11 13    13

Although a few designs fit the site, the open-socket bladevent offers several advantages. The recessed shoulder (7) allows a significant amount of bone to regrow as a shelf (8) over the central part of the implant (9), locking the implant securely in its site. This bonus feature often makes the open-socket design desirable in many situations other than a true open-socket situation. Post-operatively, bone always resorbs away from the crest as it heals, even if only slightly in the most successful implant situations. The bony shelf keeps a good protective barrier in front of the incisive shelf.

The open-socket blade's double posts also fall on each side of the midline under the central incisors. This is desirable in constructing a natural-looking prosthesis. It also gives more balanced, as well as additional, support than would a single-posted design.

When crossing the midline in a ridge with a nearby incisive canal, the implant socket is not directed palatally (10) , as is usually recommended in other situations. This more labial inclination (11) is insurance against penetrating the incisive canal. The differences in bone density will be noticed while working the bur disto-mesially. As the bur approaches the midline, it will pass from trabecular bone through dense bone and back into trabecular bone. Excessively dense bone may require using more than one fresh 700 XL bur.

The socket must follow the arch, which necessitates curving it in the majority of cases. Occasionally, the ridge may have under-gone extensive resorption which has flattened the sweep of the arch. In such cases the incisive foramen (12) is probably close to the ridge. Extra care must be taken to avoid fracturing or penetrating the labial plate, particularly at the ends of the socket (13), as the bur is working unusually close to the labial plate in order to avoid the foramen. A finger (14) on the ridge to sense the bur's location is helpful.

The bladevent itself must be curved to follow the groove, and be passively insertable. The posts must be parallel with the natural abutments to be included in the prosthesis.

Because of the unusual angulation of the implant socket toward the labial plate, a supporting finger (15) is mandatory during tapping. Care must be taken not to let the denser bone in the center of the implant act as a fulcrum for see-sawing the implant as it is tapped to the proper depth. The double-headed inserting instrument usually prevents this. If the single-headed (16) or

94