MAXILLARY SINUS ELEVATION AND BONE AUGMENTATION

I. INTRODUCTION AND RATIONALE

• Rehabilitation of the edentulous posterior maxilla with dental implants often represents a clinical challenge due to insufficient bone volume resulting from pneumatization of the maxillary sinus along with a loss of alveolar crestal bone caused by disease or remodeling.
• Prior to the utilization of bone augmentation procedures, patients with missing teeth and deficient bone in the posterior maxilla could only be rehabilitated with a removable prosthesis, short implants, or a cantilevered restoration (i.e., supported by adjacent teeth).
• Historically, the failure rate for implants placed in the posterior maxilla was significantly higher than the failure rate for implants placed in other anatomic locations due to inadequate bone volume and density.
• The edentulous posterior maxilla is particularly challenging because of a general lack of bone volume and the omnipresent poor bone quality of the area; that is, posterior maxillary bone is often sparse trabecular bone.
• Procedures such as maxillary sinus elevation and bone augmentation are used to increase vertical bone height in the posterior maxilla for implant placement.

II. HISTORICAL BACKGROUND

• In 1980, Boyne and James first described a procedure to graft the maxillary sinus floor with autogenous marrow and bone to facilitate placement of a blade-type implant.
• Access to the maxillary sinus was gained through a "Caldwell-Luc" procedure (i.e., an opening into the maxillary sinus created at the anterior-superior aspect / a superiorly located opening into the maxillary sinus).
• Since then, several techniques and approaches have been described, including variations on the lateral window osteotomy and a variety of techniques used to lift the sinus floor from a crestal approach.
• The maxillary sinus graft procedure was first described during the 1970s (unpublished oral presentations) and was originally used as a preprosthetic surgical procedure for patients with large tuberosities and pneumatized sinuses - to reduce the size of the tuberosity without creating an oral-antral defect, bone was grafted into the sinus cavity.
• The 1996 Consensus Conference on Maxillary Sinus Bone Grafting reviewed available data and concluded that allografts, alloplasts, and xenografts, alone or in combination with autogenous bone, can be effective as bone substitute graft materials for sinus bone augmentation. More importantly, it was concluded that the sinus graft procedure with implant placement is a highly predictable and effective therapeutic modality for the rehabilitation of the posterior maxilla.

III. ANATOMY AND PHYSIOLOGY OF THE MAXILLARY SINUS

• The maxillary sinus is the largest of the paranasal sinuses. It is an air-filled cavity located in the posterior maxilla superior to the teeth.
• The lateral wall of the nasal cavity borders the sinus medially; it is bordered superiorly by the floor of the orbit and laterally by the lateral wall of the maxilla, the alveolar process, and the zygomatic arch.
• It is pyramidal in shape, with its apex in the zygomatic arch and its base at the lateral wall of the nasal cavity. The size of the maxillary sinus varies from one individual to another (age and individual dependent).
• The entire maxillary sinus is lined with a thin mucosal membrane called the Schneiderian membrane. The specialized structure of the respiratory mucous membrane, with its motile cilia and rich blood supply, is well adapted to purifying, moistening, and warming air to protect the lungs.
• The entrance to the maxillary sinus, through the orifice or maxillary duct, is located at the superomedial aspect of the cavity. The orifice is relatively small, measuring only 3 to 6 mm in length and diameter. The maxillary sinus drains through the ostium into the middle meatus of the nasal cavity through the maxillary duct, which passes secretions medially to the semilunar hiatus.
• An accessory opening is occasionally found inferior and posterior to the main opening.
• Normal amounts of secretion are moved from the sinus by the spiral pattern of beating cilia surrounding the orifice. If the maxillary sinus becomes infected or chronically inflamed, swelling of the mucosa around orifices impairs drainage.
• The floor of the maxillary sinus extends down below the level of the nasal cavity into the alveolar process. The roots of the maxillary first and second molars are often close to the floor of the sinus.
• Blood supply to the maxillary sinus arises from the superior alveolar (anterior, middle, and posterior) branches of the maxillary artery. Branches of the greater palatine artery contribute to a lesser extent. Venous blood drains via the pterygoid plexus.
• Much of the vasculature travels through channels in the bony walls of the maxillary sinus, with many branches anastomosing with the highly vascularized Schneiderian membrane.
• Innervation is supplied by the superior alveolar (anterior, middle, and posterior) nerve, branches of the maxillary nerve.

• The maxillary sinus is frequently subdivided (incompletely) into recesses by one or more septa. Maxillary sinus septa vary in size and location.
• Clinical and radiographic examinations suggest that septa are frequently present (up to 35.9% of sinuses).
• Computed tomography (CT) scans are the preferred method for detecting septa because panoramic radiographs are not reliable (26.5% false diagnosis of the presence or absence of septa).
• Septa are found in the anterior (24%), middle (41%), and posterior (35%) aspects of the maxillary sinus, with the most common location between the second premolar and the first molar.
• The height of septa vary, ranging from 0 to 20.6 mm. Only 0.5% of septa form complete separations.

IV. INDICATIONS

• The primary indication for maxillary sinus elevation and bone augmentation, specific for the placement of dental implants, is an alveolar bone height in the posterior maxilla that is deficient (e.g., less than 7 or 8 mm of existing vertical bone height). (10th edition states: less than 10 mm.)
• Other factors that must be considered include the health of the patient, the condition of the remaining dentition, and the likelihood of a beneficial outcome.
• In situations where the interocclusal dimension is normal or only moderately increased, bone augmentation of the maxillary sinus is indicated.
• A thorough patient evaluation and the clinician's assessment will ultimately determine whether the procedure is indicated for a particular individual.
• Short- to long-term clinical studies of dental implants placed into grafted sinuses have demonstrated an equivalent or higher survival rate compared with implants placed in native maxillary bone.

V. CONTRAINDICATIONS

• Tumors or pathologic growth in the sinus
• Maxillary sinus infection
• Severe chronic sinusitis
• Surgical scar/deformity of sinus cavity
• Dental infection involving or in proximity to the sinus
• Severe allergic rhinitis/sinusitis
• Chronic topical steroid use
• Obstruction of the ostium

• Radiation therapy involving the maxillary sinus
• Metabolic disease (e.g., uncontrolled diabetes mellitus)
• Excessive tobacco use
• Drug/alcohol abuse
• Psychological/mental impairment

VI. PRESURGICAL EVALUATION

• Presurgical evaluation of the maxillary sinus is primarily accomplished using radiographic examination techniques.
• Several observations about the anatomy can be made with a periapical or panoramic projection, but the internal anatomy is most accurately assessed with a three-dimensional scan, such as computed tomography or cone-beam computed tomography (CBCT) scan.
• The maxillary sinus should be evaluated for any pathology, masses, or variations in sinus floor anatomy, such as the presence of septa.
• If three-dimensional scans are available, the lateral wall should also be evaluated for thickness and the presence of medium or large intraosseous vascular channels. Medium- to large-size vessels occasionally traverse the lateral wall of the maxillary sinus, and identifying them preoperatively helps avoid a bleeding problem during surgery.
• Drainage limitations should be evaluated as well. The maxillary sinus drains through the maxillary ostium, which is located at the superior-medial aspect of the maxillary sinus space. Patency of the maxillary ostium can be observed in cross-sectional views of a CBCT scan.

VII. BONE GRAFT MATERIALS

• Autogenous bone is often referred to as the "gold standard" for bone augmentation because of its osteoconductive, osteoinductive, and osteogenic properties. However, harvesting autogenous bone from intraoral or extraoral locations creates a second surgical site with additional morbidity.
• Several clinical studies have evaluated the effectiveness of the maxillary sinus bone augmentation procedure using a variety of bone-grafting materials, including:
  • Autogenous bone from the iliac crest or oral cavity
  • Freeze-dried demineralized bone (DFDBA) - The bone volume gained with DFDBA is less than that achieved with mineralized bone graft materials due to moderate postoperative shrinkage, presumably because the material is demineralized.
  • Resorbable and nonresorbable hydroxyapatite
  • Xenografts (e.g., anorganic bovine bone)
• The 1996 Consensus Conference concluded that many different bone graft materials, including allografts, alloplasts, and xenografts, alone or in combination with autogenous bone, can be effective as bone substitute graft materials for sinus bone augmentation.
• The Sinus Consensus Conference of 1996 was revisited in 2016 and reaffirmed the validity of the sinus graft. It concluded that non-inductive materials with slow resorption might be superior in forming and maintaining bone compared with inductive materials. The consensus also questioned the need for biologic enhancement with growth factors and morphogenic proteins.
• Some recent studies and systematic reviews have reported increased bone formation with sinus floor elevation and simultaneous implant placement without the addition of any bone graft materials.

VIII. SURGICAL PROCEDURES FOR MAXILLARY SINUS ELEVATION

A. LATERAL WINDOW TECHNIQUE

• The lateral window technique is probably the most effective and efficient way to access the maxillary sinus and elevate the sinus floor.
• An opening into the maxillary sinus is created in the lateral wall to elevate the Schneiderian membrane and place a bone graft in the space between the membrane and bone, immediately superior to the existing alveolar bone.

1. A full-thickness mucoperiosteal flap is elevated, exposing the lateral wall of the maxillary sinus.
2. The lateral wall osteotomy is prepared with a high-speed drill (carbide or diamond), a piezoelectric bone surgery device, or rotary instruments that were designed to selectively cut bone. All cutting is performed with irrigation.
3. Two techniques exist for the lateral window:
   • Technique 1 (Window-in technique): Some clinicians will prepare the lateral window outline only, leaving the center bone attached to the membrane as it is elevated and rotated into the sinus, thus becoming the superior wall of the space created for bone grafting and the new elevated sinus floor. It is important to create a window that is small enough relative to the mediolateral width of the maxillary sinus to allow the "window" to be pushed completely into the sinus cavity.
   • Technique 2 (Window-out technique): Other clinicians prefer to eliminate the bony window entirely by reducing it or removing it completely. The Schneiderian membrane is elevated inward and upward to become the superior containment of the grafted maxillary sinus space without a superior bony wall.
4. Elevation of the Schneiderian membrane is accomplished with hand instruments (De Marco curettes, Gracey 13/14 curette, universal curettes, large spoon curettes, medium-sized curved membrane elevators) inserted along the internal aspect of the bony walls of the sinus. Great care is taken to avoid perforation of the membrane.
5. Small instruments are introduced along the inferior, anterior, posterior, and superior aspects of the prepared antrostomy window, gradually inserting further along the bone until the membrane begins to separate and lift away from the bone. Subsequently, larger instruments are gently introduced along the bone to continue lifting the membrane to the desired levels (height, width, and depth).
6. Once elevated, the space is grafted with bone (autogenous, bone substitute, or a combination).
7. If implants are being simultaneously placed, the implant osteotomy sites should be prepared and implants placed after the medial, anterior, and posterior aspects of the sinus are filled with bone graft - thereby supporting the Schneiderian membrane up and away from the drills and implants. After implant placement, the remaining lateral aspect of the sinus is packed with bone graft.
8. Finally, the lateral window and bone graft are covered with a barrier membrane (e.g., resorbable membrane), and the flap is closed and sutured. Covering the lateral window osteotomy with a barrier membrane has been shown to increase the amount of vital bone and has a positive effect on implant survival.

• The technique of maxillary sinus floor elevation using piezoelectric surgery was studied by Vercellotti et al. (2001b). The study sample showed a clear reduction in the rate of membrane perforation (5%).
• Thin and precise cutting with piezosurgery allows proper repositioning of the lateral window (Clinical Periodontology and Implant Dentistry, 6th Ed., Chapter 48).
• To avoid any accidental, iatrogenic tearing or perforation of the Schneiderian membrane, specific blunt cutting tips secure an effective osteotomy with preservation of the underlying delicate sinus soft tissue structures.

B. CRESTAL OSTEOTOMY TECHNIQUE (OSTEOTOME SINUS FLOOR ELEVATION - OSFE)

• For cases with a moderate native bone height (e.g., 5 to 7 mm) that require only a small increase in added bone height, a crestal approach to sinus elevation may be desirable.
• Numerous techniques and procedures have been developed to increase maxillary bone height in the posterior maxilla using a crestal approach, including the use of osteotomes, piezosurgery, osseodensification burs, and more.

• The osteotome sinus floor elevation (OSFE) technique was described by Summers.
• The osteotome technique is a procedure that uses osteotomes to compress bone (internally from the alveolar crest superiorly) against the floor of the sinus, ultimately leading to a controlled "inward fracture" of the sinus floor bone along with the Schneiderian membrane, creating a tented space for grafting.
• It is 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 procedure. It is a highly technique-sensitive procedure (i.e., the operator must "feel" the procedure).

1. 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.
2. Osteotomes are used to increase compressive forces gradually against the floor of the sinus by adding small incremental quantities of graft material with osteotome compression until the floor of the sinus fractures inward (Fig. 80.7). The impact force needed to fracture the sinus floor is typically achieved by carefully tapping the osteotome with a mallet using controlled taps.
3. Care must be taken to prevent overinsertion of osteotomes beyond the level of existing sinus floor to avoid instrument perforation through the Schneiderian membrane.
4. After the controlled inward fracture of the maxillary sinus floor, bone graft materials continue to be slowly introduced, through the osteotomy site and gently pushed into the maxillary sinus, which continues to elevate the membrane - thus allowing a vertical expansion of the bone height in a localized area of the maxillary sinus. This latter elevation of the membrane is achieved by simply pushing graft material into the tented sinus space with the osteotome alone (i.e., no mallet).
5. Once the sinus membrane is elevated with bone graft material to the desired height, the implant osteotomy can be completed. The final implant osteotomy drill is used to finish preparing the lateral walls to the native bone depth only (i.e., full-depth drilling into the grafted sinus is not necessary), and the implant is inserted.
6. Multiple individual sites can be elevated and prepared simultaneously through separate crestal osteotomy sites.

• Published reports of this technique have demonstrated increased bone height from 2 to 7 mm (average, 3.8 mm). Thus, the crestal approach is a useful technique for increasing the vertical height of bone up to approximately 4 mm.
• If more vertical bone height is needed, or if multiple adjacent sites need sinus bone augmentation, then the lateral wall osteotomy approach may be more advantageous.
• The osteotome technique may be contraindicated for sinuses that have an acutely sloped floor or septa in the location of the planned osteotomy. An acutely sloped sinus floor will tend to deflect the osteotome in an undesirable direction, and the presence of septa makes it virtually impossible to fracture the sinus floor inward.
• The osteotome procedure involves repeated tapping of osteotomes with a mallet to create the necessary pressure to fracture the floor of the maxillary sinus. This tapping can be bothersome to some individuals, especially those patients who are not sedated for the procedure.

IX. SIMULTANEOUS VERSUS STAGED IMPLANT PLACEMENT

• Simultaneous implant placement is possible with sinus elevation and bone augmentation procedures if the implant can be stabilized in the desired location with the existing native bone.
• 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.
• The most important factor in determining whether implants can be placed at the time of sinus elevation and bone augmentation is the ability to achieve and maintain implant stability in the existing bone regardless of the existing bone height.
• If the quality of existing native bone is not sufficient to place and stabilize implants at the time of bone augmentation, then implants should be placed at a subsequent surgery after an appropriate healing period (staged approach).

X. RISKS AND COMPLICATIONS

A. Intraoperative Complications

• The reported incidence of perforation or tearing of the Schneiderian membrane varies greatly (up to 60%) and depends largely on the anatomy of the sinus as well as the skill and experience of the operator.
• The presence of septa in the maxillary sinus increases the likelihood of membrane perforation.
• Management:
  • Positioning of the sinus window within 2 to 4 mm from the anterior and inferior borders of the sinus makes it easier to get direct access to the bony walls and may lessen the amount of membrane perforation.
  • Small perforations can often be managed with a resorbable barrier membrane placed over the opening followed by careful packing of the bone graft material.
  • Minor membrane perforations can be treated by reflection of the membrane that folds on itself, whereas medium or large membrane perforations require the use of an absorbable membrane placed over the perforation to patch the opening.
  • If the perforation or tear is extensive, it will be necessary to abort the procedure, close the wound, and return later to attempt it again. Very large membrane tears may be too big to repair intraoperatively.
  • Careful surgical technique and the use of newer instruments (e.g., piezoelectric surgery) have significantly reduced this complication.

• Bleeding is a risk of this surgical procedure. The Schneiderian membrane is highly vascularized and may bleed significantly.
• A more serious bleeding problem can arise if an intraosseous artery is severed in the process.
• Bone wax and topical hemostatic agents must be available to manage this urgent surgical complication.
• If a medium-to-large intraosseous vascular channel is identified presurgically via three-dimensional imaging, the surgical approach can be modified to minimize or avoid the risk of a bleeding complication.

B. Postoperative Complications

• Infections have been reported in a small but significant number of cases (up to 10%) after maxillary sinus elevation and bone augmentation procedures. (Other reports state the incidence varies from 2% to 5.6%.)
• Prevention of infection is crucial for bone augmentation procedures. Surgery should always be performed using sterile techniques.
• Patients should use a presurgical antimicrobial mouthrinse (e.g., chlorhexidine) and take pre- and postoperative antibiotics.
• The clinical signs include pain, swelling, pus, fistula tracts, and "popcorn sign" (the exfoliation of graft particles).
• Sinus graft infections may result in concomitant sinusitis. Consultation with an ear, nose, and throat specialist is strongly recommended in this clinical scenario.
• Some infections resolve with antibiotic treatment alone, whereas others require surgical debridement of the infected area.

• This is a specific postoperative complication associated with the osteotome sinus elevation technique.
• During the osteotomy preparation and sinus floor elevation using the osteotome technique, the trauma induced by percussion with the surgical hammer, along with hyperextension of the neck during the operation, can displace otoliths in the inner ear and induce BPPV.
• It has been reported that 1.25% of the patients treated suffered vertigo when trying to sit up immediately after surgery and were diagnosed with BPPV.
• Because implant treatment is increasingly being carried out on older patients and because of the widespread use of bone expansion technique with osteotomes, the incidence of BPPV can be expected to increase.
• Management: The patient should be informed about the condition and referred to an otoneurologic specialist to determine which semicircular canal is affected and to carry out the appropriate otolithic reinstatement maneuver.
• Prevention: The application of manual force instead of hammer percussion and the use of a surgical fraise in combination with osteotomes can minimize the trauma to the craniofacial area, especially in older patients. Alternative methods including inflatable balloon techniques, selective drill systems, and piezoelectric surgical instruments should be considered to avoid BPPV.

• Loss of bone graft or implants is also a documented risk.

XI. CONCLUSIONS

• Advanced implant surgical procedures such as sinus elevation and bone augmentation allow clinicians to increase bone volume, thus facilitating the replacement of missing teeth with dental implants in the posterior maxilla.
• This procedure has become widely used and predictable with a variety of approaches.
• Diagnosis, treatment planning, careful execution of the surgical treatment, postoperative follow-up, and appropriate implant loading are all important factors in achieving a predictable outcome and success with these procedures.
• Maxillary sinus elevation and bone augmentation is a predictable technique to gain vertical bone height in the posterior maxilla. However, despite the high success rates, various intraoperative and postoperative complications have been reported. Patient selection, patient preparation, and precise surgical techniques are the key factors to reduce the incidence of sinus complications.
• The lateral window approach currently is the most frequently used technique. The crestal approach is becoming increasingly popular as well.
• Survival rates of implants placed in sinus-grafted areas have been high (95%).

REFERENCE LIST (SOURCES USED)