Key points
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Accurate initial data acquisition.
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Establish virtual tooth position.
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Virtual 3-dimensional diagnosis and planning.
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Design and construction of monolithic polymethylmethacrylate conversion prosthesis.
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Connection of conversion prosthesis to temporary prosthetic cylinders.
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Maintain stability a rigidity of conversion during 12-week osseointegration healing period.
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Evaluate esthetics, phonetics, and function of conversion prosthesis, making any required adjustments or refinements.
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Digital data acquisition for construction of the definitive final prosthesis.
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Delivery of definitive prosthesis, with various prosthetic designs.
Introduction
The restoration of the edentulous or soon to be edentulous maxilla with severely deficient residual bone has historically been a complex process. Designing, constructing, and delivering both an interim and a definitive prosthesis can be more challenging than for patients with ample bone and ridge support. With severe bone loss and expansion of the antrums, or in the case of pathologic or traumatic loss of facial structure, the clinician is confronted with the need to rebuild the arch form of the maxilla, from the peak of the vault to the functional occlusal surfaces of the teeth, to the lip and cheek support and the creation of an appropriate prosthetic dentition with ideal smile line, function, and esthetics.
Presurgical prosthetic planning is a major factor in producing a successful outcome , and failure to do so leads to suboptimal outcomes, the most common being palatal placement of the head of the zygoma implant. This leads to poor patient outcomes, including difficulties with speech, function, esthetics, and comfort.
When the head of the zygoma implant is placed solely to engage crestal maxillary bone without consideration of ideal tooth position ( Fig. 1 A), the resulting position commonly results in a prosthesis that is not ideal on the palatal aspect with poor patient outcomes in terms of resulting satisfaction. However, if ideal tooth position is accounted for and the placement of the head of the zygoma implant is positioned under the proposed teeth ( Fig. 1 B), the contours of the definitive restoration follow an ideal geometry resulting in positive patient satisfaction.
Presurgical prosthetic planning
Highly valuable ingredients to successful outcomes begin with a distinct coordination between the surgery and the prosthodontic treatment. The initial evaluation of the patient should include the digital acquisition of facial esthetics, digital impressions, intraoral jaw relationship records, and radiographic analysis using 3-dimensional cone beam computed tomography scanning.
All data including facial scans and intraoral digital impressions are then transferred to CAD/CAM software ( Fig. 2 ), which allows for digital smile design, which is the process of identifying the position of teeth and supporting structures based on esthetics and function in relation to the existing facial and intraoral soft tissue and bone anatomy.
Once the proposed tooth position is established, data are transferred into implant planning software ( Fig. 3 ), which contains zygoma implants in the virtual library so ideal position of the implants can be planned. A virtual plan of the implant positions can also yield a surgical template to guide the initial penetration of the planned osteotomy and provide the ideal position of the coronal aspect of the implants ( Fig. 4 ). That same virtual plan can digitally be converted to files that are used to fabricate a fully milled, monolithic polymethylmethacrylate (PMMA) conversion denture ( Fig. 5 ).
Zygoma implant placement and conversion of interim prosthesis
As mentioned elsewhere in this article, at the time of implant placement, a surgical template can be used to determine in initial drill penetration position for the crestal position of the zygoma implants. Once the implants are placed ( Fig. 6 ), transmucosal abutments are installed and prosthodontic intervention occurs with the installation of abutment level temporary prosthodontic cylinders ( Fig. 7 ). The conversion denture is adjusted to fit around the temporary cylinders ( Fig. 8 ).
A soft, flowable mix of auto polymerizing acrylic is carefully injected around the temporary prosthetic cylinders ( Fig. 9 ) and the conversion denture seated. The opposing dentition is closed in the acquired centric position to establish optimal orientation of the dentition. When the acrylic has polymerized, the conversion prosthesis is removed from the patient and refined. This process will include the addition of acrylic to fill any voids and the removal of the palate and flanges to establish a cleansable intaglio surface, and the entire conversion prosthesis is highly polished ( Fig. 10 ).
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