Implants

Indications and Techniques for Surgical Indexing at Stage I Implant Surgery

Dentistry Today July 1, 20046 Mins read3.1k Views

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In reference to prosthetic reconstruction, implants may be placed in poor alignment for a variety of reasons.¹ Difficult surgical access, failure to fabricate accurate surgical guides, and the lack of adequate bone height or width are common problems. Often, these complications are identified at the time of surgery when exposure of the surgical site indicates that the proposed alignment is unrealistic.² Misalignment of implants is a significant problem for restorative dentists.³

Implants should be planned to ensure a proper prosthetic outcome. While the surgical flap is still open, the surgeon has the opportunity to address prosthetic alignment and emergence profile by performing surgical indexing.

Surgical indexing is the process of recording the position of implants relative to adjacent teeth and the opposing occlusion at the time of implant surgery. The purpose is to communicate the position of the implant to the laboratory technician, who can then generate articulated models and dies for fabrication of abutments and provisional crowns for delivery at the time that the implants are uncovered. This facilitates an aesthetic emergence profile and optimal abutment alignment to allow ideal restoration of the occlusion (Figures 1a to 1d).⁴

Surgical indexing is not a new concept. Until now it has been taught with regard to cosmetic implant rehabilitation in the anterior aesthetic zone. But what was acceptable for posterior implant aesthetics in the past now is recognized as less than ideal in terms of posterior function and aesthetics. The emergence profile for posterior implant rehabilitation should equal the aesthetics of the teeth being replaced. Surgical indexing makes this task not only possible, but also relatively simple and cost effective.


Figure 1a. No. 19 misaligned implant corrected with surgical indexing.	Figure 1b. UCLA abutment.

Figure 1c. Final radiograph.	Figure 1d. Final restoration with appealing emergence profile.

Figure 2a. No. 21 prior to surgery.	Figure 2b. Implant placement.

Figure 2c. Impression coping placed onto an implant during stage I surgery for surgical indexing.	Figure 2d. Custom tray with access hole for coping screw.

Figure 2e. Inside of impression; the coping is seen before analog placement.	Figure 2f. Inside of impression; laboratory analog clipped into the coping and secured with the screw from the other side.

Figure 2g. Laboratory model with UCLA custom abutment in place.	Figure 2h. The 3 components received from the laboratory: abutment, provisional restoration, and screw.

Figure 2i. The 3 components fixed together.	Figure 2j. The abutment and provisional restoration at the time of second stage surgery.

INDICATIONS FOR SURGICAL INDEXING
Surgical indexing is indicated in the following circumstances:
(1) When 2-stage implant surgery is proposed and the implant team desires to deliver a laboratory-generated abutment and provisional crown at the time of implant uncovery.
(2) When an aesthetic emergence profile cannot predictably be generated from a stock healing abutment.
(3) When the alignment of a stock restorative abutment will not allow for optimal restoration of the occlusion.

TECHNIQUE
Diagnostic radiographs, articulated models, and surgical templates are prerequisites for proper implant treatment planning. For surgical indexing, additional materials and equipment must be available. These include the appropriate impression copings, drivers, impression material, impression trays, adhesive, bite registration materials, laboratory analogs, and shade guides. At the diagnostic visit, a shade should be selected for the provisional restoration.

Figures 2a to 2j are examples of surgical indexing from the preoperative situation to delivery of the abutment and provisional restoration. After surgically placing the implant(s), and just before placing the cover screw and closing the surgical area, the surgeon uses a coping to index the position of the implant. The most accurate method of indexing mimics the final restorative impression technique by attaching an impression coping to the implant and then taking an impression.

For indexing, an impression coping (the same type used by restorative dentists) is placed onto the implant and verified for proper fit. An impression is made of this seated coping with conventional impression materials. The impression tray is then removed from the mouth. After indexing, the implant surgeon should irrigate the site, inspect it for residual impression debris, and complete the surgical procedure. Bone graft material and membranes used for regeneration are easily disrupted by the impression and should be placed after the impression is completed. Modification of the implant position after indexing obviously nullifies the index impression. Further, the torque applied to the cover screw should not exceed the torque used to place the implant, because if the implant is rotated after indexing is performed, the position of the implant will not match the index impression. The surgical procedure is completed and the patient is dismissed.

If there is a choice between a closed-tray and an open-tray coping, the open-tray coping is preferred.⁵ It is important to remember that for the open-tray, pick-up technique, the retaining screw that fixes the coping to the implant must be unscrewed prior to removing the impression from the mouth. The impression coping remains embedded firmly within the impression material when the tray is removed from the mouth. With this technique the chance of laboratory error in accurately duplicating the position of the implant is reduced.

LABORATORY TECHNIQUE
The laboratory technician generates articulated die models with a laboratory analog, as is performed for restorative implant impressions. Processing the surgical indexing impression differs from that of a conventional restorative implant impression in that (1) the technician must estimate the final soft-tissue margin by mimicking the cemento-enamel junction of the adjacent teeth and (2) only a provisional restoration should be fabricated at this time.

The position of the implant relative to the adjacent teeth and the opposing occlusion is assessed. If only a minor vector correction is necessary, a stock restorative abutment can be selected. Stock machined abutments are often available from the manufacturer with up to 15 degrees of vector correction. If the vector correction is more severe, if there are multiple implants needing vector correction, or if the position of the implant is bodily translated away from a restorable axis, a custom abutment such as the UCLA abutment might be used.⁶ A provisional crown(s) is/are then fabricated with the shade selection previously recorded.

STAGE II (UNCOVERING) SURGERY
After appropriate healing, the implant surgeon uncovers the implant and removes the cover screw. Instead of placing a stock healing abutment, the surgeon places the laboratory-prepared abutment onto the implant with the final restorative screw gently hand-driven into place. A radiograph of the abutment is taken to verify intimate fit with the implant, and the provisional crown is tried in. The provisional occlusion is then checked and adjusted outside the mouth. The implant surgeon then applies the correct final torque to the abutment screw, and with the flaps still open cements the provisional crown with temporary cement. This will provide the surgeon with visual access for cement debris removal. The site is sutured closed and postoperative visits are scheduled. The patient is referred back to the restorative dentist.

DISCUSSION
Dentists who emphasize either the surgical or restorative phases of implant dentistry find surgical indexing to be a powerful tool. The abutment and provisional restoration facilitated by this procedure allows the case to proceed efficiently while preemptively correcting for implant alignment errors. Surgical indexing is particularly important for advanced cases, such as fabrication of multiple implant abutments and provisional restorations for full-arch reconstruction.

If the case is a long-span or full-arch provisional restoration to be attached to many implants, it is advisable to request that the case be sectioned at the laboratory prior to completion. Delivering a long-span laboratory provisional restoration for implants follows the same criteria for passive seating as is required for the final restoration. The different sections should be verified for passive and complete seating with radiographs. The individual sections can be luted together at the time of delivery with any of a variety of techniques (flowable composite, bisacryl, etc). Refinement of the luting stage can be performed at a later date by the restorative dentist.

Restorative dentists often find the provisionalization process, and its many modifications during reconstruction, to be taxing and difficult to schedule in coordination with the implant surgeon. Indexing the implants at the first stage surgery and then delivering a laboratory fabricated provisional restoration at uncovery bypasses many steps, making patient care more efficient.

One reason why restorative dentists who are new to implant treatment hesitate to choose the implant option is the technique sensitivity of executing the proper emergence profile. Surgical indexing essentially converts the restorative dentist’s work from implant rehabilitation to conventional prosthetics.

It is important for the implant surgeon to remember that indexing should be performed with the consent of both the patient and the referring dentist, since indexing and delivering the abutment and provisional restoration alters the conventional division of labor between implant surgeon and restorative dentist. The decision to perform indexing is ultimately dependent on what is in the best interest of the patient. The implant surgeon should explain to the patient the nature of indexing.

CONCLUSION
Replacement of missing teeth with implants is now one of the most predictable of all dental procedures. These restorations can last for decades, and an optimum outcome is achievable with proper planning.

Acknowledgment
The author wishes to acknowledge William “Coach” Bartosiak of North American Dental Laboratory (crown and bridge) and Howard Levy of Horizon Dental Laboratory (removable), the technicians responsible for all of the authors’ restorations.

References

Misch CE. Contemporary Implant Dentistry. 2nd ed. St Louis, Mo: Mosby; 1999: Chapter 27.
Wilson DJ. Ridge mapping for determination of alveolar ridge width. Int J Oral Maxillofac Implants. 1989;4:41-43.
Lewis S, Avera S, Engleman M, et al. The restoration of improperly inclined osseointegrated implants. Int J Oral Maxillofac Implants. 1989;4:147-152.
Cranin AN, Klein M, Simons M, et al. Atlas of Oral Implantology. 2nd ed. St Louis, Mo: Year Book Medical Pub; 1999: Chapter 23.
Assif D, Fenton A, Zarb G, et al. Comparative accuracy of implant impression procedures. Int J Periodontics Restorative Dent. 1992;12:112-121.
Lewis S, Beumer J III, Hornburg W, et al. The “UCLA” abutment. Int J Oral Maxillofac Implants. 1988;3:183-189.

Dr. Montrose has been practicing implant rehabilitation in his private practice in Lincolnwood, Ill, since graduating from the University of Illinois in 1986. He is a fellow of the Academy of General Dentistry. He can be reached at his practice at (847) 675-6767 or via e-mail to jmontr@comcast.net.