Instrument for determining and equalizing forces applied to individual teeth by alignment arches and otherwise

Abstract

T E application of force in orthodontic treatment has always been more or less haphazard, and limit ed chiefly by the fortitude of the patient. Since studies have been made by several researchers with a view to determining what takes place in the supporting tissues during tooth movement, it has become evident that orthodonti c procedures should be placed upon a more rational basis and the forces applied should be limited to what those students have indicated is the range of biologic tolerance. Among the first to attempt to measure the amount of force to be applied to a tooth, so far as I have been able to discover , was J oseph E . J ohnson, who made use of a modified postal scale for measuring the pressure requi red to bring an alignment wire into the bracket of a band on the tooth to be moved. Another tension tester was introduced by J . E. Robinson ; this consisted of a simple cylindr ical spr ing scale, one end of which could be used to measure the push tension, and the other the pull tension on a wire . This device was adapted for use not only on labial align ment wires, but also on th e auxilia ry spr ings of a lingual or palatal appliance. Neither of these devices could be depended upon to give reliable information where more than one toot h was to be attached, because with the at tachment of each succeeding tooth , those first att ached would have th eir tension increased owing to the decreased distan ce between th e fixed points (anchor teeth ) and the points of attachment of each additional tooth included. The instrument under consideration here is designed to provide a means by which one may measure th e tension to be applied to every tooth in malposition, equalizing it so that every tooth may be subjected to a similar and known amount of stress, regardless of whether it be push or pull, elevat ion, depression, torsion, or the power to be obtained from torque in the wir e. A brief descri ption of the instrument and th e mode of operat ion follows. Upon a base consist ing of a flat metal plat e (F ig. 1) is arranged a ser ies of threaded holes (a) in the genera l form of an arch, in to which are screwed split stubbs (b b b) which suppor t swivels (c) which telescope them and may be raised or lowered. These swivels carry friction rings (d) through which are passed the cylinders of the tubular spring scales, the sliding rods of which are provided with a prong at one end and a hook at the other.