no ridge and nondental anatomic features may be threatened by implant procedures. Either situation — good or bad — requires versatility and ingenuity on the part of the operator.

Single-Tooth Bladevents

The single-tooth bladevent differs in design and, in many ways, use from all other bladevents. It was designed to fit into a one-tooth edentulous span. Because the proximity of neighboring teeth limits its horizontal dimension, the implant must gain its mechanical advantage by vertical extension in bone. In this way the single-tooth implant is more like a natural anterior tooth than it is any other type of bladevent design. Its unusual height — slightly longer than a central incisor — limits its use in the maxilla to areas in front of the sinus. Only here is the bone potentially deep enough to accept this tall design.

The single-tooth implant can be used when only one tooth in the entire arch is missing (1) or in one-tooth spans (2) in an arch with several missing teeth. The condition of the remaining teeth and of the bone, as well as the location of the tooth loss, determine how the implant will be used.

There are two basic, single-tooth implant situations. The first is to provide a base for a single-unit, fixed restoration that does not require sacrificing the crowns of neighboring teeth for its anchor-age. This use most closely approaches the dream of "replacing a tooth with a tooth," a misleading ambition for several reasons extensively explained elsewhere.

The other use is to share and balance occlusal stresses on a multi-unit fixed prosthesis with other abutments. Because dental disease leading to tooth loss usually affects more than one tooth, this latter use is by far the more common.

The criteria for both uses differ slightly, but both require that existing periodontal conditions around neighboring teeth be cured or stabilized before implantation.

When a single-unit fixed restoration is desired, the teeth bordering the span must be healthy and firmly supported by bone (3). These teeth will be included with some form of stabilizing device for the implant, such as lateral extensions (4) from the single crown or splinting. (If the teeth have poor bone support (5), implantation is not necessarily contraindicated, but the single-unit fixed restoration is. The implant can be used to stabilize the loose teeth by providing more support in a multi-unit fixed bridge (6) .

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