Dimension discrimination at two different degrees of mouth opening and the effect of anaesthesia applied to the periodontal ligaments

Abstract

The dimension discrimination ability of twenty-five young persons was tested at two different degrees of mouth opening. One reference stick of 10-0 mm and another of 45-0 mm was placed between the teeth, alternating with test sticks of different heights. The subjects were asked to assess whether a test stick felt higher or lower than the reference stick. The experiment was performed with and without anaesthesia applied to the periodontal ligaments. Anaesthesia did not impair the discrimination ability. At dimensions in the region of the 10-0 mm stick the incorrect assessments occurred predominantly among sticks higher than the reference stick. Around the 45-0 mm stick incorrect assessments were distributed evenly between dimensions higher or lower than the reference stick.

The effect of maximal mouth opening on dimension discrimination

“…As can be seen the mistakes The dotted I'ne indicates the 10 mm reference stick. These results are from the previous experiment (Christensen & Morimoto, 1977) which did not involve maximal opening ofthe mouth before applying a test stick.…”

“…In this respect the test sticks which were lower than the reference stick were more accurately identified in the experiment cited (Christensen & Morimoto, 1977). Thus it appears when time is allowed for the polar regions to contract sufficiently on all occasions when contact is obtained between test stick and teeth, the muscle spindles will be tuned differently compared to the previous experiments.…”

“…The receptor (R) is assumed to lie in a purely elastic region of the intrafusal fibre and the response of the receptor is therefore directly proportional to the deformation in this region. Based on this model, the results from the previous experiments (Christensen & Morimoto, 1977) might be explained (Fig. 2) .When a subject bites the 10 mm reference stick, some activity will arise from gamma motor fibres in the closing muscles.…”

“…The length of the polar region is almost the same as in the case where the 10-5 mm stick is applied. This is caused by the fact that biting the 9-5 mm stick is also preceded by a slight opening of the mouth to allow the reference (Christensen & Morimoto, 1977) with the group of low sticks. The letters A, B and C indicate the varying lengths of the equatorial region.…”

“…Changes in the muscle spindle in the previous experiment(Christensen & Morimoto, 1977) with the group of high sticks. The letters A, B and C indicate the varying lengths of the equatorial region.…”