hand on the drill can easily punch through the Schneiderian membrane lining of the sinus (9), creating an oro-antral fistula.

The socket is usually not drilled to its maximum depth. Its height is less than the blade measures from the leading edge to the bottom of its post.

The bur is angled palatally to leave more bone bulk buccally as resistance against lateral forces. Because the site is narrow and fragile, the implant socket should be made in as few steps as is possible, with fingers bracing the ridge.

Dealing with such a precarious situation, the operator is advised to take special precautionary steps. An estimate is made of how many millimeters the 700 XL bur can be sunk and avoid the sinus, including a millimeter or so of safety margin. The bur (10) is used to this depth, left in the bone by disengaging it from the contra-angle, and a periapical radiograph (11) is taken. This is compared with the pre-operative Panorex showing the sweep of the sinus floor. If the bur can be further inserted without too closely approaching the lowest point of the sinus, this is done. Then the bur is run along the ridge to create the socket in one sweep (12).

For additional safety, a rubber stop can be used to mark how far the bur can be sunk safely. This guide is particularly effective when sweeping along the crest to create the socket for a long blade. The position of the stop can be determined radiographically. The bur is placed over a radiograph, and a bit of rubber (13) — borrowed from an endodontic file — is slipped up the shank of the bur to the appropriate height. Or, the bur is sunk in the ridge, disengaged, radiographed for accuracy of position, and then — if suitably deep — the stop (14) put on with the bur still in the ridge.

A stop can be improvised by cutting a small length from a rubber band and slipping it over the bur.

Caution: The socket-making technique consisting of drilling a series of holes along the ridge and then connecting them is not recommended for shallow ridges under the sinus. Sinking the separate holes invites perforation of the sinus.

Because the socket is long, it may be curved. If so, the blade-vent must be bent to fit the socket passively, to slip into the groove without binding.

The posts are compared with the other abutment posts, and their occlusal angles estimated. The bladevent is withdrawn, and the posts bent approximately, taking care not to distort the curve bent into the blade's body.

108