The patient is now guided into centric relationship (34) to take the bucco-labial impression. He or she is asked to press with

the tongue the impression material against the palatal surface of the ridge as the operator works on the bucco-labial surface.

Impression material is pressed against the buccal arm (35) of the prototype, and then in a backward and bucco-palatal direction, all excess impression material is pushed distal (36) to the tuberosity and into the hamular notch area. The tongue prevents material from flowing into the throat.

With the posterior area well packed and the prototype secured in the impression material, the operator then works gradually anteriorly, paying special attention to the area from canine eminence to canine eminence, up to the anterior nasal spine (37). He must be careful to press material into any irregularities and depressions in bone, particularly in those areas of the crest that he may have reduced to accept a strut.

This partial arch impression is allowed to harden, with the patient still biting in centric. With the impression secured in place (38), the patient is asked to open the mouth. With a scalpel, excess impression material that might interfere with the reclosure of the bite is removed. The buccal flange (39) of the impression material is cut away, as is excess material from the palatal side, particularly that extending toward the opposite tuberosity. Trimming excess impression material is imperative in making bilateral pterygoid impressions to enable the patient to rebite into centric relationship (40) without interference.

With the two-third impression trimmed and still in place, the bilateral pterygoid prototype is shaped and inserted. This prototype is also braced in place (41) and the operator repeats the process, packing the impression material first against the palatal portion of the arch, beginning posteriorly and advancing anteriorly until the material joins the previously inserted material in roughly the first bicuspid area. The patient is reguided into centric and the operator then packs the buccal surface (42) until it reaches the already set material (43).

The impression material is allowed to harden with the patient biting in centric. It is then trimmed and additional material added to establish proper bite relationships.

With the impression material still in the mouth, a plaster tray (44) is inserted. Plaster of Paris (45) is used to stabilize the impression material. This is particularly important when the impression material is thin in some areas. The laboratory instructions

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