The Force Requirements for Tooth Movement Part III: The Pressures 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^4,5 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 Storey¹ 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 occured in these experiments was 19 7 gf cm⁻².