Accuracy and Control of Bilateral Jaw Clenching Force in People with Myogenic TMD
by Vesna Heins née Zikic
Date of Examination:2024-10-24
Date of issue:2024-10-18
Advisor:Prof. Dr. Frank Petzke
Referee:Prof. Dr. Frank Petzke
Referee:Prof. Dr. Philipp Franz Meyer-Marcotty
Persistent Address:
http://dx.doi.org/10.53846/goediss-10800
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Abstract
English
TMD is often of muscular origin but also often related to the displacement of the articular discus. Both can lead to limited mouth opening, which can cause severe pain and difficulties in eating and speaking and can lead to anxiety for the affected person. Since the cause of TMD is not yet fully known, the therapy remains symptom-oriented. Therefore, the investigation of the causes of myogenic TMD remains an important component. The aim of this work is to describe and compare masticatory muscle activation and the force profile during a jaw clenching task in a sample of healthy subjects and patients with myogenic TMD. The study participants had to fill out seven questionnaires in advance about their present pain in general and with regard to pain in the masticatory system. The presence of TMD had been confirmed using the RDC-TMD criteria. The control group had to be free of TMD in the two years prior to the study. All subjects had to be free of neck pain and dysfunction for at least six months prior to the study and to have not required treatment by a physician in that period of time. During the experiments, it was necessary to ensure maximal bite force without any sources of error. The subject was seated on a comfortable chair without head support, with the trunk in an erect posture and natural head position. Both sensors were located bilaterally in- between the premolar teeth. The force signal was digitally acquired on a PC and visualized on a screen to provide the subject with a visual feedback of exerted biting force and its laterality. Before starting the bilateral task, each subject had to perform three repetitions of maximal jaw clenching, each lasting 3 seconds, provided with a visual feedback of the used force, separated by 30 seconds of rest. This step had to be performed first unilaterally right and left and then bilaterally, while both sensors had to be kept in the mouth all the time. The maximum value observed over the three contractions was taken as the maximal voluntary contraction (MVC) and used as reference for the exercises for that individual subject. The subjects were familiarized with the visual feedback for the bilateral task: they were shown an x-y graph on the screen in front of them. In this graph an individually calculated four-sided rhombus shaped figure was shown, which was based on the average MVC unilateral right and left values and the average MVC bilateral values. A target point in this rhombus had to be reached by the subjects with a cursor. The cursor position was controlled by independently grading the force on the two sides of the jaw, in order to position the target. That means that if the subject was exerting more pressure on one side of the sensor, the cursor was moving to the corresponding side on the screen. The subjects had three target points to practice and afterwards twelve target points to reach one after the other. These twelve red targets were generated in random sequence. They were distributed within the three sectors of the rhombus (left, centre, right), each containing four targets, where each of the four targets was corresponding to a different level of force required to reach it, in relation to the MVC. The outcome measures are variables extracted from the force transducers. We evaluated the experimental results qualitatively and by a quantitative analysis. The aim of our exploratory analysis was to identify variables which have the potential to differentiate between healthy subjects and patients and/or to identify a difference between the healthy and the painful sides of a TMD patient. Further, we separately analyzed the static (time in target area, target distance (mean), target distance (std. dev.)) and dynamic contraction behavior (time to target, trajectory length and trajectory (std. dev.)). Further, the results were also differentiated by time and distance to the target point. For the quantitative analysis, we used the Wilcoxon Signed Ranks Test and the Mann-Whitney-U Test to investigate both within and between subject differences. As a first option, we considered the results for the different MVCs (17.25%, 23.3%, 35%, 70%) separately, such that we performed four separate tests for each hypothesis, one for each MVC. The results of the separate analysis of MVC values did not provide any conclusive results. We initially only performed this separate analysis, but due to small number of samples decided to also consider the joint analysis of all force levels. One advantage of this approach is that the number of samples was four times larger than for each of the individual tests, such that it becomes more likely to obtain statistically significant results. However, no significant results were observed for any of the hypotheses relating to the static contraction. For the dynamic contraction scenario, the measured variables appeared to have the potential to provide significant results in future studies. Following further observations regarding the dynamic scenario were made: The observed values for the variables time to target and trajectory length appear to be consistent with the expected behavior, which is that the test for the painful side will lead to higher values (P(2-tail) value of 0.0004). The observed values for the variable trajectory (std. dev.) seem to record a behavior which contradicts our expectation. The values for the painless side seem to be significantly higher than for the painful side. Further consideration is required to provide a potential explanation for this behavior. When comparing the not painful patient side to controls, the mean and the median value for the variables time to target and trajectory length are higher for the control group than for the patients. Here, the results for the variable trajectory length appear particularly relevant. Interestingly, the mean and median values for the variable trajectory (std. dev.) are higher for the patient group than for the controls. To conclude, based on the performed analysis, the effect of TMD on muscular control and function could not be shown conclusively in patients with myogenic TMD. In the area of static contraction, no results were found that could be followed up on the basis of the hypotheses defined above and selected variables for the tests. The dynamic contraction produced significant results which should be further investigated. Therefore, further research needs to be done. As a further limitation, the patients included in the study were only mildly affected (please compare Table 1-> VAS).
Keywords: Jaw clenching force; Myogenic TMD
