C H A P TER 7
Treatment of the Edentulous Maxilla: Zygoma Implant Concept
Presence of alveolar bone in the premaxilla (zone I) and lack of bone in the bicuspid and molar regions (zones II and III, respectively) is an indication for considering a zygomatic implant. The zygomatic implant establishes posterior maxillary support by using the limited crestal alveolar bone in the bicuspid region and the os zygomaticus for establishing initial implant stability.
Radiographic Evaluation Although computed tomography (CT) or conventional tomography can be used, the panoramic radiograph is critical in initial patient evaluation.1-3 Axial CT scans and cone beam technology can be used to further evaluate the maxillary sinus. The width of the residual alveolar bone and the width and height of the zygomatic body can be visualized in frontal (Figure 7-1) or axial (Figure 7-2) reformatted sections. Further evaluation of the zygomatic bone has also been described.4 Although not absolutely necessary, the reformatted frontal images in 0.5- to 1-mm cuts afford the less experienced operator more information for surgery planning (Figure 7-3). Pathologic conditions in the sinus, including but not limited to thickening of the Schneiderian membrane as well as air-fluid levels, may be ruled out in both the panoramic radiographic examination as well as the tomographic studies (Figure 7-4). Cone beam CT scan can also be used effectively to manipulate postoperative radiographs (Figure 7-5, A). The ability to manipulate the cone beam images to demonstrate apex positioning of the zygoma implant within the zygoma body (Figure 7-5, B), as well as the relationship of the zygoma implant platform to the
crestal portion of the alveolus, leads to a better understanding of surgical technique (Figure 7-5, C).
Preoperative Considerations The surgical procedure is usually performed in the office setting under intravenous (IV) sedation,1,5 although the procedure can be performed under local anesthesia or in the operating room under general anesthesia. All patients are premedicated with 2 g of penicillin or 600 mg of clindamycin 1 hour prior to the procedure. Proper administration of sufficient local anesthesia is critical to manage patients under IV sedation. The various infiltrations and nerve blocks include circumvestibular infiltration of the maxilla and greater palatine nerve blocks, as well as bilateral transcutaneous infiltration of the temporal areas over the zygomatic body. Bilateral inferior alveolar nerve blocks are considered to allow retraction of the lower jaw during surgery without undo stimulation of the sedated patient. It is recommended that the path of the implant from the premolar area to the base of the zygoma be directly visualized whenever possible.1,6 Direct visualization of the base of the zygoma body has also been advocated by clinicians who have used computerassisted treatment planning and surgical templates for placement of zygomatic implants.6 Having a clear view of the instruments’ path while establishing the osteotomy, as well as visualizing the path of the implant during its insertion, avoids disorientation and potential complications. Generally, three potential axes for implant insertion are possible. The proper axis is a path extending from the bicuspid region through the maxillary sinus, entering the mid portion of the zygomatic body. If the entry point in the zygomatic 61
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CHAPTER 7 Treatment of the Edentulous Maxilla: Zygoma Implant Concept
FIGURE 7-1 Coronal cone beam computed tomographic scan of the bilateral maxillary sinuses and the body of the zygomatic bone.
FIGURE 7-2 Axial cone beam computed tomographic scan showing the body and arch of the zygoma.
FIGURE 7-3 Coronal series of the zygoma body.
body is anterior to this line axis, potential exists for penetration into the orbit. If the line axis is posterior to this line, potential exists for entering the pterygomaxillary space, which leads to soft tissue envelopment and subsequent lack of osseointegration of the implant, causing unexpected hemorrhage (Figure 7-6).
The zygomatic implant has a unique design. The diameter of the apical two-thirds of the implant is 4 mm and the alveolar one-third widens to a diameter of 5 mm. Zygomatic implants are available in lengths ranging from 30 to 52.5 mm. A specialized series of long zygoma drills are used to prepare the osteotomy (Figure 7-7).
Surgical Options
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Surgical Options To reconstruct an edentulous maxilla with a zygomatic implant, the traditional two-stage protocol1,7,8 or the immediate-load protocol1,6 may be considered. The two-stage protocol requires immediate cross-arch splinting of the zygoma implant at the time of the uncovering procedure. This can be accomplished efficiently using the CAL technique for fabrication of a passive bar prior to the uncovering procedure.9 Uncovered zygoma implants that have temporary abutment should not be placed under occlusal loads without having been cross-arch stabilized. To expedite the stage II surgery and deliver a passive bar in the two-stage approach, fixture-level impressions of the implants are taken prior to closure of the soft tissues at stage I (Figure 7-8). During the 6-month
FIGURE 7-4  Axial cone beam computed tomographic scan showing the presence of a maxillary polyp.
A
C
B
FIGURE 7-5  A, Three-dimensional frontal view of doublezygoma implants. B, Reformatted view of the double-zygoma implants. C, Modified cone beam computed tomographic scan of the zygoma body with double-zygoma implants.
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CHAPTER 7 Treatment of the Edentulous Maxilla: Zygoma Implant Concept osseointegration period, the CAL bar is fabricated. At stage II surgery, the implants are uncovered and the permanent abutments are placed and torqued. The CAL bar is luted to the CAL cylinders, ensuring a passive fit (Figure 7-9). The alternative immediate-load technique cross-arch splints zygomatic implants with each other by converting the patient’s existing denture into a fixed, provisional bridge (Figure 7-10). Immediate loading of zygomatic implants has been reported with favorable results.5,6
FIGURE 7-6 Various potential axes of the zygoma implant. Proper placement follows the red axis.
FIGURE 7-7 Implant and available drill sizes. Implant lengths range between 35 to 52.5 mm. (Courtesy Nobel Biocare, Yorba Linda, Calif.)
FIGURE 7-8 Fixture-level impression at phase I surgery for the two-stage, delayed-loading protocol.
Surgical Protocol The first step in the surgical procedure is to make a crestal incision across the edentulous maxillary arch. Bilateral releasing incisions are made over the
FIGURE 7-9 Clinical attachment level bar allowing crossarch stabilization of zygomatic implants at stage II, for the two-stage protocol.
FIGURE 7-10 Conversion of the denture to a provisional prosthesis at phase I surgery in the immediate-load protocol.
maxillary tuberosity similar to hockey stick incisions used to remove maxillary wisdom teeth. A vertical window is made on the lateral wall of the maxilla paralleling the junction of the posterior aspect of the lateral maxillary wall and the lateral aspect of the posterior maxillary wall accessing the sinus (Figure 7-11). The Schneiderian membrane may be removed or reflected away from the inside of the lateral wall of the maxillary sinus (Figure 7-12). It is critical to be aware of the position of the Schneiderian membrane and to ensure that it does not attach to the zygomatic implant during its insertion into the body of the zygoma. Introduction of the soft tissue Schneiderian membrane into the body of the zygoma may lead to osseointegration failure. The osteotomy for placement of the zygomatic implant is initiated using a round bur (Figure 7-13) followed by a 2.9-mm twist drill (Figure 7-14). A 2.9- to 3.5-mm pilot drill stabilizes the 3.5-mm drill, which completes the osteotomy at the maxillary crest and at
Surgical Protocol
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the body of the zygoma (Figure 7-15). If more than 3 mm of crestal bone is identified, the alveolar portion of the osteotomy is completed by introducing of the 4-mm twist drill. In cases in which there is limited crestal bone width or height, the 4-mm drill is not used. Instead, the 5-mm portion of the implant slowly expands the 3-mm osteotomy to allow complete seating of the implant at the alveolar ridge. Prior to implant placement and at all times during preparation of the osteotomy (Figure 7-16), the entire surgical paths of the drills are visualized.1,6 The 45° angulations of the zygomaticus implant (Figure 7-17) allow the implant platform to be in the same plane as the vertically placed implants in the premaxilla. To facilitate implant placement, the
FIGURE 7-13 Round drill, the initial drill used for prepara tion of the osteotomy. (Courtesy Nobel Biocare, Yorba Linda, Calif.) FIGURE 7-11 Access into the right maxillary sinus for direct visualization of the drilling and implant placement pathway.
FIGURE 7-12 Reflecting the Schneiderian membrane after accessing the sinus. (Courtesy Nobel Biocare, Yorba Linda, Calif.)
FIGURE 7-14 The 2.9-mm drill follows the marking made at the base of the zygoma body by the round drill, exiting at the outer cortex of the zygomatic body. (Courtesy Nobel Biocare, Yorba LInda, Calif.)
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CHAPTER 7 Treatment of the Edentulous Maxilla: Zygoma Implant Concept
FIGURE 7-17 The 45° “built-in” platform of the zygoma implant places the implant platform in the same axis as the axially placed anterior maxillary implant platform.
FIGURE 7-15 A 3.5-mm drill follows the 2.9-mm drill through the entire length of the zygoma body. (Courtesy Nobel Biocare, Yorba Linda, Calif.)
FIGURE 7-18 The premounted fixture carrier with the matching 45° connection to the zygomatic implant “straight ens” the implant, allowing insertion into the osteotomy site. (Courtesy Nobel Biocare, Yorba Linda, Calif.)
FIGURE 7-16 During preparation of the osteotomy, direct visualization of the drill paths is possible through the lateral maxillary window.
premounted implant carrier allows for easy handling of the implant with the straight zygomatic handpiece (Figure 7-18). To ensure proper orientation of the angulated implant head, the long axis of the screwdriver shaft placed into the screw that secures the implant carrier to the 45° zygoma implant platform is made (Figure 7-19). The shaft of this screwdriver must
be at right angles to the edentulous ridge to ensure proper orientation of the implant platform. Within the premaxilla (zone 1), a minimum of two premaxillary implants are required in conjunction with two zygomatic implants in the posterior maxilla (all-on-4 technique) (Figure 7-20). Brånemark and Skalak used four zygoma implants to support a fullarch prosthesis in their biomechanical model described in the early days of osseointegration studies (Figure 7-21).10 If four implants can be distributed evenly in the premaxilla, however, it may be considered along with two posterior maxillary zygoma implants (all-on-6 technique) (Figure 7-22). In the two-stage protocol in which both the premaxillary and the zygomatic
Surgical Protocol
implants are submerged, single-thread Nobel Groovy implants have been used. In cases in which immediate loading is considered, however, the double-thread NobelSpeedy implants have been used. The zygomatic implant is an external hex implant. Use of external hex premaxillary implants is recommended to maintain uniformity and ease during restorative treatment. All immediate premaxillary implants are placed with an initial insertion torque setting of 20 Ncm. When the handpiece “stalls,” the insertion torque setting is increased to 40 Ncm, allowing complete implant insertion and seating. The “onion” hand-insertion
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instrument (Figure 7-23) is used in cases in which the handpiece stalls at the 40-Ncm setting. The zygomatic implant is hand-driven to its final insertion depth where the implant platform is intimately in contact with the lateral wall of the maxillary alveolus. The J
G Zygomatic fixtures
K
L
Brånemark fixtures A
X1
F
X3
X3
X2
X2
B
E C
D
X1
Bridge
FIGURE 7-21 Zhao, Skalak, and Brånemark’s biomechani cal analysis.
FIGURE 7-19 The perpendicular axis of the screwdriver shaft placed into the fixture mount it relates to in the eden tulous crest confirms the proper orientation of the zygoma implant platform. (Courtesy Nobel Biocare, Yorba Linda, Calif.)
A
FIGURE 7-22 Platform of the zygoma implants in the same plane as premaxillary implants.
B
FIGURE 7-20 A, Two premaxillary implants and two zygoma implants. B, Zygoma implant with a minimum of two premaxillary implants.
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CHAPTER 7 Treatment of the Edentulous Maxilla: Zygoma Implant Concept
FIGURE 7-24 Temporary titanium cylinders ready for luting to the denture base. FIGURE 7-23 The “onion” driver is used to manually place the implant and complete seating within the osteotomy. (Courtesy Nobel Biocare, Yorba Linda, Calif.)
criteria for immediate loading of premaxillary and zygoma implants include a minimum of 40 Ncm of insertion torque.5 The surgical wound is closed using 4-0 polyglycolic acid sutures in cases in which the two-stage implant surgery has been performed. The denture base over the zygomatic implants is relieved to avoid loading and wound breakdown. In patients who received immediate provisional fixed prostheses, 3-0 gut sutures are used to close the soft tissue wound and the existing full denture is converted to the immediate provisional fixed prostheses using multiunit abutments and titanium temporary cylinders (Figure 7-24).
References 1. Bedrossian E, Stumpel LJ: The zygomatic implant: Preliminary data on treatment of severely resorbed maxillae. A clinical report. Int J Oral Maxillofac Implants 17:861-865, 2002.
2. Malevez C, Abarca M, Durdu F, et al: Clinical outcome of 103 consecutive zygomatic implants: A 6-48 month followup study. Clin Oral Implant Res 115:18-22, 2004. 3. Aparicio C, Ouazzani W, Garcia R, et al: A prospective clinical study on titanium implants in the zygomatic arch for prosthetic rehabilitation of the atrophic maxilla: A follow-up of 6 months to 5 years. Clin Implant Dent Res 8:114-122, 2006. 4. Nkenke E, Hahn M, Lell M, et al: Anatomic site evaluation of the zygomatic bone for dental implant placement. Clin Oral Implants Res 14:72-79, 2003. 5. Bedrossian E, Rangert B, Stumpel L, et al: Immediate function with the zygomatic implant—A graftless solution for the patient with mild to advanced atrophy of the maxilla. Int J Oral Maxillofac Surg 21:1-6, 2006. 6. Chow J, Hui E, Lee P, et al: Zygomatic implants—Protocol for immediate loading: A preliminary report. J Oral Maxillofac Surg 64:804-811, 2006. 7. Bedrossian E, Tawfilis A, Alijanian A: Int J Oral Maxillofac Implants 15:853-858, 2000. 8. Stevenson ARL, Austin BW: Zygomatic fixtures—The Sydney experience. Ann R Australas Coll Dent Surg 15:337, 2000. 9. Bedrossian E, Stumpel L: Immediate stabilization at phase II of zygomaticus fixtures: A simplified technique. J Prosthet Dent 86(1):10-14, 2001. 10. Zhao Y, Skalak R, Brånemark PI: Analysis of a dental prosthesis supported by zygomatic fixtures. The Institute for Applied Biotechnology, Gothenberg, Sweden.