Causes of implant failure 617

A

B

C

D

E

Fig. 14-16. A to C, These radiographs reveal resorption of bone directly under the superficially placed shoulders of the blade implants. D to F, Implants that are not parallel to each other and to the remaining teeth can cause difficulty in seating the bridge. Also, and even more important, is that if they are not placed vertical to the occlusal forces, bone breakdown can occur as a result of unequal destruction of the forces that are brought to bear upon them.

Fig. 14-17. A Lew screw failing for several reasons: the implant was not set parallel to the remaining teeth, and since it was distally tipped, the forces brought to bear upon it caused the distal proximal surface of the bone to resorb. The trephining may have been made larger than the screw threads. The neck is not reduced.

dible where a truly three-dimensional triplant can be formed without perforating a cortical plate of bone. Therefore a great many pin implants must be placed in one plane, rather than in three or even two planes. As a result, many times the entire bridge with the pins attached can be easily removed (Fig. 14-20). A triplant placed in one plane is far less

Fig. 14-18. A posteroanterior x-ray illustrates a large periapical rarefaction underneath the right molar and the left posterior two spiral-shaft implants. Since an entire prosthesis was supported by only these three remaining abutments, resorption had to occur. There must always be enough abutments present, whether they are natural teeth or implants.