Full-Arch, Implant-Supported Monolithic Zirconia Prosthetic Treatment

Use of an interim hybrid prosthesis permits verification of function and esthetics

Niloufar Rezakhani, DMD | Gregori M. Kurtzman, DDS | Arun K. Garg, DDS

Clinically, there has been an increase in the use of implant-supported, fixed full-arch prostheses to treat patients with full-arch edentulism or who will become edentulous in an entire arch following the extraction of their remaining teeth. When fabricating an implant-retained prosthesis, it can be designed to either be cemented or screw retained. Screw-retained hybrid bridges offer benefits over their cemented counterparts and are frequently selected as a preferred treatment option.

The dental materials that are available for the fabrication of implant-supported hybrid prostheses have changed during the past decade.^1,2 Traditionally, full-arch prostheses were fabricated by affixing denture teeth to a metal frame with denture acrylic. Typically, over a period of time that varied from patient to patient, the plastic denture teeth would demonstrate wear, and occasionally, a tooth would pop off of the prosthesis. To combat those issues, some practitioners and laboratories began providing cast, and later milled, metal frameworks to which either ceramic was fired or individual crowns were fabricated and luted. This provided a more durable prosthesis, but the resulting esthetics were often less than optimal due to the shadowing created by the underlying metal frame. With the introduction of monolithic zirconia available in a puck that could be milled, the profession began to transition to this material for the creation of implant-retained, full-arch hybrid prostheses.³

Initial concerns regarding the use of a zirconia frame without metal reinforcement focused on whether its strength was comparable to metal substructures. A 3D finite element analysis that compared frameworks for hybrid prostheses that were fabricated from monolithic zirconia with those that were fabricated from milled titanium found that the stress that was generated was not significantly influenced by the framework's material and that a zirconia framework exhibited biomechanical behavior similar to that of a titanium framework.⁴ Because monolithic zirconia is a hard material that resists fracture under function, another concern has been the wear of natural and composite antagonists over time. Although clinically acceptable wear has been reported, zirconia's use in a full arch will not lead to excessive wear of the opposing arch.⁵ Zirconia stabilized with yttrium oxide exhibits high flexural strength and resistance to fracture. Damage to zirconia frameworks has rarely been encountered, but the fracture of veneering porcelains is the most common technical complication encountered with implant-supported zirconia restorations; therefore, the use of a monolithic prosthesis eliminates the potential for ceramic chipping that may be encountered when ceramics are layered to a zirconia frame.⁶

To fabricate a full-arch zirconia prosthesis, virtual design is utilized in conjunction with dental milling.⁷ One approach involves scanning a model containing the implant analogs as well as a denture setup and then combining the two data sets in the software to create the design of the final prosthesis. However, there are some potential problems associated with this approach, and the orientation of the access channels on the prosthesis may not completely match the positions of the implants. This can be avoided by creating an interim hybrid prosthesis from acrylic and denture teeth that can be inserted to verify the esthetics and occlusion before having the laboratory fabricate the final monolithic zirconia prosthesis. An additional benefit of this approach is that the patient can "test drive" the prosthesis, verifying that he or she is happy with the function and esthetics before committing to the final prosthesis.⁸

Case Report

A 63-year-old male patient presented to the office with complaints related to his missing mandibular anterior teeth and the mobility of his remaining maxillary teeth. In addition, he expressed his desire to eliminate the removable partial denture in his maxillary arch and improve his overall esthetics and function. The patient reported that he had difficulty eating because of the poor intercuspation of his teeth and that he had feelings of social embarrassment related to his smile. His medical history was reviewed, and the only notable finding was high blood pressure, which he was controlling with physician-prescribed medication. A panoramic radiograph was taken to evaluate the condition of the remaining dentition and determine the availability of bone for implant placement (Figure 1).

The patient's remaining maxillary teeth consisted of a span from the right lateral incisor through the left canine. Each of those teeth presented with grade 1 mobility, bordering on grade 2, and periapical pathosis. The patient indicated that his posterior maxillary teeth had been extracted a number of years ago and that he had been wearing a partial denture to replace them. Bilateral enlargement of the maxillary sinus was noted with insufficient available crestal height to house implants. Regarding the patient's mandibular teeth, his central incisors and all of his molars were missing. No mobility or apical pathosis was noted among the remaining mandibular teeth. The patient indicated that he had been wearing a mandibular partial denture; however, as one of his treatment goals, he did not want to have any removable prosthetics.

Following an analysis of the patient's clinical condition and expressed treatment goals, a treatment plan was proposed for his maxillary arch that consisted of bilateral sinus augmentation, extraction of the remaining maxillary teeth, placement of eight implants after sinus graft healing, and restoration with a fixed hybrid prosthesis fabricated from monolithic zirconia. For his mandibular arch, a 6-unit bridge would be fixed to his natural teeth from canine to canine to replace the missing central incisors and treat the presence of wear. Also recommended was the placement of two implants in the right posterior region and two implants in the left posterior region that would be restored with individual crowns to replace his missing mandibular molars. The patient accepted the proposed treatment plan with the exception of the mandibular posterior implants due to the limits of his budget. The maxillary treatment would require a staged approach with the use of a provisional traditional denture in the interim, which would help determine tooth position for esthetics and phonetics and guide the design of the final prosthesis. Impressions and interocclusal records were taken and then sent to the laboratory with instructions to fabricate the provisional denture.

Extraction and Sinus Augmentation

At the first surgical appointment, a local anesthetic (Astracaine^® 4% [articaine HCL with epinephrine 1:100,000], Dentsply Sirona) was administered to the maxillary left posterior and maxillary anterior regions. Prior to the initiation of the surgical treatment, blood was drawn from the patient into glass-walled red-top tubes that contained no anticoagulant. These were immediately centrifuged at 2,200 rpm for 3 minutes to separate the components of the blood into layers. The plasma, which is yellow in color and contains a high amount of fibrin and platelets, was mixed with cancellous freeze-dried bone (OsteoLife Mineralized Freeze-Dried Bone, OsteoLife Biomedical) and allowed to congeal in a sterile dish to create "gummy bone."

Once profound anesthesia was achieved, teeth Nos. 7 through 11 were atraumatically extracted with forceps after luxation with elevators. The extraction sockets were then filled with the previously created gummy bone to preserve the osseous contours and then closed with 4-0 resorbable sutures (Vilet^™ 4-0 Polyglactin, OsteoLife Biomedical) in an interrupted pattern.

Next, using a No. 15 scalpel blade, a crestal incision was made that started at the center of the left tuberosity and continued to the first premolar area. At the anterior termination of the crestal incision, a vertical releasing incision was made on the buccal aspect of the ridge, and a full-thickness flap was elevated to expose the lateral aspect of the maxilla in anticipation of sinus augmentation via a lateral approach. Access to the left maxillary sinus was achieved using a lateral sinus augmentation kit (TOLA KIT II, Surgident), and once the sinus membrane was elevated, the area below it was packed with additional gummy bone to improve the crestal height for later implant placement. The flap was then repositioned and closed with the resorbable sutures in an interrupted fashion. After the provisional maxillary denture was tried in and adjusted as needed, the patient was dismissed. He returned a week later for augmentation of the right sinus, and the same procedure that was performed on the left sinus was repeated. Two weeks later, all sutures were removed and the absence of soft-tissue inflammation as well as coverage of the anterior sites with keratinized tissue was noted. The bilateral sinus augmentation and the anterior socket preservation were allowed to heal for a period of 5 months to accomplish graft conversion and maturation.

Implant Placement

At the implant surgical appointment, a local anesthetic was administered across the patient's entire maxilla. Using a No. 15 scalpel blade, a crestal incision was made from the right tuberosity to the left tuberosity with no releasing incisions, and the crestal bone was exposed by flap reflection. Osteotomies were created to accommodate the implants (ImplantVision Tapered Implant, MedEquip Dental Supplies), which were placed at the sites of teeth Nos. 2, 3, 14, and 15 (4.2 mm x 10 mm); teeth Nos. 5 and 12 (3.2 mm x 10 mm); tooth No. 8 (3.2 mm x 8 mm); and tooth No. 9 (3.8 mm x 8 mm). After the implants were placed, the flap margins were reapproximated and secured with 5-0 resorbable sutures (Vilet^™ 5-0 Polyglactin, OsteoLife Biomedical) in an interrupted fashion. The interior of the provisional denture was relined with a self-curing edentulous tissue conditioner (COE-COMFORT^™, GC America) over the implant sites, and the patient was dismissed. He returned 2 weeks later for suture removal, and the soft tissue demonstrated a lack of inflammation.

Five months after implant placement, the patient returned, and a panoramic radiograph was taken to evaluate the healing of the graft and implants (Figure 2). Following administration of a local anesthetic, a tissue punch was used to expose the cover screws on the implants. The cover screws were removed, and healing abutments were placed into each implant. The tissue conditioner material was removed from the provisional denture, and its interior was then modified to seat passively over the healing abutments and relined with new tissue conditioner.

Restoration and Provisional Prosthesis

Four weeks after implant exposure, the patient presented to initiate the restorative phase of treatment (Figure 3). Local anesthetic was placed in the mandibular anterior using bilateral mental blocks, and the canines and lateral incisors were prepared bilaterally to accommodate the planned 6-unit fixed bridge. Following preparation, an impression was taken of the mandibular arch. Next, the healing abutments were removed so that closed tray impression abutments could be placed into each of the implants, then a duplicate of the provisional denture was modified to fit over the impression abutments, and a bite registration was taken (Futar^®, Kettenbach Dental) of the denture in occlusion. The duplicate denture was removed, and vinyl polysiloxane (VPS) adhesive was painted onto the interior of the prosthesis. After heavy body VPS impression material (Panasil^®, Kettenbach Dental) was used to fill the relieved areas in the denture, and light body VPS impression material (Panasil^®, Kettenbach Dental) was expressed around the impression abutments intraorally, the denture was seated, and the patient was guided into the previously taken occlusal bite. Upon setting, the impression in the duplicate denture was removed from the mouth, and the healing abutments were reinserted. The impression in the duplicate denture would allow the laboratory to mount the casts and fabricate a provisional prosthesis for try-in. The prepared mandibular teeth were then temporized.

Three weeks later, the laboratory returned a screw-retained, acrylic full-arch interim hybrid prosthesis (Figure 4 and Figure 5). The healing abutments were removed, the provisional prosthesis was inserted, and the fixation screws were tightened. After seeing the prosthesis in his mouth, the patient indicated that he was happy with the esthetics. Radiographs were taken to verify the fit and mating of the interim hybrid prosthesis (Figure 6).

Regarding the mandibular teeth, the provisional bridge was removed, and a milled high translucency zirconia (GC Initial^®, GC America) monolithic bridge was tried in to verify the fit and esthetics. Once verified, the final bridge was luted with a self-adhesive resin cement (G-CEM LinkAce^®, GC America), the margins were tack cured with a curing light, and any excess cement was removed. The occlusion was checked and adjusted where needed. To obturate the screw access channels, cotton pellets were placed over the screw heads, and a temporary filling material (Cavit^™, 3M) was placed.

The patient wore the maxillary interim hybrid prosthesis for a period of 3 weeks to confirm the occlusion and verify that the esthetics met his expectations.

The Definitive Prosthesis

After the verification period, the patient approved the interim hybrid prosthesis, and the laboratory was notified that no modifications would be needed and that they could proceed with fabrication of the final maxillary prosthesis. They had previously scanned the acrylic interim hybrid prosthesis on the model and would use that to virtually design the final monolithic zirconia hybrid prosthesis (Figure 7). The screw access channels would emerge through either the lingual aspects of the anterior teeth or the occlusal surfaces of the posterior teeth, placing them in nonesthetic areas. Following design, the bridge was milled from high translucency zirconia (GC Initial^® Zirconia Disk, GC America), and universal stains (GC Initial Spectrum Stain, GC America) were brushed on to create natural looking effects and eliminate the monochromatic look of the teeth. Gingival tone coloration (GC Initial IQ Lustre Pastes NF Gum Shades, GC America) was then applied to the gingival aspect of the zirconia to create natural-looking effects and esthetics. Once stained, a glaze was applied over the entire prosthesis, and it was fired. Metal copings were then luted into the connector aspect on the tissue side of the prosthesis with a self-adhesive resin cement and allowed to self cure. Any excess resin was cleaned from the interface, and the bridge was returned to the office for insertion.

The provisional acrylic hybrid prosthesis was removed from the mouth and compared extraorally with the monolithic zirconia hybrid prosthesis, which demonstrated identical tooth positions and esthetics that had been approved by the patient (Figure 8). When the acrylic screw-retained hybrid prosthesis was removed, the underlying soft tissue demonstrated a healthy noninflamed gingival cuff at each implant site. For the screw access channel of the right canine-premolar implant to be placed in a nonesthetic location, a multi-unit abutment was required to correct the emergence angle (Figure 9). This multi-unit abutment had been placed when the acrylic hybrid prosthesis was initially inserted. The zirconia full-arch hybrid prosthesis was seated on the maxillary arch, and the fixation screws were torqued to the manufacturer's recommended value (Figure 10). Once seated, periapical radiographs were taken to verify that the prosthetics properly mated with the implants without any misfit at the connectors (Figure 11). The screw access channels in the zirconia monolithic full-arch hybrid prosthesis were then filled with polytetrafluoroethylene (PTFE) (ie, plumber's) tape to block the screw heads and then restored with composite (Filtek^™, 3M) to seal the access openings (Figure 12). The occlusion was checked, and no adjustments were required. At the completion of the case, the resulting stable prosthesis met the patient's initially expressed goals, providing esthetics and a return to function (Figure 13 and Figure 14).

Conclusion

Advances in prosthetic material science have provided materials that are more esthetic and that offer that offer sufficient strength without the inclusion of a metal substructure to permit their use for the fabrication of full-arch implant hybrid prostheses. Following milling, monolithic zirconia materials can be colored to replicate nuances in tooth shading as well as to present as gingival tissue. The virtual design of these prostheses can include the creation of a provisional hybrid prosthesis, allowing the patient to test drive the esthetics and function before the final prosthesis is fabricated.

Acknowledgment

The authors would like to thank Luke S. Kahng, CDT, and LSK121 Oral Prosthetics for the laboratory work that was performed in this case.

About the Authors

Niloufar Rezakhani, DMD
Private Practice
Hallandale Beach, Florida

Gregori M. Kurtzman, DDS
Master
Academy of General Dentistry

Diplomate
International Congress of Oral Implantologists

Private Practice
Silver Spring, Maryland

Arun K. Garg, DDS
Founder
Implant Seminars

Private Practice
Miami, Florida

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