Measurement of the short-term viscoelastic properties of the periodontal ligament using stress relaxation

The periodontal ligament (PDL) plays an important role in initiating tooth movement when loads are applied to teeth with orthodontic appliances. It is also the most accessible ligament in the human body as it can be directly manipulated (via the teeth) without surgical intervention. Findings are presented here from a prototype palpation device for making load-displacement measurements, intended ultimately for in vivo use on humans. Here, the device is applied in vitro to a number of pig-jaws to assess its ability to distinguish visco-elastic properties of the PDL. Four jaws were tested, each test consisting of the application of a series of step displacements to the second mandibular premolar, and allowing the stress to relax over a period of up to 35 seconds. The resulting stress relaxation curves are described by a three-parameter visco-elastic model with two elastic parameters and one viscous parameter. The values of these parameters are consistent between animals and between tests on a given animal, and are reasonably consistent with other authors. © 2009 Springer Berlin Heidelberg.