Causes of implant failure 627

tubercles, and neurovascular bundles of nerves exiting the mental foramina. If these are not properly exposed for a good impression, there is an excellent chance that the implant framework will be inadequate.

Poor fit of the implant. The implant must fit its site exactly (Fig. 14-45). This can be ensured not only by taking an accurate impression over ex-posed bone but also by availing oneself of the best possible laboratory.

Improper incision of the soft tissues. The mucosal and submucosal tissues must be incised cleanly and accurately right down to the bone, and the tissue must be retracted without tearing it in order to re-duce postoperative edema. Tearing or mutilating

Fig. 14-44. Periapical radiograph reveals resorption underneath unilateral subperiosteal implant, since it was seated in an area where much alveolar bone still existed.

Fig. 14-45. A Panorex shows poor adaptation of the bilateral subperiosteal implants to the bone caused by a poor fit.

A

B

Fig. 14-46. A, Poor suturing. The sutures were made too far lingually, excessively stretching the buccal tissue. The knots also lie over the wound, irritating it and retarding healing. B, The sutures are too few, too irregular, and too far apart. Compare with Fig. 14-47, A and B.