Chapter 4 Maxillary Sinus Grafting
Bone availability is the key to successful placement of endosseous implants 10 mm or longer in the posterior maxilla. When the thickness of the bone between the maxillary sinus and the alveolar crest is less than 10 mm, increasing the thickness of the alveolar sinus floor by bone grafting is one option that will support implants and prosthetic restoration. The graft material chosen must provide adequate viable bone to stabilize the implant initially and encourage osseointegration. Materials used for sinus floor grafting include autogenous bone, allogeneic bone, xenograft anorganic bone preparations, and alloplastic materials. Autogenous bone fulfills the criteria for an ideal graft.1
Long-term assessment of the amount of bone remaining around the implants has not been included in initial reports.2–24 However, a more recent report examined the use of tomography to assess the bone level (relative to the apical portion of the implant) and the height of alveolar ridge.25 This report indicated that after 5 to 10 years of function, bone formed in autogenous bone–grafted sinuses and was retained.25–33 The population in this study had simultaneous placement of hydroxylapatite (HA)–coated implants (e.g., cylinders, screw shapes) with autogenous bone grafts. After 5 to 10 years of function, bone was still present around the implants. Of the implants studied, 90% had bone covering the apical portion of the implant. This study supports the use of autogenous bone for sinus grafting. The techniques described in this chapter are similar to those mentioned in the long-term tomography study.25
In the tomography study, no attempt was made to differentiate prosthesis design, length and diameter of implants, or small variations in surgical technique (e.g., antibiotic coverage, flap design, type of implants used). Nevertheless, failure of the implants and grafts was rare. The prostheses fabricated for these patients followed well-known techniques. However, the effects of specific prostheses on graft maintenance and implant survival were not evaluated.25
The differences among types of grafts indicate that the addition of demineralized, freeze-dried bone (DFDB) to the iliac grafts slightly lowered the eventual bone level. Although this difference was statistically significant, the clinical difference was small, because the implants were still covered with bone. In some clinical situations, the amount of bone harvested from the donor site is less than ideal. In these cases, DFDB is added to increase the volume of the graft. Interestingly, the addition of DFDB does not increase the eventual graft volume on a long-term basis.
The autogenous cancellous bone graft contains endosteal osteoblasts that can survive the transplantation process when handled appropriately, and this graft subsequently forms bone.34–37 A corticocancellous block graft provides transplanted osteoblasts and growth factors, as well as structural rigidity, which frequently is required when implants are placed simultaneously.38 However, the cortical portion of the graft is slow to revascularize. The structural rigidity of the graft allows accurate implant placement, independent of the thickness of the sinus floor. The healing of these bone grafts follows a course that starts with basic wound healing and proceeds with bone remodeling.39–42
What alternatives might be used instead of autogenous bone and demineralized bone? Evidence is mounting that bovine bone (a xenograft) combined with autogenous bone or used by itself can induce bone formation within the graft and support implants.43–45 The use of fibrin glue creates cohesion of the composite particles, which limits their migration after placement of the graft in the sinus. Another alternative for the primary graft material is bone morphogenetic protein (BMP).46,47 BMP can be used to form bone within the sinus without the use of other materials. However, at this time, BMP combined with allografts do not have evidence-based clinical data on the incidence of bone formation in the sinus. It is expected that other combinations of materials that promote bone formation with the use of a scaffold will prove effective at solving the problem of vertical height deficiency in the future.
The residual alveolar bone thickness at the time of sinus grafting guides the surgeon to choose a particulate or solid block bone graft. Vertically deficient ridges (less than 3 mm), for which the treatment plan includes simultaneous grafting and implant placement, are augmented by placement into the sinus of iliac crest block grafts rather than particulate cancellous bone grafts. If particulate bone is used, implant placement is delayed for at least 6 months until the graft has consolidated. If the patient has 3 mm or more of bone height, the surgeon can perform simultaneous autogenous bone grafting and insert HA-coated implants rather than wait 6 months or longer.
Presurgical screening of patients in preparation for sinus grafting must include questions about factors that affect the successful formation of bone within the graft material chosen for the sinus augmentation procedure.
The preoperative radiographic examination begins with a panoramic radiograph. The clarity of the maxillary sinus, the presence of septa in the proposed surgical site, and an approximation of the thickness of the alveolar bone are visualized. Periapical radiographs do not usually contribute to the screening of the patient for sinus grafts. However, the panoramic radiograph has approximately 20% magnification error; also, detail is lacking on the facial-palatal thickness, morphologic structure of the alveolar bone and sinus floor, and status of the sinus membrane. Therefore, a reformatted computed tomography (CT) scan may be indicated for selected patients when more detail is desired (Figure 4-1, A-B).
• FIGURE 4-1 A, Computed tomography (CT) scan of the maxilla showing the reconstructed panoramic image and the axial cut. Before the bone graft is placed, a radiopaque stent with holes drilled into the planned implant site are used to determine the bone thickness at the proposed site.
• FIGURE 4-1 B, Reformatted cross section of the maxilla shown in Figure 4-1, A, showing the location of the cross section by number as it relates to the proposed implant location. The crosshatches at the bottom represent 1-mm increments, which allow thickness measurements of the bone. The proposed implant axial emergence is clearly evident in the stent.
CT scans are especially recommended for patients in whom the surgeon suspects multiple sinus septa or a pathologic condition in the sinus. The scans can document the thickness of the alveolar crest at the surgical sites and the thickness of the membrane. Before a CT scan is taken, all presurgical prosthetic planning should be complete, and a radiopaque stent indicating the positions of the planned restoration should be made. The scan is used to identify the specific locations of the planned implant sites and to provide the surgeon with an accurate understanding of the anatomy in the surgical location (see Figure 4-1).
The surgical procedure involves the removal or medial rotation of a window of cortical bone over the lateral aspect of the maxilla without perforation of the sinus membrane. Incisions should be made so as to allow adequate exposure of the surgical site and to avoid the placement of the incisions over the sinus window. After the lateral wall of the maxilla has been exposed, four linear ostectomies are performed to outline the window. The inferior horizontal ostectomy should be made as close to the floor of the sinus as possible to facilitate membrane dissection. The vertical ostectomies should be made close to the maxillary buttress and lateral nasal wall, again to facilitate membrane elevation. The superior horizontal cut should be made at the level of the planned augmentation height, which should allow placement of implants 15 mm long (DVD Figure 4-1, A). After the window has been created, the lateral bone still adherent to the sinus membrane can be either rotated medially (DVD Figure 4-1, B) or removed.
Surgery is performed in the operating room (OR) with the patient under general nasoendotracheal anesthesia or in an outpatient setting using local anesthesia and sedation as necessary. At surgery, an antibacterial rinse or povidone-iodine (Betadine) solution (or both) is used to reduce the bacterial count in the mouth. Steroids and antibiotics can be given intravenously before surgery. A local anesthetic, typically 2% lidocaine (Xylocaine) with 1:100,000 epinephrine and a longer-acting anesthetic, is administered to the maxillary vestibule and crestal tissues.
After a minimum of 5 minutes is allowed for the vasoconstrictor to take effect, a crestal incision is made. For the totally edentulous maxilla, two incisions are made, one on each side, sparing the anterior incisive canal region. Each incision is made on the crest, with anterior release starting in the lateral incisor region and extending vertically past the junction of the attached and unattached gingivae. Posteriorly, a vertical releasing incision is made in the second or third molar region and extending into the unattached gingiva. Incisions that cross the midline are avoided unless anterior onlay grafting is also planned.
For the patient with a partially edentulous maxilla with retained anterior teeth, the incision is crestal with the vertical release made anteriorly, avoiding the band of attached gingiva on the teeth, into the unattached gingiva. Posteriorly, the release is similar to that in the patient with a totally edentulous maxilla, but it may be directed over the tuberosity if tuberosity bone harvest is planned.
After the periosteum has been reflected superiorly, exposing the lateral wall of the maxilla, the planned ostectomy is visualized to start at the level of the maxillary sinus floor. The vertical osteotomies are parallel to both the lateral nasal wall and the anterior border of the maxillary tuberosity, where the maxilla curves posteriorly. The superior horizontal ostectomy is located where the vertical position of the augmentation is planned. A fiber-optic light source can be placed in the nose or against the palate to illuminate the sinus, allowing the surgeon to visualize the specific landmarks (e.g., floor of the sinus) and to perform an accurate ostectomy.
A round bur with irrigation is used to remove cortical bone and expose the gray, glistening sinus membrane (Figure 4-2, A). The lateral maxillary wall can be left intact and rotated inward as the new floor of the maxillary sinus, or it can be removed, depending on the clinician’s preference. A smooth, relatively new elevator is used to peel the sinus membrane from the floor of the maxillary sinus and lateral nasal wall (Figure 4-2, B). The membrane is elevated to the height of the desired augmentation. The edges of the sinus membrane are elevated initially, gradually increasing the distance of membrane elevation. Excessive elevation of one isolated portion of the membrane is avoided, because this would result in tension on the nonelevated membrane. The membrane must be sufficiently elevated to avoid excessive pressure when the sinus graft material is placed.
• FIGURE 4-2 A, Surgical photograph showing an incision at the crest of the ridge, followed by a full-thickness, mucoperiosteal reflection to expose the lateral wall of the maxilla. A round bur has been used to remove the cortical bone, exposing the underlying sinus membrane.
Perforations of the sinus membrane may occur, depending on the experience of the operator, location of the horizontal ostectomy, presence of septa, and thickness of the sinus membrane (Figure 4-2, C). Small perforations are left untreated. If large perforations are present, the procedure is aborted and attempted at a minimum of 4 months later. Use of a patch, such as a collagen membrane or other resorbable membrane, is at the discretion of the operator, with the understanding that the addition of such materials may increase the chances of postoperative infection. If solid blocks of bone are to be used, an intact sinus membrane may be less important. After the membrane has been elevated, the bone harvest procedure is performed.
• FIGURE 4-2 C, Sinus membrane is raised, and the lateral wall of the maxilla is then rotated medially into the sinus. The membrane is elevated with a small perforation. Small perforations (such as the one shown) can be left alone with no treatment. If a large perforation is made, the procedure may be aborted, unless a solid block of bone is used rather than particulate bone. When the membrane is elevated and positioned in the superomedial aspect of the sinus, it often folds on itself; this folding closes over any perforations.
A small amount of marrow (1 to 2 ml) can be harvested from the maxillary tuberosity in the area of the third molars. An incision is made posterior to the hamular notch, with anterior or posterior release as needed. If the surgeon anticipates using the maxillary tuberosity as the graft harvest site, the crestal incision made to expose the maxilla is extended posteriorly to allow harvesting of the posterior maxillary bone. The periosteum is reflected to expose the posterior aspect of the maxilla. Rongeur forceps are used to harvest the bone, with care taken to avoid the sinus membrane and the large blood vessels located in the pterygoid fissure. Often, up to 2 ml of cancellous bone can be harvested from a maxillary tuberosity.
Another source of bone from the jaws is the symphysis. To gain access to the chin, the surgeon can make a sulcular or vestibular incision. The periosteum is elevated to place the osteotomy 10 mm inferior to the apex of any incisor teeth. The bone then can be collected with the use of a trephine, and the cortical plate can be removed and the marrow harvested. A collecting device can be used in the suction line when bone is drilled from the chin or ramus regions or bone scrapings are produced. The goal is to harvest viable endosteal osteoblasts, which can participate in the first phase of bone formation.
For the patient undergoing unilateral sinus graft surgery, the surgeon usually can harvest bone from the posterior maxilla, the mandibular third molar site, or the chin to obtain sufficient autogenous bone, mixed with an equal amount of DFDB, to augment one sinus (Figure 4-3, A-H). A scraping device can be used on the mandibular third molar sites to harvest cortical bone and a small amount of cancellous bone (Figure 4-4, A-H). The cortical portion of the mandible has very few viable osteoblasts. To gain additional bone, the surgeon also can use the chin as a harvest site. The chin cortex is removed with a round bur, and a sieve collection device is placed in the suction line. The round bur then is used within the confines of the cortical bone to harvest cancellous bone, which should contain viable osteoblasts.
• FIGURE 4-3 A, This 50-year-old man was referred for a left sinus graft to allow placement of three implants 15 mm long for an implant-borne restoration. This occlusal view shows a long span between the maxillary left canine and the maxillary left second molar. Both teeth are marginal abutments secondary to bone levels and root contours.
• FIGURE 4-3 B, Crestal incision is made with anterior and posterior vertical release. After the lateral wall of the maxilla has been exposed, the ostectomy is performed; the sinus membrane is elevated with no perforations.
• FIGURE 4-3 C, New temporary bridge is made, which is duplicated and used as the surgical guide. Holes are drilled as prescribed by the prosthodontist. The surgical guide is placed on the tooth preparations. The drilling sequence is completed with the membrane safely elevated superiorly.
• FIGURE 4-3 D, Bone graft is harvested from the chin. After a local anesthetic has been infiltrated, a vestibular incision is made, followed by sharp and blunt dissection to expose the symphysis. A sagittal saw is used to perform corticotomies, and the cortical plate is removed. The cancellous bone under the cortex of the symphysis is removed with the aid of a curette and an osteotome. After the bone graft has been harvested, the mentalis musculature is anatomically reapproximated, and the mucosa is closed with polyglactin 4-0 sutures using an atraumatic needle.
• FIGURE 4-3 E, Bone graft is combined with demineralized, freeze-dried bone (DFDB) in a 1:1 ratio to yield approximately 8 ml of graft. The graft is placed into the medial aspect of the sinus, followed by the implants and additional graft material. Additional material then is placed to augment the thin alveolar ridge.
• FIGURE 4-4 B, Incision is made slightly palatal to the crest, with anterior and posterior vertical releasing incisions proximal and distal to the sinus graft window. The ostectomy is performed, and the lateral bone is removed. The intact sinus membrane is observed.
• FIGURE 4-4 D, To harvest intraoral bone, the surgeon makes a retromolar incision to expose the external oblique ridge. A bone collecting scraping device is used to collect shavings of cortical bone from the external oblique ridge. Approximately 2 ml of cortical shavings, with a small amount of cancellous bone, is harvested from the ramus.
• FIGURE 4-4 E, To increase the amount of available bone, the surgeon exposes the symphysis and uses a round bur at approximately 1000 rpm with a sieve in the suction line to collect cortical and cancellous bone.
When bone from the jaws is used, the volume of the graft usually must be augmented with either an allograft or a xenograft, depending on the clinician’s preference. Future use of alloplasts in various forms or recombinant proteins may affect the need for harvesting cancellous marrow.
The advantages of harvesting bone from the tibia are decreased postoperative morbidity and the ease with which the procedure can be performed under intravenous sedation in the surgical office. Disadvantages of tibia graft harvesting are the potential risks of leg fracture and possible prolonged edema in overweight patients.
In either the surgical office or the OR, the leg and foot must be prepared with meticulous sterile scrub, paint, and sterile wraps to ensure a sterile field. Often the sinus membrane elevation is accomplished first; the surgeons then rescrub, regown, and prepare the tibia for graft harvest. If attention to sterile detail is thorough, infection at the graft harvest site is rare.
The harvesting of tibial bone involves identifying Gerdy’s tubercle, after which a sharp dissection to the periosteum overlying the tibial cortex is performed (Figure 4-5, A-I). Two techniques can be used to harvest tibial cancellous bone: (1) a periosteal osteocortical flap can be elevated, based on intact periosteum along the superior aspect of the cortical window, or (2) a small cortical window can be created, which is covered with periosteum after the bone has been harvested.
• FIGURE 4-5 A, Tibia can be used as the bone graft harvest site. The leg is prepared and draped. The anatomic landmarks, including the head of the fibula, the patellar tendon, and Gerdy’s tubercle, have been drawn on the leg. The incision line drawn across Gerdy’s tubercle is shown.
• FIGURE 4-5 B, Tibia has a wide plateau region with a bump (Gerdy’s tubercle), which is the entry site into the cancellous portion of the tibia. The bone is harvested across the wide portion of the tibia and inferiorly; in this way, thinning of the superior, weight-bearing portion of the tibia is avoided.
• FIGURE 4-5 C, After administration of a local anesthetic to anesthetize the periosteum of the tibia, a skin incision is made. Hemostasis is meticulously maintained with electrocautery. Sharp dissection is used to reach the periosteum of the tibia overlying Gerdy’s tubercle.
• FIGURE 4-5 D, If a periosteal osteocortical flap is to be raised, incisions are made through the periosteum to expose the bone along two vertical sites and one horizontal location. A fissure bur can be used to create a trough through the cortex. The cortex is elevated from the tibia with the periosteum intact on the flap of bone. This elevation allows replacement of the cortex, maintaining its vascularized attachment to the periosteum.
After the periosteum has been identified, a scalpel is used to score it along two vertical lines, each approximately 10 mm long, with a horizontal line at the inferior aspect of the vertical lines. A thin fissure bur is used to create a corticotomy through the three lines, leaving the superior aspect intact. The tibial cortex is elevated by performing a greenstick fracture of the cortex, exposing the cancellous bone within the tibia. The marrow is removed from the cancellous space along the level of the window—inferiorly, not superiorly. After the marrow has been harvested, the area is irrigated thoroughly and closed in layers. The periosteum is sutured to reapproximate the cortical window and close the cortical defect. The subcutaneous tissues are closed, and the skin is closed with a subcuticular suture, with or without the addition of skin sutures as necessary.
After the skin has been incised and the periosteum has been exposed with blunt and sharp dissection, an incision is made in the periosteum, and the periosteum is elevated to expose the cortical bone at Gerdy’s tubercle. A T-shaped periosteal incision facilitates reflection of the periosteum, which can be quite tenacious. Under copious irrigation, a bur is used to remove a cortical window 8 to 10 mm in diameter, and the cancellous bone is then harvested. After irrigation, the periosteum is sutured, and the wound is closed in layers.
For either technique, the patient is instructed to avoid impact loading of the leg for at least 6 to 8 weeks. The leg should be elevated, and ice should be applied to the surgical site for 24 hours. The patient is warned to avoid soaking the leg in a bath for at least 10 days. The patient is examined the next day so that the dressing can be cleaned and questions addressed. Antibiotics to cover gram-positive cocci and pain medication are prescribed for postoperative management.
In addition to the tibia, the iliac crest can serve as the source of large amounts (more than 20 ml) of cancellous marrow. The technique for harvesting iliac crest cancellous marrow involves elevation of the iliac cortical crest and curettage of the marrow. The cortical plates are replaced and sutured back into position.
Multiple approaches can be used to reach and harvest bone from the iliac crest. For sinus grafting, the anterior approach usually is performed, because it does not require turning the patient after the sinus elevation has been completed. In addition, a satisfactory amount of bone usually can be harvested from the anterior approach. To limit blood loss and minimize gait disturbances, the technique most often used involves a relatively avascular approach, with great care taken to avoid the sensory nerves that traverse the iliac crest region. After a sterile preparation and draping of the anterior iliac crest, a local anesthetic is administered. Blunt dissection with hemostatic control using electrocautery is used to approach the anterior iliac crest. The approach should be performed from the lateral anterior aspect to prevent reflection of the insertion of the tensor fasciae latae muscle, which will minimize long-term gait disturbances. The muscles are separated rather than incised, with the dissection medial to the gluteus medius muscle and lateral to the iliacus muscle. In the area of the iliac tubercle, fibers from the external oblique and other muscles may need to be elevated when large pieces of bone are harvested, but these fibers should be left intact if possible. The sensory nerves usually pass over the anterior and posterior spines and are encountered in fewer than 2% of patients. Usually they can be retracted, and sensory loss thus is a rare complication from iliac crest bone harvest.48
For the harvesting of cancellous bone only, the iliac crest is approached, and the periosteum is not reflected. Incisions through the periosteum are made only where the osteotomes are used to create a linear bony incision with two anterior and posterior bony releases. These cortical cuts can be made with a saw or sharp osteotomes. The cortical plates of the crest then are outfractured, maintaining the soft tissue attachments to the periosteum. The cancellous bone is collected with bone curettes; suturing of the periosteum reapproximates the crestal bone cuts, and the wound is closed in layers.
For the harvesting of blocks of corticocancellous bone, either the lateral or the medial cortical plates of the iliac bone are stripped of periosteum (Figures 4-6, A-E, and 4-7, A-M). A saw with copious irrigation or sharp osteotomes are used to outline and remove a piece of bone. Additional cancellous bone can then be collected, after which the wound is closed in layers.
• FIGURE 4-6 A, Panoramic radiograph showing a patient with less than 2 mm of maxillary bone between the oral cavity and sinuses. The treatment plan calls for harvesting blocks of bone from the iliac crest and simultaneous placement of eight implants.