are re-approximated. The measurements are included in the laboratory instructions.

A periodontal probe (14) is appropriate. The entire span that will lie under the bar should be measured; differences (15, 16) in soft tissue thickness are common.

It may be necessary to deglove excessively thick tissue (17) if constructing the bar and restoration to accommodate such tissues will open the bite.

Another method for getting the required measurements is deducing them from a soft tissue impression of the entire arch taken prior to surgery, together with a lower jaw impression and bite.

Upon examination, the maxillary bony landscape may appear to contraindicate using the pterygoid extension implant. The hamular notch may seem too shallow (18). It can be deepened (19) with a bur, using great care not to direct the bur toward the greater palatine vessels, which lie somewhat anteriorly on the palate.

In a great many cases, the anterior ridge is not a smooth mound with gently diverging walls, but a narrow ridge with a deep undercut or a concavity that makes it impossible to seat a rigid, one-piece implant without distorting the implant or injuring the bone. In such cases, the ridge may be notched in to accept the implant. Preferably this is done in the canine eminence area (20) which contains unusually thick bone for the maxillae and is also a prosthodontically advantageous site. Notching may be necessary uni- or bilaterally.

The bone is cut down to make a distinct "trough" between the labial and palatal portions of the ridge. The trough should be wide enough to accommodate the labial extension arising from the premaxillary portion of the implant. The walls of the notch may be smoothed (22) to reduce irritation to overlying tissues when replaced and to remove bony spurs that might easily chip away. Extensive remodeling is inadvisable. "Ramping" (23) unnecessarily removes bone that can help support soft tissue bulk, as does extensive remodeling of a crest that will not bear weight and thus needs no "protective" alveoplasty.

The recommended impression material is heavy-bodied silicone used without a tray and with a specially designed prototype. This prototype, the pterygoid extension prototype, is recommended for getting a truly accurate impression of the hamular notch-pterygoid process area. Manual packing alone rarely gives an accurate impression: the material is difficult to manipulate in the narrow crevice with its nearby interfering anatomic features and tight

117