Delivery of a Posterior Full-Contour Zirconia Implant Crown
Utilization of 3D restorative planning
Richard M. Sullivan, DDS
If a patient is confronted with imminent loss of a posterior tooth and has an otherwise intact dentition, the benefit of an implant-supported ceramic or zirconia restoration is a compelling choice for the patient.1,2 Many potential variations of the treatment delivery process are available, ranging from same-visit tooth removal, implant placement, and provisional restoration to staged treatment with removal of the tooth only, with or without site augmentation, followed by implant placement and restoration over a period of months.3-6 There are also several ways to restore this single implant. Today, a cemented crown restoration to an abutment of some sort is the most common approach. Still, recognizing the potential to avoid cement, streamline delivery, and provide a robust restoration at the most reasonable comparative cost, a one-piece screw-retained restoration fastened directly to the implant is a viable option.7-9
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.
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).
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.