The influence of mouth opening on the thickness discrimination ability

Objectives: Interdental thickness discrimination test might be considered as one of the sensory testing tools for investigating jaw function. However, little is known about the influences of tasks for the masticatory system on this test. The objective of this study was to examine the influence of mouth opening tasks on the thickness discrimination ability. Methods: Twenty healthy young adults participated in this study. Interdental thickness discrimination test was performed at maxillary and mandibular central incisors with 2- and 10-mm thickness standard blocks. The test blocks of which thickness were different (every 0.25 mm, ±1.5 mm maximum) from the corresponding standard block were applied after the application of the standard block, then subjects were asked to answer whether the test blocks were felt thicker or thinner than the standard block. The following 4 tasks were given before the application of test blocks: (1) no task (control), (2) maximum mouth opening in a moment (MO1), (3) maximum mouth opening for 5s (MO5), (4) physiologic rest position for 5s (RP5). The number of wrong answers was submitted to the data analysis. Results: There was a significant main effect in the number of wrong answers for the test blocks thicker than the 2-mm standard block among control, MO1 and MO5 (P<0.05, one way ANOVA). There were significantly more wrong answers in MO5 than in control or MO1 (P<0.05, Scheffe). There was a significant main effect for the test blocks thicker than the 2-mm standard block among control, MO5 and RP5 (P<0.05, one way ANOVA). There were significantly more wrong answers in MO5 than in control or RP5 (P<0.05, Scheffe). Conclusion: The results indicated that the continuous mouth opening decreased the thickness discrimination ability in healthy dentate individuals. Supported by a Grant-in-Aid for Scientific Research (#17592028) from the Japan Society for the Promotion of Science.