Bar-Retained Zygomatic Implant Overdenture as a First Line of Treatment

For the purpose of this article this discussion will focus on the maxillary dental implant reconstruction. Maxillary treatment options presented to the patient included traditional alternatives such as sinus lifts, alveolar ridge bone grafting, and immediate and delayed dental implants with all-on-X approaches. The risks, complications, and the necessary time for healing of each procedure were also discussed with the patient. Healing time and predictability of her implant reconstruction became the patient's priorities. Her concerns appeared to be alleviated upon discussion of zygomatic implants as an immediate, graftless first line of treatment. A quad-zygomatic approach was chosen.

Next, the discussion centered on an ideal dental prosthesis. The benefits and limitations of fixed-hybrid prostheses and bar-retained overdentures were considered. The patient opted for the latter after considering the relative ease of cleaning involved with the zygomatic implants/bar system and avoiding the known potential complications associated with some zygomatic implant cases such as soft-tissue peri-implantitis (with or without gingiva recession) and sinusitis.^1-4 A palateless locator bar with three abutments was then planned. Lastly, the decision of immediate loading versus a two-stage approach was discussed. The final decision would depend on torque insertion and the availability of residual alveolar ridge bone for further stability during the surgical procedure.

An upper denture was fabricated prior to surgery. A maxillary impression was carefully made to ensure that the mobile maxillary bridge did not get caught in the impression material. A thick blue bite registration was made to ensure the correct vertical dimension. A final try-in was completed for the immediate maxillary denture prior to processing.

Implant Placement

The surgical procedure was done in the operating room under general anesthesia. The implant in site No. 2 was removed with no complications. Teeth Nos. 5, 6, and 10 through 14 were atraumatically extracted. Mucoperiosteal flaps were elevated after vertical releases were done in the mid-maxilla and just posterior to the zygomaticomaxillary buttress bilaterally. Important landmarks were exposed and properly identified, including the infraorbital rim and nerve, the piriform aperture, and the zygomatic incisura.

A watermelon bur was used to create a flat platform in the residual alveolar ridge. Exposure of the base of the zygoma bone (roof of the maxillary sinus) was executed by performing a trapezoid window using a round bur without the need to preserve the maxillary sinus membrane. For maximum anteroposterior spread, the ideal anteroposterior position of the implant platform in cases of quad-zygomas is around the lateral-canine region for the anterior implant and second premolar-first molar area for the posterior implant. To position the implant platform in the ideal buccopalatal position within the alveolar ridge, a channel or groove was made to allow the placement of the implant adjacent to the palatal plate. Frequently, there is no residual buccal plate, or it resorbs while healing occurs. A more anterior or centered location of the implant within the ridge increases the risk of having the implant platform floating buccally.

Two 55-mm and two 42.5-mm Straumann^® ZAGA^™ Round zygomatic implants (Straumann, straumann.com) were placed anteriorly and posteriorly, respectively, with no complications. A combination of suboptimal torque insertion for immediate loading, lack of buccal alveolar ridge bone for further stability, and an opposing natural dentition determined the need for a two-stage approach (Figure 2 through Figure 4). Wounds were closed in standard fashion. The patient was extubated with no complications. Postoperative instructions included pain medication, antibiotics, sinus precautions, and soft diet.

Healing Period

Clinical and radiographical examination 10 days after surgery demonstrated normal healing with mild pain and inflammation typical for this timeline following surgery. Imaging showed proper placement of the implants (Figure 5 and Figure 6). The patient's maxillary immediate denture was delivered after her flanges were adjusted. During the healing phase her interim denture was relined three times to compensate for aging of material and ridge contour changes while healing. Otherwise, the remaining postoperative course was uneventful.

Restoration Phase

After a healing period of 4 months following implant placement, multi-unit abutments were placed under local anesthesia by performing a small incision and minimal dissection (Figure 7). The patient's denture was inserted with blue bite material to mark the position of the zygomatic implants. The prosthesis was relieved and her reline material was removed. Additional reline was performed to ensure uniform force and to avoid uneven forces on the implants.

The final restoration was fabricated after the following steps were completed: alginate preliminary impression, custom open-tray impression, wax rim try-in with verification jig, and wax tooth try-in. After determining the ideal tooth position, the case was sent to the laboratory for design of the custom bar framework using Straumann's Scan and Shape service (Figure 8).

Because of patient concerns over having to change locator inserts frequently, Hader bar clips and traditional locators were avoided. Instead Straumann Novaloc^® inserts and abutments were selected because of their longevity (Figure 9).

Upon delivery of the prosthesis, a postoperative panoramic radiograph was made to ensure passive fit of the locator bar and prosthetic screws (Figure 10 and Figure 11). Prosthetic screws were torqued into place at 15 Ncm. The denture teeth were adjusted slightly to balance occlusion. The patient was very satisfied with the retention and esthetics of her prosthesis. She was able to easily remove it with digital force (Figure 12).

Discussion

As clinical expertise and exposure to zygomatic implants has increased, their indications have expanded to beyond the traditional severely atrophic maxilla in the presence of previously failed implant/bone graft reconstructions. Their safety and predictability permit their use as a primary approach.^1-4 In the present case, the patient was concerned about how her age was going to influence the quality of her maxillary bone, her ability to heal from bone grafting, and the potential prolonged treatment time required with conventional implant and bone graft methods. The immediate placement of four zygomatic implants was a well-suited option for her. The use of zygomatic implants removes concerns about not having enough quality and/or quantity of alveolar bone for primary implant stability because their stability is based primarily on their bicortical placement into the zygoma bone. Applying this same rationale, bone grafting is not necessary for the stability of zygomatic implants, thus bone graft healing is not a concern.

The immediate return of esthetics and function without having to wait for healing in a delayed approach has been the chief reason why immediate loading with a fixed prosthesis is considered to be the best treatment option for zygomatic implant reconstruction. Other benefits include less postoperative pain and discomfort compared to the use of an interim prosthesis.

While a patient's psychological perception of having a fixed reconstruction is important and may be their first concern, long-term maintenance and cleansibility are even more important with zygomatic implants as the interface between the soft tissues and the fixed prosthesis can be unpredictable and more difficult to clean.  Accessibility to the implants for cleaning purposes is crucial. Lack of proper hygiene could lead to soft-tissue peri-implantitis and sinusitis. Another concern against the selection of an immediate fixed prosthesis is the lack of buccal alveolar bone over the anterior zygomatic implants against natural dentition. Although zygomatic implants have enough primary stability at the zygoma bone level, they can still flex anteriorly with lateral forces even when cross-arch stabilization exists. This finding appears to be clinically significant in the authors' practice as screw fractures (prosthesis-multi-unit connection) have been found in some cases that are restored with a fixed prosthesis opposing a natural mandibular dentition. This problem can be avoided by placing an additional dental implant in the area of the maxillary incisors, but when this is not possible a bar-retained overdenture may then be selected. A bar-retained overdenture offers great esthetics and function but, more importantly, allows for better hygiene of the implant/bar system.

An occlusal guard over the locator bar at night should also be considered if the patient plans on maintaining opposing dentition, because the patient could still overload the locator bar with parafunction. In the present case, a nightguard was deferred as the patient was likely going to have future extractions and implant rehabilitation in her lower arch.

Conclusion

Zygomatic implants are a safe and predictable technique for maxillary reconstruction not only in severely atrophic maxillary cases with previously failed methods but also as a first line of treatment. Although immediate loading and fixed-hybrid reconstructions are the most common way to restore them, delayed loading and a bar-retained overdenture are also successful and well tolerated by patients.

ACKNOWLEDGMENTS

The authors thank David Jackson of Midsouth Dental Lab and Nicole Wyatt for their contributions to this article.

Disclosure

This article was commercially supported by Straumann.

About the Authors

Luis Vega, DDS
Associate Professor and Oral and Maxillofacial Surgery Residency Program Director, Department of Oral and Maxillofacial Surgery, Vanderbilt University Medical Center, Nashville, Tennessee

Rachel Strait, DMD, MD
Private Practice, Nashville, Tennessee

Tyler E. Ames, DMD
Chief and Assistant Professor, Division of Dentistry, Department of Oral and Maxillo­facial Surgery, Vanderbilt University Medical Center,
Nashville, Tennessee