Patterns of change in human mandibular arch width during jaw excursions

Abstract

The purpose of this investigation was (1) to design a device that could record the dynamics of mandibular arch width change, and (2) to record the patterns of change associated with various movements of the mandible in man. A strip of beryllium copper, 6.5 mm wide and 0.21 mm thick was shaped to form a vertical arch, and two type A-18 strain gauges were cemented to it above and below the greatest curvature of the arch. The instrument was placed between the jaws of a micrometer caliper and coupled to a polygraph for calibration and testing. The magnitude of mandibular arch width changes could be calculated as mm polygraphic pen deflection × 0.028 (calibration factor) ±0.034. Compensation was determined for effects of temperature changes upon the apparatus and the reproducibility of instruments. The device was then used on 25 male dentists and dental students to record changes in arch width. The apparatus was affixed to right and left manibular first molars and coupled to a polygraph while the subject was instructed to perform various mandibular movements. Protraction, opening and lateral movements from rest position produced a decrease in arch width, protraction causing the greatest decrease and wide opening the second greatest. Maximum decrease was not maintained when the fully protracted or open positions were held for 6–10 sec. Force applied to the jaw to resist closure caused a decrease in arch width. Retraction caused an increase.