perpendicular to the occlusal plane and parallel to other abutments. Countersinking may be necessary in one site, but not in another.

When using two individual bladevents and the more posterior blade closely approaches the canal, it may be necessary to modify its distal edge as insurance against intruding into the canal. First the bladevent is compared to the radiographs, and the possibly intruding portion noted (14). This offending portion can be reduced with a 700 XL carbide bur (15). The altered segment is then trimmed to re-establish the wedge-shape on the leading edge of the implant (16). This wedge need not be as sharp as the manufactured one because of its proximity to the canal.

Bone porosity often differs in each site. Making each socket separately (17, 18) gives greater control over socket depth and implant insertion.

Problem Ridge:

Undercuts (Severe Concavities)

The shape of the ridge—from canine region to canine region—tends to be concave labially (1). This results from the normal inclination of the anterior teeth. As the ridge recedes after tooth loss, the concavity tends to become more pronounced (2). Perhaps crestal bone remains in the shape of a bulb-like knob (3).

A concavity deepened by resorption reflects the history of the ridge. Because all teeth are not lost simultaneously by natural processes, the concavity is rarely a geometrically precise or balanced shape. A recently vacated left lateral incisor area may be much less concave (4) than its bilateral counterpart (5).

Furthermore, disease often induces a more exaggerated or an atypical resorption pattern. A fenestrated site (6) can leave a pronounced concavity (7), more precisely described as an "undercut". An abscess can cause a concavity which would not normally result from disuse atrophy, for example, on the lingual surface (8).

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