(4). If the site is prosthodontically desirable and not too narrow, the implant groove should be centered in the narrower area (5) and directed miso-distally into the wider area, treating the situation as a narrow ridge implantation.

An atypical design—the open-socket bladevent—is appropriate. The open-socket blade is inserted as is any other bladevent. The groove must follow the dental arch, and bisect the ridge at its narrowest point. The recessed shoulder (6) must be set beneath the dip in the ridge, firmly in bone. The design is double-posted, so that occlusal forces will be directed into the stronger bone on either side of the defect.

The posts must be bent (7) to the correct angle, and touch the crest on all faces. This usually means that countersinking (8) is necessary.

A double-headed seating instrument can be used to seat an open-socket bladevent in a slightly inclined socket (9) . Or, if the socket has an exaggerated curve, a single-headed instrument can be rotated from post to post to gradually sink the implant. If the posts have been acutely bent away from the socket's inclination, the pointed seating instrument (10) may be used.

Sometimes a very rugged outline remains. This type of ridge may also be complicated by narrowness and undercuts. Small bony spurs (11) should be removed with a bur or rongeurs. The spurs tend to chip off or irritate replaced wounded soft tissues. An angular shelf or bone (12) should be reduced if it forms a narrow prominence (13) in or near the implant site. Such a fragile projection cannot be used as an implant site, and tends to fracture or otherwise interfere with implant insertion.

When only one abutment post is needed in the anterior mandibular area, any of several bladevent designs can be angled into the remaining bone. The chosen design is inserted according to the

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