Dental Biomechanics
A tooth is secured to the alveolar bone by fibrous connective tissue that is called the periodontal ligament (PDL). The PDL not only strongly binds the tooth root to the supporting alveolar bone but also absorbs occlusal loads and distributes the resulting stress over the alveolar bone. The mechanical properties of the PDL are, therefore, essential parameters for understanding the mechanical behaviour of a tooth root and that of surrounding tissues. The
PDL also plays an important role in the mechanical adaptation of the dentition, based on alveolar bone remodelling induced by a change in mechanical stress or strain around a tooth root. This adaptability is important for the maintenance of optimal occlusion at a proper vertical dimension and is also utilised for orthodontic treatment in which an optimal orthodontic force is applied so as to induce maximum cellular activities, resulting in the most efficient tooth movement.
It is of fundamental importance in the field of dental biomechanics to know how a force is transferred to a tooth root and the surrounding tissues. Because of the difficulty in measuring physical parameters in this region, stress–strain distributions have usually been estimated by finite element analysis. In this analysis, material constants of a tooth and the surrounding tissues, including the PDL, are indispensable parameters. Although there is an abundance of information on the mechanical properties of teeth and alveolar bone, little is known about those of the PDL, due to difficulties in examining this thin tissue, which is only about 0.2 mm in thickness.
Theoretical and experimental approaches to investigating the mechanical properties of the PDL are discussed, and then measurements of the elastic properties of this thin tissue using a newly developed miniature testing machine are presented.
