Presurgical Evaluation of Maxillary Sinus.

Presurgical evaluation of the maxillary sinus is primarily accomplished using radiographic examination techniques (Figure 77-1). Several observations about the anatomy can be made with a periapical or panoramic projection, but the internal anatomy is more accurately assessed with a three-dimensional scan, such as computed tomography (CT) or cone-beam CT (CBCT) scan. The maxillary sinus should be evaluated for any pathology, masses, or the presence of septa. If three-dimensional scans are available, the lateral wall should also be evaluated for the presence of medium or large intraosseous vascular channels (see Figure 54-15). Medium- to large-sized vessels occasionally traverse the lateral wall of the maxillary sinus, and identifying them is helpful in avoiding a bleeding problem during surgery (see Chapter 54).²⁵

Simultaneous Implant Placement.

Simultaneous implant placement is possible with sinus elevation and bone augmentation procedures as long as the implant can be stabilized in the desired location with the existing native bone (Figure 77-2).

It has been suggested that a minimum of 5 mm of existing native bone in the alveolar crest is required for simultaneous implant placement. However, some clinicians claim that it is possible to place implants simultaneously with as little as 1 mm of remaining bone.23,48 The most important factor in determining whether implant(s) can be placed at the time of sinus bone augmentation is the ability to achieve implant stability in the existing bone rather than any measure of bone height. Factors that influence implant stability include bone height, bone quality, precision of osteotomy preparation, and the surgeon’s skill and experience. If inadequate native bone exists to place implants at the time of the bone augmentation procedure, they can be placed at a subsequent surgery after an appropriate healing period (Figure 77-3).

Bone Graft Materials.

Autogenous bone is often considered the “gold standard” for bone augmentation because of its osteoconductive, osteoinductive, and osteogenic properties.⁴ However, harvesting autogenous bone from intraoral or extraoral locations creates a second surgical site with additional morbidity. Numerous studies have demonstrated clinical success using many variations of bone graft materials and combinations.^18,42

Several recent clinical studies and reports have attempted to evaluate the maxillary sinus augmentation procedures using a variety of bone-grafting materials, including autogenous bone from the iliac crest or oral cavity and bone substitutes such as freeze-dried demineralized bone, resorbable and nonresorbable hydroxyapatite, and xenografts. However, only a few studies have critically evaluated the long-term clinical outcome of this procedure, and most have used a small study population. Short- to long-term clinical studies of dental implants placed into grafted sinuses demonstrate an equivalent or higher survival rate as compared to implants placed in native maxillary bone (i.e., without the need of sinus augmentation).18,42 The results of these studies support the clinical predictability of maxillary sinus augmentation procedures for the rehabilitation of the edentulous posterior maxilla with implant-supported prostheses (Figure 77-4).

The use of bone-substitute graft materials can reduce the morbidity introduced by a second surgical site while maintaining equally good implant success rates.¹⁸ Anorganic bovine bone-derived mineral (ABBM; ABBM has also been referred to in the literature as deproteinized bovine bone mineral, deproteinized anorganic bovine bone, and anorganic bovine bone) has also been used successfully for sinus augmentation.⁴⁶ This graft material has demonstrated good dimensional stability and high implant survival rates.¹⁰ These materials form an osteoconductive scaffold for bone growth but do not have any osteoinductive properties. A possible exception is demineralized freeze-dried bone allograft (DFDBA). This material has demonstrated osteoinductive potential but has not proved to be particularly advantageous in the maxillary sinus bone augmentation.^18,45 In fact, the bone volume gained with the use of DFDBA is less than that achieved with mineralized graft materials as a result of moderate postoperative shrinkage of DFDBA-grafted bone.

Crestal Osteotomy Technique.

In cases with moderate bone height (e.g., 7 to 9 mm) that require limited sinus bone augmentation, a crestal approach to elevation may be desirable. The osteotome technique is a procedure that uses osteotomes (Figure 77-5) to compress bone (internally from the alveolar crest upward) against the floor of the sinus, ultimately leading to a controlled “inward fracture” of the sinus floor bone and the schneiderian membrane, which should remain intact above the inward-fractured bone.

The osteotome sinus floor elevation technique was described by Summers.35,36 It is considered to be a “conservative” approach to sinus elevation, but it is also a “blind” technique because it does not allow the operator to visualize the schneiderian membrane during the osteotomy. For this reason, it is a technique-sensitive procedure as well (i.e., the operator must “feel” the bone fracture and the membrane elevation). Verification of success can only be observed with radiographs and visualization of the bone graft material in the sinus cavity.

Procedure.

An osteotomy site is prepared with a series of drills (e.g., initial drills used for implant site preparation) to a depth that is approximately 1 to 2 mm from the floor of the maxillary sinus. Osteotomes are used to increase compressive forces gradually against the floor of the sinus by adding incremental quantities of graft material until the floor of the sinus fractures inward (Figure 77-6). After the controlled inward fracture of the maxillary sinus floor, bone graft materials continue to be slowly introduced, through the osteotomy site and into the maxillary sinus, which continues to elevate the membrane and thus allows a vertical expansion of the bone height in a localized area of the maxillary sinus. Once the sinus membrane is elevated with bone graft material to the desired height, the implant osteotomy can be completed, with a final drill used to finish preparation of the site, and an implant can be inserted. Multiple individual sites can be elevated and prepared simultaneously through separate osteotomy sites.