tooth in its shape and character, the more ideal will the ridge be. However, once the teeth no longer exist in an arch, the bone trabeculae inside the arch become thinner, less numerous, and the overall dimensions of the arch are diminished.

A totally ideal ridge in an edentulous arch, however, is rare after being with no teeth for a good number of years. The cause of tooth loss and the effects of disuse and misuse have had time to take their toll. To assume, however, that the entire ridge of a totally edentulous arch exhibits the same bone all around—and that implantation in a totally edentulous ridge is always difficult, would be a mistake. Even if all the teeth were lost at the same time the internal and external portions of the bony arch would develop in different ways due to natural and artificially induced wear patterns as well as from the various types of forces placed upon it. Therefore, a completely edentulous mandibular ridge usually has a varying range of implant potential usually with more than adequate bone in the anterior portion.

In the anterior portion of a partially edentulous mandible with limited tooth loss, as for example in a young adult whose remaining teeth are still present and well attended, a good ridge is not unusual. The edentulous area may be the site of a recent extraction, with the healed socket receiving some osteogenic stimulation from the neigh-boring teeth in good occlusion.

The problems of a totally edentulous ridge differ slightly from those of a partially edentulous arch, even if the actual implant site is in the same position in both.

The purpose of this volume, however, is to explain specific concepts in detail, the totally edentulous arch situations are first presented to illustrate generalizations about a specific area. Partially edentulous situations tend to be modifications or elaborations of the basic surgical concepts and, therefore, are covered as addenda.

The Single Posted Bladevent

In any implant procedure, a balanced support for a fixed pros-thesis is the goal.

Balanced support may be achieved in a totally edentulous arch by inserting four endosteal bladevents strategically around the arch. Ideally, the two posterior blades should have a double post and the two anterior blades a single abutment post. These posts

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