Electromyographic, ultrasonographic and bite force evaluation in children with TMD

Objective: To analyze the electromyographic activity and muscle thickness of masseter and temporal muscles, as well as the maximum molar bite force in children with TMD. Methods: Nine three individuals aged 7-11 years-old were evaluated. Based on the Helkimo's Clinical Dysfunction Index, 45 children were assigned to 4 groups (G1- control, G2- mild TMD, G3- moderate TMD, G4- severe TMD). Electromyographic records were performed during rest and activity. Muscle thickness was analyzed by the SonoSite Titan Nationalized ultrasonography equipment. Bite force was obtained by a dynamometer IDDK model, with a capacity of 100 Kgf. Standardized electromyographic data, ultrasound findings and bite force results were analyzed by ANOVA followed by t- test to determine differences in bite force between right and left sides (p<0.05). Results: Electromyographic activity in children with symptoms of TMD was lower than in children without symptoms of this dysfunction. In clinical conditions of resting and right and left laterality there was a statistically significant difference (p<0.05) among the groups, for the left temporal muscle, and maximum habitual intercuspation for the left masseter and temporal muscles. The muscle thickness evaluation showed no significant differences among the groups. Maximum molar bite force was higher in the groups with mild and moderate TMD, and lower in the group with severe TMD. Maximum molar bite force on the left side was different (p<0.05) among the groups, yet no significant difference was observed between sides. Conclusion: The severity of symptoms of TMD was reflected in the electromyographic activity but it did not generate structural changes in the masticatory muscles. In the initial phases of TMD, individuals had a relatively stronger bite force than normal subjects during mastication and there was a decrease in the magnitude of this force secondary to painful symptoms in more severe cases.