262 Theories and techniques of oral implantology

burs, taps, and implants through a preconceived device is not advised.

Tips. When using the screw type implant there are a number of operative and surgical tips that help avoid mistakes and alleviate difficulties.

Angulation. Angulation based on visual interpretation and x-rays alone is often faulty (Fig. 7-7). Bidigital palpation of the soft tissues over both plates of bone and explorations with the injection needle are sometimes helpful in determining the choice location for the implant, but the most accurate method is incising and reflecting the soft tissue to expose the underlying bone.

Although it may seem unnecessary to employ a contra-angle instead of a straight handpiece, it is often almost impossible to correctly angle the drilling tools with a straight handpiece. This is particularly true when trying to insert implants in the anterior part of the maxilla (Fig. 7-8) . The mandibular teeth and/or chin are invariably in the way, and they force angulation in a palatal direction that al-most assures perforation. The boring axis must be midway between the external and internal faces of the jaw, along the so-called imaginary line of mean thickness of the osseous table (Fig. 7-9) . Only the contra-angle allows enough maneuverability, and teeth do not interfere with angling it.

Flattening knife-edge ridges. When a tall, narrow ridge of alveolar bone exists above the canal and a post type implant is desired, the knife-edged bone can and should be flattened. To do this an incision about 8 to 10 mm. long is made over the crest of the ridge and the bone exposed. The sharp edge is flattened with a heatless stone, and cool water is sprayed on it continually to avoid burning. After the implant has been set in this exposed and flattened bone, the site is sutured closed with black 000 silk, making sure to place a suture close to the neck on each side of the implant.

Drilling and boring. When using the contra-angle for drilling bone, the grip is different than when drilling teeth. To avoid an oblong atypical boring, which would create too large a site, the head of the contra-angle should be supported just over the bur with the forefinger (Fig. 7-10). This finger holds the head in place and guides it. The fingers of the other hand should play only a supporting role, holding the arm of the contra-angle very lightly. There should be no wrist action; all pressure should be created with the forefinger.

Sometimes the helical bur jams inside the bone. When this happens, the bur should be backed out,

the drill run at full speed, and the bone reentered.
As soon as the bur passes beyond the area of resist-
ance, the speed should be slowed down considerably.
Perforation. Perforation is more common during
maxillary implantations than during mandibular in-
terventions. Because perforations rarely occur on the
palatal side of the maxilla in the posterior areas, the

Fig. 7-10. Correct grip for the contra-angle.

Fig. 7-11. If there is danger of perforating the cortical plate, the tool may be backed out and reangled. Frequently this creates too large a site and another must be chosen.