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plane. The deeper end is tapped first (18), with a finger on the shallow end's post to prevent it from popping up (19).

Caution: Special attention should be paid when tapping the shallower end to avoid knocking the implant into the canal.

Problem Ridge:

Unilateral Subperiosteal Implant

When less than seven mm. of bone separates the mandibular nerve from the alveolar crest, and a deep submandibular fossa exists preventing the utilization of an endosteal bladevent, either the unilateral or universal subperiosteal implant procedure can be introduced, depending upon how many remaining teeth are left in the arch and whether the arch is unilaterally posteriorly edentulous or bilaterally posteriorly edentulous.

If it is only unilaterally edentulous then a unilateral rather than a universal subperiosteal implant would be the choice if it is to be done at all. When edentulous areas appear in both posterior quadrants, it is preferable to fabricate a universal subperiosteal implant thus taking advantage of a full arch implant support which includes the symphysis and genial tubercles rather than not to include these areas thus contributing to increased overall retention of the implant.

The following technique is prescribed for the unilateral subperiosteal implant:

The anterior abutment teeth that are to be the anterior sup-ports of the fixed prosthesis should first be prepared (1). An incision is made from the retromolar pad area to the disto-proximal surface of the nearest anterior abutment tooth and should continue buccally and lingually along the gingival attachments of at least two of these anterior abutments and reflecting these tissues downward to expose clearly the neuro-vascular bundle of nerves exiting the mental foramen (2) , the external oblique ridge (3) , and should include some of the bone near the inferior border of the mandible anterior to the foramen, but above the most bulbous portion of the bone. Lingually, the tissue should be reflected further downward as it approaches the anterior tooth abutments and should be reflected below the mylohoid ridge, the depth being determined by the height of the ridge and the flare and extent of the lingual concavity (4). With a #558 fissure bur anywhere from

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