The implant is properly seated when the bottom of its post rests on the alveolar crest (35) . It should resist being moved. Upon tapping the protruding post a sharp "thock" should be heard. A dull "thud" indicates a loose implant.

In summary, the better the ridge, the better the prognosis for a long-term, stable bladevent. Even in the best morphological situation, however, it is possible to make surgical errors because of over-confidence. Cautious surgery is essential in every situation, not just the most difficult.

The Double-Posted Bladevent

The double-posted bladevent provides two abutments in a single implant site. It is most commonly used in the anterior portion of the maxilla to provide unusually strong support when posterior implant sites are poor or limited.

A double-posted bladevent is inserted in much the same manner as is a single-posted bladevent. However, a double-posted blade is from one-half to two times longer than a typical single-posted design. Correspondingly, its socket is longer and usually curves to follow the arch.

To provide maximum contact with bone, the largest implant of a suitable design should be selected. Its placement depends for the most part upon the anterior extent of the sinus and its shape, and the size and lateral extent of the anterior palatine foramen.

When the bone is thick labio-palatally, often the groove can start labial to the anterior palatine foramen. Thus its posts will extend into the central incisor and cuspid regions. If the foramen is large or close to the ridge, the groove must keep away from the midline. The posts will then protrude into the lateral incisor and first bicuspid regions. The posterior extent of the socket must avoid the sinus (1). It may stop in front of the sinus, or — if the ridge is deep — extend under it (2) .

68