A biomechanical study of the human periodontal ligament.

The mechanical properties of the normal human periodontal ligament (PDL) were investigated at eight different root levels. One millimetre transverse sections of teeth, PDL and alveolar bone of mandibular premolars were examined in a materials testing machine. During testing bone was supported by metal rings and teeth by metal cylinders of individually adjusted sizes. Having corrected for differences of size and width of the PDL the influence of root level was estimated using a multivariate analysis of variance. The shear strength was almost constant at the upper part of the root, diminishing in apical direction. The shear extensibility and the relative failure energy in shear were higher at the middle of the root, diminishing coronally and apically. Only the elastic stiffness did not vary significantly along the root. These results demonstrate that in order to compare the mechanical properties of PDL care should be taken to compare areas at the same root level.