Dr.Enas Fadhil Kadhim
The maxillary sinus is the pneumatic space that is lodged inside the body of the maxilla and that communicates with environment by way of the middle nasal meatus and the nasal vestibule.
The horizontal shift of palatal shelves and subsequent fusion of the shelves with one another and with the nasal septum separate the secondary oral cavity from two secondary nasal chambers . This modification presumably influences further expansion of the lateral nasal wall in that the wall begins to fold; thus three nasal conchae and three subjacent meatuses arise. The inferior and superior meatuses remain as shallow depressions along the lateral nasal wall for approximately the first half of the intrauterine life; the middle meatus expands immediately into the lateral nasal wall. Because the cartilaginous skeleton of the lateral nasal capsule is already established, expansion of the middle meatus proceeds primarily in an inferior direction, occupying progressively more of the future maxillary body.
Although the exact time at which the human maxillary sinus attains its definite size is not known, the sinus appears to expand and modify in form until the time of eruption of all permanent teeth.
STRUCTURE AND VARIATIONS
The maxillary sinus is subject to a great extent of variation in shape, size, and mode of developmental pattern. It is inconceivable the sinus is described as a four-sided pyramid, the base of which is facing medially toward the nasal cavity and the apex of which is pointed laterally toward the body of the zygomatic bone . The four sides are related to the surface of
the maxilla in the following manner:
(1) anterior, to the facial surface of the body;
(2) inferior, to the alveolar and zygomatic processes;
(3) superior, to the orbital surface;
(4) posterior,to the infratemporal surface.
The four sides of the sinus, whichare usually distant from one another medially, converge laterally and meet at an obtuse angle. The identity of each of the four sides is somewhat difficult to discern, and the transition of the surface from one side to the other is usually poorly defined. The base of the sinus, which is the thinnest of all the walls, presents a perforation, the ostium, at the level of the middle nasal meatus . In some individuals, in addition tothe main ostium, two or many more accessory ostia connect the sinus with the middle nasal meatus.
In the course of development the maxillary sinus often pneumatizes the maxilla beyond the boundaries of the maxillary body. Some of the processes of the maxilla consequently become invaded by the air space. These expansions, referred to as the recesses, are found in the alveolar process, zygomatic process , frontal process (40.5% of all instances), and palatine process of the maxilla.The occurrence of the zygomatic recess usually brings the superior alveolar neurovascular bundles into proximity with the space of the sinus. The frontal recess invades and sometimes surrounds the content of the infraorbital canal, whereas the alveolopalatine recesses reduce the amount of the bone between the dental apices and the sinus space. The latter development most often pneumatizes the floor of the sinus adjacent to the roots of the first molar and less often to the roots of the second premolar, first premolar, and second molar, in that order of frequency. The fully developed alveolar recess is characterized by three depressions separated by two incomplete bony septa. The anterior depression, or fossa, corresponds to the original site of premolar buds, the middle to the molar buds, and the posterior to the third molar bud
Very little is known about the participation of the paranasal sinuses in the functioning of either the nasal cavity or the respiratory system as a whole. This is partially because of the relative inaccessibility of the sinuses to the systemic functional studies and because of the great variation in size of sinuses and their relationship to and communication with the nasal cavity.
The sinus is regarded by some as an accessory space to the nasal cavity, occurring only as a result of an inadequate process of ossification. In contrast, others report the functional contributions of the maxillary sinus in many aspects of olfactory and respiratory physiology. In individuals in whom the maxillary ostium is large enough and conveniently situated in the hiatus
semilunaris the air pressure in the sinus fluctuates from ±0.7 to ±4 mm of water between the nasal expiration and inspiration. This dependence of the pressure in the sinus on the wave of respiration is, however, less probable in instances of either the small maxillary ostium or the ostium hidden in the depth of the hiatus semilunaris. On the basis of the same two conditions
related to the structure and topography of the ostium, the functions attributed to the sinus like humidification andwarming of inspired air and contribution to the olfaction, for instance are subject to controversy. However, it is possible that if air is arrested in the sinus for a certain time, it quickly reaches body temperature and thus protects the internal structures,
particularly the brain, and probably the eyeball as well, against exposure to cold air. The other contributions by paranasal cavities to the resonance of voice, lightening of the skull weight, enhancement of faciocranial resistance to mechanical shock.
The developmental anomalies discusses several modifications of genetic and other origins in the developmental pathways of the maxillary sinus (agenesia, aplasia, hypoplasia, and supernumerary sinus). Some other criteria that correlate the extent of pneumatization by sinuses with the general dysfunctions of the endocrine system are by now developed. In case
of pituitary gigantism, for example, all sinuses assume a much larger volume than in healthy individuals of the same geographic environment. It is also known that in some congenital infections such as by spirochetes in congenital syphilis the pneumatic processes are greatly suppressed, resulting in small sinuses. Since the upper first molar tooth is most often closest to the floor of the maxillary sinus, surgical manipulation on this tooth is most likely to break through the partitioning bony lamina and thus to establish an oroantral fistulaIf untreated, the lumen of such fistulas might epithelialize and permanently connect the maxillary space with the oral cavity. A similar condition might arise as a result of either a molar or a premolar radicular cyst, granuloma, or abscess. Hypercementosis of root apices and subsequent extraction of the affected tooth may also lead to a perforation. It is necessary therefore to consider on a radiograph the relationship between any such premolar or molar tooth with the floor of the maxillary sinus prior to surgical intervention. The chronic infections of the mucoperiosteal layer of the sinus, on the other hand, might involve superior alveolar nerves if these nerves are closely related to the sinus and cause the neuralgia that mimics possible dental origin. In this instance the diagnosis must be based on a careful inspection of all the upper teeth as well as of the maxillary sinus to differentiate cause and eventual result of this condition. It is important to note that walls of the sinus are with the nerves coursing through them. Infraorbital nerve in the roof, anterosuperior alveolar nerve in the anterior wall, middle superior alveolar nerve in the lateral aspect, posterosuperior alveolar nerve in the posterior wall and greater and lesser palatine nerves on posteromedial aspect run very closely. The neuralgia of the maxillary nerve could also have an etiologicorigin in the superior dental apparatus or the mucoperiosteal layer of the sinus or both. For the diagnosis and treatment of this condition, it is most important to determine precisely the causal focus. Because of overlap of innervated territories and close topographic relationships between the teeth and the sinus, however, the causal focus is often difficult to assess. The pathogenic association of the sinus with the orodentalsystem, or vice versa, is based, in addition to a close topographic relationship, on an extensive vascular connection between these two regions by the superior alveolar vessels. As a consequence of this vascular arrangement, nonspecific bacterial sinusitis may be followed by some oral manifestations. Also the infections caused by the streptococci, staphylococci, pneumococci, or the virus of the common cold are likely to spread from either of the two regions to involve the other one. Finally, malignant lesions (e.g., adenocarcinoma, squamous cell carcinoma, osteosarcoma,fibrosarcoma, lymphosarcoma) of the maxillary sinus may produce their primary manifestation in the maxillary teeth. This may consist of pain, loosening supraeruption, or bleeding in their gingival tissue.