they can be "unscrewed" by hand may be immediately replaced by an open-socket bladevent. There is usually enough bone under the nasal vestibulum to bury the bladevent correctly.

In addition to its original purpose, the open-socket bladevent has come to have even wider applications. A ridge may be very uneven (3), with sharp walls. The open-socket bladevent is appropriate for this situation. The sharp walls (4) may be retained to avoid countersinking the implant posts, although in many cases the sharp angles taper to less than 2.5 mm and must be remodeled.

When used in an even ridge with no dips or open sockets, the recessed shoulder allows a tall shelf of bone (5) to regrow over it. The bony shelf is a bonus against tongue thrusts and other forces tending to cause lateral displacement.

Because the open-socket bladevent is a deep-bodied design, its use is limited in the maxilla to anterior situations. Because there is more implantation potential for this particular design in mandibular open-socket situations, it will be extensively covered in that volume.

Midline Implant

The midline has a few inherent characteristics that make it a less desirable or difficult implant site. The bone of the ridge progresses from the relatively cancellous alveoli of the incisors (1) to the hard, compact bone that forms the juncture — the midline (2) — of the opposing maxillae.

Usually the ridge is sufficiently wide and tall at the midline to accept a bladevent. The primary morphological problem is the incisive, or anterior palatine, foramen.

The incisive foramen lies along the midline (3) , and is closely associated with the alveolar ridge. Its distance from the crest varies from person to person and alters as the ridge resorbs (4). If the foramen lies close to (5) or within the ridge (6) , it may be difficult or impossible to avoid during the socket-making procedures. The site should then be contraindicated. When contemplating crossing the midline with an implant, careful anterior peri-apical radio-graphic studies are essential, as well as full exposure of the bony ridge.

Sometimes artificial abutments are desirable in the midline area. Perhaps the bone in more distal, and prosthodontically desirable, sites is pinched or flawed. Or, only incisors are missing and the remaining teeth would benefit from some form of artificial anterior support.

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