The prevalence of symptomatic temporomandibular joint (TMJ) disorders (TMD) has been reported to be 20–25 % of the population (Leresche, 1997). Among these cases, at least 70 % of the patients with TMD experience pathology or malpositioning of the TMJ articular disc (Katzberg et al., 1996, Tasaki et al., 1996, Iwanaga et al., 2023). One of the most common pathological conditions of the TMJ is an intra-articular disorder (Schiffman et al., 2014). Intra-articular disorders of the TMJ have been defined as abnormal positional relationships between the articular disc and condyle, articular eminence, or articular fossa (Murakami et al., 1993). The articular disc can be displaced in any direction, including anterior, posterior, lateral, or medial (de Leeuw R, 2008), with anterior disc displacement being the most common (Tasaki et al., 1996).

The lateral pterygoid muscle (LPM) inserts into the pterygoid fovea of the condyle and the articular disc. A recent magnetic resonance imaging (MRI) study by Soydan Çabuk et al. (2021) revealed that the degree of anterior disc displacement affects the LPM signal. Thus, the correlation between the LPM and anterior disc displacement has been investigated owing to their anatomical relationship. However, other masticatory muscles, such as the masseter, temporalis, and medial pterygoid muscles, have not been considered to be contributors to anterior disc displacement, as they are believed to lack a direct attachment to the articular disc.

Muscle training and oral appliance therapy can improve mouth opening and reduce pain in patients with TMD experiencing disc displacement and reduction (Olbort et al., 2023). This indicates that not only the LPM but also the other masticatory muscles and associated masticatory fascia could directly affect TMJ function. Previous anatomical studies identified the muscles attached to the articular disc as the LPM, mid-medial muscle bundle, and disco temporalis (Matsunaga et al., 2009, Sakaguchi-Kuma et al., 2016, Akita et al., 2019). However, these studies did not completely explain that the muscles, fasciae, and joints (capsule and articular disc) influence each other and all contribute to joint stabilization. The present study aimed to reveal the relationship between the masticatory muscles, related masticatory fascia, articular discs, and joint capsules in the stabilization of the TMJ and elucidate the current understanding of TMD.