[The effect of physiological tooth mobility on the friction between the bracket and the arch]

This study compared frictional forces which occurred in vivo and in vitro. A testing device was used which allowed reproduction of friction measurements carried out on upper central incisors of volunteers under laboratory conditions with the bracket fixed immovable. By this means changes of friction due to physiological tooth mobility and occlusal load of the bonded teeth could be investigated. While the friction measured in vitro with immovable brackets and in vivo without occlusal load did not differ significantly, additional tooth movement by occlusal load resulted in significant reduction of friction magnitude. It should be kept in mind that the mobility of those teeth investigated was absolutely normal, while it is usually increased during orthodontic treatment. Due to this effect and influences resulting from chewing various kinds of food, it can be estimated that the frictional forces occurring with orthodontic treatment are even smaller in comparison to in vitro experiments with immovable brackets.