Biomechanical aspects of two different implant-prosthetic concepts for edentulous maxillae.

Two essentially different implant-prosthetic concepts are known for the treatment of edentulous maxillae. One concept propagates a "concentrated" arrangement of four to six implants in the premolar and anterior regions with a fixed cantilever superstructure. An alternative is a "spread-out" implant arrangement of six implants placed in the tuberosity, premolar, and anterior regions. The prosthetic rehabilitation consists of a fixed horseshoe-shaped bar and a removable prosthesis. A cantilever situation is avoided. The biomechanical aspects of these implant-prosthetic concepts were studied with clinical strain-gauge measurements and theoretical three-dimensional analysis using the finite element method. Results revealed that the distribution of bone stresses is more favorable with a spread-out implant arrangement than with a concentrated implant arrangement and cantilever restoration. The resistance to bending of a superstructure has an influence on bone stress concentration that should not be ignored. Stresses are controlled not only by the number or distribution of implants, but also by the material and design of the superstructure.