Chapter 5 Zygomaticus Implants and Angled Implants for the Edentulous Maxilla
Examination of the patient with a totally edentulous maxilla may reveal a lack of adequate bone in the posterior maxilla for the placement of standard endosseous implants. These patients may desire an implant-borne, full-arch maxillary restoration without grafting of the sinus. Bone grafting can be avoided by using placement of a longer implant, the zygomaticus fixture, as an alterative method. The zygomaticus implant is a threaded titanium implant that is 3.75 mm in diameter, graduating in size to 4 mm. It is available in lengths up to 55 mm.
Branemark has reported the use of the zygomaticus fixture with follow-up of function for 10 years in a small number of patients; follow-up of function has been reported in larger numbers for 5 years. The patient population treated by Branemark includes those with totally edentulous, intact maxillae and those who have undergone maxillectomies after tumor resection. The reported success rate is greater than 96%.1–3
The recommended protocol includes placement of two zygomaticus implants—one on each side of the maxilla—in combination with two to four anteriorly placed, standard-length endosseous implants (Figure 5-1; also DVD Figure 5-1, A-B, which shows text Figure 5-1 along with a diagram of the intended location of the zygomaticus implants). After 6 months has been allowed for integration of the zygomaticus fixture to the zygomatic bone, the restoration is completed with the fabrication of a rigid bar connecting the two zygomaticus implants to the anterior implants. Rigid cross-arch stabilization is the key to the success of this system. The final prosthesis is an implant-supported, full-arch fixed prosthesis or a fixed-removable prosthesis.
The advantages of the zygomaticus implants are that (1) they eliminate the need for a sinus bone grafting procedure, (2) they eliminate the morbidity of harvesting bone from the iliac crest or the tibia, and (3) fewer implants are required than with the conventional eight implant–borne maxillary restoration.
The disadvantages of this longer implant are (1) the need for deep sedation or general anesthesia for placement of the prosthesis and (2) the lack of stability if one of the zygomaticus implants fails.
As the 10-year, 95% success rate data from Sweden are confirmed by other clinicians, this implant technique may eliminate the need for sinus augmentation procedures for the patient with an edentulous maxilla.
The patient must have satisfactory health to undergo deep sedation or general anesthesia. The patient also must have sufficient anterior bone for the placement of two to four anterior implants to stabilize the restoration. Preoperative radiographs should reveal a healthy maxillary sinus without polyps or other significant pathologic conditions. Axial and reconstructed computed tomography (CT) scans should indicate 8 to 12 mm of bone in the zygomas, as well as appropriate morphologic bone structure to allow placement of the zygomaticus implants within the confines of the lateral aspect of the maxilla. A consultation with the restorative dentist should confirm that immediate fabrication of a temporary cross-arch bar will be possible at the time of exposure, ensuring the stabilization of the maxillary implants.
As mentioned, the patient may have either general anesthesia or deep sedation for this surgery. The incision is made and released to allow the subperiosteal reflection to extend over the superior aspect of the zygoma (Figure 5-2; and DVD Figure 5-2, A-B, which shows text Figure 5-2 along with a diagram of the extent of dissection). The incision can be made in the vestibule, directly over the alveolar crest, or slightly palatal to the crest. This author prefers the incision to be slightly palatal to the crest. The incision extends from the second molar region to the midline with a vertical release in the midline of the maxilla. One side of the maxilla is operated on first; the contralateral dissection then is performed.
• FIGURE 5-2 Incision is made slightly palatal to the crest, and a full-thickness reflection is performed to expose the lateral aspect of the maxilla, orbital rim, superior and medial aspects of the zygoma, and zygomatic arch.
After the incision has been made, a full-thickness mucoperiosteal flap is elevated. Occasionally, a posterior release incision is necessary. The subperiosteal reflection is performed to expose bilaterally the following:
After exposure of the lateral aspect of the maxillary bone, the palatal mucosa is elevated from the first molar to the incisive canal region for placement of the implants. An instrument is aligned from the palate to the zygoma to approximate the planned path of the zygomaticus implant. This path enables the surgeon to locate the proposed implant site and perform the sinus membrane elevation (Figure 5-3).
This author uses a round bur to prepare the site for the maxillary sinus membrane elevation. A rectangular piece of bone, approximately 8 × 20 mm, is carefully removed while the integrity of the underlying sinus membrane is maintained. The sinus membrane is elevated from the inner aspect of the maxillary sinus to allow direct visualization of the entry of the zygomaticus drills, to place the implant into the zygoma, and to prevent membrane entrapment between the implant and bone (Figures 5-4 and 5-5).
After the membrane has been elevated, the long round bur is used. The drill is angled to place the entry point in the maxilla within the crest of the alveolus, often palatal to the crest (Figure 5-6). The drill should enter the maxillary sinus and engage the inner aspect of the zygoma. The drill should be completely within the confines of the lateral wall of the maxilla. The round bur is used to create a purchase point for the next drill.
The next drill is 2.9 mm in diameter, matching the diameter of the previously used round bur (DVD Figure 5-3). This drill is taken through the palatal site, traversing the maxillary sinus, to prepare the implant site from the inner aspect of the zygoma; it passes through the lateral aspect of the zygoma superiorly. The orbital rim must be avoided.
The next drill is a transition drill, which has a guide to enter the 2.9-mm-diameter hole in the palate and zygoma (Figure 5-7). This drill opens the hole to the final size in the zygoma. This transition drill is not intended to complete the implant site. The next drill is the 3.5-mm-diameter twist drill, which is taken through the superior aspect of the zygoma. If the palatal bone is thick, the 4.0-mm twist drill can be used to complete the palatal site. If the maxillary alveolar bone is thin, the 3.5-mm drill is used, and the 3.5-mm drill is used in the zygoma.
At this point in the procedure, the surgeon is ready to place the zygomaticus implant. However, the necessary length of the implant must be confirmed before an implant is removed from its container. The measuring instrument, which has the implant’s length etched by sequential lines, is placed into the site, entering the palatal hole and exiting the zygoma site. The length of the implant is determined by identifying the line of corresponding length at the palatal site (Figure 5-8; and DVD Figure 5-4, A-B, which shows Figure 5-8 along with a diagram of the delivery of the zygomaticus fixture).
• FIGURE 5-8 After the final twist drill has been used, the length of the zygomaticus fixture is determined by direct measurement using the depth gauge. The implant is chosen and removed from its sheath. The cover screw is removed and placed in a safe place. The implant is delivered either with a rotating handpiece at 10 rpm or with the hand instrument.
The appropriate-length implant is chosen and placed onto the sterile field. The glass container is opened, and the implant is carefully removed with its sheath. The two wings of the sheath are expanded and removed, exposing the cover screw on the implant. The cover screw is removed and placed onto a sterile tray. The implant is mounted on the delivering handpiece adapter and is placed into the palatal site. As the implant enters the dense zygoma bone, the torque of the drill most likely will be exceeded. The handpiece adapter is removed, and the manual turning instrument is used to complete placement of the implant. The angle of the driving mount screw should be inferiorly oriented. The driving mount is removed, and the external hex of the implant is visible. The cover screw is placed to cover the external hex. The same procedure is performed on the contralateral side of the maxilla (Figures 5-9 through 5-13; and DVD Figures 5-5 and 5-6, A-B). After the two zygomaticus implants have been placed, two to four anterior implants are placed. The wound is irrigated thoroughly and closed. Nonresorbable sutures are recommended.
• FIGURE 5-9 Hex drive instrument is placed into the retaining screw of the driving mount to ensure that the final orientation of the zygomaticus implant is correct. Confirmation of the correct position of the implant is important before the driving mount is removed, because replacement of the driving mount to the implant is difficult.