taking the impression. To protect the bladevent sockets, a rubber dam material or wax can be used to prevent impression material from clogging the socket over the buried bladevent. Impression material must not be left in the tissues; it is highly irritating, retards healing, and causes bone destruction.

The impression technique is a split-impression technique similar to that used for the one-piece pterygoid. The prototype (9) is braced (10) in the hamular notch area, and the impression material is worked postero-anteriorly, first on the palatal surface (11), then the bucco-labial. Special attention is paid to the premaxillary area (12) behind the bladevents' posts and the labial bone over the bladevents and flanking (13) them a short distance on each side. The material is checked to see if it completely covers the arch and bladevent copings. The unilateral impression is then trimmed, and the process repeated bilaterally until both bladevent abutments (14) and both prototypes (15) are included in the impression. The impression may be picked up in plaster of Paris if it threatens to distort during removal. The impression will include the copings (16) and the prototypes (17) .

A stone model is cast from the impression, and the implantologist designs the implant. Die pins (18) are inserted into the plastic copings in the model to represent the bladevents. The subperiosteal portions obey the same dictates as those for the single-unit pterygoid extension. Posteriorly, a strut angles up onto the buccal face (19) of the tuberosity, distal to the sinus! This strut is continuous with a segment passing behind the tuberosity in the hamular notch (20) and onto the palatal surface of the ridge. This piece continues forward on the hard palatal residual ridge (21) to the premaxillary portion (22), a fenestrated or open plate. The labial extension of this plate passes up over the ridge, incorporates the bladevent (die pin) (18), and continues high on the labial surface of the arch

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