A double-posted bladevent is preferable for narrow-waist situations. A double-posted design places the abutments in stronger bone (10) where they share the forces brought to bear upon the site. The post of a single-posted blade would fall at or near the bone's weakest point, its narrow "waist" (11). Another advantage is provided by using the open-socket bladevent. Its recessed shoulder, falling in the narrowest area, will allow the regrowth of a tall shelf of bone over the most fragile area.

As in other precarious socket-making situations, the bur is sunk to its entire depth (12), then its shank is backed out and the biting portion is worked mesially into wider bone (13), then distally (14), or vice versa — operator's preference. Note that this approach is different. Whereas the socket in an evenly wide ridge is initiated at one end and worked toward the other, the groove here is initiated in the narrowest portion for greater control over its direction.

In many narrow-waist situations, particularly when remodeling of the crest is required, the implant cannot be correctly seated without countersinking the posts (15). Bone must be reshaped mesially and distally (16), to properly seat the implant with the bottom of both posts touching the crest (17).

Occasionally the shape of a pinched ridge may require curving the groove (18) counter to the curve of the dental arch. This is an exceedingly delicate situation. A short, shallow bladevent de-sign must be used to avoid perforating the labial walls. The neck (19) of the implant must be twisted so that the post will follow the normal dental arch (20) .

Finding Bone for Two Anterior Abutments

When two anterior abutments are needed and the crest has a relatively long "waist" (1), the approach, as usual, depends upon the morphology. If the ridge's walls diverge above the narrow crest and have no severe undercuts, the crest can be reduced to 2.5 mm wide (2) to prepare the ridge for a single, double-posted blade-vent. However, attempts to accommodate an implant design should be subservient to morphological considerations. Only a minimal amount of bone should be removed. Reducing the alveolar ridge increases the proximity to anatomic landmarks (3).

The implant socket is centered in the reduced crest, and directed palatally if possible. Because of a double-posted blade-vent's length, the socket will curve around the dental arch.

77