Background, general principles, and techniques

Bone availability is the key to successful placement of endosseous implants in the posterior maxilla. When the thickness of the bone between the maxillary sinus and the alveolar crest is less than 9 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, sintered xenograft, and recombinant bone morphogenetic protein (BMP).¹

Long-term assessment of the amount of grafted bone in the sinus, remaining adjacent to implants placed into the grafts, has been reported within case reports, small case series, and limited retrospective reports.2–24 One 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, was retained; this was confirmed by others.^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 present. A total of 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. The effects of specific prostheses on graft maintenance and implant survival were not evaluated.²⁵

Combinations of bone materials have been suggested to lower the necessary volume of harvested autogenous bone and to extend the graft’s volume. The addition of demineralized, freeze-dried bone (DFDB) to iliac cancellous bone grafts slightly lowered the eventual bone level.²⁵ Although this difference was statistically significant compared with autogenous bone alone, 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 required. In these cases, DFDB was added to increase the volume of the graft. The addition of DFDB did not increase the eventual graft volume over the long term.

An 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-based clinical data supports the use of sintered xenograft (bovine or equine) combined with autogenous bone or used by itself to induce or conduct bone formation within the graft and support implants.43–45 To control the graft’s position and decrease particle migration, fibrin glue can be added to create cohesion of the composite graft particles, which limits their migration after placement of the graft in the sinus. Another alternative for the primary graft material is the use of BMP.^46,47 BMP can be placed within the sinus under an elevated membrane and forms bone within the sinus without the use of other materials. Recombinant BMP is expensive and when used by itself can result in increased swelling in the patient. To decrease the amount or dose of BMP used and to decrease cost to the patient, BMP has been combined with mineralized bone allograft. Long-term evidence-based clinical data on the incidence of bone formation in the sinus have been minimally reported. 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.^48–55

In the past, the amount of bone available on the alveolar crest dictated the source of bone graft material, whether it was an autogenous block or particulate cancellous bone, and whether implants were placed simultaneously or delayed regarding graft placement. Clinical evidence indicates that less morbid alternatives are bioequivalent to autogenous bone with less morbidity and less need for general anesthetics for bone harvesting.^56,57

The consensus conference sponsored by the Academy of Osseointegration⁵⁷ and other studies indicate that xenografts used by themselves or combined with autogenous bone worked as well as autogenous bone alone.⁴⁴ Demineralized bone alone did not result in predictable bone formation. This opened the spectrum of using a less morbid approach by avoiding hip or tibia bone harvesting to grow bone within the sinus to support dental implants.

The clinical use of iliac crest or tibia cancellous bone harvesting has decreased and has been substituted by the use of BMP with mineralized bone allograft, BMP used alone or xenografts with or without the addition of autogenous bone, fibrin glue, or both. There is excellent evidence for the use of BMP alone or xenograft with autogenous bone or with a fibrin glue cohesive product. Clinical data are limited using the combination of BMP and allograft. However, its use in cervical spine fusion and in basic science publications indicates that the combination of BMP and mineralized bone is an obvious choice.⁵⁸

Early clinical data and animal studies indicate that sintered xenograft and nonresorbable alloplastic materials do not allow for bone formation in the scaffolds compared with mineralized bone. ^58,59 When recombinant human BMP (rhBMP) is combined with sintered xenograft, there is a negative effect on bone formation in the maxillary sinus. This may be the result of more scar formation and less vascular infiltration for cellular recruitment in the graft.⁵⁹ There is less bone formation using demineralized bone with BMP than when BMP is used alone.⁶⁰ rhBMP has been used with mineralized bone allograft for continuity repair on the mandible.⁶¹ When used alone in the sinus, rhBMP forms bone that is adequate for implant placement and function.⁶²

The experience of this author includes the use of rhBMP combined with allograft in 12 patients. These patients had sinus augmentation performed as an isolated procedure. After 6 months, implants were placed and restored after a 4-month period of integration. No implants were lost in this small series. An average of 10 mm of new bone was formed with implant placement 6 months after the sinus rhBMP–allograft was placed. The method is discussed in this chapter.

Preoperative radiographic screening

The preoperative radiographic examination begins with a cone-beam scan. The traditional panoramic radiograph has excessive magnification error and is unable to determine the cross-section location of the bone and associate septi. A cone-beam is the current method of choice to determine bone morphology and sinus disease before sinus augmentation. Because the radiation dose of current cone-beam scanners is decreasing to match traditional panoramic radiographs, a preliminary cone-beam scan of the patient is appropriate and allows for accurate treatment planning. The scan is evaluated, and depending on clinician preference, computed tomography (CT) planning software can be used to create a virtual plan. In selected cases, a prosthetic plan can be mocked for the initial scan to allow for less radiation dose to the patient and to be more efficient at the treatment planning phase of therapy

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. Some patients have large aerated sinuses. Some patients have smaller sinus cavities with the lateral nasal wall more laterally positioned than others. Some of these sites have a well-defined concave site with the surrounding walls creating a well-defined space for an anatomically driven graft. Periapical radiographs do not usually contribute to the screening of the patient for sinus grafts. Therefore, a cone-beam scan is absolutely indicated for patients who are candidates for implants in the posterior maxilla (Figure 6-1). These observations help determine the ideal material for each patient.

Anatomic considerations for material and method for sinus augmentation

For this author, if the vertical bone thickness is 6 mm or greater, then the sinus floor is usually elevated through the implant preparation site with placement of an implant 3 to 4 mm taller than the height of the residual bone. If the bone thickness is 6 mm, then a 9-mm-tall implant is used. If the floor thickness is 8 mm, then an 11-mm-tall implant is chosen. If the vertical alveolar height is less than 6 mm or if because of mechanical considerations greater length implants are indicated, then a lateral window approach is used. Patient morbidity is greater with lateral window approaches, hence the rationale to use the least morbid procedure to achieve a long-lasting functional result.

When removing a posterior maxillary tooth, alveolar bone height can be developed in two stages using intrasocket osteotomies to elevate the sinus floor. When a posterior maxillary tooth is to be removed and there is less than 7 mm of residual bone available at the time of tooth removal, the bone within the socket can elevated 3 to 4 mm to increase the alveolar height close to 7 or 8 mm.⁶³ Implant placement, after the bone has formed within the extraction socket, is performed usually 4 months after tooth removal. If needed, additional bone height is developed by osteotome methods through the implant site, which avoids a lateral window approach. This is discussed later in this chapter.

The residual alveolar bone thickness at the time of sinus grafting guides the surgeon to choose a method for augmentation as well as the material. Vertically deficient ridges with less than 6 mm, for which the treatment plan includes grafting and implant placement, are augmented by placement of the particulate graft. Simultaneous implant placement depends on the ability to gain primary stability and patient considerations. A conservative method is to place implants after bone has formed, typically 6 months after the sinus augmentation surgery. If the patient has more than 6 mm of bone height, the sinus augmentation can be performed through the implant preparation site.

Surgical technique

Lateral window approach

The surgical procedure involves the removal or medial rotation of a window of cortical bone from the lateral aspect of the maxilla without perforation of the sinus membrane. Incisions should be made 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. These ostectomies are located along the bony borders of the sinus, specifically the floor and lateral nasal wall. Transillumination of the sinus from the palate guides the surgeon to locate these landmarks. The accuracy of the cone-beam scan also is an important aid to locate the ostectomies on the ideal locations.

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 (Figure 6-2). The superior horizontal cut should be made at the level of the planned augmentation height, which should allow placement of implants at least 11 mm long. After the window has been created, the lateral bone still adherent to the sinus membrane can be either rotated medially (see Figure 6-2) or removed.

Another method to expose the sinus membrane is the use of a piezosurgery device. This author uses a round carbide bur to outline the planned window. An insert with a flat surface can be used to scrape the bone from the lateral window site, thinning it gradually. This scraped bone can be collected using a bone sieve placed in the suction line. As the bone is thinned, the surgeon can return to the carbide drill if desired or use a diamond-surfaced piezosurgery insert to complete bone removal. This author outlines the window with a round bur, uses the scraper to remove most of the overlying bone, and gently lifts off the lateral bone with an elevator. The membrane is exposed and ready for its separation from the overlying maxilla.

In the past because of harvesting bone from the hip, sinus augmentation surgery was performed in the operating room with the patient under general nasoendotracheal anesthesia. Since the use of other graft materials, this procedure is performed in the office setting using local anesthesia and sedation as necessary. Before surgery, an antibacterial rinse is used, and immediately before surgery a povidone–iodine (Betadine) solution is used to reduce the bacterial count in the mouth.

A local anesthetic, typically 2% lidocaine with 1:100,000 epinephrine, is administered to the maxillary vestibule and crestal tissues. After a minimum of 10 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 a 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 a 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 light source can be placed toward the palate without touching the tissues to avoid heat damage, and the lighting is decreased. The light will transilluminate the sinus, and the walls of the sinus can be identified. A sterile pencil is used to mark the bone as an outline of where to make the ostectomies close to the borders of the sinus (Figure 6-3).

A round bur with irrigation is used to remove cortical bone and expose the gray, glistening sinus membrane (see Figure 6-2). 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 (see Figure 6-2). 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.

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 (see Figure 6-2). 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.

Bone-harvesting techniques

Autogenous bone was the standard material used for sinus augmentation until the evidence base knowledge was established for rhBMP or the use of sintered xenografts in combination with small amount of autogenous bone. Currently, the need to harvest iliac crest bone is limited to extreme cases. For historical reasons and for those isolated cases, the following sections have been shortened compared with prior editions but are included to provide readers with reference material if autogenous bone collection if necessary for other bone grafting procedures involving the face.

Autogenous intraoral grafts

A small amount of marrow (1–2 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 intraoral bone is the symphysis. To gain access to the chin, the surgeon can make either a sulcular or vestibular incision. The periosteum is elevated to place the osteotomy 10 mm inferior to the apex of any incisor teeth. If the ostectomy is closer than 10 mm, then innervation to these teeth may be compromised. The bone is collected with the use of a trephine, or the cortical plate can be removed and the marrow harvested. A bone collection sieve can be used within the suction line. Bone can be collected by using a drill with copious irrigation, removing bone from the chin or ramus regions, or bone scrapings are collected. The goal is to harvest viable endosteal osteoblasts, which can participate in the first phase of bone formation. The older the patient, the less marrow space in the symphyseal region.

For a patient undergoing unilateral sinus graft surgery, with the plan to combine autogenous bone with sintered xenograft, the surgeon usually can harvest the needed bone from the posterior maxilla, the mandibular third molar site, or the chin to obtain sufficient autogenous bone, mixed with an equal amount of sintered xenograft, to augment one sinus (Figure 6-4).

Another intraoral option is to use a scraping device on the mandibular third molar ramus site to harvest cortical bone and a small amount of cancellous bone (Figure 6-5). The cortical portion of the mandible has very few viable osteoblasts. If is now rare to use the chin to harvest bone for sinus augmentation, with the modern advent of using rhBMP or sintered xenograft combined with smaller volumes of autogenous bone.

When bone from the jaws is used, the graft is combined in a ratio approximating 1:2 and ideally 1:1, with a xenograft, depending on the clinician’s preference.

Iliac crest grafts

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.⁶⁴

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 6-6 and 6-7). 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.

If the patient requires either inferior or superior repositioning of the maxilla, a Le Fort I osteotomy can be performed with simultaneous sinus grafting. For this procedure, the incision is made in the vestibule, and the maxillary osteotomy is performed. The sinus membrane is removed after the maxilla has been downfractured. The bone of the maxilla is removed as necessary for the planned skeletal movements, and a wax pattern of the sinus is made. Corticocancellous blocks are harvested from the posterior or anterior iliac crest. The grafts are carefully trimmed to mortise into the sinus. Implants may be placed to secure the grafts in position. The maxilla then is plated to its planned location.

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