Immediate-Load Fixed Hybrid Dentures

The most effective way to accomplish the first step, the final impression, is by using the provisional. This eliminates the need to take impressions with impression posts, verification jigs, and bite rims. It also eliminates the need to re-establish vertical and centric occlusions. The provisional prosthesis that the patient has been wearing provides valuable information to the restorative team, such as approval or changes needed to the functional, occlusal, and esthetic aspects of the final prosthesis. The provisional is used for the final impression by extruding impression material under the intaglio surface, then using a modified stock tray to remove the provisional with the impression. To create the modified tray, take a stock plastic tray and cut a channel across the tray to fully access the screws retaining the provisional in the mouth (Figure 1).

Once it is verified that the tray provides full access to all the screws, one continuous piece of rope wax is placed over the screw accesses. Light body impression material is extruded under the provisional by the dentist (Figure 2), while the dental assistant places medium body impression material in the prepared tray. The master impression needs to extend distally past the perimeters of our provisional. The assistant must use adequate impression material distal to our tray access channel (Figure 3). Provisionals are never cantilevered, as that could interrupt osseointegration of the implants with micromotion from cantilever load stresses. The final prosthesis may incorporate a cantilever, taking into account implant placement (anterior/posterior spread), bone quality, opposing dentition and bite, parafunctional habits, and health. The modified and loaded tray is placed in the mouth. A finger can be used to remove impression material from the rope wax to facilitate removal after final set of the impression material; then the rope wax is removed. This opens up a clear channel to easily remove the screws holding the provisional and the tray with the provisional is removed (Figure 4). Tissue “comfy caps” are placed on the abutments in order to keep the tissue from “rebounding” over the abutments while laboratory procedures are performed.

After the impression is removed, box the master impression, add a soft tissue moulage around the analogs, and pour the impression in die stone (Figure 5). Next, the case is articulated on a fully adjustable articulator. After matrices are made of the position of the provisional teeth (Figure 6), the provisional is returned to the dentist and placed in the patient’s mouth. The provisional provides the technicians with information on the vertical, centric occlusion, verification of the accurate position of model analogs in the cast, and position and esthetics of teeth, as well as any changes required.

This information allows the technician to create a wax set-up of the definitive prosthesis for patient try-in and approval (Figure 7). After approval, the verified master cast, wax set-up, and completed Rx are sent to the PREAT Corporation PRISM team for design and printing of the titanium substructure. SLM “printed” suprastructures provide the benefits of superior mechanical retention, space-saving design, screw access channel angulation, and a stronger alloy than milled and cast suprastructures. The initial design by PRISM technicians is provided with either screen shots or a 3D viewer for approval of the design (Figure 8). The author prefers the Montreal-style design of substructure, a highly polished titanium intaglio for easy cleaning, and an acrylic anterior flange that can be adjusted to satisfy patient needs for the position of the labial flange. The author has found that some patients require closer adaptation to the tissue to prevent food entrapment and “air escape,” while others will require a more “high water” design for easier cleaning. Using acrylic for this flange allows the technician to adapt the flange over the years and compensate for gingival and anatomic changes. A unique design by the PRISM team is the scalloping of the substructure lingual to the denture teeth. The final structure is cantilevered to support the first molars (Figure 9). Before final approval, the technician reviews the screw access holes. The PRISM team can move the access holes up to 30° to improve esthetics and function. Once the design is approved, the case enters SLM/additive metal production.

After the printed bar is returned, a silicone matrix of the try-in is fabricated (Figure 10). The teeth are removed from the baseplate and transferred in the same position to the titanium structure. The teeth are waxed and tried in the patient’s mouth for final approval. At this point, screw accesses are prepared in the denture teeth as needed (Figure 11).

When the suprastructure and teeth are approved by both patient and dentist, a silicon model is fabricated on the intaglio side of the completed wax-up. Metal posts from brush wheel shanks are cut into small pieces and placed into the screw access channels. Leave a small amount of the posts above the screw holes to simplify removal of the posts after processing; this will keep our screw access holes open during processing (Figure 12). The prosthesis is invested in a flask and boiled out, the substructure is painted with pink opaque, and acrylic is injected. After processing, the prosthesis is broken out from the investment, the metal block-out pins are removed from the screw channels using pliers, and any flashing in the screw channel is removed with a scaler.

The definitive prosthesis is then finished and polished without stippling. The highly polished surface is easier for the patient to keep clean (Figure 13). Finally, the finished prosthesis is ready for delivery in the patient’s mouth (Figure 14).

Chris Norris, CDT, is a US Air Force-trained technician with 36 years experience. He is the Removable Technical Manager at Image Dental Arts in Asheville, North Carolina.

Disclaimer: The statements and opinions contained in the preceding material are not of the editors, publisher, or the Editorial Board of Inside Dental Technology.

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