INTRODUCTION
Dr. Leonard Linkow, one of the pioneers of implant dentistry, once noted that to successfully treat the maxilla with dental implants, new techniques would be required to circumvent maxillary problem areas to establish solid anchorage for fixed restorations.1 Years later, while seeking alternative anchorage sites for patients with severe maxillary atrophy, the widely recognized father of modern implant dentistry, Dr. Per Ingvar Brånemark, expounded on Linkow’s sentiment, noting “Mother Nature provided an area of dense and extensive bone, near the area of the jaw, which could provide good anchorage prognosis.”2 Dr. Brånemark was referring to the zygoma, and a multitude of advancements over the past 35 years have made this a reliable site for establishing prosthetic support in severely atrophic maxillae.3 While zygomatic implants are not new to many in the dental implant community, a number of practitioners continue to remain unaware of this treatment option. As such, the goal of this article is to provide an introduction to zygomatic implants and shed light on the patients who may be appropriate candidates for this treatment modality.
Background
Since its introduction to dental literature in 2003, the All-on-4 treatment concept has proven to be a predictable and cost-effective method of full-arch dental implant rehabilitation.4-6 True adherence to this manner of treatment involves restoring an arch with at least 4 dental implants, the distal of which are tilted up to 45°, and immediately loading a screw-retained, provisional prosthesis.3-5 A number of articles have documented both short- and long-term success rates for All-on-4-style treatment with dental implants and prosthetic survival consistently exceeding 98%.4,5,7 In the maxilla, extreme sinus pneumatization, premaxillary bone atrophy, low bone density, etc, often create situations where standard All-on-4 treatment becomes challenging, if not impossible. For such patients, zygomatic implants offer same-day, immediate-loading solutions without the need for bone grafting.3 The elimination of bone grafting is a game changer for these patients. In addition to reducing cost, morbidity, and healing time, zygomatic implants have a much higher survival rate than conventional implants placed into large maxillary bone grafts.8 As a matter of fact, this was one of the main reasons why Dr. Brånemark and colleagues pursued the development of zygomatic implants.3 Since that time in the late 1980s, zygomatic implant treatment has continuously evolved, and conventional uses of the fixtures have documented survival rates ranging from 94.9% to 96.7%.9 These remote anchorage fixtures gain their stability from the robust bone of the zygoma. The zygomatic bone is described as having a “trapezoidal” shape from a lateral view and a narrow inferior base that widens superiorly.10,11 Mean zygomatic bone height in males is 20.72 mm and 19.66 mm in females. Width ranges from 4.39 mm to 8.10 mm.11-16 This bone does not atrophy with age nor edentulism and has a composition that routinely averages 80% cortical vs 20% trabecular.13,14 Potential bone-to-implant contact for zygomatic implants can range from 14.11 to 17.92 mm, and engagement with such a high amount of cortical bone leads to strong insertion torque that regularly exceeds 45 Ncm.17-22 In cases of severe maxillary atrophy, a single zygoma can withstand the application of multiple fixtures to provide supporting fixation for full-arch prosthetics.23-25 This fact allows virtually every patient who walks into a dental clinic the option for same-day, immediately loaded maxillary dental implant treatment.
While zygomatic implants have relatively low complication rates, these maladies can be quite different than those of conventional implants. Intrasurgical complications unique to zygomatic implants include damage to zygomaticofacial and/or infraorbital nerves, zygoma fracture, infratemporal fossa penetration, and orbital violation.3,25-27 The most common postsurgical issues associated with zygomatic implants are maxillary sinusitis, oroantral fistulas, and transient paresthesia of facial skin.3,28 The complex nature of zygomatic implant treatment and its possible serious postsurgical complications deem that it should be performed by experienced and highly trained clinicians. While this article is a cursory introduction to zygomatic implants, significantly more information is available in a 492-page textbook I recently published: Remote Anchorage Solutions for Severe Maxillary Atrophy: Zygomatic, Pterygoid, Transnasal, Piriform Rim, Nasopalatine, and Trans-Sinus Dental Implants (available at Amazon).
CASE REPORTS
Case 1
A healthy, 82-year-old, female patient presented to our clinic with a chief complaint of wanting “permanent” teeth. She had been previously functioning with an implant-supported removable denture for many years. She was not entirely happy with the performance of the restoration due to palatal coverage, taste interruption, speech difficulties, and reduced chewing capacity. Additionally, because the implants were primarily supported by regenerated bone from prior subantral augmentations, the many years of use with a non-rigid, fixated restoration resulted in bone loss around many of the fixtures (Figure 1). Following the induction of general and local anesthesia, a mucoperiosteal flap was achieved, and dissection was performed to expose the zygomatic notches, infraorbital nerves, and piriform rims bilaterally. All pre-existing dental implants were easily removed with implant-retrieval tools via reverse torque application. The remaining maxillary alveolar ridge was extremely thin (Figures 2 and 3) and not conducive to the placement of conventional dental implants. Following the PATZi remote anchorage protocol3,29 (discussed in detail in the textbook), pterygoid implants were placed initially. Next, zygomatic implants were prepped using an extrasinus protocol to maximize bone-to-implant contact and improve prosthetic screw access positioning. The maxillary sinus was accessed, and the Schneiderian membrane was elevated to access the base of the zygoma. A diamond barrel bur was inserted in the sinus window and used to create a conservative slot (Figure 4), which would guide subsequent osteotomy drills. A series of zygomatic-specific drills was then used with care to intentionally perforate the external zygomatic cortex for the purpose of achieving multi-cortical engagement (Figure 5). Zygomatic depth probing (Figure 6) was utilized to measure zygomatic implant length, and a corresponding fixture was placed following copious irrigation of the surgical site. With the posteroinferior zygomatic implant placed, a second fixture was placed in a similar fashion with care to avoid penetration into the orbital cavity. Both implants achieved extremely high insertion torque, vastly exceeding 60 Ncm. The same procedures were then performed on the contralateral maxilla. Because zygomatic implants, especially quad-zygomatics, are placed at increasingly acute angles, multi-unit abutments of angles up to 60° are required to achieve proper prosthetic positioning (Figure 7). While All-on-X dental literature often cites 120 Ncm of composite torque value as a minimum requirement for success in immediately loaded full-arch dental implant protocols,30 the cumulative insertion torque of the fixtures in this case exceeded 400 Ncm. To reduce the chances of future mucogingival recession exposing the extrasinus portions of the zygomatic implants, buccal fat pad pedicles were advanced to thicken overlying tissues (Figure 8).31 Flap closure was achieved using 4-0 chromic gut sutures in Holtzclaw’s Texas 2-Step technique (Figure 9).1,3 Digital scanning, design, and 3D printing protocols were used to fabricate a screw-retained restoration for immediate loading (Figure 10). Postsurgical CBCT scanning was performed to confirm the proper placement of the remote anchorage fixtures (Figures 11 and 12).
Case 2
A 38-year-old male patient was referred to our office for rescue treatment of the maxilla. The patient was originally treated by a dentist who attempted bilateral sinus augmentations and dental implants. Both the implants and the sinus treatments failed, and the patient was ultimately seen by a second dentist. The second dentist treated the issues from the first failed treatments and, after healing, attempted a second round of sinus lifts and dental implants. Unfortunately, the attempt at revision surgery also failed to achieve the desired results for both the dentist and the patient. It was at this point that I was asked to help on this case. Presurgical radiographic evaluation suggested the following: (1) bilateral sinus lifts with xenograft housing axial dental implants, (2) a trans-sinus dental implant on the right side, and (3) two anteriorly placed dental implants engaging the nasal rim (Figure 13). Intraorally, the patient presented with a relatively flat maxilla due to the lack of a premaxillary alveolar ridge. Under-reduction of the maxillary tuberosities created a reverse smile-line situation for the patient (Figure 14).
After induction of general and local anesthesia, full-thickness mucoperiosteal flaps were elevated to expose the infraorbital nerves, piriform rim, and malar processes. Very large defects were noted in the posterior alveolar ridges at the sites of the previously attempted sinus augmentations. Although the last attempt at sinus graft placement was more than 6 months prior, the xenograft in both sinuses remained unincorporated and had minimal turnover (Figure 15). The axial implants in the graft were freely mobile and easily removed (Figure 16). Likewise, the unincorporated xenograft was also removed with little effort via simple curettage and irrigation. Following the removal of the sinus xenograft, the trans-sinus dental implant only had osseous engagement at the lateral nasal wall. Despite having 6 months of osseointegration, the trans-sinus implant was removed using only 20 Ncm of reverse torque. The anterior implants engaging the nasal rim were solid and had minimal bone loss (Figure 17). Following the PATZi protocol,3,29 pterygoid implants were first placed bilaterally. The right pterygoid implant was easily placed as the bone in the posterior sinus and the maxillary tuberosity remained relatively intact. This implant achieved more than 50 Ncm of insertion torque. The left pterygoid implant was a bit more challenging due to the more extensive bony destruction in this area. As the osseous defect here extended to the posterior sinus wall, the pterygoid implant directly entered the pyramidal process of the palatine bone via an intrasinus approach. As such, the left pterygoid implant was afforded stability from only the pyramidal process and the pterygoid pillar but still achieved 50 Ncm of insertion torque. Anterior support for the PATZi protocol was already being provided by the previously placed and osseointegrated nasal rim implants. As tilted implants (trans-sinus) had already failed for this patient and minimal bone remained for placement of additional such implants, zygomatic implants were placed next. Entering through the pre-existing sinus defects (Figures 18 and 19), zygomatic implants were placed under copious irrigation. Both zygomatic implants achieved very high insertion torque, exceeding 60 Ncm. Multi-unit abutments were placed to achieve ideal screw access channel locations and torqued to place (Figures 20 and 21). To cover the exposed portions of the extrasinus zygomatic implants and obliterate the residual defects in the maxillary sinuses, large buccal fat pad pedicles were harvested and secured with 4-0 chromic gut sutures (Figure 22). As osseous grafting in the sinuses had failed twice previously in this case, bone grafting was shunned in favor of buccal fat to eliminate dead space. The mucoperiosteal flaps were recontoured with scalpels and 6-0 biopsy punches to accommodate the multi-unit abutments and replaced to their original position with 4-0 chromic gut sutures via Holtzclaw’s Texas 2-Step protocol (Figure 23).1,3 The patient’s pre-existing denture was then picked up according to the Smart Denture Conversion protocol and converted into a screw-retained transitional bridge. Following delivery to the patient, occlusal adjustment, and a post-surgical CBCT scan (Figure 24), the patient was returned to his referring dentist for completion of restorative treatment.
