able prominence begins only in the bicuspid region, and becomes more obvious as it continues posteriorly. This prominence, the mylohyoid ridge, is almost continuous posteriorly with a ridge of bone that strengthens the coronoid process.

There are considerable differences in the shape and position of the mylohyoid ridge, and these differences affect implant potential. The ridge may range from a slight, smooth elevation (1) along its entire length, to a markedly bulky process with a smooth contour (2) or a sharply pointed crest (3). The ridge may be plump (4), or have concave walls superiorly (5), inferiorly (6), or both superiorly and inferiorly (7).

An unanticipated inferior concavity, or undercut, is particularly treacherous in implant surgery. Although exposing the entire implant site is mandatory in most other situations, tissue retraction to visualize the inferior limits of the ridge would require severing the tendonous attachment of the mylohyoid muscle to the ridge. Fortunately this is not necessary. The muscle (8) is a thin, flexible sheet and the tissues below it, including the submandibular (sub-maxillary) gland (9) are easily moved. To determine the shape of the mylohyoid ridge's lower border, the operator can palpate the inferior portion with his finger. The finger should probe the entire length of the intended implant site, because irregularity of contour and bulk are common. A nice plump bulge may abruptly become concave.

Viewed occlusally, the crest of the ridge also exhibits variability. The crest may form a smooth continuous line (10) that gradually blends into the overall horseshoe shape of the mandibular body; abruptly join the body in the bicuspid region (11) ; or be highly irregular along its entire length (12). The crest may also come to a relatively sharp point in some places, and be smoothly rounded and blunt in others.

The density of the bone forming the mylohyoid ridge is also an important implant consideration. The amount of trabeculation

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