Plasma Membrane Disruption in Orthodontic Tooth Movement

Abstract

(Introduction) One hundred years ago, in 1900, Dr. Edward H. Angle and a dozen colleagues came together to establish dentistry's first specialty, which is known today as orthodontics and dentofacial orthopedics. Orthodontics is a science and an art. It is the art o f creating healthy, beautiful smiles by moving teeth with precise, gradual force expertly applied, and the science concerned with the study o f the growth o f the craniofacial complex, the development o f occlusion and the treatment o f dentofacial abnormalities. Mechanical forces exerted on tooth roots and transmitted to the periodontal tissues initiate the remodeling activity that facilitates the movement o f teeth through bone. The specific changes in the bone surrounding the root o f an orthodontically moved tooth are characterized as resorption and deposition. Resorption o f bone is seen on the compression side o f the tooth. In contrast, bone is deposited in the tension side of the tooth that is being moved in the opposite direction. The biologic response to sustained force against the teeth is a function o f force magnitude; forces great enough to occlude blood vessels lead to pain, sterile necrosis and a process described as undermining resorption that inevitably leads to a delay in tooth movement. Lighter forces allow activation o f osteoclasts, and thus the removal of bone from the compression side by the painless process o ffrontal resorption. Clinicians face the challenge o f maintaining tissue vitality by avoiding undermining resorption, while applying forces heavy enough to produce frontal resorption. An understanding of the cellular and molecular mechanisms that enable bone to adapt to changes in its mechanical environment is important for solving the different challenges o f clinical orthodontics. Almost a century of research has been devoted to examining this phenomenon by morphologic methods. The histologic changes have consequently been well documented, but there are many unanswered questions that must be addressed in order to explain how mechanical deformation is transduced into a desirable biologic response. The aim o f the present investigation was to characterize a novel cellular mechanism for uptake and release of molecules important in bone remodeling by periodontal ligament cells. Specifically, the plasma membrane disruption theory was examined in light o f its role in mechanotransduction in orthodontic tooth movement. These are the first studies linking the placement o f mechanical loading, as occurs in orthodontic tooth movement, with plasma membrane disruption and resealing of periodontal ligament cells. The release o f bFGF and II-ip from the cells of the periodontal ligament was also examined following application o f in vivo strain.