extent of the sinus (53) so there is little danger of accidentally perforating the sinus. If the buccal tuberosity strut is accurately positioned, the cross-strut linking it to the palatal peripheral strut should automatically fall in the correct position — behind the most posterior extent of the sinus. Thus there is little danger of the cross-strut's accidentally fracturing the bone or perforating the sinus.

In the first pterygoid extension implants, the hamular notchpterygoid process portion of the implant gave rise to the modified-vertical bar to bear the restoration. This extreme position contra-indicated the implant for a significant number of patients by interfering with widely opening the mouth and/or obstructing the ascending ramus. Also, in some cases, it was necessary to situate the bar in loose tissues rather than the firm ones desirable for maximal reattachment of tissue to bone. By positioning the terminus for the bar more anteriorly on a cross-strut, most of these problems have been eliminated.

When the fabricated pterygoid extension implant is returned from the laboratory, it is examined for flaws. The commercial radiograph of the implant, included in the delivery from the laboratory, is checked for irregularities in the casting. The implant should fit the stone model exactly. If it is loose on the stone model, it will be loose in the mouth and should be remade. If an implant that exactly fits the stone model can be easily dislodged by light lateral pressure (54), either the implant has been poorly designed or the site was inadequate for this type of implant.

The height of the modified Andrews or Dolder bar should be checked for clearance of the soft tissues prior to insertion. If the pontics are too tall and might interfere with closure, they can be ground with a stone outside the mouth. With the sole exception of a bladevent immediately after insertion in good bone, no implant should be ground inside the mouth.

The implant is tried for fit in the patient's mouth by re-exposing the site. The implant (55) should simply snap on with manual pressure. It should not be pried on with an instrument, using the bone as a fulcrum. If the implant does not fit snugly at this point, the fault probably lies with the original impression. Another impression should be taken, and the implant redesigned.

If the ridge with a severe undercut was notched in one or both canine regions, the labial cross-strut may not closely fit be-cause of bone dieback and remodeling. These problems should re-solve as the bone heals, as long as the other portions of the implant fit correctly and stabilize the implant.

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