cally, the bone is fragile and offers little resistance. A heavy hand

on the drill can easily punch through the superior wall of the canal

(10), creating an almost positive paresthesia. It is advisable to

radiograph the bur before it reaches its final depth in these situations (11).

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 groove made more lingually 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 canal, including a millimeter or so of safety margin. The bur (12) is used to this depth, left in the bone by disengaging it from the contra-angle, and a periapical radiograph (13) is taken. This is compared with the pre-operative panorex showing the extent of the mandibular canal. If the bur can be further inserted without too closely approaching the highest point of the canal, this is done. Then the bur is run along the ridge to create the socket in one sweep (14) .

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 depth of the bur in the groove can be determined radiographically. An intra-oral radiograph is taken of the bur with a metal "0" ring (15) slipped up the shank of the bur to the appropriate height. Or, the bur is sunk in the ridge, disengaged from contra-angle and radiographed for accuracy of position, with the metal stop (16) on the bur still in the ridge and a periapical film is taken.

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 above the canal. Sinking the separate holes invites perforation of the canal or the labial plate.

Because the socket is long, it may be curved. If so, the bladevent must be bent to fit the socket passively, to slip into the groove with-out binding.

The posts are compared with the other abutment posts, and their

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