in which the blood vessels and nerves lie. These vessels are encased in loose, connective tissue (14) which does not firmly re-attach to bone. Another reason for not invading this site is that the bulk of the struts might impede circulation.

Bucally/labially, the closer the resorbed ridge approaches the vestibular fornix (15), the greater the chances of placing a strut under loose areolar tissue. Therefore, choosing a buccal (or labial) area with some ridge height is essential to obtain a tall enough band of dense, connective tissue to overlap the superior strut(s).

Until recently, the inability to provide secure posterior anchor-age with implants also severely limited anterior implant potential in a totally edentulous upper arch. Ideally, abutments should pro-vide strong support balanced antero-posteriorly and laterally. Many totally edentulous cases have been contraindicated for a fixed pros-thesis because of the posterior situation, and partially edentulous arches have been relegated to more conventional restorative procedures that often threaten the stability of the remaining teeth or that require the extraction of these teeth for the convenience of a full, upper, removable denture.

The maxillae do contain the hard compact bone ideal for seating a subperiosteal implant. The palatal surface of the dental arch is hard and compact, as is the labial surface from canine region up to the anterior nasal spine. The premaxillary region of the hard palate is not only hard, but thick. However, it was not the lack of suitable bone anteriorly that fooled implantologists, but the scarcity of it posteriorly.

Suitable hard, compact bone is available posteriorly in the tuberosity region (16) where the sinus has not invaginated, and in the hamular notch area (17) . Utilizing this latter area was neglected until the author began bracing the most posterior portion of a modified subperiosteal implant in the hamular notch, against the pterygoid process (18) of the sphenoid bone. Using this area has successfully provided the potential for stable posterior abutments in totally and in unilateral and bilateral partially edentulous situations. The secure posterior locale has given the implant its name, the pterygoid extension implant — a name currently applied to a subperiosteal implant whose posterior is braced against the pterygoid process of the sphenoid bone. Such anchorage currently has a widening number of applications for the totally edentulous and partially edentulous upper arch.

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