Effect of cantilever length on stress transfer by implant-supported prostheses

Cantilever lengths for fixed implant supported prostheses have been based largely on empirical judgment. This study determined the effects of cantilever length on load transfer to the mandible. A photoelastic model of a moderately resorbed edentulous human mandible with five 13 mm Bränemark implants was constructed. Simulated occlusal loads at varying cantilever lengths were applied to the occlusal surface of a routinely fabricated fixed prosthesis. The highest stresses were located at the ridge crest on the distal surface of the distal implant for all cantilever lengths. Apical stresses at this implant developed in reciprocation to the effect of the distal tipping force on the cantilever. Curves describing the effect of cantilever length on maximal stress are presented. Little load transfer to adjacent implants was found. Disproportionate increases in maximum stress with increasing cantilever length occurred. Minor variations in implant angulation had a distinct effect on stress magnitude.