A new concept: Impulse in orthodontics

One of the important uses of extraoral appliances is to counterbalance force systems placed on the reactive, anchor teeth by intraoral appliances such as space closure springs. Extraoral appliances are often worn less than full time, whereas intraoral springs act full time. Anecdotal evidence indicates that sufficient part-time extraoral appliance wear with appropriate force level is sufficient to balance intraoral appliance activity while preserving anchorage. A rational explanation is presented to substantiate this clinical evidence through equating extraoral impulse (force x time and/or moment x time) to the impulse conveyed to the teeth by intraoral appliance. By adjusting force and/or moment magnitude in combination with the correct time of application, the clinician can achieve appropriate energy levels for anchorage in three dimensions.