Causes of implant failure 619

Fig. 14-21. Another case clearly showing osteolysis around the two mesial pins that were not directed at different angles.

Fig. 14-22. A lateral plate roentgenogram and an intraoral periapical x-ray illustrate bone resorption in the areas where the pins are crossing over one another in the bone.

functional and resists lateral forces far less than does a three-dimensional triplant.

The deeper the triplant pins are set into bone and the more divergent they are, the greater the chance of success. The pins should diverge from one another, wherever possible, at least at a 45-degree angle. When they are too close to one another, bone resorption occurs (Fig. 14-21). Also, the pins should not cross one another in bone (Fig. 14-22).

To prevent bone loss at the crest of the alveolar ridge, the pins should converge at an angle that leaves a few millimeters of bone between each pin (Fig. 14-23). This is tricky, because the pins must also be close enough to one another so that a moderately sized acrylic core can be built to carry a normal tooth restoration. The solution in most cases is to angle the pins to leave enough space between them and to bend them together where they emerge into the oral cavity.

Improperly stabilized triplants. Triplant pins

Fig. 14-23. A, Immediate postoperative x-ray showing that two of the three pins are much too close to one another. B, In only 6 months' time a great deal of bone resorption is clearly evident.

A

B