The force requirements for tooth movement. Part III: The pressure hypothesis tested.

Many experiments have investigated the force requirements for tooth movement; the diverse results so obtained have lead to controversy and resulted in an incomplete understanding of the true nature of tooth movement. This study analyses the results of two experiments which investigated the relation between the force applied and the rate of tooth movement from the standpoint of the pressures exerted by the tooth root on the surrounding tooth-periodontal membrane complex. The pressure hypothesis suggested by Smith and Storey is tested using the estimated projected area of the teeth moved in the experiments as a means of calculating the estimated pressures resulting from the application of orthodontic forces. The average pressure at which optimal rates of tooth movement occurred in these experiments was 197 gf cm-2.