buccal surface of the maxilla above the dental ridge for any form of subperiosteal implant.

Although its bone may have been lost, the maxillary dental ridge rarely diminishes to the point where mucogingival junction reaches the crest (9) . Generally, some "ridge" height is maintained by a thickening of the submucosa (10) at the crest. If the upper arch does flatten so much that loose alveolar mucosa forms on the buccal surface of the ridge, palatal tissues can be repositioned buccally.

The maxillary mucoperiosteal tissues are particularly note-worthy for their concealment of the true bone picture. Unlike the mandible, where the mucoperiosteal tissues tend to remain relatively thin and closely follow the shape of the ridge, maxillary soft tissues usually thicken after tooth loss. This tendency is so marked that a totally edentulous upper arch may appear unchanged (11) years after tooth loss. Upon palpation, the deep U-shaped arch is firm, leading to the assumption that the bony ridge underlying the tissues is tall and broad (12). However, this is almost never the case. Perhaps in response to trauma, maxillary mucoperiosteal tissues thicken and stiffen, camouflaging the true picture of the bony dental arch. The apparently ideal arch's soft tissues may be uphol-

stering a knife-edge ridge (13) , padding a bony defect, filling out

an undercut (14), and so on. The incontrovertible fact is that the

loss of mechanical stimulation within alveolar bone leads to bone

loss, and that loss should be anticipated in most totally and partially

edentulous cases — no matter how the arch appears to the eye or

upon palpation.

The thickening of the maxillary soft tissues is probably the major contributing factor to the common misconception of maxillary ridge resorption. The bone of a residual ridge (15) is usually depicted as gradually flattening, with a relatively thin covering of soft tissues (16) closely following its decline. However, current investigations indicate that as bone is initially lost (17) — principally from the labial/buccal surface — the width of the ridge (18) is maintained by a thickening of the submucosal tissues. The ridge

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