Rehabilitation with a Unique Full-Arch Prosthesis

It is estimated that 8% of the general US population suffers from sleep bruxism and that 20% unconsciously grind or clench their teeth during awake activity.²Although the literature is not definitive, the prevalence of bruxism has been demonstrated to be a contributing factor to a range of oral health problems, including periodontal disease, bone loss, tooth mobility, and implant or implant suprastructure failures.^3-7 Treating patients diagnosed with sleep-related bruxing disorders requires a comprehensive rehabilitative treatment plan as well as careful consideration of restorative material selection and clinical techniques to mitigate the destructive forces of these parafunctional habits.^8,9

Collaborating with other dental healthcare professionals and the laboratory team to create a treatment plan and select restorative materials that address the underlying causative factors, as well as any current diagnostic findings, while still meeting the functional and esthetic demands of the patient is critical to achieving a successful long-term outcome. In addition, educating the patient about all of the available restorative options based on the diagnostic findings is essential to garnering treatment acceptance. This article demonstrates a holistic collaborative approach for treating partially edentulous patients who present with a history of failing natural dentition and implant restorations and illustrates a unique rehabilitative implant-supported prosthetic solution.

Case Report

A new, 58-year-old female patient presented to the practice with partial edentulism and two failed implant restorations in her maxillary arch in the positions of teeth Nos. 6 and 13. Her chief complaints were frustration with her limited chewing functionality, which was due to her failed upper dentition, and limited social interaction, which was due to the loss of esthetics caused by her partial edentulism and failed implant restorations (Figure 1 and Figure 2).

The clinician performed initial radiography, including a panoramic x-ray scan and a CBCT scan, to evaluate the bone and remaining dentition in the maxillary and mandibular arches. At the initial examination, it was also noted that the patient's overall dentition bore the signs of sleep bruxism and that she was at risk for sleep-disordered breathing, for which she was referred for analysis and underwent treatment. The x-ray scans, panoramic radiograph, and CBCT scan results showed significant bone loss at the two maxillary implant sites, and the prognosis for the remaining maxillary dentition was deemed fair but guarded in terms of survival. The natural dentition in the mandibular arch was deemed healthy.

Treatment Planning

The patient was presented with a thorough treatment plan that included many prosthodontic options, and the time frames, expectations, financial considerations, and operational risks for each were discussed. She was adamant that a removable full-arch or partial prosthetic was not an acceptable restorative solution and that neither were a monolithic overdenture or an implant-retained monolithic overdenture. She wanted a final comprehensive solution that functioned and appeared as natural as possible and that was easily repairable if necessary.

Because of the unique needs of the patient and the complexity of the case, the restorative dentist conferred with an oral surgeon to whom the patient was referred. Because implant reconstruction is predicated on a surgical foundation that supports both long-term function and esthetics, the diagnostic imaging and the prosthodontic treatment plan were shared with the oral surgeon to ensure proper implant placement.

At the appointment, the oral surgeon advised the patient about her compromised implants and discussed treatment options with her. To correct the severe atrophy of her maxillary arch, he recommended bone grafting across the entire maxillary jaw with an oval window in the upper posterior. The surgeon also recommended the placement of six implants (Straumann) with healing caps in the positions of teeth Nos. 5, 6, 8, 9, 11, and 13. To provide cover and function during her healing period, a temporary maxillary complete denture would be delivered, and then she would receive a fixed, implant-retained full-arch prosthesis. The treatment plan was accepted by the patient.

To achieve the ideal positions for parallel placement of the implants with attention to the details of the therapeutic process, a team approach to treatment planning was employed involving the restorative dentist, the surgeon, and the laboratory. Prior to surgery, the team virtually treatment planned the implant placement using 3D implant planning software (Invivo, Anatomage, Inc.) and established a proper timeline for the healing of the bone and osseointegration of the implant fixtures. The final prosthetic design would be a milled, full-arch maxillary implant-retained bar framework with individually fabricated denture teeth.

Material Selection and Restorative Design

In order to help the laboratory team determine the correct tooth and tissue shades, the clinician took preoperative photographs of the patient's teeth and gingival tissue with a shade guide. The material chosen for the implant-retained framework was a high-performance polymer (Pekkton^® Ivory, anaxdent North America). With a compressive strength comparable to that of cortical bone and dentin, the properties of this material would be optimal to withstand the massive forces of the patient's bruxism habit.¹⁰ To meet the patient's desire for a final restoration that was easily repairable, the treatment team recommended the use of a screwless, cementless, and easily retrievable attachment system. For the final individual prosthetic teeth, the team selected milled full-contour zirconia units (IPS e.max^® ZirCAD^® Prime, Ivoclar Vivadent).¹¹

The carefully selected materials for this case combined a screwless and cementless attachment solution that eliminated the need for access holes in the prosthesis with the esthetics and retrievability of individually cemented crowns. The primary advantages of this solution were the ease with which the individual teeth could be replaced should a fracture occur and the compressive strength of the implant bar, which could withstand excessive loading due to bruxing. Other solutions that were considered but rejected included a hybrid fixed denture, which would generally require the entire fixed prosthesis to be remade in the case of a tooth fracture, and a hybrid acrylic fixed denture, which has been shown to fail due to fractures and breakage after 5 to 6 years in function.^12-14

Therapeutic Phase

After the bone grafting treatment, guided implant placement, and a 5-month osseointegration period, the therapeutic process began. Photography and documentation were completed for communication with the laboratory. The vertical dimension of occlusion, smile line, lip support, phonetics, shade, and esthetics were all established in agreement with the patient and her preferences. She wanted a prosthesis that was as realistic, polychromatic, and natural-looking as possible.

To capture the actual vertical dimension in the physiologic rest position for her denture, the laboratory team provided the dental office with a wax occlusal rim on a base with a custom tray, which was placed with the patient in an upright position (Figure 3). Establishing the vertical dimension of occlusion can be one of the most challenging clinical procedures that a dentist encounters.^15-19 Although the clinician in this case used many of the available clinical methods to determine the vertical jaw relation, pre-extraction records and radiographs are not always available. A phonetic test with particular attention given to the activity of the muscles of facial expression can be quite reliable.

To administer a phonetic test in this case, the assistant placed one small ink dot on the patient's maxillary lip at the junction of the philtrum and septum and a second ink dot on the most forward point of the patient's chin. The patient was asked to pronounce the letter "M" and to maintain the final position of her lower jaw following the complete pronunciation of the letter. The clinician then recorded the distance between the two dots in millimeters, measured at the physiologic rest position. This procedure was repeated several times, and an average of the distances was calculated. In some patients, the skin can move over the chin without movement of the mandible, which may account for variation in the measurement.

Next, the clinician captured an implant-level impression using impression copings (Straumann) (Figure 4). An open tray method was chosen to ensure the most accurate transfer of the implant positions.

After the bite was recorded using the bite rim, the laboratory team mounted the upper model to the lower model in a semi-adjustable articulator and fabricated a trial denture to verify the bite, lip line, smile line, overjet, overbite, and smile design. The trial denture was sent to the practice, where the physiologic rest position was rechecked (Figure 5).

Master Model and Abutment Level Impression

To fabricate the master model and replicate the exact position of the implants in the mouth, die stone (Dental Stone, ETI Empire Direct), model analogs, and a medium soft tissue mask were used. The tissue depth was measured, and multi-unit abutments with the necessary cuff heights were ordered. The goal was to keep the posterior margin line of the abutments equal to the gingival margin or 0.5-mm supragingival.

Once delivered, the multi-unit abutments were placed at all six locations on the model implant analogs and tightened (Figure 6). For the implant in the position of tooth No. 8, an abutment with a 2.5-mm cuff height was chosen. The remaining implants would receive abutments with 4-mm cuff heights because of their deep placement.

After the impression copings were hand tightened onto the abutments, the laboratory team fabricated a sectioned verification jig using acrylic material (Pattern Resin^™ LS, GC America Inc.) (Figure 7). Each section was marked with a number to allow for easy chairside identification. The model with the jig in place was then scanned in a custom open tray, holes were designed in the CAD software (3Shape Dental Software, 3Shape), and it was printed on a 3D printer (Carbon M2, Carbon).

When the patient returned to the practice, the clinician removed the healing caps from the implants and torqued the abutments into place. To ensure that the socket was fully engaged and seated on the abutment before and during torquing, the clinician maintained downward pressure using his finger (Figure 8). The clinician then placed the verification jig sections on the multi-unit abutments and hand tightened them. Next, the verification jig sections were luted together one at a time, allowing the resin to finish curing before moving to the next section (Figure 9). After all of the parts were fully cured, an open tray impression was taken over the verification jig, and then the verification jig screws were unscrewed, and the impression tray was removed from the patient's mouth. To protect the torqued-in multi-unit abutments from damage, the healing caps were hand tightened over them (Figure 10), and the intaglio surface of her temporary denture was adjusted to seat over the healing cap-covered abutments.

Final Prosthesis Fabrication Model and Scanning

After the laboratory team verified the impression for a stable position of the impression copings, they attached the multi-unit abutment analogs and hand tightened them. A stone model was poured with soft tissue mask (Figure 11), and after 24 hours of setting time, the impression was unscrewed from the model. The laboratory then created a new order form in the CAD software (Figure 12), selecting the abutments as screw retained. The usual design procedure for screw-retained abutments involves scanning the pre-preparation model first, then the upper and lower arch, followed by the bite wax rim and single dies. For this case, the temporary denture was secured on the model and scanned as the pre-preparation model. Before scanning, marks were ground into the stone with a carbide bur at the implant positions. These would help to accurately align all of the virtual models in the future. Using the bite wax rim, the upper and lower bite relation was scanned. Finally, the lower antagonist single arch and the upper arch were scanned and aligned to the bite. To scan and align the upper arch to the bite, smaller hand-tightened screws were used to attach each of the copings onto the model analogs without the gingiva in place. CAD/CAM scan spray was also used to dull the metal surface of the abutments to achieve better scan quality (Figure 13).

To avoid any misalignment of the scans and to ensure a proper fit of the final prosthesis in the mouth, particular care was taken to ensure a snug fit when hand tightening the abutments. After successfully scanning the upper arch and aligning the scan flags with the screw access holes on the upper model scan, the copings and attachments were removed, the tissue mask was placed onto the model, and the model was scanned in as a gingiva scan. The final step was to align the model to the bite scan.

Prosthetic Framework Design and Try-In

When digitally designing the PEKK framework, all of the preparations were positioned with the help of the pre-preparation scan (eg, the approved denture) to ensure optimal tissue and tooth display (Figure 14). In the CAD software, the finished design was copied and appended to the preparation scan, and a new order form was created to design the crowns. The crown design, which was selected from the laboratory's studio, followed the form and shape of the denture teeth from the pre-preparation model (Figure 15). A 2D image of the patient with the try-in denture virtually in place was used as a background guide to verify the smile line, lip line, and buccal corridors as well as the shape, contour, and overall design (Figure 16). For the margin line offset, a setting of 0.12 mm was chosen to ensure that the margin was as thin as possible to avoid the need for post-sintering adjustments to the zirconia crowns. The design of the final unit was shared with and approved by the clinician.

To verify the design of the framework and the smile design, the laboratory team created a try-in of the final prosthetic by milling the framework and single crown units out of PMMA (Multi-Layer PMMA, Harvest Dental). First, the PMMA single units were cemented onto the frame using resin cement (Multilink^®, Ivoclar Vivadent). Then, after a second set of the titanium copings was secured onto the multi-unit abutments, the PMMA frame was cemented onto the copings and cured. This try-in prosthetic was delivered to the practice for verification of the smile line, lip line, and occlusion (Figure 17). Once adjusted, the PMMA frame was sent back to the laboratory and scanned, and then the scan was aligned as a pre-preparation scan with the original design file to apply the modifications for final fabrication.

Final Denture Tooth Fabrication

The individual crowns were milled on a 5-axis milling machine (Zenotec Select, Wieland Dental), and then the facial and occlusal anatomy of each unit was redefined with sharp fine flame diamond burs. After sintering, the units were seated on the PEKK framework and the proximal contacts and occlusion were refined. Using silicone wheels, select line angles were adjusted and highlighted (Figure 18). All of the units were then glazed (MiYO^® Liquid Ceramic, Jensen Dental), which allowed the overall chroma of the zirconia to be modified (MiYO^® Translucent Shade A, Jensen Dental) and also lowered its value at the incisal third (MiYO^® Translucent Smoke, Jensen Dental), which appeared slightly too high in value after sintering. Additional shades were used to refine the final esthetics, and then the units were fired in a porcelain furnace (Programat^® P510, Ivoclar Vivadent) at 725 ° C (Figure 19).

Assembly of the Final Prosthetic

The milled PEKK framework was surface roughened with a diamond bur at a low speed (eg, 5,000 rpm) and with light pressure to avoid overheating. It was then cleaned with steam and rubbing alcohol before its entire surface was sandblasted with 110-µm aluminum oxide from a distance of 15 cm and at a pressure of 2 bar to avoid damaging it. To prepare the crowns, the intaglio surface of each unit was sandblasted with 110-µm aluminum oxide and treated with a light film of universal primer (Monobond^® Plus, Ivoclar Vivadent) that was allowed to react for a minimum of 30 seconds. After the preparation surfaces on the frame were treated with a light coating of bonding agent (PEKKbond, anaxdent North America) and light cured, each crown was injected with a self-cure resin cement (Multilink^® Hybrid Abutment, Ivoclar Vivadent) and positioned on the framework. Any excess cement was removed from around the margins with a small brush.

The outsides of the titanium copings were sandblasted, and the try-in abutments were positioned on the multi-unit abutments on the model and snapped onto the retrievable crown retention units. Next, the inside of the framework's coping space was sandblasted, cleaned with alcohol, and treated with a light coating of the bonding agent before the self-cure cement was injected and the frame was positioned on the model with the gingiva mask removed. After curing, the try-in retrievable prosthetic retention units were released by applying heat from the steam cleaner.

Before applying gingiva-colored material onto the framework, it was sandblasted, cleaned with alcohol, brushed with the bonding agent, and light cured. The gingiva aspect of the unit was created by layering pink composites (anaxgum, anaxdent North America), and then the entire frame was light cured. After a cover gel (eg, oxygen inhibitor) was brushed onto the cured pink composite to remove the inhibition layer, it was accented with red and blue stains, a lacquer was applied (Dreve NanoVarnish, anaxdent North America), and it was light cured again (Figure 20).

Delivery of Final Prosthetic

The patient returned to the practice, and her six healing caps, which had been hand tightened to only 15 Ncm each, were removed. The final prosthetic was test fitted onto the abutments, and adjustments were made to the intaglio surface and occlusion, as needed. With help from the dental assistant, the clinician fitted the retrievable prosthetic retention attachments onto each abutment (Figure 21 and Figure 22). The prosthesis was seated, and the clinician firmly pushed down on each attachment location to engage the copings onto the abutments. The patient was then asked to bite down firmly on a wood or plastic bite stick at each attachment location to ensure that the prosthesis was fully seated (Figure 23).

Next, the clinician checked the occlusion to ensure that there were no premature contacts, no class 1 to 4 interferences, and no pitch, roll, or yaw issues, applying standard principles of gnathology and micro-occlusion. Final radiographs were taken, and final occlusion, chewing cycles, and function were verified with solid foods (ie, carrots and apples). After the patient reconfirmed her acceptance of the esthetics, the final photography was completed with proper lighting and control (Figure 24 through Figure 26).

Acknowledgements

The author would like to thank the technical team at MicroDental Laboratories for their work on this case as well as the collaborating oral surgeon, Eric Nordstrom, DDS, MD, Alaska Center for Oral and Facial Surgery, Anchorage, Alaska.

About the Author

Jerry Hu, DDS
Diplomate, American Board of Dental Sleep Medicine
Master, International Congress of Oral Implantologists
Private Practice
Anchorage, Alaska