Anatomical factors influencing temporomandibular joint clicking in young adults: temporomandibular joint structure disorder or lateral pterygoid muscle dysfunction?

Abstract

Objective: This study aimed to investigate the selected anatomical factors that can potentially influence temporomandibular joint (TMJ) clicking in young adults by assessing TMJ structures and lateral pterygoid muscle (LPM) function using magnetic resonance imaging (MRI). Methods: The patients were divided into four groups: the healthy control group; the clicking on mouth opening group; the clicking on mouth closing group; and the clicking on mouth opening and closing group. Additionally, we used clinical palpation to evaluate the masticatory muscles' functional state and employed MRI using the OCOR-T1WI-FSE-CLOSED, OSAG-PDW-FSE-CLOSED, and OSAG-PDW-FSE-OPEN sequences to analyze the texture of the lateral pterygoid muscle (LPM). Results: The proportion of any articular disc or condylar morphology class did not differ significantly between the TMJ clicking and HC groups. The articular disc position did not differ significantly between the TMJ clicking and HC groups. In the TMJ clicking group, the presence of masticatory muscle dysfunction differed significantly between the clicking and non-clicking sides. Moreover, the LPM accounted for the highest proportion among masticatory muscles with tenderness in all TMJ clicking subgroups (77.78%-100%). Therefore, in the TMJ clicking group, the LPM texture was less defined, more uniform in gray scale, and more similar to local texture (p < 0.0001). Conclusion: The occurrence of TMJ clicking in young adults is unrelated to the TMJ structure but related to the function of masticatory muscles, particularly the LPM.

Keywords: joint structure; lateral pterygoid muscle; masticatory muscle function; temporomandibular joint clicking; texture analysis.

FIGURE 1

Process of patient selection and classification. (A) Allocation of patients in the healthy control (HC) group. (B) Allocation of patients in the clicking on mouth opening (CMO), clicking on mouth closing (CMC), and clicking on mouth opening and closing (CMOC) groups.

FIGURE 2

TMJ structure and measurement method. (A) View from the oblique sagittal plane; I: condylar process; II: glenoid fossa; a: anterior band; b: intermediate zone; c: posterior band; d: bilaminar zone; e: superior joint cavity; f: inferior joint cavity; ①: anterior temporal attachment; ②: anterior mandibular attachment; ③: posterior mandibular attachment; ④: posterior temporal attachment; ⑤: superior head of the LPM; ⑥: inferior head of the LPM. (B) View from the oblique coronal plane. I: condylar process; II: glenoid fossa; e: superior joint cavity; f: inferior joint cavity; g: articular disc; ⑦: medial disc ligament; ⑧: lateral disc ligament. (C) Use of the condylar apex method to measure the articular disc position (∠aOy). O: condylar apex. (D) The condylar length “L” (“y1–y2” is the vertical line passing through both sides of the condyle; “L” is the line connecting the intersection point of the two perpendicular lines and the condyle), medial displacement distance “Dm,” and lateral displacement distance “Dl” of the articular disk were measured in the oblique coronal plane (“b–c” is the tangent drawn at the intersection of both sides of the condyle; “d–e” is parallel to “c–d” and passes through both ends of the disk; and “Dm–Dl” is the distance between “e–c” and “d–f”). (E) Articular disc morphology; a: biconcave; b: thickening posterior; c: thickening anterior; d: biplanar; e: biconvex; f: folded. (F) Condylar morphology; a: round; b: flattened; c: beak-like. TMJ, temporomandibular joint; LPM, lateral pterygoid muscle.

FIGURE 3

Numerical rating scale (NRS) is used to quantify the tenderness felt by the patients.

FIGURE 4

TA parameters of the LPM obtained with the OSAG-PDW-FSE-CLOSED and OSAGPDW-FSE-OPEN MRI sequences. The first step was the selection of the region of interest of the LPM with the graph selection tool, avoiding the inclusion of peripheral blood vessels, nerves, and other structures. The LPM boundary is outlined with yellow in the three images. The second step was the selection of “plugins” for the TA. The selected conditions are shown. The corresponding results were calculated by checking the five TA parameters (angular second moment, contrast, correlation, inverse difference moment, and entropy). LPM, lateral pterygoid muscle; TA, texture analysis.

FIGURE 5

Schematic diagram of the articular disk morphology with distribution rates. (A) (a) biconcave; (b) thickening posterior; (c) thickening anterior; and (d) biplanar. (B) Proportion of each articular disk morphology class.

FIGURE 6

Schematic diagram of the condylar morphology with distribution rates. (A) (a) round; (b) flattened; (c) beak-like. (B) Proportion of each condylar morphology class.