38: Maxillary Sinus Anatomy, Pathology, and Graft Surgery

Chapter 38 Maxillary Sinus Anatomy, Pathology, and Graft Surgery

Maxillary posterior partial or complete edentulism is one of the most common conditions in dentistry.1 Thirty million people in the United States, or 17.5% of the adult population, are missing all of their maxillary teeth. In addition, 20% to 30% of the adult partially edentulous population older than 45 years is missing maxillary posterior teeth in one quadrant, and 15% of this age group is missing the maxillary dentition in both posterior regions. In other words, approximately 40% of adult patients are missing at least some maxillary posterior teeth. This chapter addresses the treatment concepts specific to the maxillary posterior partial or complete edentulous regions.

The maxillary posterior edentulous region presents many unique and challenging conditions in implant dentistry. Most noteworthy surgical methods include sinus grafts to increase available bone height, onlay grafts to increase bone width, and modified surgical approaches to insert implants in areas with poorer bone density.2 Grafting of the maxillary sinus to overcome the problem of reduced vertical available bone has become a very popular and predictable procedure over the last decades. After the initial introduction by Tatum in the mid 1970s and the initial publication of Boyne and James in 1980, many studies have been published about sinus grafting with positive results.338 In 1983, Misch2 observed the most predictable intraoral region to grow bone height is on the maxillary sinus floor, once the sinus mucosa has been elevated. This statement still holds true today.

ANATOMICAL CONSIDERATIONS OF THE POSTERIOR MAXILLA

The maxilla has a thinner cortical plate on the facial compared with any region of the mandible. In addition, the trabecular bone in the posterior maxilla is finer than other dentate regions. The loss of maxillary posterior teeth results in an initial decrease in bone width at the expense of the labial bony plate. The width of the posterior maxilla decreases at a more rapid rate than in any other region of the jaws.39 The resorption phenomenon is accelerated by the loss of vascularization of the alveolar bone and the existing fine trabecular bone type. However, because the initial residual ridge is so wide in the posterior maxilla, even with a 60% decrease in the width of the ridge, adequate-diameter root form implants usually can be placed. However, the ridge progressively shifts toward the palate until the ridge is resorbed into a medially positioned narrower bone volume.40 The posterior maxilla continues to progressively remodel toward the midline as the bone resorption process continues. This results in the buccal cusp of the final restoration often being cantilevered facially to satisfy esthetic requirements at the expense of biomechanics in the moderate to severe atrophic ridges.41

DENTAL CONTRAINDICATIONS FOR IMPLANT TREATMENT OF THE POSTERIOR MAXILLA

A rule in traditional prosthodontics is that a fixed prosthesis is contraindicated when the canine and two adjacent teeth are missing. Therefore, when the canine and both premolars are missing, a fixed restoration is contraindicated. A removable prosthesis that has no movement under function is considered a fixed prosthesis and therefore should follow the rules of treatment planning for a fixed prosthesis in relation to implant number and position. A minimum of a healthy natural canine tooth or an implant abutment in the canine region is required before posterior implants are considered in the quadrant.

Abnormal intraoral conditions may compromise the final outcome of sinus-grafting procedures and/or the survival rates of dental implants placed in the grafted sinuses. These contraindications are similar to those reported for standard implant treatment of edentulous patients and may be summarized as follows:

Decreased Crown Height Space

The crown height space (CHS) should be evaluated before implant placement. Once the occlusal plane is properly restored or modified, the CHS should be greater than 8 mm (Figure 38-1). If less space is available for prosthodontic reconstruction, then a gingivectomy is first considered because it is not uncommon for excess tissue thickness to be present in this region. However, if tissue reduction cannot correct the CHS problem, then osteoplasty and/or vertical osteotomy of the maxillary posterior alveolar process are indicated to improve the vertical ridge orientation before implant surgery.

Poor Bone Density

In general, the bone quality is poorest in the posterior maxilla compared with any other intraoral region.42 A literature review of clinical studies from 1981 to 2001 reveals the poorest bone density may decrease implant loading survival by an average of 16%, and it has been reported as low as 40%.43 The cause of these failures is related to several factors. Bone strength is directly related to its density, and the poor-density bone of this region is often five to 10 times weaker compared with bone found in the anterior mandible.44 Bone densities directly influence the bone-implant contact percent (BIC), which accounts for the force transmission to the bone. The BIC is least in D4 bone, and the stress patterns in this bone migrate farther toward the apex of the implant (Figure 38-2). As a result, bone loss is more pronounced and occurs also along the implant body, rather than only crestally as in other denser bone conditions. D4 bone also exhibits the greatest biomechanical elastic modulus difference when compared with titanium under load.44 As such, strategic choices to increase BIC are suggested.

In the posterior maxilla, the deficient osseous structures and an absence of cortical plate on the crest of the ridge is often observed, which further compromises the initial implant stability at the time of insertion. The labial cortical plate is thin, and the ridge is often wide. As a result, the lateral cortical BIC to stabilize the implant is often insignificant. Implant surgery more often uses bone compression rather than bone extraction to create the implant osteotomy to compensate for these deficiencies. As a consequence, initial healing of an implant in D4 bone is often compromised.

MAXILLARY SINUS

The anatomy of the maxillary sinuses was first illustrated and described by Leonardo da Vinci in 1489 and later documented by the English anatomist Nathaniel Highmore in 1651.45 The maxillary sinus (or antrum of Highmore) lies within the body of the maxillary bone and is the largest of the paranasal sinuses, as well as the first to develop (Figure 38-3).

Maxillary Sinus Development

A primary pneumatization of the maxillary sinus occurs at about 3 months of fetal development by an out-pouching of the nasal mucosa within the ethmoid infundibulum. At this time the maxillary sinus is a bud situated at the infralateral surface of the ethmoid infundibulum between the upper and middle meatus.46 Prenatally, a secondary pneumatization occurs. At birth, the sinuses are filled with fluid and the maxillary sinus is still an oblong groove on the mesial side of the maxilla, just above the germ of the first deciduous molar.47

Postnatally and until the child is 3 months of age, the growth of the maxillary sinus is closely related to the pressure exerted by the eye on the orbit floor, the tension of the superficial musculature on the maxilla, and the forming dentition. As the skull matures, these three elements influence its three-dimensional (3D) development. At 5 months, the sinus appears as a triangular area medial to the infraorbital foramen.48

During the child’s first year, the maxillary sinus expands laterally underneath the infraorbital canal, which is protected by a thin bony ridge. The antrum grows apically and progressively replaces the space formerly occupied by the developing dentition. The growth in height is best reflected by the relative position of the sinus floor. At 12 years of age, pneumatization extends to the plane of the lateral orbital wall, and the sinus floor is level with the floor of the nose. The main development of the antrum occurs as the permanent dentition erupts and pneumatization extends throughout the body of the maxilla and the maxillary process of the zygomatic bone. Extension into the alveolar process lowers the floor of the sinus about 5 mm (Figure 38-4). Anteroposteriorly, the sinus expansion corresponds to the growth of the midface and is completed only with the eruption of the third permanent molars when the young person is about 16 to 18 years of age.4648

In the adult, the sinus appears as a pyramid of five thin, bony walls. The base of this pyramid faces the lateral nasal wall and often measures 33 × 33 mm; its apex extends approximately 23 mm toward the zygomatic bone.49,50 The dentate adult maxillary sinus has an average volume of 15 mL, although the range is 9.5 to 20 mL.51 The floor of the maxillary sinus cavity is reinforced by bony or membranous septa joining obliquely or transversely from the medial and/or lateral walls with buttresslike webs. They may be genetic or develop as a result of stress transfer within the bone over the roots of teeth. These have the appearance of reinforcement webs in a wooden boat and rarely divide the antrum into separate compartments. These elements are present from the canine to the molar region, and Misch41 has observed they tend to disappear in the maxilla of the long-term edentulous patient when stresses to the bone are reduced. Karmody et al.52 found that the most common oblique septum is located in the superior anterior corner of the sinus or infraorbital recess (which may expand anteriorly to the nasolacrimal duct). The medial wall is juxtaposed with the middle and inferior meatus of the nose.

Although the adult maxillary sinus maintains its overall size while the teeth are present, a rather rapid expansion phenomenon of the maxillary sinus occurs with the loss of posterior teeth. In fact, even with the loss of a single molar, the sinus expands between the adjacent tooth roots. In the edentulous maxilla, the antrum expands in both inferior and lateral dimensions and may even invade the canine eminence region and proceed to the lateral piriform rim of the nose. This results in a lack of available bone in the posterior maxilla and a greatly decreased height from both the sinus expansion and the crestal resorption. Frequently, less than 10 mm remains between the alveolar ridge crest and the floor of the maxillary sinus in the edentulous posterior maxilla. This limited dimension is compounded by the problem of bone of reduced quality and the resultant medial posterior position of the ridge after resorption of bone width. As a result, compromises in the long-term prognosis of many endosteal implant systems are reported.43

Maxillary Sinus Anatomy

Maxillary sinus grafts have become a predictable procedure before or in conjunction with implant insertion. However, infections of the maxillary sinus are common and may not only cause implant failure but also may be life-threatening to the patient. As a result, the dentist should be knowledgeable of both the macroscopic and microscopic anatomy, as well as the pathologic conditions that may occur before or postoperative to the sinus graft procedure.

Six bony walls that contain many structures of concern during sinus graft surgery surround the maxillary sinus.45,53 Knowledge of these structures is crucial for both preoperative assessment and postsurgical complications.

Superior Wall

The superior wall of the maxillary sinus is shared with the thin orbital floor (Figure 38-6). The orbital floor slants inferiorly in a mediolateral direction and is convex into the sinus cavity. A bony ridge is usually present in this wall that houses the infraorbital canal containing the infraorbital nerve and associated blood vessels. Dehiscence of the bony chamber may be present, resulting in direct contact between the infraorbital structures and the sinus mucosa. Ocular symptoms may result from infections or tumors in the superior aspects of the sinus region and may include proptosis (bulging of the eye) and diplopia (double vision). When these problems occur, the patient is closely supervised and a medical consult is advised to decrease the risk of severe complications that may result from the spread of infection in a superior direction. Superior spreading infections may lead to a brain abscess and death. As a result, when these symptoms appear, aggressive therapy to decrease the spread of infection is indicated. Overpacking the maxillary sinus with bone graft material during a sinus graft may result in pressure against the superior wall if a sinus infection develops.

Medial Wall

The medial wall of the antrum coincides with the lateral wall of the nasal cavity and is the most complex of the various walls of the sinus (see Figure 38-6). On the nasal aspect, the lower section of the medial wall corresponds to the lower meatus and floor of the nasal fossa; the upper aspect corresponds to the middle meatus. The medial wall is vertical and smooth on the antral side. Located in the superior aspect of the medial wall is the maxillary or primary ostium. This structure is the main opening through which the maxillary sinus drains its secretions via the ethmoid infundibulum through the hiatus semilunaris into the middle meatus of the nasal cavity. The infundibulum is approximately 5 to 10 mm long and drains via ciliary action in a superior and medial direction. This opening corresponds to the initial site of embryonic evagination from the nasal chamber. The ostium diameter averages 2.4 mm in health; however, pathologic conditions may alter the size to vary from 1 to 17 mm. Smaller, accessory or secondary ostia may be present that are usually located in the middle meatus posterior to the main ostium. These additional ostia are usually the result of chronic sinus inflammation and mucous membrane breakdown. They are present in approximately 30% of skulls, range from a fraction of a millimeter to 0.5 cm, and are commonly found within the membranous fontanelles of the lateral nasal wall.54 Fontanelles are usually classified either as anterior fontanelles (AFs) or posterior fontanelles (PFs) and termed by their relation to the uncinate process. These weak areas in the sinus wall are sometimes used to create additional openings into the sinus for treatment of chronic sinus infections. Primary and secondary ostia may, on occasion, combine and form a large ostium within the infundibulum.

Inferior Wall

The inferior wall or floor of the maxillary sinus is in close relationship with the apices of the maxillary molars and premolars (see Figure 38-6). The teeth usually are separated by the sinus mucosa by a thin layer of bone; however, on occasion, teeth may perforate the floor of the sinus and be in direct contact with the sinus lining. Studies have shown that the first molar has the most common dehiscent tooth root, occurring approximately 2.2% of the time. In dentate patients, the floor is approximately at the level of the nasal floor. In edentulous posterior maxillae, the sinus floor is often 1 cm below the level of the nasal floor. Complete or incomplete bony septa may exist on the floor in a vertical or horizontal plane. Almost 30% of the dentate maxillae have septa, with three fourths appearing in the premolar region.55,56 Complete septa separating the sinus into compartments are very rare, occurring in only 1.0% to 2.5% of maxillary sinuses.

Maxillary Sinus: Vascular Supply and Innervation

The blood supply to the maxillary sinus comes directly from the maxillary artery, which emanates from the external carotid artery. The maxillary artery supplies the bone surrounding the sinus cavity and also the sinus membrane. Branches of the maxillary artery, which most often include the posterior superior alveolar artery and infraorbital artery, form endosseous and extraosseous anastomoses that encompass the maxillary sinus. The endosseous anastomosis is found within the lateral wall of the sinus and supplies this structure and the lateral aspect of the sinus membrane. A posterior lateral nasal artery (a branch of the sphenopalatine artery that also rises from the maxillary artery) also supplies this region from the medial aspect of the sinus.

The formation of the endosseous and extraosseous anastomoses in the maxillary sinus is termed the double arterial arcade. The extraosseous anastomosis is less common (present in 44% of the population) and is found near the periosteum of the lateral wall. The extraosseous anastomosis is superior to the endosseous unit, which is approximately 15 to 20 mm from the dentate alveolar crest. In addition to the double arterial arcade, a blood supply from the sphenopalatine artery supplies the central and medial parts of the sinus membrane. This artery is also a branch of the maxillary artery and enters the maxillary sinus on the medial aspect via the maxillary ostium57(Box 38-1).

In an edentulous maxilla with posterior vertical bone loss, the endosseous anastamosis may be 5 to 10 mm from the edentulous ridge. The endosseous artery was able to be observed on computed tomography (CT) scans in approximately one half of the patients requiring a sinus graft.58 In a long-term edentulous patient with a thin lateral wall, the artery may be atrophied and almost nonexistent. On rare occasions, this anatomical structure may be a concern for arterial bleeding complications during lateral-approach sinus elevation surgery.

Most often, implants of 12 to 16 mm in length should be used to support prostheses in the posterior maxilla, because the bone quality is poor and the occlusal force factors are high. Because the endosseous anastomosis is often present and ranges from 5 to 20 mm from the residual crest of the ridge, the lateral-access window for the sinus graft procedure often violates this arterial supply. However, this is usually of little concern during the surgical procedure and may even be of benefit postsurgery to provide a blood supply to the graft.

The size of the lateral-wall arterial anastomoses usually approximates 1.5 mm in a dentate patient and has little arterial pressure. Although the artery is often in the pathway of surgery for the Tatum lateral-wall approach to sinus grafting, endosseous bleeding is rarely observed as a pulsating rhythm and may be easily arrested by the following: (1) cutting the bone and vessel with a high-speed diamond and no irrigation (which cauterizes the vessel), (2) using electrosurgery on the vessel, and/or (3) elevating the head and using a surgical sponge (gauze) and slight pressure over the region for a few minutes. A hemostat may also be used to clamp the vessel, because it is readily observed; however, fracture of the lateral wall may occur.

The medial and posterior aspects of the maxillary sinus mucosa receive their blood supply from the posterior lateral nasal artery. The sphenopalatine artery is the third or fourth branch of the maxillary artery and enters the nasal cavity through the sphenopalatine foramen, which is near the posterior portion of the superior meatus of the nose. Once through the foramen, the sphenopalatine artery branches into the posterior lateral nasal artery and the posterior septal artery. The posterior lateral nasal artery supplies the medial and posterior walls of the antrum (nasal cavity).

The entire circulatory system in the maxillary sinus is a vital part of the healing and regeneration of bone after a sinus graft. Different factors can alter the vascularization in this area. With increasing age, the number and size of blood vessels in the maxilla decrease. As bone resorption increases, the cortical bone becomes thin, resulting in less vascularization. As the lateral wall becomes thinner, the blood supply to the lateral wall and lateral aspect of the bone graft comes primarily from the periosteum, resulting in a compromised vascularization to the region (Figure 38-8). After surgery the arterial supply in the lateral outer wall (in spite of being severed during the procedure) may help vascularize the sinus graft, because the anastomoses may vascularize the graft from both the posterior region and anterior region.

The venous drainage of the maxillary sinus originates from a vascular plexus near the maxillary ostium that drains anteriorly into the facial vein and posteriorly into the maxillary and jugular veins.

The nerve supply to the maxillary sinus is via numerous branches of the second division of the trigeminal nerve, including the posterior alveolar nerves, anterior palatine, and infraorbital nerves. The infraorbital nerve is of concern in sinus elevation surgery because of its anatomical position. This nerve enters the orbit via the inferior orbital fissure and continues anteriorly; the nerve lies in a groove in the orbital floor (which is also the maxillary sinus superior wall) before exiting the infraorbital foramen. Anatomical variants have been reported to include a dehiscence and malpositioned infraorbital foramen, along with the nerve transversing the lumen of the maxillary sinus rather than coursing through the bone within the sinus ceiling (orbital floor).

Maxillary Sinus Mucosa: Microscopic Anatomy

The microscopic primary epithelial cells of the maxillary sinus are a continuation of the nasal mucosa and classified as a pseudostratified, ciliated columnar epithelium. However, the epithelial lining of the maxillary sinus is much thinner and contains fewer blood vessels compared with the nasal epithelium. This accounts for the membrane’s paler color and bluish hue. Five primary cell types exist in this tissue: (1) ciliated columnar epithelial cells, (2) nonciliated columnar cells, (3) basal cells, (4) goblet cells, and (5) seromucinous cells. The ciliated cells contain approximately 50 to 200 cilia per cell. In a healthy patient, they help to clear mucus from the sinus and into the nose. The nonciliated cells comprise the apical aspect of the membrane, contain microvilli, and serve to increase surface area. These cells have been theorized to facilitate humidification and warming of inspired air. The basal cell’s function serves most likely as a stem cell that can differentiate as needed. The goblet cells produce glycoproteins that are responsible for the viscosity and elasticity of the mucus produced. The maxillary sinus has the highest concentration of goblet cells in comparison with the other paranasal sinuses.

Although the sinus mucosa has been called a mucoperiosteum, Sharawy and Misch59 suggested that the periosteal portion of this membrane is not similar to the periosteum covering the cortical plates of the maxillary or mandibular residual ridges of the jaws and should not be considered a mucoperiosteum (Figure 38-9). The very minimal and usual absence of osteoblasts in this tissue and, instead, the presence of osteoclasts, may account for the enlargement of the antrum after tooth loss. The maxillary sinus membrane also exhibits few elastic fibers attached to the bone,59 which simplifies elevation of this tissue from the bone. The thickness of the sinus mucosa varies, but is generally 0.3 to 0.8 mm.60 In smokers, it varies from very thin and almost nonexistent to very thick, with a squamous type of epithelium.

Maxillary Sinus Mucous Clearance

The mucus of the maxillary sinuses is produced from serous and goblet cells, which produce 1 L of mucus each day in healthy conditions. The cilia in the maxillary sinus beat toward the ostium. A blanket of mucus is propelled toward the ostium by the beating motion of the ciliated lining cells. The mucous material of the sinus in health has two layers: (1) a top mucoid layer and (2) a bottom serous layer (Figure 38-10). The top layer is sticky and collects bacteria and other debris, whereas the serous layer is thin and acts as a lubricant. The cilia of the columnar epithelium beat toward the ostium at 15 cycles per minute, with a stiff stroke through the serous layer, reaching into the mucoid layer. The cilia recover with a limp reverse stroke within the serous layer. This mechanism slowly propels the mucoid layer toward the ostium at a rate of 9 mm per minute and into the middle meatus of the nose.60

Various elements may decrease the number of cilia and slow their beating efficiency. Viral infections, pollution, allergic reactions, and certain medications may affect the cilia in this way.6163 Genetic disorders (e.g., dyskinetic cilia syndrome) and factors such as long-standing dehydration, anticholinergic medications and antihistamines, cigarette smoke, and chemical toxins also can affect ciliary action. Certain pathogens (Haemophilus influenzae, Streptococcus pneumoniae, Pseudomonas aeruginosa) associated with sinusitis have been shown to release a compound that slows and disorganizes ciliary beating along with affecting mucous transport. Various medications have also been shown to affect ciliary action. Decongestant medications may alter the various layers of the sinus membranes, thus interrupting normal ciliary activity. On the other hand, long-term antibiotic medications have been shown to have a significant increase in ciliary beat frequency.61

In a healthy sinus, an adequate system of mucus production, clearance, and drainage is maintained. The key to normal sinus physiologic condition is the proper function of the cilia, which are the main component of the mucociliary transport system. These cilia work to move contaminants toward the natural ostium and then to the nasopharynx. The flow of mucus is toward the ostium, which leads to the infundibulum, through the hiatus semilunaris, into the middle meatus of the nose, and ultimately into the nasopharynx (Figure 38-11). An alteration in the sinus ostium patency or the quality of secretions can lead to disruption in ciliary action resulting in sinusitis. For clearance to be maintained, adequate ventilation is necessary. Ventilation and drainage is dependent on the osteomeatal unit, which is the main sinus opening. Ciliary movements of ciliated epithelial cells dictate clearance of the maxillary sinus.

The maxillary ostium and infundibulum are part of the anterior ethmoid middle meatal complex, the region through which the frontal and maxillary sinuses drain, which is primarily responsible for mucociliary clearance of the sinuses to the nasopharynx.64 As a result, pathogenesis of sinusitis is usually the development of obstruction in one or more areas of this complex.65 Symptomatic sinusitis corresponds to the blockage of the osteomeatal complex that drains the paranasal sinuses. Symptoms of sinusitis may be minimal, even in the presence of extensive radiographic findings, as long as the patency of the ostium is maintained.66

Mucoid fluid is transported toward the ostium of the maxillary sinus and drained into the nasal cavity, eliminating inhaled small particles and microorganisms. This mucociliary transport system is an active transport system that relies heavily on oxygen. The amount of oxygen absorbed from the blood is not adequate to maintain this drainage system. Additional oxygen has to be absorbed from the air in the sinus; this is why the patency of the ostium is pivotal in maintaining this transport system. Mucociliary transport may be compromised by abnormalities in the cilia, which include a decrease in the number and poor coordination of movement. After sinus infections, the quantitative loss of cilia is reversed except when severe empyema with scarring occurs, which results in the ciliated epithelium being replaced by squamous epithelium.

Maxillary Sinus Bacterial Flora

Much debate concerns the bacterial flora of the maxillary sinus. Maxillary sinuses have been considered to be sterile in health; however, bacteria can colonize within them without producing symptoms. In theory, the mechanism by which a sterile environment is maintained includes the mucociliary clearance system, immune system, and the production of nitrous oxide within the sinus cavity. In a study of patients who underwent surgical repositioning of the maxilla, Cook and Haber67 reported that 80% of the patients showed no bacterial growth. The remaining 20% had some bacterial growth but in negligible numbers. All specimens showed some degree of inflammatory cell infiltrate, more acute in the presence of microorganisms. They concluded that the asymptomatic adult maxillary sinus is usually sterile, but a few transient bacteria may exist in a clinically asymptomatic antrum.

However, recent endoscopically normal sinuses were shown to be nonsterile, with 62.3% exhibiting bacterial colonization. The most common bacteria cultured were Streptococcus viridans, Staphylococcus epidermidis, and Streptococcus pneumoniae.68 The culture findings for secretions in acute maxillary sinusitis yielded high numbers of leukocytes, S. pneumoniae, or Streptococcus pyogenes, and Haemophilus influenzae was recovered from the purulent exudates with lower numbers of staphylococci. In fact, the macroscopic appearance of the secretion should not be used to screen samples, because several cases with H. influenzae grew also from nonpurulent samples. Other reports have indicated the bacterial flora of the maxillary sinus consists of nonhemolytic and α-hemolytic streptococci, as well as Neisseria spp. Additional microorganisms identifiable in various quantities belong to the staphylococci, Haemophilus spp., pneumococci, Mycoplasma spp., and Bacteroides spp. This is important to note because the sinus graft procedure often violates the sinus mucosa, and bacteria may contaminate the graft site.

Maxillary Sinus: Clinical Assessment

To establish an adequate osseous morphologic condition for the placement of endosteal implants in the resorbed maxillary posterior region, various grafting techniques have been developed to increase bone volume. In 1987, Misch69 developed four different categories for the treatment of the posterior maxilla (termed subantral [SA]), as SA-1 through SA-4 (Figure 38-12). The SA-1 posterior maxilla allows implant placement inferior to the sinus cavity without sinus manipulation, thus not altering the sinus floor or membrane. As such, if the patient has a preexisting maxillary sinus condition or develops a sinus infection after implant placement, then implants are not at risk of becoming contaminated. However, the SA-2 to SA-4 surgical procedures do alter the sinus membrane and sinus floor. With these treatment options, a thorough preoperative evaluation is completed to rule out existing pathologic condition in the maxillary sinus. In this way, the risk of mucus and bacteria contaminating the graft and creating a bacterial smear layer on the implant, which results in impaired bone formation during healing, is reduced. In addition, because of the proximity of the maxillary sinus to numerous vital structures, postoperative complications can be very severe and even life threatening.

Pathologic conditions associated with the paranasal sinuses are common ailments and afflict more than 31 million people each year. Approximately 16 million people will seek medical assistance related to sinusitis; yet sinusitis is one of the most commonly overlooked diseases in clinical practice.70 Potential infection in the region of the sinuses may result in severe complications. Infections in this area have been reported to result in sinusitis, orbital cellulitis, meningitis, osteomyelitis, and cavernous sinus thrombosis. In fact, paranasal sinus infection accounts for approximately 5% to 10% of all brain abscesses reported each year.70

A physical examination of the maxillary sinus evaluates the middle third of the face for the presence of asymmetry, deformity, swelling, erythema, ecchymosis, hematoma, or facial tenderness (Table 38-1). Nasal congestion or obstruction, prevalent nasal discharge, epistaxis (bleeding from the nose), anosmia (the loss of the sense of smell), and/or halitosis (bad breath) are noted.

Table 38-1 Preoperative and Postoperative Physical Examination

SITE SIGNS OF INFECTION
Inferior wall Bulge in hard palate, ill-fitting denture, loose teeth, hypesthesia or nonvital teeth, bleeding, palatal erosion, oroantral fistula
Medial wall Nasal obstruction, nasal discharge, epistaxis, cacosmia, visible mass in nostril
Anterior wall Swelling, pain, skin changes
Lateral wall Trismus, bulging mass, exudate from incision line
Posterior wall Midface pain, hypesthesia of one half of face, loss of function of lower cranial nerves
Superior wall Diplopia (double vision), proptosis (eye bulging out), chemosis, pain or hypesthesia, decreased visual acuity

The clinical examination for maxillary sinusitis concerns the regions surrounding the maxillary antrum. The examination is conducted to assess each wall surrounding the maxillary sinus separately. The infraorbital foramen on the facial wall of the antrum is palpated through the soft tissue of the cheeks or intraorally to determine whether tenderness or discomfort is present. The intraoral examination assesses the floor of the antrum by alveolar ulceration, expansion, tenderness, paresthesia, and oroantral fistulae. The eyes are examined to evaluate the superior wall of the sinus for proptosis, pupillary level, lack of eye movement, and diplopia. The nasal fluids may be used to evaluate the medial wall of the sinus by asking the patient to blow the nose in a waxed paper. The mucus should be clear and thin in nature. A yellow or greenish tint or thickened discharge indicates infection. Infected maxillary sinuses typically are symptomatic, which can exhibit exudate in the middle meatus and may be inspected with a nasal speculum and headlight (rhinoscopy) through the nares.

Other methods of examination of the infected maxillary sinus may include transillumination, nasoendoscopy, bacteriology, cytology, fiber optic antroscopy, and radiography (conventional, CT, or magnetic resonance imaging [MRI]).

Maxillary Sinus Radiographic Evaluation

The maxillary sinus is often pneumatized in partial or completely edentulous patients and requires grafting. Therefore visualization of the maxillary sinus and surrounding structures are crucial for the proper diagnosis and treatment planning of the partial or complete edentulous posterior maxilla. Numerous preoperative radiographic modalities are available to evaluate the posterior maxilla and maxillary sinuses.

Panoramic Radiographs

The panoramic radiograph is often used as a preliminary diagnostic radiograph in implant dentistry. This radiograph can provide direct visualization of the anterior, lateral, and inferior regions of the maxillary sinus. It is often sufficient to evaluate the amount of bone present below the maxillary sinus (Figure 38-13).

When a panoramic radiograph is first evaluated, attention is brought to the amount of bone height in the posterior maxilla from the crest of the ridge to the floor of the maxillary sinus. This available bone height may place the patient in a category of SA-1 (obviously enough bone below the antrum for implants) or SA-4 (obviously not enough bone for implants). The SA-2 and SA-3 categories are less obvious, because the specific bone height range of 5 or 10 mm of bone may be influenced by film magnification.

The hard palate appears as two radiopaque lines on the panoramic radiograph: one line represents the structure on that side, and a second, lighter and fuzzier line represents the ghost image from the other side. When these lines are observed several millimeters above the floor of the antrum, the posterior maxilla has good surgical access for a lateral-wall approach for an SA-3 or SA-4 sinus graft option. When the palate line is near the crest of the edentulous ridge, surgical access is more difficult and the surgical lateral-access wall may even be within the zygomatic process.

The panoramic radiograph is useful for preliminary evaluation of the posterior maxilla. However, it is not the standard radiograph used to evaluate the maxillary sinus for abnormalities or pathologic conditions. Ghost and overlapping images will often obscure or distort the anatomy of the maxillary sinus. If the patient is positioned upward with respect to the Frankfort horizontal plane, then the hard palate and the shadow of the occipital bone will obscure the sinus. Another common positioning mistake is not placing the tongue in the roof of the mouth. This will result in radiolucency over the maxilla that represents the palatoglossal air space, as well as a radiopaque region from the tongue. This radiopaque region may be misinterpreted as a pathologic condition. The posterior wall of the maxillary sinus is often misinterpreted as the panoramic innominate line. This artifact is a thin, vertical radiopaque line in the posterior one third of the maxillary sinus that corresponds to the superimposition of the zygomatic process of the maxilla and the frontal process of the zygoma. The posterior region behind this innominate line is often more radiopaque and may be misinterpreted as available bone “behind the sinus” for endosteal implants (Figure 38-14).72

The panoramic radiograph may be used as the only radiographic tool in an SA-1 treatment option. Because the sinus and/or floor is not manipulated during the surgery, the condition of the sinus proper is much less relevant to implant insertion. Because the SA-3 or SA-4 sinus graft procedure augments the posterior maxilla, it transforms the region to an SA-1 condition after graft maturity. Therefore after a sinus graft has positively modified the existing bone volume, a panoramic radiograph is often the only radiographic modality used before implant surgery.

Maxillary Sinus: Computed Tomography Radiographic Anatomy

Over the years, preoperative CT scan evaluation has become the standard method for evaluating the pathologic condition of the sinuses before sinus graft procedures. Therefore the practitioner should have an understanding of the CT radiographic anatomy and the pathologic conditions associated with the posterior maxilla and maxillary sinus regions.

Maxillary Sinus: Anatomical Variants

Numerous anatomical variants arise that can predispose a patient to postsurgical complications. When these conditions are noted, a pharmacologic discipline may be altered and/or implants may be placed after the sinus graft has matured, rather than predisposing them to an increased risk by inserting them at the same time as the sinus graft. As stated previously, patency of the ostium is paramount to maintain drainage. Preexisting skeletal and bony abnormalities of the osteomeatal complex may compromise the unit, leading to maxillary sinusitis.

Middle Turbinate Variants

The middle turbinate plays a significant role in proper drainage of the maxillary sinus. A concha bullosa is a pneumatization within the middle turbinate and may occlude the osteomeatal complex, thus compromising adequate drainage. This variant is seen in approximately 4% to 15% of the population (see Figure 38-11).77 Another variant in this anatomical structure is a paradoxically curved middle turbinate, which presents a concavity toward the septum, thus decreasing the size of the meatus. This also predisposes the patient to sinus disease.

INFLAMMATION

Inflammatory conditions can affect the maxillary sinus from odontogenic and nonodontogenic causes.

Odontogenic Sinusitis (Periapical Mucositis)

The close proximity of the roots of the maxillary posterior teeth to the floor of the sinus means that any inflammatory changes in the periodontium or surrounding alveolar bone may cause pathologic conditions in the maxillary sinus.

Acute Rhinosinusitis

A nonodontogenic pathologic condition may also result in inflammation in the form of sinusitis. The most common type of sinusitis is acute rhinosinusitis. The signs and symptoms of acute rhinosinusitis are rather nonspecific, making it difficult to differentiate from the common cold, influenza type of symptoms, and allergic rhinitis. However, the most common symptoms include purulent nasal discharge, facial pain and tenderness, nasal congestion, and possible fever.

Acute maxillary rhinosinusitis results in 22 to 25 million patient visits to a physician in the United States each year, with a direct or indirect cost of 6 billion U.S. dollars. Although four paranasal sinuses exist in the skull, the most common involved in sinusitis are the maxillary and frontal sinuses.70

Etiology

An inflammatory process that extends from the nasal cavity after a viral upper respiratory infection often causes acute maxillary sinusitis. Microbiological cultures have shown the most common pathogens causing acute rhinosinusitis are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. These pathogens include approximately 20% to 27% β-lactamase–resistant bacteria. Staphylococcus aureus has also been cited with the microbiology of acute rhinosinusitis. However, this pathogen is usually only seen in nosocomial (hospital induced) sinusitis and is unlikely to be seen in an elective sinus graft patient.

The most important factor in the pathogenesis of acute rhinosinusitis is the patency of the ostium.80,82 Local predisposing causes of sinusitis include inflammation and edema associated with a viral upper respiratory tract infection or allergic rhinitis. As a consequence, mucous production within the sinus may be abnormal in quality or quantity, along with a compromised mucociliary transport. In an occluded sinus, an accumulation of inflammatory cells, bacteria, and mucus exists. Phagocytosis of the bacteria is impaired with immunoglobulin (Ig)-dependent activities decreased by the low concentration of IgA, IgG, and IgM found in infected secretions.

The oxygen tension inside the maxillary sinus has significant effects on pathologic conditions. When the oxygen tension in the sinus is altered, resultant sinusitis occurs. Growth of anaerobic and facultative organisms proliferate in this environment.83 Many factors may alter the normal oxygen tension within the sinuses. A direct correlation exists between the ostium size and the oxygen tension in the sinus. In patients with recurrent episodes of sinusitis, oxygen tension is often reduced, even when infection is not present. As a consequence, a history of recurrent acute rhinosinusitis is relevant to determine whether an implant may be at increased risk when inserted at the same time as the sinus graft.

Chronic Rhinosinusitis

Chronic rhinosinusitis is a term used for a sinusitis that does not resolve in 6 weeks and also has recurrent episodes. It is the most common chronic disease in the United States, affecting approximately 37 million people. Symptoms of chronic sinusitis are associated with periodic episodes of purulent nasal discharge, nasal congestion, and facial pain.

Allergic Sinusitis

Jan 7, 2015 | Posted by in Implantology | Comments Off on 38: Maxillary Sinus Anatomy, Pathology, and Graft Surgery
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