Prosthodontic Protocols for Fixed Hybrid Implant Restorations

A guide to successful, consistent outcomes on implant-based full-mouth restorations

By Joshua Polansky, MDC; Michael Monokian, DMD; and David Monokian, DDS

Advances in modern dental materials have given rise to full-mouth restorative implant cases being prescribed and sent to dental laboratories throughout the country. These complex cases require many checks and balances in order for successful outcomes to be achieved. If the protocols are followed strictly, then these cases become very consistent and easy for both the restorative dentist and the technician. However, if one step is ignored or skipped, the case can be compromised in the process and it can quickly become a difficult situation for all parties involved. Regardless of the material selected for the final prostheses, the required fabrication steps are the same in order to arrive at a successful outcome for these types of implant-supported prostheses. This article will examine the protocol, from arrival in the laboratory to completion, using two of the most widely prescribed materials that are utilized today for these types of restorations: composite and zirconia.

Retention Method and Diagnostics

The first component to consider for a hybrid implant prosthesis is whether the case will be screw-retained, cement-retained, or a combination of both. A screw-retained prosthesis is preferable for this type of case, due to the ability and ease of retrieval should any problems occur; it is also better for patient maintenance and routine hygiene checks. A cement-retained prosthesis is not highly recommended for these type of cases, because if a problem arises, the only option for the restorative team is to remove the compromised prosthesis and take an impression for the fabrication of a new restoration. A combination of screw- and cement-retained is also an option; utilizing a strong temporary cement can allow the restorative team to get around poorly angled anterior abutments while making the case retrievable.

Large implant cases most often arrive at the laboratory as fixture-level impressions (Figure 1). A fixture-level impression provides the technician with the opportunity to pour the cast and select the placement of each implant (Figure 2). The guide pins and/or driver will provide a good perspective on the angulation of the implants and the access holes (Figure 3). A quick setup can be completed over the abutments to analyze the desired contour in relation to the implant positions (Figure 4). Once the setup is complete, a matrix can be taken and proper abutments can be chosen to convert the fixture-level case to a multi-unit case and correct any draw or angulation problems; in Figure 5, Dynamic Abutments (PREAT Corporation, preat.com) were chosen. Once the setup is tried in and verified, the wax setup can be scanned and a temporary restoration milled. In Figure 6, the milled PMMA temporaries (Harvest Dental Products, harvestdental.com) with the multi-unit abutments correct the poorly placed implant angulation and now offer lingual access for a screw-retained restoration. With the provisional inserted in the mouth, all the information the restorative team needs in terms of implant direction, material, and necessary adjustment is available to complete the final prosthesis (Fig 7).

Case 1: Fixed Composite Hybrid

A patient presented with an old, failing hybrid restoration. He was not satisfied with the esthetics, and the prosthesis had broken many times in the past (Figure 8). The implants had been placed previously, making the process easier. At the first appointment, a fixture-level impression was taken of the intraoral situation and sent to the laboratory (Figure 9). The laboratory fabricated a bite rim and verification jig to confirm the accuracy of the model. The screw-retained bite rims were created as a two-part piece, so the dentist during the second visit could screw in the first structure and then simply snap on the rim. This allowed the dentist to screw the structure in place once and make any adjustments to the bite with ease. At the same appointment, a verification jig was confirmed and X-rayed to ensure an accurate master cast (Figure 10). Once the casts and the vertical bite were verified, the technician proceeded with the wax-up for try-in. The wax try-in was fabricated from the original bite rim to ensure consistency and allow the prosthesis to be inserted in and removed from the mouth for easy adjustments (Figure 11). This information was then taken directly from the mouth to the CAD scanner (S600 ARTI, Zirkonzahn, zirkonzahn.com) for a full scan (Figure 12 and Figure 13).

The CAD software accepts the precise scan of the position, contour, and any adjustments made intraorally, which helps with the desired final restoration. In this case, the restorative team prescribed a fixed composite hybrid. An implant bar was designed to be milled in titanium as a screw-retained fixed prosthesis (Figure 14). Once this information was run through the milling strategies, the final titanium bar was milled to completion (Figure 15).

As soon as all these steps were checked and confirmed, the final restoration could be completed with confidence (Figure 16). Because all the steps were followed, the final seating appointment was completed with ease and with no stress on the clinician or patient (Figure 17). This process allows the restorative team to consistently provide patients with new and improved smiles on highly complex cases.

Case 2: Fixed Zirconia Hybrid

For zirconia hybrid implant cases, a majority of the steps described above are followed, with the exception of a few that must be altered. In this case, as in the previous one, the initial impression was taken and sent to the laboratory (Figure 18). The bite rims and verification jigs were fabricated by the laboratory and confirmed by the clinician.

The technician fabricated the wax try-in (Figure 19) and at the next appointment, occlusion was checked, as well as the esthetics with the patient’s smile (Figure 20). From the information gathered at this appointment, the wax-up was scanned and milled in PMMA for a transitional restoration. The PMMA restoration was inserted and worn by the patient for 4-6 weeks to fine-tune the occlusion and any other needed adjustments (Figure 21).

At the same appointment, a master jig was taken for the master zirconia scan. The jig captured the exact implant location, angulation, orientation, and tissue condition (Figure 22). Because zirconia is a very hard material, the PMMA provisional helped to determine the occlusal/muscle relationship. The wear that occurred compensated for the loss of periodontal ligaments.

Once the patient was comfortable with the fit, the final adjustments were scanned for the definitive zirconia framework (Figure 23). The zirconia framework was then milled and sintered with the confidence that the structure would meet the necessary standards for both strength and esthetics (Figure 24). The restoration was layered to completion with the desired ceramic overlay material (GC ZR-FS, GC America Inc., gcamerica.com) (Figure 25).

Because the fixed protocol was followed, the final full-mouth restoration was inserted with confidence (Figure 26). The restorative team was able to provide not only a strong prosthesis that fit well, but also a high degree of esthetics (Figure 27 and Figure 28).

Working with zirconia cases, scanning the final provisional to eliminate any unnecessary weight is crucial. Zirconia restorations can become heavy, so scanning the exact provisional design eliminates extra weight. For this case, the weight of the final zirconia restoration was compared with the weight of the extracted teeth to ensure the final restoration was reasonably comparable (Figure 29).

Conclusion

Hybrid restorations can be simplified by following a strict protocol to acquire and check information. The casts and vertical dimension must be verified at the first appointment. The second appointment consists of a wax prototype try-in, when adjustments and corrections will occur. The third appointment will consist of a frame try-in to verify fit. In the final appointment, if all these steps are followed, the protocol should allow for a predictable final restoration.