[Immediate and delayed effects of working interferences on human mastication].

Abstract

The purpose of the present study was to observe the effects of working interferences on masticatory movements. Metal overlays were inserted on buccal cusps of upper 2nd premolar and 1st molar of healthy human subjects. Jaw movements were recorded by using the LED system at five sessions: before application (Wo), immediately after (W1), and one day (W2), one week (W3), and one month (W4) after application. It was found that (1) TMJ disorder or MPDS was not found in 10 subjects. (2) Six of the 10 subjects had extended border area after overlay insertion, and 4 subjects had restricted border area. (3) The mean closing angle at Wo was 41.2 +/- 13.3 degrees while at session W1 it was 28.1 +/- 14.7 degrees. The difference was significant (P less than 0.05). At sessions W2, W3 & W4 this angle was around 30 degrees. (4) The axis of the chewing cycle on frontal plane became more medially oriented at sessions W1, W2, W3, and W4. (5) Two distinctive types of chewing cycle were seen in few subjects at session W1. The first type had more vertical displacement with a twisted or deflected closing path. The second type occurred after about ten strokes of chewing, and the axis became more medially or vertically oriented. The vertical displacement was shorter and the horizontal displacement was relatively wider. (6) Ninety % of all subjects showed increased opening velocity and decreased closing velocity at session W1. The opening velocity and closing velocity increased consistently at sessions thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)