Alteration in directional specificity of interdental dimension discrimination with the degree of mouth opening.
The interdental dimension discrimination (IDD) ability was tested at seven different degrees of mouth opening: 40 mm, 30 mm, 20 mm and 10 mm openings for the dentate subjects, and 10 mm opening, intercuspal position (ICP) and the ICP minus 5 mm for the edentulous subjects. The subjects were asked to discriminate between pairs of sticks held alternately between the upper and lower incisors. The IDD ability, evaluated in terms of the 50% difference limen (DL), did not differ significantly between any two of the tests conducted at seven different openings, although the number of misjudgments of the dentate subjects tended to increase with the degree of mouth opening. On the other hand, the directional specificity of the IDD, which is a tendency to overestimate the dimension of the first stick of each pair, developed almost linearly with a decrease in the opening degree. These findings indicate that the behaviour of the receptors concerned varies with the intermaxillary distance. Some edentulous subjects could not perceive the presence of a small test stick at the overclosed position (ICP -5 mm), but vibration applied to the mandible enabled the subjects to detect the stick at the same opening. These results support the assumption that the muscle spindles of the jaw-closing muscles are the receptors responsible for the IDD.
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008410:Masticatory Muscles / Q000502:physiology; D008875:Middle Aged; D009055:Mouth / Q000502:physiology*; D009066:Mouth, Edentulous / Q000503:physiopathology; D014070:Tooth / Q000502:physiology*; D014110:Touch; D014716:Vertical Dimension