Reference charts for controlled extraoral force application to maxillary molars

Abstract

A lthough headgear appliances were originally designed by Norman William Kingsley in 1892, half a century elapsed before orthodontists began to employ extraoral force extensively. 1 Kloehn’$ results with the cervical neckstrap actually provided the impetus to preserve extraoral traction from near obliteration. Subsequently, a va-riety of methods have been developed to employ extraoral force in conjunction with almost every type of orthodontic appliance. Yet extraoral force is primarily used for two purposes: (1) to correct dental arch relationships and (2) as anchorage to support teeth that would be displaced while other movements are being carried out. The most commonly used extraoral devices are the neckstrap for cervical pull and headcaps for straight pull and for higher pull. Force delivery to the teeth is usually accomplished by means of a face-bow attached to an intraoral bow which is inserted into buccal tubes on the maxillary molar ba.nds or by direct attachment of the headgear arms to hooks on the maxillary arch wire itself. Extraoral traction has many advantages when used properly, but it may produce unfavorable tooth movements and treatment results when basic biomechanical principles governing the direction of the applied force are disregarded. The most common adverse effects are extrusion and tipping of molar teeth. Furthermore, Schudy3 stressed that molar elongation must be avoided in persons with retrognathic facial profiles since extrusion of posterior teeth tends to rotate the mandible dorsally, thereby aggravating their facial disfigurement. Poulton* warned particularly against the indiscriminate use of the cervical neckstrap because it harbors a considerable vertical force component. Kuhn5 considered the control of posterior tooth eruption a major factor in attempts to modify or maintain lower face height. Whatever the merits of these concepts and critiques may be, an understand-