Delivery of a Posterior Full-Contour Zirconia Implant Crown

This article will focus on a patient that would already be receiving a cone-beam computed tomography (CBCT) scan as preparation for a posterior single-tooth implant and a combined crown–abutment restoration without the use of cement. The purpose is to demonstrate a representative example of diagnostic, planning, and treatment delivery methods that can utilize CT data to plan optimal implant placement as the foundation for the identified restoration. There are several somewhat parallel combinations of integrated methods available today focused on a similar outcome from planning through delivery; these systems may have different features, sequences, and utilization of the digital process. This is intended to bring to light the possible benefits and opportunities for routine implementation of the concept presented with the understanding that it would be possible to provide in several variations.

Case Presentation

A 50-year-old man in good health had lost a lower left first molar secondary to chronic infection after previous endodontic therapy. After removal of the tooth, soft tissue debridement, and socket grafting, the patient received a periapical radiograph at 4 months that indicated stable bone fill. With consideration of the significant bone destruction preceding tooth removal for this patient and the bone fill required to support molar function with an implant, a CBCT was taken.

The restorative plan was to provide a full-contour zirconia abutment including crown restoration fastened directly to the implant.10,11 Study models were produced with a wax-up representing tooth No. 19 (Figure 1). A wax-up was not necessary but was included because the planning value of this process, including the wax-up, increases for anterior maxillary and multiple unit restorations. Both the model and the wax-up received a surface scan (NobelProcera® 2G Scanner, Nobel Biocare, www.nobelbiocare.com).

The patient’s CBCT, surface scan of the lower study model, and separate scan of the wax-up were all integrated into planning software (NobelClinician®, Nobel Biocare) (Figure 2). Individual planes of patient scan, study model, wax-up, and virtual components are independently visible or able to be hidden. In the example here, the virtual wax-up was adjusted to be somewhat transparent, revealing a virtual abutment. The axial view cross-section clearly shows the inferior alveolar canal, depth of soft tissue available, and appropriate restorative emergence profile that could be achieved.

The axial cross-section on the right enables a side view of the lower ridge, a planning perspective that was not possible with routine dental radiography. Immediately visible from the scan itself are the available bone width and volume above the cross-section of the inferior alveolar canal. The import of the surface scan of the cast is a salmon color, precisely showing the depth of the soft tissue at the site. The wax-up shows emergence profile possibilities through the soft tissue and amount of restorative space available to the opposing arch. Together, this information provides a much more complete picture of the restorative challenge than a scan of the bone by itself. Planning becomes a simultaneous consideration of restorative, soft tissue, and osseous requirements. This provides a useful communication platform for the treatment team and the patient.

Recognizing the multiple approaches and preferences possible from this point, the treatment team decided to make a fully restrictive surgical template (Figure 3).^12-15 Using a commercial surgical template (NobelGuide®, Nobel Biocare), the digital planning information was transferred through the plane of a sleeve suspended a fixed distance above the implant platform, axially centered and with a parallel horizontal plane to the planned implant platform. With intermediary drill guides and site preparation, the implant can be delivered through this surgical template.

When working with a one-piece crown/abutment complex as the desired definitive restoration, there is no need to wait for stable soft tissue healing to begin the restorative process. Provided the implant has achieved a minimum threshold of stability when challenged to rotation, an implant-level impression for the restoration may be taken at the time the implant is placed (Figure 4). The ideal emergence profile design of the one-piece restoration as determined by the dentist and dental technician can be committed to without consideration of margin height or cement removal access. This leads to production of a full-contour zirconia crown that is attached directly to the implant using a titanium pedestal-type base fastened with an abutment screw (NobelProcera™, Nobel Biocare) (Figure 5).

The full-contour zirconia crown/abutment has been stained but there is no veneering porcelain (Figure 6). After contacts and occlusion were checked, the abutment screw was fastened according to specifications and the screw access hole was closed first with silicone tape followed by a temporary filling material (Fermit™, Ivoclar Vivadent, www.ivoclarvivadent.com) (Figure 7). The screw access hole is then typically closed with composite 6 to 12 months later. With tetracycline staining and some vintage dental restorations, complex shading is not possible with full contour and staining only, but this was preferred by the patient for the potential longevity with absence of porcelain fracture (Figure 8). A bitewing radiograph at 6 months after restoration shows a baseline stability to follow over time (Figure 9).

Discussion

Patient safety is greatly increased through the visualization of bone volumes and support potential relative to vital structures, which helps determine the feasibility of treatment preoperatively, even at an initial consultation. While the scans are beneficial this way, from a surgeon’s perspective, they can better contribute to restorative planning and delivery of the restoration.

A screw-retained, single-tooth approach can be supported if the restoration is planned for an optimal position before the implant is placed. Optimal is intended to mean the best implant positioning considering alignment with the occlusal surface, emergence profile possibilities for the restoration based on soft tissue depth, and the available bone to place the implant. If CBCT is used, the scan file can be further utilized in the work up and preparation for the restoration.

The foundation for the restorative design begins at a platform, or fixed plane:
• horizontally variable relative to teeth and soft tissue.
• vertically variable relative to teeth and soft tissue.
• variable by tilting and affecting the plane’s perpendicular axial trajectory as it interfaces with soft tissue emergence and extends to the occlusal plane or incisal edges of the teeth being replaced.

Chinese philosopher Lao-Tzu wrote, “We mold clay into a pot, but it is the emptiness inside that makes the vessel useful.” Similarly, a dental implant may be produced on a CNC machine and placed in a surgery, but it is the empty space inside that makes it useful. The only reason the patient is receiving a posterior single implant is to provide support for a tooth. The truly relevant factor for the patient, restorative doctor, and dental laboratory technician is the empty but threaded space on the inside of the implant (Figure 10). What differentiates optimal from clinically acceptable is the positioning of the implant platform and the empty space inside of it to receive the restoration, accept a lifelong load transfer, and maintain a biologic interface with soft tissue and bone. Observing available bone, soft tissue depth, and restorative emergence from the implant or abutment and subsequently positioning within the occlusal table facilitates optimal implant positioning. This has become practical enough to provide on a routine basis for the additional information it provides.

Any new technology must be easy to understand, practical to implement, and cost-effective by returning either time savings or increased short- or long-term revenues for the expenditure. It only requires 5 minutes total for a surgeon to plan the single-tooth restoration using this method while effectively producing twice the amount of beneficial information on the patient’s behalf. No additional time is required if the plan includes a surgical template. Depending on experience and other conditions, the conversion of the plan into a surgical template can provide an additional return in time savings and routinely straightforward results with more routine restorative and laboratory fees.

There are documented benefits of efficiency comparing digital and analog restorative delivery.¹⁶ Utilization of diagnostic benefits integrated with implant placement, abutment and restorative design, and production show the potential to bring these efficiencies to an even higher level without any compromise or even improvement of results. In addition, the laboratory invoice will tend to be less with a crown/abutment placed directly to the implant compared to an abutment of titanium or zirconia and a separate cemented crown. Think of the restoration as a “one-piece crown/abutment complex,” taking the virtual planning through computer milled production into reality.

Conclusion

A full-contour zirconia implant restoration provides a predictable and straightforward restorative solution for replacement of posterior single teeth. To design the desired restoration and import the proposed design into the preoperative scan, along with soft tissue information, provides significant added value from the scan for the patient and treatment team. There are many opportunities for using integrated and combined digital processes to facilitate this process. For patients receiving scans, having optimal restorative planning preoperatively superimposed onto the scan can contribute toward optimal results on a routine basis beyond utilization of a bone-only scan.

This technique eliminates the biologic concerns of inadequate cement removal while providing a lower dental laboratory investment without compromise. Optimal implant placement to support this restorative design relative to axial trajectory, soft tissue emergence profile affecting implant seating depth, and the available bone is now possible to more fully utilize the CT-scan exposure on the patient’s behalf. These informative planning images can be beneficial for both patient communication and discussion by the treatment team.

Acknowledgements

The author wishes to thank Momo Vasilic, CDT, for his support in the planning and restorative process.

Disclosure

Richard M. Sullivan, DDS, is an employee of Nobel Biocare, and is a manufacturer and developer of the products and software used in this article.