The Solid Zirconia Implant-Retained Prosthesis: An Excellent Full-Arch Alternative to the Fixed Hybrid Denture

INTRODUCTION
Full-arch implant restorations afford life-changing benefits to the fully edentulous patient. Their superior prosthetic stability and dental function, along with their capacity to mitigate bone loss and preserve the oral and facial structures of the patient, make them a much better option than the traditional denture.^1-3 For clinicians offering implant treatment to their edentulous patients, there are many restorative options, ranging from the placement of 2 dental implants to hold a removable overdenture in place to the delivery of a fixed full-arch restoration over 4 or more implants.

Although both removable and fixed implant restorations represent a significant advancement over the stability and aesthetics offered by traditional dentures, the screw-retained prosthesis has emerged as the premium treatment option. By permanently attaching to the implants, the fixed full-arch implant restoration most closely replicates the form and function of natural teeth. Patients who have had an edentulous arch restored with a fixed implant prosthesis report higher levels of comfort, dental function, and quality of life than those treated with a removable overdenture.^4,5

The fixed full-arch prosthesis has typically connected to the implants through a metal framework via screws that can only be removed by the practitioner. The body of the prosthesis has consisted of acrylic, in which prosthetic teeth are bonded in the manner of a traditional denture. Although these screw-retained hybrid dentures have performed exceptionally well, breakage has been an issue, the most common causes being fracture of the acrylic base and debonding of the prosthetic teeth.⁶

With the arrival of the solid zirconia full-arch implant retained prosthesis (such as the BruxZir Full-Arch Implant Prosthesis [Glidewell Laboratories]), we now have a prosthetic option that provides the stability and function of the screw-retained hybrid denture, but with a monolithic construction that avoids the cracks, chipping, and staining that often compromise acrylic appliances. In clinical studies, zirconia-based full-arch implant restorations have performed exceptionally well.^7,8 While porcelain veneer chipping has been an issue in a small number of cases, this is not a concern for these prostheses, which are constructed of 100% monolithic zirconia.

To provide patients with this aesthetic, more durable restoration, a clinical protocol has been established that is nearly identical to that of the fixed hybrid denture. The key difference is the inclusion of a temporary polymethyl methacrylate (PMMA) implant prosthesis that maximizes the accuracy of the restorative process by providing the patient with an opportunity to “test drive” the definitive prosthetic design before the final restoration is milled from the solid zirconia. The end result is a fixed prosthesis that, like the hybrid denture, exhibits the form and function of natural teeth, but has a monolithic construction that is optimally suited to withstand the impact of dental functioning in the long term.

Clinical Considerations and Diagnosis and Treatment Planning
When considering the BruxZir Full-Arch Implant Prosthesis for the individual patient, the same clinical considerations involved in treatment planning a fixed hybrid denture apply, including an evaluation of vital anatomical structures, vertical dimension of occlusion (VDO), phonetics, aesthetics, and dental function. Preliminary impressions, radiography and, in many cases, CBCT scanning, are needed for a thorough analysis of the edentulous arch and underlying anatomy. The data gained from CBCT scanning can also help in determining the optimal positioning, diameter, and length of the implants. The longer the patient has gone without teeth, the less bone volume the patient is likely to have, making CBCT scanning an especially valuable tool in cases in which the patient presents for treatment as a denture-wearer. Like the hybrid denture, a minimum of 4 implants must be placed to support the full-arch solid zirconia implant-retained prosthesis.

As with any implant restoration, the edentulous patient’s quantity of available bone must be assessed to determine whether a monolithic zirconia implant restoration is indicated. This is usually not an issue, for even patients who have experienced significant vertical bone loss in the posterior can have the implants angled to avoid the sinus cavities or mental foramens in an all-on-4 or all-on-6 configuration. Similar to the hybrid denture, 17° or 30° multiunit abutments can be used in tandem with angulated posterior implant positioning to establish a sufficient anterior-posterior (A-P) spread for a fixed restoration.

The patient’s VDO should also be assessed to ensure that there is sufficient restorative space. These prostheses require a minimum of 10 mm of vertical clearance, which will not be an issue for most patients. Note that screw-retained hybrid dentures can require as much as 20 mm of vertical dimension for each arch without compromising the height of the bar, acrylic or prosthetic teeth, making monolithic zirconia an advantageous option when interarch occlusal space is limited.

Patient finances are obviously an important consideration. Explaining the benefits of implant treatment, including the mitigation of bone loss, can be crucial in garnering patient acceptance of treatment. Treatment options should be discussed with the patient to ascertain whether a removable or fixed prosthesis is desired. Walking patients through the cost-benefit analysis of removable versus fixed implant restorations is essential. With the understanding that a fixed restoration provides superior stability and function and the monolithic zirconia option affords long-term cost savings by avoiding the need for prosthetic repairs or replacement, many patients will opt for the premium form of treatment.

CBCT scanning and digital treatment planning images can be used to demonstrate the planned surgical placement and prosthetic restoration. Physical or digital diagnostic wax-ups can also help ease a patient’s understanding of the procedure and its long-term benefits. Presenting this information can help illustrate how the prosthetically driven treatment plan situates the implants in a maximal amount of bone while establishing the restorative platform needed for a highly aesthetic, functional outcome.

The inclusion of the PMMA provisional implant prosthesis, which is worn for a trial period, should also be explained during presentation of the treatment plan, as it can help instill confidence in the patient, who will have an opportunity to verify the fit, aesthetics, function, and phonetics of the prosthetic design prior to the fabrication of the final restoration. Any needed adjustments can be made to the provisional, which are then duplicated in the definitive prosthesis. This differs from the restorative workflow for a fixed hybrid prosthesis, which does not typically include a provisional for the patient to test-drive, introducing the possibility of the final restoration having to be sent back to the lab for adjustments.

The following case report explores the step-by-step protocol for the BruxZir Full-Arch Implant Prosthesis, from implant placement to delivery of the final monolithic zirconia restoration, with details of a fully edentulous patient who underwent a complete oral rehabilitation. The end result demonstrates how an exceptionally durable restoration can be delivered by following a restorative process that is nearly identical to that of the fixed acrylic hybrid denture.

CASE REPORT
Diagnosis and Treatment Planning
A 59-year-old female presented for treatment with a maxilla that exhibited signs of severe periodontal disease accompanied by purulence and halitosis (Figure 1). The patient had been wearing a lower complete denture for nearly 20 years, and her mandible suffered from the pronounced bone resorption that occurs in the absence of teeth or dental implants (Figure 2). The gaps between her teeth had widened as her periodontal disease worsened, and the surrounding tissues had become swollen and infected (Figure 3).

Figure 1. Preoperative situation of the patient, who suffered from periodontal disease in the maxilla and had been wearing a mandibular denture for many years.	Figure 2. Lateral extraoral view of the patient’s preoperative state. Mandibular bone loss had compromised her facial aesthetics, including a reduced vertical dimension in the maxilla and the forward rotation of her chin.

Figure 4. Occlusal preoperative view exhibits highly resorbed state of the patient’s mandible.

Bone support for her maxillary dentition had diminished to the point where her teeth had become mobile and could not be saved. Further, her condition made her self-conscious about her smile and caused great discomfort. This, along with the loose-fitting state of her lower denture, which had become less stable and retentive over the years as the resorption of her mandible progressed, necessitated a full-mouth implant rehabilitation (Figure 4).

Upon consulting the patient, it became immediately clear that she strongly desired a fixed solution. After suffering with a poorly functioning lower denture for so many years, the patient had delayed seeking treatment for fear of losing her terminal maxillary dentition. Now that it was clear that her upper teeth could not be saved, she was eager for a restoration that as closely resembled the form and function of natural teeth as possible, making a fixed implant restoration the ideal solution.

The BruxZir Full-Arch Implant Prosthesis was proposed to and accepted by the patient for both arches. The long-term prognosis and optimal durability of the monolithic prosthesis appealed strongly to the patient, who needed a prosthesis she could depend on for many years. The patient also insisted upon leaving the extraction and implant placement appointment with teeth in place, so immediate denture conversion was treatment planned for the surgical appointment. Note that this protocol—in which a fixed restoration is planned, the teeth removed, and the implant sites temporized with an immediately converted denture—is an approach that appeals to many patients who present with terminal dentition.

CBCT scans were taken using an i-CAT FLX (Imaging Sciences International) and sent to 3D Diagnostix (3DDX) so a virtual treatment plan could be created. The digital treatment plan generated from the CBCT scans helped to determine the implant positions needed to avoid the patient’s mental foramens. The virtual wax-ups also helped facilitate the patient’s acceptance of the treatment plan, as it illustrated how the implants could be predictably and precisely placed to accommodate fixed full-arch restorations (Figure 5). Lastly, the CBCT scans were used to design bone-supported surgical guides that would control the depth and angulation of the osteotomies.

The patient’s bone loss was particularly severe in the posterior mandible, where insufficient vertical height required angulation of the distal-most implants and the use of 30° multiunit abutments to avoid the mental foramens. Tilting the posterior implants distally in an all-on-4 protocol would provide the A-P spread needed to support a fixed full-arch restoration and would avoid the need for vertical bone grafting.

For the upper arch, 6 implants were treatment planned to maximize support for the prosthesis in the relatively soft bone of the maxilla. Multiunit abutments were also needed to correct the angulation of the maxillary anterior implants, which had to be tilted axially to accommodate the patient’s available bone. The 6 implants would be positioned so the implant platforms would emerge in the key positions along the arch, including the molar, canine, and central regions. Placing 6 implants instead of 4 would help reduce the overall stress on each implant and would minimize the impact of immediate loading on the osseointegration process.

Surgical Implant Placement
On the day of surgery, the patient’s maxillary dentition was atraumatically extracted (Figure 6). Then, the surgical guide was tried in and the guide pins tightened (Figure 7). The 6 osteotomies were created with a sequence of drills through metal sleeves incorporated in the surgical guide. Four 3.5 mm x 10 mm implants were then threaded into place, as well as two 3.5 mm x 11.5 mm implants in the posterior-most locations. The same protocol was followed in the mandible before placing four 3.5 mm x 10 mm implants through the lower surgical guide (Figure 8).

Figure 6. The patient’s maxillary teeth were removed in preparation for immediate implant placement.	Figure 7. The surgical guide was affixed to the maxillary arch and controlled the positioning of the osteotomy drills throughout the procedure.

Figure 9. Final positioning of the implants. Note the tilted angulation of the posterior mandibular implants as well as the anterior-most maxillary implants, which were positioned as such to accommodate the available amounts of bone and corrected for by the multiunit abutments.

Final placement of the implants was checked radiographically and aligned precisely with the predetermined positions called for by the virtual treatment plan (Figure 9). Because the implants achieved sufficient primary stability for temporization, the patient’s existing lower denture, as well as the new traditional upper denture that was fabricated in advance of the surgical appointment, were converted to serve as stable, relatively comfortable fixed interim restorations that the patient could function with during the healing phase.

Immediate Denture Conversion
To begin the conversion process, openings were created in the dentures so they could be retrofitted to accommodate temporary cylinders that would seat over and connect the prostheses to multiunit abutments in the patient’s mouth (Figure 10). The temporary cylinders were bonded into the openings using Quick Up (VOCO America), acrylic was added to the prostheses where needed, and the flanges and palate were removed from the dentures.

The denture conversion process also involved removing the cantilevers of the prostheses in order to reduce the forces that would be applied to the implants during healing (Figure 11). With the all-on-6 arrangement in the maxilla, this resulted in a molar-to-molar temporary upper denture, while the lower temporary denture extended to the premolar regions of the mandible. Following osseointegration, both of the final prostheses would be designed in a molar-to-molar configuration.

Figures 10a to 10c. Temporary cylinders were seated over the multiunit abutments so holes could be created in the appropriate locations within the interim dentures. The cylinders were then bonded into the openings so they could attach to the multiunit abutments, converting the dentures into implant-supported temporaries.

Figure 11. The cantilevers were removed from the immediate dentures in order to minimize the impact on the implants during the period of osseointegration.

Figure 13. After 4 months of osseointegration, the lab-fabricated working casts and produced wax rims from the impressions of the patient’s healed maxillary and mandibular arches.

After polishing the converted dentures, they were seated, and screws were threaded into the multiunit abutments through the temporary cylinders (Figure 12). This immediate conversion procedure provided the patient with implant-supported temporary restorations, satisfying her desire to leave the surgical appointment with fixed teeth of some kind in place.

Impressions, Jaw Relation Records, and Wax Setups
After 4 months of healing, the patient returned to the office. The converted dentures were removed so impressions could be taken of the healed implant sites. The patient’s soft tissue exhibited excellent health and the integration of the implants had progressed nicely. After submitting the impressions to the lab, wax rims were produced by the lab so the jaw relation records could be taken using standard denture technique (Figure 13). After recording the jaw relationship and returning the wax rims to the lab team, wax setups were produced for the next appointment.

The wax setups were tried in, and the VDO, interocclusal relationship, phonetics, and aesthetics were evaluated (Figure 14). Then, the implant verification jigs, which were provided by the lab to ensure that the relative positions of the implants are accurately captured in the final impression, were connected to the multiunit abutments. The individual sections of the implant verification jigs were luted together using Camouflage Flowable NanoHybrid Composite (Glidewell Direct), and the final open-tray impressions were taken (Figure 15).

With the final impressions taken and the final wax setups approved by the patient, the laboratory team created master casts that were scanned along with the final wax setup to create a virtual model upon which the provisional implant prostheses were designed. Advanced CAD software was used to create the prosthetic designs, with access holes established in precise alignment with the implant positions captured by the final impressions (Figure 16). The provisional implant prostheses were then milled from PMMA and sent out for patient try-in (Figure 17).

Provisional PMMA Implant Prosthesis
The provisionals were tried-in at the next appointment and helped confirm the form, function, and phonetics of the restorative design, including nuances such as the VDO, centric relationship, occlusion, midline, lip support, nasal-labial angle, buccal corridor, tooth display, freeway space, incisal edges, and cantilevers (Figure 18). Slight adjustments were made and the patient left with the provisionals in place in order to test-drive the prostheses in real-life situations.

The provisional PMMA implant prosthesis is the most important element of the restorative protocol, giving the patient an opportunity to evaluate the proposed prosthetic design during a trial period of 2 weeks or more, as opposed to the limited chairside time afforded by the traditional wax setup approval process. If any additive and subtractive adjustments are needed, they can be made to the PMMA and are carried through to the final restoration, giving the patient and doctor an extra measure of confidence.

Figure 19. After wearing the provisional PMMA implant prostheses for a trial period, the patient was extremely happy with the prosthetic designs and provided approval for the fabrication of the final restorations.

After wearing the provisional implant prostheses for 3 weeks, the patient was extremely pleased with their aesthetics, comfort and function (Figure 19). Thus, the case was returned to the dental laboratory. The lab team incorporated the modifications made to the provisionals into the final CAD design with precision. Then, the final restorations were milled from BruxZir Solid Zirconia, with the patient-approved provisionals serving as blueprints for the definitive prostheses (Figure 20).

Delivery of the Prosthesis
Lastly, the patient returned for delivery of the monolithic zirconia implant prostheses. The final restorations were seated and the prosthetic screws tightened through the titanium copings that connect the prostheses to the multiunit abutments. Because the final restorations were precise reproductions of the final-approved provisionals, they met the exact functional and aesthetic requirements of the patient (Figure 21). The screw access holes of the prostheses were then covered with composite, completing a predictable treatment protocol that provided the patient with a long-lasting, life-changing restoration.

Figures 21a to 21c. The final monolithic zirconia restorations were delivered, exhibiting a precise fit, natural-looking aesthetics, and the high level of comfort and stability that the patient had come to expect after the trial period spent wearing the provisionals.

CLOSING COMMENTS
The viability of fixed full-arch implant restorations is well established. By permanently attaching to implants, they mimic the structure of natural teeth, preventing bone resorption while providing patients with a degree of function, stability, and quality of life that is unrivaled by other prosthetic options. Although breakage has been known to compromise the fixed acrylic hybrid denture, the ability to fabricate full-arch implant prostheses from monolithic zirconia presents a more durable alternative.

References

1. Jacobs R, Schotte A, van Steenberghe D, et al. Posterior jaw bone resorption in osseointegrated implant-supported overdentures. Clin Oral Implants Res. 1992;3:63-70.
2. Turkyilmaz I, Company AM, McGlumphy EA. Should edentulous patients be constrained to removable complete dentures? The use of dental implants to improve the quality of life for edentulous patients. Gerodontology. 2010;27:3-10.
3. Rossein KD. Alternative treatment plans: implant-supported mandibular dentures. Inside Dentistry. 2006;2:42-43.
4. Preciado A, Del Río J, Lynch CD, et al. Impact of various screwed implant prostheses on oral health-related quality of life as measured with the QoLIP-10 and OHIP-14 scales: a cross-sectional study. J Dent. 2013;41:1196-1207.
5. Brennan M, Houston F, O’Sullivan M, et al. Patient satisfaction and oral health-related quality of life outcomes of implant overdentures and fixed complete dentures. Int J Oral Maxillofac Implants. 2010;25:791-800.
6. Gallucci GO, Doughtie CB, Hwang JW, et al. Five-year results of fixed implant-supported rehabilitations with distal cantilevers for the edentulous mandible. Clin Oral Implants Res. 2009;20:601-607.
7. Carames J, Tovar Suinaga L, Yu YC, et al. Clinical advantages and limitations of monolithic zirconia restorations full arch implant supported reconstruction: case series. Int J Dent. 2015;2015:392496.
8. Pozzi A, Holst S, Fabbri G, et al. Clinical reliability of CAD/CAM cross-arch zirconia bridges on immediately loaded implants placed with computer-assisted/template-guided surgery: a retrospective study with a follow-up between 3 and 5 years. Clin Implant Dent Relat Res. 2015;17(suppl 1):e86-e96.

Dr. Patel is a graduate of the University of North Carolina at Chapel Hill School of Dentistry and the Medical College of Georgia/American Academy of Implant Dentistry (AAID) MaxiCourse. He is co-founder of the American Academy of Small Diameter Implants and a clinical instructor at the Reconstructive Dentistry Institute. He can be reached at pareshpateldds2@gmail.com or via the website dentalminiimplant.com.

Disclosure: Dr. Patel reports no disclosures.