Impaired tongue motor control after temporomandibular disorder: A proof-of-concept case-control study of tongue print

Abstract

Background: Temporomandibular disorder (TMD) perturbs the tongue motor control and consequently impairs oral function, but strength training reduces this impairment. However, tongue motor control is widely reduced to a matter of strength.

Objectives: To investigate the accuracy of the tongue placement as a measure of tongue motor control in patients with TMD compared with age- and sex-matched healthy participants.

Material and methods: This proof-of-concept case-control study was prospective, observational, and part of the TMIQ study (NCT04102306). After pointing against a wood stick while maintaining the tongue as sharp as possible, the examinator drew the contour of the tongue print on the wood stick, which was then scanned for image analyses to compute the area for each participant using ImageJ.

Results: A total of 94 participants were included, all patients with TMD (n = 47) diagnosed with myalgia, 61% with intra-articular joint disorder accordingly to the DC/TMD. The median (IQR) tongue print area was 117 (111) mm² for the TMD group and 93.5 (76.2) mm² for the control group (V = 352, p = .04) and the median [95% confidence interval] difference was 25.4 [1.3; 51.0] mm². Overlapping of the 95% confidence intervals of the area evidenced no significant difference between the categories of the DC/TMD. The corrected each area-total correlation (r = .24) suggests a reasonably homogenous thus valid measure.

Conclusion: The results suggest that TMD impairs the motor control of the tongue. Therefore, the sharpest tongue pointing test may constitute a simple and accessible clinical tool to assess the accuracy of tongue placement in TMD patients. The study was registered on ClinicalTrial.gov with identification number NCT04102306.

Keywords: clinical assessment; mental representation; physiotherapy; rehabilitation.

Figure 1

Installation and instructions for the sharpest tongue pointing test. a: Head against the wall; b: proximal extremity of the stick held vertically in front of the participant's mouth. Participants received the following instruction: pushing for 2–3 s the wood tick against their tongue while being instructed by the examiner to maintain the tongue as sharp as possible (i.e., resisting with the sharpest tongue to the slight pressure applied by the wood stick); c: wood stick held vertically; d: hand against the trunk holding firmly and vertically the wood stick; e: trunk against the wall

Figure 2

Flowchart summarizing the different steps of the study, including enrollment, allocation, measurement, and analysis. ^†Confirmed medical TMD diagnostic before the study inclusion and completion of the DC/TMD classification by the physiotherapist at Saint Alexandre private

Figure 3

Significantly larger tongue print area for the temporomandibular disorder (TMD) group compared with the control group. (a) Boxplot representing the area of the tongue print where bottom, top, and middle lines in the box represent 1st, 3rd quartiles, and median, respectively, and the two vertical bars extend to the minimum to maximum values (b); ellipses representing the median (dark line) and the lower and upper limit of the 95% confidence interval of the median (light lines and gray area) of participants of the control group (left panel) and TMD group (right panel). The estimated median group difference (EGD) and its 95% confidence interval was a tongue print area larger by 25.5 [1.3; 51.0] mm² for patients with TMD as compared with control participants

Figure 4

Tongue print sorted by size for each participant of the (a) control group and (b) temporomandibular disorder (TMD) group