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 »  Home  »  Endodontic Articles 2  »  Endodontic implications of the maxillary sinus: a review
Endodontic implications of the maxillary sinus: a review

The anatomical and clinical significance of the maxillary sinus was first described by Nathaniel Highmore (Highmore 1651) in 1651 with a report on the drainage of an infected sinus through the extraction socket of a canine tooth. Since that report, the maxillary sinus or antrum of Highmore has played an important part in the dental treatment of maxillary teeth.
The dental literature contains many references to the extension of periapical inflammation to the maxillary sinus (Bauer 1943, Selden & August 1970, Selden 1974, Selden 1989, Selden 1999). Stafne (1985) estimated that 15–75% of the time, sinusitis occurs through a dental cause although the true incidence is difficult to determine accurately. Ingle (1965) believed that contact between the maxillary sinus floor and inflammatory lesions resulted in the development of chronic sinusitis. It is also accepted that symptoms of maxillary sinusitis can emulate pain of dental origin, and a careful differential diagnosis is thus essential when dealing with pain in the maxillary posterior area (Schwartz & Cohen 1992).

Development, anatomy and physiology of the maxillary sinus.
The maxillary sinus is the first of the paranasal sinuses to develop in human foetal life. During the fifth foetal month, secondary pneumatization starts as the maxillary sinus grows beyond the nasal capsule into the maxilla (Koch 1930). At birth, the sinus is approximately 10 3 4 mm in dimension and continues to grow slowly until the age of 7 years when expansion occurs more rapidly until all the permanent teeth have erupted. The average dimensions of the maxillary sinus of the adult are 40 26 28 mm with an average volume of 15 mL (Bailey 1998, Sadler 1995).
The maxillary sinus is typically pyramidal in shape with the base of the pyramid forming the lateral nasal wall and the apex extending into the zygoma (Bailey 1998). The roof of the sinus, which also forms the floor of the orbit, is composed of thin bone with the infraorbital neurovascular bundle found in the central portion of the bone. This nerve is dehiscent in 14% of the population and may be damaged during manipulation in this area (Donald et al . 1995). The anterior wall corresponds to the canine fossa of the anterior maxilla. The posterior wall separates the sinus from the contents of the infratemporal and pterygomaxillary fossae. The floor of the sinus is formed by the alveolar process of the maxilla and partially by the hard palate. Whilst it lies 4 mm above the floor of the nasal cavity in children, it ultimately lies 4–5 mm below the floor of the nasal cavity in adults (Bailey 1998). The adult sinus is variable in its extension. In about 50% of the population, it may expand into the alveolar process of the maxilla, forming an alveolar recess. In these cases the maxillary sinus comes in close relation to the roots of the maxillary molar and premolar teeth, particularly the second premolar and the first and second permanent molars. In rare cases the sinus floor can extend as far as the region of the canine root (Schuh et al . 1984). The sinus floor exhibits recesses extending between adjacent teeth or between individual roots of teeth. The alveolar bone can become thinner with increasing age, particularly in the areas surrounding the apices of teeth, so that root tips projecting into the sinus are covered only by an extremely thin (sometimes absent) bony lamella and the sinus membrane. The deepest point of the maxillary sinus is normally located in the region of the molar roots with the first and second molars the two most commonly dehiscent teeth in the maxillary sinus at 2.2% and 2.0%, respectively (Lang 1989). However, with extensive pneumatization, the third molar, premolars and canine teeth may all be exposed into the sinus (Bailey 1998). This places the neurovascular bundle of the teeth in danger during curettage of the sinus. Furthermore, the extraction of teeth owing to apical pathology may result in an oroantral communication or fistula (Bailey 1998). In response to reduced function associated with the loss of posterior teeth the sinus may expand further into the alveolar bone, occasionally extending to the alveolar ridge (White & Pharoah 2000).
The medial wall of the maxillary sinus or lateral wall of the nose contains the sinus ostium, which opens into the middle meatus of the nose and provides essential drainage. The ostium lies approximately two thirds up the medial wall of the sinus, anatomically making drainage of the sinus inherently difficult. In 15% to 40% of cases a very small, accessory ostium is also found (Bailey 1998). Blockage of the ostium can easily occur when swelling or thickening of the mucosal lining of the ostium develops.
The maxillary sinus is supplied by branches of the maxillary and facial arteries, partly by endosseous vessels, partly by periosteal vessels (Watzek et al . 1997). Periosteal supply is provided by the sinus membrane which in turn, is supplied by the posterior–superior dental artery or by the infraorbital artery (buccally) and the palatine artery (palatally). Venous drainage occurs via the facial vein, the sphenopalatine vein and the pterygoid plexus. The significance of the vascular drainage of the sinus lies in the fact that apart from joining typical pathways in the maxilla to the jugular veins, it can also drain upward into the ethmoidal and frontal sinuses and eventually reach the cavernous sinus in the floor of the brain. Spread of infection via this route is a serious complication of maxillary sinus infections.
The innervation of the sinus is of particular interest from a diagnostic standpoint. The nerve supply is from the maxillary division of the trigeminal nerve, with branches coming directly from the posterior, middle and anterior superior alveolar nerves, the infraorbital nerve and the anterior palatine nerve. The posterior wall of the sinus receives its nerve supply from the posterior and middle superior alveolar nerves, whilst the anterior wall is supplied by the anterior superior nerve (Watzek et al . 1997). These nerves travel enclosed in the wall of the sinus innervating the related teeth (Wallace 1996). It could, thus, be difficult to distinguish pain of dental origin from that of sinus origin. Also, a buccal surgical endodontic approach involving the sinus does not generally produce bleeding problems (Altonen 1975, Waite 1971) but it does involve the nerves and may induce paraesthesia (Wallace 1996).
The function of the paranasal sinuses remains largely unknown. Theories include roles such as: humidification and warming of inspired air, assisting in regulating intranasal pressure, increasing the surface area of the olfactory membrane, lightening the skull to maintain proper head balance, imparting resonance to the voice, absorption of shocks to the head, contributing to facial growth and lastly, exist as evolutionary remains of useless air spaces (Bailey 1998).
The pathophysiology of sinus disease is related to three factors: patency of the ostia, function of the cilia and the quality of the nasal secretions (Bailey 1998). These factors contribute to the adequate drainage of the sinus. Treatment of sinus disease is based on establishing and then maintaining adequate drainage.
The prime functional structure of the nasal fossa and paranasal sinuses is the mucosal lining. The mucosa of the paranasal sinuses is continuous with the nasal cavity and, although much thinner, is also composed of ciliated and nonciliated pseudostratified columnar epithelium interspersed with goblet cells. The goblet cells produce thick mucus in response to irritation (Bailey 1998). The ciliated and nonciliated columnar cells possess microvilli that are 1.5 m in length and 0.08 m in diameter (Petruson et al . 1984). The microvilli help expand the surface area of the epithelium to improve humidification and warming of air (Petruson et al . 1984). Serous and mucinous glands are located under the basement membrane and produce thick and thin mucus in response to the autonomic nervous system (Bailey 1998). The cilia are essential to the maintenance of sinus health. They function in mass action, producing co-ordinated sequential beating, thus creating a wave-like motion, generally in the direction of the ostium. The mucus flows constantly, propelled by the underlying cilia. The film of mucus moves in a spiral direction upward, towards the ostium. A new mucinous blanket is formed every half hour. It is thus easy to understand how loss of cilia will interfere with elimination of the continuously forming mucus.