those suitable for use in both arches. However, no matter which bladevent is selected, it must be inserted according to rules applying to all bladevents. These rules are essential to the bladevent's stability and, therefore, its success as an artificial abutment. If these rules cannot be followed exactly because of morphological or surgical limitations, the site is contraindicated for a bladevent.

1. The bladevent is correctly seated in bone when all faces of the bottom of its post touch the crest. Except in very fragile bone cases, this requires drilling the socket at least as deep as the bladevent measures from its leading edge to the bottom of its post.

2. The bladevent must wedge in its socket firmly from the moment of its insertion. The groove, or socket, must be made as narrow as is possible bucco-lingually, preferably no wider than the diameter of the 700 XL bur.

3. The groove must be at least as long — preferably slightly longer — than the mesio-distal length of the bladevent to avoid resistance from uncut bone on either end of the socket.

4. If the groove has been curved to follow the arch, the bladevent must be bent to fit passively into it. Strongly forcing a bladevent into its socket can spread the bone beyond its physiological capacity.

5. The post of the bladevent must be parallel to the other abutments. In many cases, this means bending the neck of the post — outside the mouth — to the correct angle prior to final seating.

6. The bladevent must be buried to the appropriate depth by tap-ping it home. The tapping force should be directed along the axis of the socket, not toward the buccal or labial plate.

7. If the bladevent cannot be seated to its proper depth without hammering, it is removed and the socket checked for depth or interfering bone prominences.

Great care should be exercised during all phases of the intervention to avoid excessive damaging of the bone. The burs should be changed frequently and water used copiously as a coolant to avoid overheating the bone.

The Subperiosteal Implant

Designing a subperiosteal implant — one which sits on dense cortical bone rather than in cancellous alveolar bone — is more difficult in the maxillary arch than in the mandibular. The primary reason for this, of course, is morphology. The maxillary subperiosteal implant must meet the same basic criteria as the mandibular

58