Zygoma Implants or Sinus Lift for the Atrophic Maxilla with a Dentate Mandible

Rehabilitation of maxillary atrophy with dental implants is challenging to the clinician despite the wide variety of surgical techniques available. Finding the right indication for a procedure is highly important for the long-term stability of dental implants. With the introduction of the concept of “teeth-in-a-day,” clinicians have explored innovative techniques to attain the goal of immediate implant-supported provisional prosthesis. However, costs and comorbidities are limitations to advancing these techniques. This article focuses on algorithms to rehabilitate the atrophic maxilla with the purpose of providing immediate provisional prosthetic teeth regardless of the mandibular dentition.

Key points

  • “Teeth-in-a-day” in atrophic maxilla is achieved by immediate loading of zygomatic implants following the concept of cross-arch stabilization.

  • Placement of zygomatic implant is technique sensitive and requires knowledge of the local anatomy. However, it reduces the treatment time before the prosthetic reconstruction.

  • In cases of severe maxillary anatomic constraints, zygomatic implant to rehabilitate maxillary atrophy is considered a valid alternative treatment to maxillary sinus graft or alveolar ridge bone augmentation.

  • Zygomatic implant is performed in atrophic maxilla with dentate mandible. Restoration varies depending on the residual maxillary anatomy.

Introduction

Maxillary atrophy represents a challenge for surgeons and restorative providers. Ideally, prosthetic restoration should restore mastication, comfort, and phonation, allowing for an improved quality of life. Autogenous bone graft is considered the gold standard technique because of its osteogenic, osteoconductive, and osteoinductive properties. Historically, restoration of the severely atrophic maxilla involved obtaining bone graft from the iliac crest for onlay or interpositional techniques. Such surgical procedures required multiple surgical sites, prolonged hospital stays, and possible donor site morbidities. Potential complications encountered include sinusitis, graft exposure or resorption, infection, neurosensory deficits, and insufficient bone quantity or quality. In addition, failure and unpredictable outcome of such autogenous grafting techniques often reduced patient acceptance.

To avoid the disadvantages of autogenous bone grafting, bone substitutes and biologics (bone morphogenetic proteins, membranes, platelet-rich plasma, platelet-rich fibrin) are commonly used. However, they remain inferior to clinical outcomes achieved by using autogenous bone grafts.

Sinus Augmentation

Maxillary sinus augmentation and bone grafting has provided an alternative treatment option to augment maxillary atrophic ridges, allowing for restoration with immediate or delayed implant placement. Primary implant stability requires a minimum of 3 to 5 mm of crestal bone to justify simultaneous implant placement with maxillary sinus lift and bone grafting. When inadequate alveolar bone height is present, a maxillary sinus graft and 4 to 8 months healing time is required before the implant placement. In addition, a third surgical procedure is needed to uncover the implants for the final prosthetic rehabilitation. Three surgical stages is still a common practice in many clinics; however, it prolongs the time before the prosthetic reconstruction.

Chin introduced a dental implant stabilization system for simultaneous sinus lift and implant placement when poor primary stability is present that allows the osseointegration to occur in conjunction with bone healing. This technique is applied to single or multiple implants and is combined with temporary implants for immediate provisional prosthetic anchorage.

All-on-X

The introduction of all-on-four by Malo and coworkers has changed the clinical protocols emphasizing the use of available bone with predictable bone maintenance and implant success. He demonstrated the use of longer, wider implants with deeper threads and newer implant surfaces. In addition, tilted implants with multiunit abutments placed at different angulations allow the clinician to immediately deliver the provisional prosthesis and avoid additional surgical procedures, such as maxillary sinus and ridge augmentation. The definitive restoration may be delivered after 3 or 4 months of healing. To overcome anatomic limitations to atrophic maxillae, all-on-four is modified to include placement of zygoma implants.

Zygoma Implants

The use of zygoma implants in the posterior maxilla and conventional implants in the anterior zone offers the possibility to provide anchorage for immediate provisional teeth in the upper arch.

This technique eliminates donor site morbidity and reduces the treatment time. Zygoma implants engage multiple cortical walls, allowing for adequate primary stability for immediate loading. Implants are inserted through the crestal bone into the bicortical zygoma with adequate quality and quantity of bone. Even when crestal bone of the maxillary alveolar ridge is not adequate, the implant fixtures allow a minimum of 8 to 10 mm of bone contact within the body of the zygoma for primary stability. The zygomatic implant platform is straight (0°) or angled up to 45° to allow the platforms to be in the same plane as the conventional implants for passive prosthetic insertion. Cross-arch distribution of the functional is essential to prevent undesirable forces, osseointegration failure, and prosthetic complications. The prosthesis must be reinforced with a rigid bar for cross-arch stabilization.

Surgical approaches for various anatomic presentations

The maxillary anatomy as assessed is divided into three radiographic zones as described by Bedrossian and colleagues. Zone 1 is the maxillary anterior teeth, zone 2 is the premolar region, and zone 3 is at the molar region. We use this classification to stratify our treatment as seen next.

Ideal Bone Morphology

Modified classical implant distribution and immediate loading

When ideal bone quantity and quality are present in all zones of the maxilla, six parallel implants are placed in sites 3, 5, 7, 10, 12, and 14 (wide implants in sites 3 and 14, if possible). After implants are integrated, a fixed prosthesis is installed. Bone reduction may be required to allow room for the prosthetic suprastructure.

Large Maxillary Sinus with Moderate Posterior Vertical Bone Deficiency

All-on-X concept (five or six fixtures) with immediate loading

Sinus pneumatization decreases the amount of available vertical bone in the posterior maxilla (zone 3). Two tilted implants (up to 45°) avoiding the sinus floor cavity can be placed in sites 4 and 13. Three or four additional implants are placed anteriorly in sites 6, 8, 9, and 11. Bone reduction (ostectomy) may be required for insertion of a prosthesis. Immediate loading with provisional teeth is often predictable because of the cross-arch stabilization concept ( Fig. 1 ).

Fig. 1
Implants avoiding the sinus. ( A ) Panoramic view showing angulated implants avoiding the maxillary sinus. ( B ) Immediate temporary dental rehabilitation. ( C ) Verifying parallelism and adjusting the need to move the implant ( arrow ) for passive prosthetic Insertiton. ( D ) Implants placed and wounds sutured with perfect emergence profile.

Large Maxillary Sinus with Severe Posterior Vertical Bone Deficiency

Two- or three-stage surgery (treatment time 24–36 months)

The maxillary sinus graft is completed first, followed by 5 to 6 months of healing time. Next, the implants are placed and an additional 4 to 6 months of healing time is needed for osseointegration of the implants. Temporary implants are placed during the maturation of the bone and osseointegration, allowing immediate provisional prosthesis ( Fig. 2 ).

Fig. 2
( A–D ) Lateral window approach for Schneiderian membrane elevation. Bone graft is placed in the floor of the sinus. Membrane is placed to cover the window and avoid mucosal invagination and flap sutured. Pre and post-op panorex showing ( E ) Severe maxillary sinus pneumatization bilaterally with no room for implant placement ( F ) Long term follow-up with implants and final restoorations in place. (14 years F/U). ( G ) Final restorations radiographically and clinically after 14 years of follow-up. ( Courtesy of Robert Gilbert Triplett, DDS, Dallas, TX.)

Large Maxillary Sinus with Severe Posterior Bone Deficiency

Two surgical stages (treatment time 6–9 months)

When less than 3 to 5 mm of crestal bone is present, simultaneous sinus lift, implant placement and plate stabilization are used for long-term predictability as described by Chin ( Fig. 3 ).

Fig. 3
Martin Chin’s protocol. ( A ) Intraoperative view with implant stabilized with a three-hole microplate fixed to buccal and palate and the middle hole is stabilizing the implant by inserting a cover screw through the plate into the implant. ( B ) Preoperative radiograph showing the severe alveolar crest defect with sinus pneumatization. ( C ) Immediate postoperative radiograph to confirm position of the plate and implant. The anterior implant had enough bone for primary stability and did not require sinus lift or plate stabilization. ( D ) Radiographic confirmation of adequate osseointegration of the implants and ready for functional loading. ( E, F ) Intraoral views with healing abutments in place to guide soft tissue healing and final rehabilitation.

Moderate to Severe Generalized Maxillary Atrophy

All-on-X concept with immediate loading

When generalized maxillary atrophy is present (zones 1, 2, and 3), all-on-X is accomplished by placing implants in sites 4, 6, 11, and 13. Long implants placed in the piriform rims are preferred coupled with a wide short implant in the maxillary midline. If inadequate bone is present in sites 4 and 13, an alternative option is placement of angled implants in the tuberosity/pterygoid plate. The stability of these implants is obtained from the pterygoid plate. The wide anteroposterior distribution of implants allows immediate loading ( Fig. 4 ).

Fig. 4
This case was treated with combined techniques: Angled implants to avoid the maxillary sinus on the right side and unilateral zygoma implants on the left. ( A, B ) Intraoral and occlusal views showing the posterior edentulism. ( C, D ) Right tuberosity implant with two conventional anterior implants. Left; two zygoma implants and one conventional anterior. ( E, F ) Pre and post-op Panoramic radiographs showing right side sinus pneumatization and final restoration with tuberosity and two anterior conventional implants and left side with severe maxillary sinus pneumatization and the final restoration with two unilateral zygoma and one anterior conventional implants. ( G ) Occlusal views showing the failed dentition and edentulous sites and final rehabilitation.

Extremely Severe Generalized Maxillary Atrophy

Multiple zygoma implants with immediate loading

Patients with severe maxillary atrophy, poor alveolar bone quality, or excessive masticatory load have the highest failure rate of maxillary implants. Placement of implant should take into consideration the load distribution to follow a short cantilever principle. Three-dimensional placement of anterior and posterior zygoma implants is considered. Other options are used and are described later in the surgical procedure section.

Apr 27, 2020 | Posted by in General Dentistry | Comments Off on Zygoma Implants or Sinus Lift for the Atrophic Maxilla with a Dentate Mandible
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