Modeling Stress Relaxation Behavior of the Periodontal Ligament During the Initial Phase of Orthodontic Treatment

Abstract

The periodontal ligament is the tissue that provides early tooth motion as a result of applied forces during orthodontic treatment: a forcedisplacement behavior characterized by an instantaneous displacement followed by a creep phase and a stress relaxation phase. Stress relaxation behavior is that which provides the longterm loading to and causes remodelling of the alveolar bone, which is responsible for the longterm permanent displacement of the tooth. In this study, the objective was to assess six viscoelastic models to predict stress relaxation behavior of rabbit periodontal ligament (PDL). Using rabbit stress relaxation data found in the literature, it was found that the modified superposition theory (MST) model best predicts the rabbit PDL behavior as compared to nonstraindependent and straindependent versions of the Burgers fourparameter and the fiveparameter viscoelastic models, as well as predictions by Schapery's viscoelastic model. Furthermore, it is established that using a quadratic form for MST strain dependency provides more stable solutions than the cubic form seen in previous studies.