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.

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.

References

1. Walton TR. An up-to-15-year comparison of the survival and complication burden of three-unit tooth-supported fixed dental prostheses and implant-supported single crowns. Int J Oral Maxillofac lmplants.2015; 30(4):851-861.

2. Lai HC, Si MS, Zhuang LF, et al. Long-term outcomes of short dental implants supporting single crowns in posterior region: a clinical retrospective study of 5-10 years. Clin Oral lmplants Res. 2013;24(2):230-237.

3. Kolinski ML, Cherry JE, McAllister BS, et al. Eval­uation of a variable-thread tapered implant in extraction sites with immediate temporization: a 3-year multicenter clinical study. J Periodontol. 2014;85(3):386-394.

4. Rocci A, Rocci M, Rocci C, et al. Immediate loading of Brånemark system TiUnite and machined-surface implants in the posterior mandible, part II: a randomized open-ended 9-year follow-up clinical trial. Int J Oral Maxillofac lmplants. 2013;28(3):891-895.

5. Guljé FL, Raghoebar GM, Vissink A, Meijer HJ. Single crowns in the resorbed posterior maxilla supported by either 6-mm implants or by 11-mm implants combined with sinus floor elevation surgery: a 1-year randomised controlled trial. Eur J Oral lmplantol. 2014;7(3):247-255.

6. Mezzomo LA, Miller R, Triches D, et al. Meta-analysis of single crowns supported by short (<10 mm) implants in the posterior region. J Clin Periodontol. 2014; 41(2):191-213.

7. Wilson TG Jr. The positive relationship between excess cement and peri-implant disease: a prospective clinical endoscopic study. J Periodontol. 2009;80 (9):1388-1392.

8. Weber HP, Kim DM, Ng MW, et al. Peri-implant soft-tissue health surrounding cement- and screw-retained implant restorations: a multi-center, 3-year prospective study. Clin Oral Implants Res. 2006;17(4):375-379.

9. Sailer I, Mühlemann S, Zwahlen M, et al. Cemented and screw-retained implant reconstructions: a systematic review of the survival and complication rates. Clin Oral lmplants Res. 2012;23(suppl 6):163-201.

10. Zembic A, Bösch A, Jung RE, et al. Five-year results of a randomized controlled clinical trial comparing zirconia and titanium abutments supporting single-implant crowns in canine and posterior regions. Clin Oral lmplants Res. 2013;24(4):384-390.

11. Lops D, Bressan E, Chiapasco M, et al. Zirconia and titanium implant abutments for single-tooth implant prostheses after 5 years of function in posterior regions. Int J Oral Maxillofac lmplants. 2013;28(1):281-287.

12. Orentlicher G, Horowitz A, Abboud M. What’s hindering dentistry from the widespread adoption of CT-guided surgery? Compend Contin Educ Dent. 2015;36(10):762-765.

13. Schnitman PA, Hayashi C, Han RK. Why guided when freehand is easier, quicker, and less costly? J Oral Implantol. 2014;40(6):670-678.

14. Orentlicher G, Horowitz A, Goldsmith D, et al. Cumulative survival rate of implants placed “fully guided” using CT-guided surgery: a 7-year retrospective study. Compend Contin Educ Dent. 2014;35(8):590-598, 600.

15. Pozzi A, Sannino G, Barlattani A. Minimally invasive treatment of the atrophic posterior maxilla: a proof-of-concept prospective study with a follow-up of between 36 and 54 months. J Prosthet Dent. 2012; 108(5):286-297.

16. Joda T, Brägger U. Digital vs. conventional implant prosthetic workflows: a cost/time analysis. Clin Oral Implants Res. 2015;26(12):1430-1435.