols. Additionally, while public awareness and patients’ desire for implant treatment continue to escalate, many clinicians tasked with restoring the cases have never had the opportunity to gain adequate prosthetic implant training. The technique of cementing the prosthesis is not a new one in implant dentistry,3 however there are continuing reports of complications associated with the process.4,5
Numerous clinical trials have shown cemented implant prostheses to be quite successful.6-14 Implant treatment in the esthetic zone oftentimes necessitates a cemented prosthesis due to screw access through the facial or buccal surfaces1,2,15 (though esoteric, lingual set-screw prostheses are an alternative). Screw-retained restorations provide a certain ease of retrievability and prevent the possibility of retaining cement subgingivally.16
Successful treatment with cemented implant prostheses requires the following criteria be met: a minimum band of 2 mm of mature and keratinized peri-implant gingiva, a gentle and continuous “s” curve emergence profile of the abutment, abutment margin placement within 2 mm of the definitive free gingival margin, thorough cement removal, and use of a semi-soluble cement.1,17 Anecdotally, many of the cemented restorations that require removal have had one or more of these criteria violated.
The need to retrieve a cemented implant prosthesis can be due to several factors, including: loose screw,18 poor fitting margins (Figure 1), subgingival cement (Figure 2), irresolvable peri-implantitis,19,20 bone loss, poor occlusion,21 fractured porcelain22-25 (Figure 3), unsatisfactory esthetics, etc. Depending on the reason for removal, in some instances the problem can be resolved and the restoration reused as a screw-retained definitive or provisional restoration. In such cases it is desirable to keep the access as small as possible (Figure 4) to maintain integrity of the overlying porcelain. During removal, it is imperative to avoid damage to the implant body. The clinician should ensure that all necessary armamentarium (drivers, healing abutments, etc.) are available prior to starting the removal procedure.
Technique: Cemented Implant Crown Removal
The proposed technique for the removal of a cement implant crown is as follows:
1. Determine the implant brand and type to ensure that the appropriate driver is available once the screw is located.
2. Estimate the approximate mesial-distal distance from the screw access to a nearby landmark using an appropriate radiograph (Figure 5). The clinician must use caution and good judgment in this process, as this is only an approximation of the access and cannot account for buccal-lingual angulation or radiographic magnification. If the implant is of a known diameter, this can serve as a relative, radiographic ruler.
3. Palpate the peri-implant bone to assist in determining buccal-lingual angulation of the implant.
4. Measure from the radiographic landmark to the estimated access location.
5. Cut the initial access approximately 2 mm in diameter. A depth of 2 mm to 4 mm should allow the screw access chamber to be found (Figure 6). If it does not, enlarge the access buccally or lingually until it is found.
6. Enlarge the access with the bur to the full diameter of the abutment chamber—generally about 3 mm.
7. Remove the obturation material (Figure 7); the most commonly used materials are cotton, gutta percha, provisional composites, temporary cements, polytetrafluoroethylene (PTFE) tape,26 or polyvinyl siloxane (PVS) impression materials. Most of these materials can be removed with a small spoon excavator, explorer, and barbed broach.
8. Thoroughly clean the head of the screw with a periodontal probe and irrigation before attempting to remove it. Check to ensure that no debris remains.
9. Insert the appropriate driver and, using a torque wrench, unscrew in a counter-clockwise direction.
Removal of a cement-retained implant prosthesis is rarely as simple as stated above. Often, the clinician removing the prosthesis was not involved in placing it, and, thus, many unknown variables can complicate the removal. The most troubling problems arise when:
• the screw access has been filled with a permanent material (ie, resin cement)
• the incorrect screw was used, or
• the screw was stripped.
When removing an implant prosthesis, the clinician should be prepared for such difficulties. All of these problems can be addressed through the technique delineated below. This procedure can be performed through a narrow occlusal access, or the crown can be sectioned and removed if needed. On rare occasions, the abutment itself may need to be sectioned. However, it is important to understand that abutments should only be sectioned for removal if the operator is certain that the implant is an external hex design or that the abutment and the implant interface are two separate components (as with some zirconia/titanium two-piece cemented abutments.) Sectioning and splitting one-piece internal connection abutments carries a high risk of catastrophic fracturing of the implant head. If this were to happen, the implant would need to be extracted or buried. Most currently used implants are internal connection-type and, therefore, are not good candidates for sectioning the abutment.
Removal of a Stripped Implant Screw
The steps for removal of a stripped implant screw are as follows:
1. Obtain a flat-ended implant driver along with a round carbide bur that matches the width of the narrow dimension of the driver (usually 1/4 or 1/2 round) (Figure 8).
2. Clear the debris and/or cement from the head of the screw.
3. Using the round bur, “feel” the edges of the screw head from one side to the opposite side. At this point the handpiece is not yet running.
4. Starting with the bur against one side, move the bur slightly off the wall, run it to full speed, and cut out and up in one smooth motion. Stop the handpiece, but do not move it. This should create a slot-shaped cut in one of the screw-head walls.
5. Without removing the bur, move it to the opposite side of the screw head and repeat. Check to ensure that the slot cut has been successful (Figure 9).
6. Irrigate and remove debris.
7. Insert the flat-ended driver. Using firm pressure, seat the driver into the slots on each side of the screw head. Check to see that the driver is engaged by attempting to rotate it by hand. Keep applying apical pressure while using the torque wrench to rotate the screw in a counter-clockwise direction, removing the crowns (Figure 10).
This technique for removing a stripped implant screw is quite reliable, though should be practiced in vitro before attempting on a patient. Care must be taken to create clean slots at opposite ends of the screw head. If the cuts are irregular or not opposite each other, attempted removal may simply result in stripping the screw head further. If this happens, a 557 or similar bur can be used to completely remove the head of the screw. With the screw head removed, the prosthesis can simply be slipped off the remaining screw segment. The remaining screw segment can be teased out by rotating it in a counter-clockwise direction with an explorer.27 This technique also applies for removing screws that have fractured. Many implant manufacturers have produced screw extraction kits that may be a useful adjunct to this approach.
It should be clearly understood that removal of implant prostheses is a challenging procedure and should be approached with the utmost caution and respect for the process. A mistake could compromise the implant itself and the surrounding tissues. The techniques described here are intended to aid clinicians who are faced with the difficult task of removing a failed prosthesis. With pre-treatment research, proper protocols, and preparation for complications, the clinician greatly increases the predictability of retreatment. As with many procedures in dentistry, the clinician’s ability to reliably identify the etiology of and resolve such failures enhances his or her ability to provide successful future treatment.
ABOUT THE AUTHORS
Todd R. Schoenbaum, DDS, FACD
Assistant Clinical Professor, UCLA School of Dentistry, Division of Restorative Dentistry; Acting Director, UCLA Department of Continuing Education; Private Practice, Los Angeles, California
Edward A. McLaren, DDS, MDC
Professor, UCLA School of Dentistry, Division of Restorative Dentistry; Founder and Director, UCLA Post Graduate Esthetics; Director, UCLA Center for Esthetic Dentistry; Founder and Director, UCLA Master Dental Ceramist Program, Los Angeles, California; Private Practice, Los Angeles, California
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