Custom Abutments and Monolithic Zirconia: Aesthetic, Cementable Solutions for Complete Edentulism

INTRODUCTION
Patients facing the loss of their natural dentition have more treatment options than ever before. The traditional complete denture, once the standard of care for the fully edentulous patient, is slowly but surely giving way to fixed and removable full-arch implant restorations as their superior stability, function, and aesthetics become more well known. Furthermore, prosthetic materials have advanced in leaps and bounds, and monolithic zirconia can now be milled for fixed full-arch indications. By moving beyond acrylic and its vulnerability to wear, chipping, stains, and fracture, this option adds long-term durability to the qualities that make the fixed implant prosthesis the ultimate restorative option for fully edentulous cases.

Screw-Retained Option
Due to the versatility of dental CAD/CAM technology and the material properties of monolithic zirconia, high-strength restorations can be fabricated for the fully edentulous patient in various configurations. For example, because of its flexural strength of up to 1,465 MPa, BruxZir Solid Zirconia (Glidewell Laboratories) can be milled into thin layers and can maintain the high level of durability for which the material has become known. This allows for the fabrication of restorations ranging from the monolithic zirconia full-arch implant prosthesis—which resembles a screw-retained hybrid denture in form—to cementable prostheses that attach to custom abutments in the manner of traditional crown and bridge work.

Cementable Option
While the screw-retained monolithic zirconia full-arch implant restoration has grown increasingly popular in recent years, the cementable alternative is well suited to many patients. When sufficient hard and soft tissue are present, prostheses can be designed to emerge directly from the gingiva, creating the aesthetics and feel of natural dentition. Additionally, the use of custom abutments to support a cementable full-arch bridge allows for low-profile restorations with minimal facial-lingual width. This is appealing to many patients and can indicate a fixed solution in cases of limited vertical clearance.

Cementable monolithic zirconia implant prostheses can be fabricated in various designs as described by Dr. Carl Misch’s prosthodontic classifications.1 While they are most commonly indicated in fixed prosthesis 1 (FP1) and FP2 cases, in which the prosthetic teeth rise from the gums like natural teeth, they can also be used in FP3 cases, where the monolithic prosthesis includes pink gingival areas in order to reconstitute the soft tissue.1 Whichever prosthesis type is indicated, the precision of dental CAD/CAM technology and versatility of full-contour zirconia allow the entire restoration to be milled from a single block of the material, adding to the overall strength. All of these prosthesis types afford in bone preservation and improved dental function, as well as the psychological benefits and enhanced quality of life associated with fixed implant prostheses, which come the closest to natural dentition of all restorative options.2,3

Advantages Using Custom Abutments
The use of custom abutments for this type of restoration (and all cementable prostheses, for that matter) is essential as it allows for the creation of margins that are gingival or just slightly subgingival, which enhances crown retention, cervical soft-tissue margins, and the final emergence profile.4,5 The precision and flexibility in prosthetic positioning allowed for by custom abutments also make it easier to achieve a passive fit for the restoration and correct for divergent angulation of implants.

Figure 1. Initial condition of the patient, who sought treatment after the cantilever bridge (teeth Nos. 12 to 14) broke off. Note the bilateral asymmetry resulting from an accident that had required reconstructive jaw surgery.

The following case report features a full-mouth reconstruction via cementable full-arch BruxZir bridges (Glidewell Laboratories) over Inclusive Titanium Custom Abutments (Glidewell Laboratories). The treatment protocol for this type of restoration will be illustrated, as well as the general parameters for determining whether this solution is indicated for the individual patient. Standard denture technique, digital treatment planning, CAD/CAM technology, and try-in bridges are used to achieve an excellent result in an aesthetically challenging case.

CASE REPORT
Initial Consultation and Diagnosis

A 63-year-old male presented with a chief complaint of a cantilever bridge that had fractured and fallen off due to recurrent decay (Figure 1). Intraoral evaluation revealed deterioration of the natural abutments that had been supporting the bridge, as well as substantial decay present on the patient’s lower anterior teeth (Figure 2). Panoramic radiography indicated that the rest of the patient’s extensive crown and bridgework was succumbing to recurrent caries and failing root canals (Figure 3).

Figure 2. Preoperative maxillary and mandibular occlusal views. Note the recurrent decay on natural teeth abutments Nos. 12 and 13 that became exposed when the cantilever bridge broke off and the severe caries at the cervical portions of the mandibular anterior dentition.
Figure 3. Panoramic radiograph shows extensive caries, failed root canals, and fixtures placed during previous orthognathic jaw surgery.

Analysis of the patient’s radiographs and CBCT scans indicated sufficient bone quantity to accommodate fixed full-arch implant restorations. A streamlined treatment protocol was proposed to the patient, who had never considered traditional complete dentures an option. His nonrestorable teeth would be extracted, followed by the immediate placement of 9 implants in his maxilla and 10 in his mandible via guided surgery. Financing options (Lending Club) were discussed. This discussion can be an important part of facilitating patient acceptance of implant therapy, since it makes the cost of treatment more feasible in many situations.

Digital treatment planning and guided surgery were necessary because of the patient’s bone quality and the orthognathic fixtures in his jaws that were placed many years prior. The quantity of implants was chosen in order to maximize the distribution of functional forces around the arch, minimize pontics, and to ensure the best long-term prognosis possible for the restorations. The immediate implantation approach appealed to the patient because he wanted to have his teeth replaced as quickly, and in as few surgical appointments as possible.

Although various combinations of fixed full-arch prostheses and removable implant overdentures were indicated and presented to the patient as options, he strongly preferred nonremovable restorations for both arches. The patient’s dentition would be replaced via cemented full-arch BruxZir bridges over Inclusive Titanium Custom Abutments. The high strength of monolithic zirconia was particularly suitable for this patient, a large man with considerable bite force. Restoration design would be a challenge due to the patient’s crooked smile and uneven jaws resulting from a prior accident and reconstructive surgery, so the precision and versatility of dental CAD/CAM technology would be essential in producing an aesthetic outcome.

Treatment Planning
CBCT images utilizing the CS 8100 3D (Care­stream Dental) were converted into virtual models of the upper and lower arches in order to ascertain the location of the patient’s bone, sinus and nasal cavities, and inferior alveolar nerve (Figure 4). A digital treatment plan was developed using coDiagnostiX software (Dental Wings). Along with diagnostic models, the digital treatment planning software was used to preplan the placement of the implants (Figure 5).

Figure 4. The 3-D models of the patient’s existing dentition and anatomy were generated from CBCT scans.
Figure 5. The digital models were used to preplan surgery within the patient’s available bone and at a safe distance from vital anatomy and orthognathic fixtures.

Bone-level surgical guides were fabricated by 3D Diagnostix based on the digital treatment plan. These guides were to be used during surgery to ensure that the osteotomies situated the implants in their exact and predetermined positions. This approach would help to avoid vital anatomical landmarks and execute a prosthetic-driven treatment plan, which was essential given the aesthetic difficulties presented by the bilateral asymmetry of the patient’s arches.6,7

The mandibular restoration would be classified as an FP2 prosthesis, in which a portion of the roots as well as the crowns of the teeth would be replaced. The FP2 design results in elongated prosthetic teeth, as indicated in this situation since the lower halves of the patient’s mandibular dentition were not in the aesthetic zone. This was specifically the case for the area of the restoration in the lower right quadrant, which needed to be extended to account for the uneven mandibular incline. Even with the elongated teeth, the FP2 prosthesis would have a low profile for a full-arch restoration, helping to accommodate the limited vertical clearance between the patient’s upper and lower arches.

An FP3 prosthesis would be fabricated for the patient’s upper restoration. The pink gingival areas of this prosthesis type were indicated to reconstitute the maxillary tissue contours, as substantial bone leveling would be required to even out the patient’s smile. Note that both restorations were prescribed under the dental laboratory’s large case protocol that ensured pricing comparable to that of screw-retained monolithic zirconia restorations and fixed acrylic hybrids.

Implant Surgery Protocol
To begin the surgical process, the patient’s bridgework was removed (Figure 6). The patient’s teeth were then atraumatically extracted (Physics Forceps [Golden Dental Solutions]). After reflecting soft-tissue flaps, the bone-supported surgical guides were seated (Figure 7). Fixation pins were tightened through openings in the guides to hold the appliances in place during the surgical procedure. The implant osteotomies were created using the AEU 7000 Surgical Motor/Handpiece (Aseptico) in positions that would minimize pontics between the abutments, avoid cantilevers, and situate the implants in the key positions of the edentulous arch (according to Dr. Carl Misch)—including the first molar, first premolar, canine, and central or lateral regions.1 Following the placement of Engage (OCO Biomedical) dental implants, bone grafting material was used to augment the areas of his ridges impacted by his various dental ailments (Figure 8).

Figure 6. The patient’s existing bridges were removed in preparation for teeth extraction, uncovering the extensive recurrent decay that had rendered his maxillary dentition nonrestorable. Figure 7. After extracting the teeth and reflecting a soft-tissue flap, the bone-supported surgical guide was seated.
Figure 8. After attaching healing caps and temporary abutments to the implants, the edentulous arches were augmented with grafting material to maximize ridge thickness and reconstitute bone in areas where defects were present.


After verifying the initial stability of the mandibular implants,8,9 which was adequate except for the 2 posterior-most implants, a BioTemps (Glidewell Laboratories) provisional bridge was connected to prepared stock abutments using a resin temporary cement (TempBond Clear [Kerr]). The temporary res­toration would help sculpt the soft tissue during healing and develop an aesthetic emergence profile in preparation for the FP2 prosthesis.10 Healing abutments were placed in the posterior-most mandibular implants. While the patient desired fixed prostheses for both arches, the Type IV bone quality of the maxilla was not sufficient to achieve the primary stability needed for provisionalization, so an immediate denture was provided for the upper arch with Sofreliner Tough (Tokuyama Dental America) (Figure 9).

Figure 9. Upper immediate denture and lower fixed BioTemps (Glidewell Laboratories) provisional in place. Figure 10. Facial view shows the dramatic transformation evident after extraction,
immediate implantation, and delivery of temporary prostheses.
Figure 11. Postsurgical radiograph exhibited healing abutments in the maxillary implants and temporary
abutments in the mandible; except for the distal-most implants in the molar regions that did not achieve sufficient primary stability for loading.

At the end of the surgical appointment, the patient was extremely pleased with how treatment was progressing as the aesthetic reconstruction of his dentition was already well under way (Figure 10). Postoperative radiography confirmed placement of the implants in their ideal preplanned positions (Figure 11).

Impressions, Wax Rims, and Setups
The patient returned 4 months after the surgery appointment for an assessment of tissue healing and implant osseointegration. Removal of the tem­porary appliances and abutments revealed that the tissue surrounding the implant sites had healed well (Figure 12). An Osstell implant stability quotient (ISQ) meter (Osstell USA) was used to check the integration of the implants (Figure 13). Once integration was confirmed, vinyl polysiloxane (Take 1 Advanced [Kerr]) impressions were taken to initiate the restorative phase of treatment (Figure 14). Using the impressions, the lab team first produced master casts and then wax rims that were connected to the implants through temporary cylinders at the next appointment. The jaw relationship was recorded according to the standard denture technique, and an occlusal bite registration (anterior stick-bite) was taken (Figure 15). Wax setups were then created by the lab team and tried in during the patient’s next visit. The midline, vertical dimension of occlusion, interocclusal relationship, aesthetics, teeth positioning, and phonetics were all evaluated. Then adjustments were made until the proper prosthetic design was established.

Figure 12. The patient returned 4 months after surgery. Note the excellent gingival tissue health.
Figure 13. Integration was comfirmed with the implant stability meter reading (Osstell ISQ meter [Osstell USA]).
Figure 14. Transfer posts were attached to the implants and closed-tray impressions were taken and submitted to the dental lab.
Figure 15. The wax rims were attached to the implants, the jaw relationship was determined, and a bite registration was taken. Figure 16. The proposed prosthetic designs were used to mill try-in bridges (top) and BioTemps prostheses (bottom).
Figure 17. The titanium custom abutments (Inclusive Titanium Custom Abutments [Glidewell Labortories]) were placed using the acrylic delivery jigs provided by the lab team, helping to ensure proper prosthetic orientation.
Figure 18. The fit of the custom abutments was perfect, adhering to the exact sulcus shapes of the individual implant sites while establishing gingival margins that would ease cementation of the full-arch bridges.

Custom Abutment Delivery and Try-In Bridges
After scanning the master casts and approved wax setups, the lab team then designed custom abutments and full-arch prostheses in tandem, using advanced dental CAD software to ensure a mutual fit and optimal emergence profiles. The custom abutments were milled along with full-arch try-in bridges, ensuring that the prosthetic designs were accurate prior to fabrication of the final restorations. BioTemps restorations were also milled at the request of the doctor (Figure 16).

At the next appointment, the Inclusive Titanium Custom Abutments were delivered (Figure 17). Because the custom abutments were designed based on the soft-tissue anatomy captured in the impressions, they established a precise fit upon delivery (Fig­ure 18). The try-in bridges were seated in order to verify that the proposed restorations conformed to the oral anatomy and contours, as well as the functional and aesthetic needs of the patient (Figure 19).

The form, function, margins, emergence profiles, and occlusion of the try-in bridges were verified, and some minor adjustments were made. Then, the full-arch BioTemps (which would serve as temporaries while the final restorations were produced and would help contour the soft tissue in preparation for the definitive prostheses) were delivered over the custom abutments (Figure 20). The modified try-in bridges were scanned at the dental laboratory, and then the changes were incorporated into the final digital design. The lab team then milled the final full-arch restorations (BruxZir Solid Zirconia).

Figure 19. The full-arch try-in bridges were seated to verify the proposed prosthetic designs. Minor modifications were made to the occlusion and margins, and a new bite registration was taken.
Figure 20. The BioTemps prostheses were delivered to serve as fixed temporary appliances while the final restorations were milled from monolithic zirconia.

Final Restoration Delivery
At the final delivery appointment, temporary cement was used to affix the final monolithic zirconia restorations to the custom abutments. This was done to ensure that the prostheses could be removed at a later date if necessary (Figure 21). The low profile of the cementable restorations provided the feel and aesthetics that the patient desired, while the use of monolithic zirconia afforded the necessary level of long-term durability (Figure 22).

The patient was overjoyed with the final prosthetic outcome (Figure 23). Final radiography confirmed complete integration of the implants, which, in combination with monolithic zirconia, provided the patient an excellent long-term prognosis and a minimal likelihood that the prostheses would ever need to be replaced (Figure 24).

Figure 21. The final full-arch BruxZir Solid Zirconia (Glidewell Laboratories) bridges were cemented over the custom abutments (Inclusive Titanium Custom Abutments), achieving a predictable result in line with what the patient expected after verifying the prosthetic designs with the try-in bridges.
Figure 22. Occlusal views of final restorations in place. Note the slim horizontal width and absence of screw access holes, establishing the lifelike restoration that made cementable prostheses the ideal choice for this patient.
Figure 23. The patient was ecstatic with the final outcome that had been predictably achieved by following a streamlined treatment protocol. Figure 24. Final radiograph illustrates stable bone levels around the maxillary and mandibular implants, as well as the monolithic zirconia construction of his full-mouth restoration.

CLOSING COMMENTS
As a practitioner, delivering a restoration that is aesthetic and built to stand the test of time is both rewarding and reassuring. The odds that the patient will ever return with a broken prosthesis are extremely low. For practitioners looking to harness the superior durability of monolithic zirconia for the benefit of their fully edentulous patients, having the clinical flexibility to choose between a cementable and screw-retained prosthesis can help address the unique circumstances of each case.


References

  1. Misch CE. Contemporary Implant Dentistry. 3rd ed. St. Louis, MO: Mosby Elsevier; 2007:94-100.
  2. Oh SH, Kim Y, Park JY, et al. Comparison of fixed implant-supported prostheses, removable implant-supported prostheses, and complete dentures: patient satisfaction and oral health-related quality of life. Clin Oral Implants Res. 2014 Oct 24. [Epub ahead of print]
  3. John MT, Slade GD, Szentpétery A, et al. Oral health-related quality of life in patients treated with fixed, removable, and complete dentures 1 month and 6 to 12 months after treatment. Int J Prosthodont. 2004;17:503-511.
  4. Borges T, Lima T, Carvalho A, et al. Clinical outcome of inter-proximal papilla between a tooth and a single implant treated with CAD/CAM abutments: a cross-sectional study. J Oral Maxillofac Res. 2012;3:e4.
  5. Misch CE. Dental Implant Prosthetics. 2nd ed. St. Louis, MO: Mosby Elsevier; 2005.
  6. Tischler M, Ganz SD. The CT/CBCT-based team approach to care. Part 1: Identifying the implant patient and prosthetic options. Dent Today. 2012;31:74-79.
  7. Tischler M, Ganz SD. The CT/CBCT-based team approach to care. Part 3: Identifying prosthetic options through team communication. Dent Today. 2012;31:56-63.
  8. Dierens M, Collaert B, Deschepper E, et al. Patient-centered outcome of immediately loaded implants in the rehabilitation of fully edentulous jaws. Clin Oral Implants Res. 2009;20:1070-1077.
  9. Colomina LE. Immediate loading of implant-fixed mandibular prostheses: a prospective 18-month follow-up clinical study—preliminary report. Implant Dent. 2001;10(1):23-29.
  10. Schwartz-Arad D, Chaushu G. The ways and wherefores of immediate placement of implants into fresh extraction sites. A literature review. J Perio­dontol. 1997;68(10):915-923.

Dr. Nazarian maintains a private practice in Troy, Mich, with an emphasis on comprehensive and restorative care. He is a Diplomate in the International Congress of Oral Implantologists and the director of the Reconstructive Dentistry Institute. His articles have been published in many of today’s popular dental publications, and he has conducted lectures and hands-on workshops on aesthetic materials and dental implants throughout the United States, Europe, New Zealand, and Australia. He can be reached at (248) 457-0500 or via the website located at aranazariandds.com.

Disclosure: Dr. Nazarian reports no disclosures.

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