The effect of muscle function in discriminating thickness differences interocclusally and the duration of the perceptive memory

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Abstract
The thresholds in discriminating the thickness differences interocclusally were measured with three different mouth openings on subjects having natural dentitions. Also the duration of the perceptive memory was studied. The results showed that the functional activation or fatiguing of masticatory muscles and the degree of mouth opening affect size discrimination interocclusally. The ability to perceive thickness differences between the incisors was more accurate after 1 hour's chewing than normally. The trend was significant with 0.5 mm and 10 mm mouth openings (2P < 0.01) and highly significant with an 20 mm mouth opening (2 P < 0.001). With a 20 mm mouth opening (2 P < 0.01) and 10 mm mouth opening (2 P < 0.05) size discrimination was less accurate after two hours' fatiguing chewing than after one hour's conventional chewing. After 30 seconds' forceful isometric contraction and with a 20 mm mouth opening discrimination was more accurate than normally (2 P < 0.01). The trend was the same with a 10 mm mouth opening, but no difference could be observed when the mouth opening was 0.5 mm. The memory tests showed that with a 0.5 mm mouth opening thickness differences of 0.3–0.5 mm were most commonly correctly perceived twenty-four hours later, but when the mouth openings were 10 and 20 mm an interval of only 1 min between the reference and test piece trial impaired the performance.