unusually prominent palatine torus. The palatal vault ranges from narrow to wide. The presence or absence of teeth affects both its depth and width. In an arch with teeth, the deeper portion lies anteriorly and the widest diameter is between the last molars. Also, anteriorly the roof slopes gradually into the alveolar crest, whereas in the molar region the hard palate and alveolar process meet at almost right angles. However, alveolar bone resorption due to disuse atrophy or occlusal trauma can alter this prototype significantly.

The hard palate is composed of dense cortical bone enclosing a narrow core of cancellous bone. Both the hard palate's composition and its vaulting-arch shape help it serve as linking buttresses for the alveolar processes in which originate the three main stress-distributing pillars of the maxillary skeleton.

The cancellous core may be affected when its mechanical function is reduced by tooth loss. It is not rare for an enlarged maxillary sinus to invade the palate, leaving only the cortical plates to separate the oral and nasal cavities. Such invagination usually interferes little with palatal functions, although it may aggravate a sinus condition by forming pockets that trap infected fluids. More commonly, disuse atrophy leads to an overall thinning of the bony wall between the cavities. With even the thinnest hard palate, there is rarely any danger of perforation during any implant procedure. When the hard palate is used as an implant site, it is used for a subperiosteal implant — which sits on the bone. In addition, sinus invagination, if it does occur, usually takes place in the posterior portion of the vault. It rarely advances beyond the first bicuspid. The anterior region — a more common implant site — remains relatively thick with cortical bone.

The pressure brought to bear on thin palatal bone when an implant is in functional use is neither concentrated nor forceful enough to fracture the bone. Because the hard palate is composed primarily of compact bone, it is little affected by the stresses exerted upon it by a correctly designed and fitted subperiosteal implant in balanced use. Compact bone does not resorb under surface pressure, as alveolar bone does.

The four bony parts of the hard palate — the paired maxillary palatine processes (1) and the paired horizontal plates of the palatine bones (2) — form a cross-shaped suture (3), also known as the intermaxillary suture. This suture marks the juncture of each side of the hard palate; and the transverse suture (4), the junction of the maxillary and palatine bones. In the child, the suture (5) between the premaxillae (6) and the maxillae (7) can also be

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