The tissues involved in implant procedures 33

Fig. 2-13. Lateral radiographs show the extent and boundaries of the maxillary sinus, mandibular canal, and mental foramen. Note the amount of alveolar bone above the canal and below the sinus in these healthy jaws. (From Updegrave, W. J.: New horizons in periapical and interproximal radiography, Elgin, Illinois, 1966, Rinn Corporation.)

The palatine process projects horizontally from the lower part of the medial surface to form the anterior two-thirds of the hard palate; its smooth upper surface lies in the floor of the nasal cavity while its lower surface forms the roof of the mouth. At the two ends of its medial border are the nasal crest and anterior nasal spine, which support the nasal septum. The maxilla seen from various angles is shown in Fig. 2-11.

The landmark to be most carefully studied and avoided in a maxilla is the maxillary sinus, or antrum of Highmore (Fig. 2-12). This sinus is an air-filled chamber that is an extension of the nasal cavity. It is lined with a mucous membrane that is continuous with that of the nasal cavity. The posterior superior dental, infraorbital, and anterior superior dental nerves and their accompanying vessels lie in the mucosa of the posterior wall, roof, and anterior wall of the sinus, respectively.

In the adult, the maxillary sinus is a large, pyramid-shaped cavity with its apex in the zygo

matic process of the maxilla and its base at the lower part of the lateral wall of the nose. The roof of the sinus is the floor of the orbit, and its own narrow floor lies over the alveolar process in the region of the molar and premolar teeth. The sinus is irregular in shape. Normally its deepest part lies over the second premolar and first molar teeth. However, its floor may extend no farther than the three molars, or it may extend as far forward as the canine teeth.

The roots of the teeth, particularly the first two molars, may produce eminences in the floor and even penetrate the sinus. Usually the sinuses are symmetrical, that is, that in the left maxilla is approximately the same size and shape as that in the right maxilla. Differences, however, are not rare. The sinuses are normally larger in men than in women, and they serve to lighten what would other-wise be rather heavy bone (Fig. 2-13) .

At birth the sinus is no more than a groove by the lateral wall of the nasal fossa. Growth, which is accompanied by an evagination of the mucous mem-