Dealing With a "Pinched Waist"

In some cases, the ridge may have a definite pinched area, or "waist." This feature may be labio-lingually centered in the ridge (1), or, more typically, offset lingually (2) . The width of the waist and the shape of the bone above the crest and mesial and distal to the waist determine the implant approach.

If the waist is less than 2.5 mm wide (3) and the deeper bone remains narrow (4) or is undercut (5), the ridge must be treated as two separate sites. No single bladevent can span the waist.

If the waist is at least 2.5 mm wide and there are no severe undercuts, the site is treated as a narrow ridge site. The guiding dimension is the width of the narrowest portion (6). The groove is centered in this, with the bur directed slightly lingually (7). The length of the groove—and of the bladevent—depends on the character of the mesial and distal portions of the ridge (8). Undercuts (9) or converging walls (10) may require using a mesio-distally shorter implant (11) .

If the pinched waist is narrower than 2.5 mm, and a single implant site is desirable, it may be possible to reduce the waist (12) until the ridge is wide enough.

A double-posted bladevent is preferable for narrow-waist situations. A double-posted design places the abutments in stronger bone (13) 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" (14) . Another advantage is provided by using the open-socket bladevent (15). Its recessed shoulder, falling in the narrowest area, (16) will allow the re-growth 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 (17) to duplicate the depth of the bladevent, Base to Shoulder, being extremely conscious of landmark areas

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