Influence of Tongue Movements on Masticatory Muscle Activity

Objectives: To test relationships between tongue movements and electromyographic activity (EMA) of suprahyoid muscles and clarify their influence on masticatory efficiency.
Methods: The subjects were 6 adults with a normal stomatognathic system. Experiment 1: Each subject performed six types of tongue movement: 1. extrusive, 2. right-and-left lateral, 3. upward, 4. downward, 5. touching the palate with the tongue tip, 6. touching the palatal aspects of the maxillary second molars, while EMAs were recorded with a wireless electrode-type system in the suprahyoid, digastric and masseter muscles. EMAs of tongue movements without mouth opening (2, 5, and 6) were compared with a resting EMA with the mouth closed, and EMAs with mouth opening (1, 3, and 4) were compared with resting EMAs with the mouth open. Experiment 2: Tongue movement was restricted with a device fitted into the floor of the mouth. Then compared were masticatory efficiency and EMA when tongue movements were (a) restricted, (b) not restricted, and (c) when free mastication was allowed without use of the tongue movement restriction. Masticatory efficiency was measured as by Manly RS et al.(1950).
Results: In Experiment 1, EMAs of all tongue movements were significantly higher than resting EMAs.In Experiment 2(a), masticatory efficiencies and EMAs were significantly lower than those of (c). Comparing (a) and (c), 3 test subjects in (a) had significantly longer masticatory cycles. Comparing (b) and (c), no significant difference was found in either masticatory efficiency or EMA. In (c), a significant positive correlation was found between masticatory efficiency and the EMA of the suprahyoid muscles.
Conclusions: The EMA of the suprahyoid muscles reflected the tongue movements and the EMAs of the suprahyoid muscles correlated with the masticatory efficiency in free mastication. This indicates that tongue movements significantly influence masticatory efficiency.