Caution: Whereas a shallow groove may be preferable in a wide fragile ridge, a completely drilled groove is essential in a narrow situation. The deep socket gives greater control over final seating of the implant, and prevents overspreading or fracturing the ridge.

When bending the blade to follow the groove, avoid tipping the implant into and out of the socket to see if it "fits." Bending may fracture the crest, and it may not be possible to deepen the socket below the fracture.

If fingers obscure the view of the operative site, use a carrying instrument (22) to compare the blade to its groove.

The correctly bent blade is inserted, and the angle of its post checked with those of other abutments. If it is not parallel it is removed, and pliers are used to bend the neck of its post to the correct angle. Again, try to establish the correct angle the first time out of the mouth. Avoid replacing and removing the blade. A slip in the angle of insertion or retraction is hazardous in a knife-edge ridge.

The prepared socket is checked for obstructions and gently cleaned. The implant is replaced and ready to be tapped home.

Final seating is cautiously executed in a narrow ridge situation. Even with fingers bracing the bone, off-center or unbalanced tap-ping can break the thin fragile wall of the socket. The pointed (shoulder-set) seating instrument is inadvisable for the first few taps because it can slip easily and chip the ridge. Therefore, an atypical procedure is followed—bending the post is delayed. The single-headed seating instrument is used on the unbent post to tap the implant almost completely to its proper depth. Then the implant is removed, its neck bent, and the implant is replaced. It is now seated deeper and is firmly held by bone. Thus secured, the shoulder-set point instrument (23) can be used to tap the implant home.

Both faces of the knife-edge ridge are supported by the fingers as the bladevent is tapped home. The plates will spread slightly as the bladevent is inserted, making the ridge wider than it was prior to implant insertion. Evidence so far indicates that the slight spreading does not exceed the physiological limits of bone. To the contrary, the spreading appears to stimulate more rapid bone re-growth.

In the incisor areas particularly the labial plate of bone (24) may have almost entirely resorbed due to over-retained periodontally involved teeth (25). Consequently, when the teeth are lost,

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