A Technique for Obtaining Accurate Full-Arch Implant Impressions

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Numerous impression techniques have evolved to improve accuracy.12-16 One technique involves tying open-tray impression copings together with floss, then splinting them together with self-curing resin. Another technique entails the fabrication of an implant verification jig (IVJ). In this procedure, a conventional implant-level impression is made and the master cast is poured. Temporary cylinders are splinted together on the model with resin or acrylic to fabricate the IVJ. The splinted assembly is then tried-in clinically. If the IVJ seats passively, the accuracy of the master cast is verified. If the IVJ does not fit passively, it is sectioned and reluted together in the mouth. The IVJ is then removed, implant analogs are attached to the copings, and the bases of the copings are seated in a stone base. Then, the IVJ is used to reposition the offending implant analog in the master cast. In both of these techniques, the copings are rigidly splinted together to prevent movement.

Following is a clinical technique we have found to be simple but accurate. It involves luting a sectioned IVJ together intraorally, then picking up the assembly with an open-tray impression technique.

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Clinical Procedure
(Clinical dentistry by Drs. Hugh Murray and Al Manesh)

The healing abutments were removed from the implants (Fig. 5). The sections of the IVJ were seated as they were on the model and the guide pins were tightened (Fig. 6). If necessary, periapical radiographs can be taken to verify complete seating of the temporary cylinders on the implants. The custom tray was tried in (Fig. 7). The heads of the guide pins should extend through the access openings. The tray should be adjusted if it comes into contact with the guide pins or the IVJ.

NOTE: If an overdenture is the planned prosthesis, the custom tray can be border-molded following standard procedures.

The IVJ sections were then luted together (Fig. 8). Once set or cured (Fig. 9), the IVJ was removed and inspected. Additional material can be added, if necessary, to strengthen the joints.

NOTE: In this case, Triad DuaLine was used. The curing light provides an initial set. The assembly should be placed in the Triad Curing Unit for a complete cure.

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Rope wax can be placed over the access openings to control excess impression material (Fig. 12). The intaglio surface of the tray was painted with adhesive. Impression material was injected under the IVJ (Fig. 13).

NOTE: This is important: The area under the IVJ should be completely filled with impression material to capture the soft tissue contours.

The filled tray was completely seated, ensuring that the guide pins extended through the access openings (Fig. 14). Once the impression material had set and the guide pins were completely loosened (Fig. 15), the impression was carefully removed and examined for accuracy (Fig. 16). The IVJ was picked up in the impression.

NOTE: The non-engaging cylinders allow the impression to be pulled even if the implants are divergent.

Master Cast Fabrication
Implant analogs were seated on the temporary cylinders and the guide pins were tightened. A soft tissue model was poured (Fig. 17).

Precautions
While this technique is relatively straightforward, there are situations that could complicate the procedure. The patient must have adequate vertical opening to accommodate the guide pins. The more posterior the implants, the more challenging it can become to seat the tall guide pins. Shorter screws may be an option.

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In these cases, the final impression should be made at the abutment level, rather than at the implant level. Whether angled abutments are necessary can be determined by working the case up through a trial denture set-up. The trajectory of the implant can then be evaluated in relation to the positions of the teeth to be replaced on the model. Once the appropriate abutments are selected, the sectioned IVJ and custom tray can be fabricated and the final impression made.

Conclusion
Splinting temporary cylinders together intraorally and then picking the assembly up in an open-tray procedure provides an accurate impression technique. The combination of an extremely accurate impression and CAD/CAM fabrication of the framework has brought implant prosthetics to a new level. Taking one's time and paying attention to detail during the impression procedure will simplify the rest of the restorative process and result in a superior prosthesis.