January 30, 2013
Dentists have long known that orthodontia can straighten misaligned teeth. What they have lacked are the needed scientific tools to define the natural interplay between the mechanical force that moves a tooth and the biological response that makes the realignment permanent. These tools will allow them to learn to better model the process and ultimately provide better orthodontic care.
The problem on the mechanical side is teeth, like a good man, don’t stand alone. They derive support from two helpmates: the bone in which they are embedded and their tether-like periodontal ligaments. For researchers, measuring this three-part, force-absorbing system while it is rooted and functional in the mouth has been a technological non-starter. Neither have they succeeded in developing a mechanically accurate model of the tooth-periodontal ligament-bone complex to simulate in the laboratory their sliding, force-absorbing properties.
That is, until now. A team of NIDCR grantees reports in the journal Angle Orthodontist it has developed a viable artificial tooth-periodontal ligament-bone complex, or ATPBC. The complex consists of a socket that hosts the artificial tooth and a 0.3 millimeter two-silicone mixture in between to mimic the natural viscoelasticity of the periodontal ligament. To validate their design, the researchers attached the ATPBC to a customized, in-house device that applies a controlled, predetermined force directly to the crown of the artificial tooth and then measures its displacement. The device also allowed the scientists to evaluate additional mechanical behaviors involving tooth realignment, including immediate stress relaxation after displacement, creep (displacement stress relaxation over time), and hysteresis (displacement changes when loading and unloading the crown). Based on these tests and existing biology-based studies as a guide, the scientists determined that the ATPBC simulated well the biomechanics of an actual tooth, bone, periodontal ligament.
“The results demonstrate that the ATPBC preserves the general biological viscoelastic behavior and produces similar crown load-displacement relationship shown in human,” the authors concluded. “This behavior is critical when the load system of sliding mechanics is measured. Thus, it can be used to quantify the load system of a sliding mechanics. However, the behavior is equivalent to a biological TPBC only from the perspective of crown displacement.”
- Xia Z, Chen J. Biomechanical validation of an artificial tooth-periodontal ligament-bone complex for in vitro orthodontic load measurement, Angle Orthod 2012 Sep 12 [Epub ahead of print]