The lateral pterygoid muscle (LPM) is important in the physiology and dysfunction of the temporomandibular joint (TMJ), which has described the presence of a third head in the lateral pterygoid muscle (THLPM). The purpose of this study was to evaluate the prevalence of THLPM and its relationship with the TMJ disc through magnetic resonance imaging (MRI). It was evaluated 178 MRI of the TMJ of healthy individuals, in images that presented THLPM, and these were defined and measured at the surface inserted into the disc. The prevalence of THLPM was 20.22% (n = 36). Insertion of THLPM was made entirely on the TMJ disc, the average area of insertion was 4.14mm (SD 1.35) in women and 4.67 (SD 2.68) in men, but these differences were not significant. We concluded that the LPM has a complex structure, and that a THLPM could contribute in the development of TMJ disc function alterations and anterior disc displacement.

SUMMARY:The constitution and shape of superior head of the lateral pterygoid muscle (SHLP) inserts remains a topic of interest in the literature. The purpose of this study was to analyze by magnetic resonance imaging (MRI) the temporomandibular joint (TMJ) of individuals without signs of temporomandibular dysfunction. One hundred seventy-eight MRI images of one hundred and three patients were utilized, and the surface and percentage of the SHLP insert into the articular disc and condilar process was determined. In women, the average insertion into the disc was found to be between 5.7-5.5mm (SD 1.5-1.3), corresponding to 69.8-70.7% of the SHLP. In men, the average insertion into the disc was between 6.2-6.12mm (SD 1.8-1.9), or 68.9-74.2%. There were no differences in terms of the sex of the patients or the side of the joint. We found a significant percentage of SHLP fibers embedded in the disc of asymptomatic TMJs, and its role in the anterior disc displacement and the development of the temporomandibular dysfunction should be revised.

Temporomandibular disorder (TMD) is a term that encompasses a series of dysfunctions and disorders that affect the temporomandibular joint (TMJ), masticatory muscles and associated structures. These disorders are characterized by a set of signs and symptoms that may include joint noises, such as clicking and crackling, tooth wear, limited mandibular movement, accompanied or not by facial, cranial and periauricular pain. Here, we reported the clinical conduct of a patient with muscle TMD. Patient with chronic pain complaint in the cervico-craniofacial region, signs of bruxism, mouth opening limitation and masseteric hypertonia. The diagnosis was TMD of bilateral masseteric muscle origin, without trigger points. Heat thermotherapy was prescribed, myofacial and myofunctional physiotherapy, rigid Michigan stabilizer plate making, postural correction, and cognitive-behavioral therapy. The patient presented a gradual evolution of the clinical condition and after 90 days reported remission of approximately 95% of the symptomatological complaints, such as an improvement in the quality of sleep at night, without medication assistance, reduction in pain crises, and full mouth opening (44mm). It is concluded that the correct diagnosis and full patient adherence to the treatment proposed in this study provided relief in painful symptoms and biopsychosocial aspects.

The objective of this study was to assess the association between an increase in the proportion of the superior head of the lateral pterygoid muscle (SHLP) inserted into the temporomandibular joint (TMJ) disc and the presence of anterior disc displacement diagnosed by using MRI. We analyzed 75 images of patients with anterior displacement and 75 controls with normal relationship between the mandibular head and the articular tubercle also diagnosed by MRI. Levels of insertion were measured. Descriptive and analytic statistics were calculated. Analyses of differences were made by Fischer's exact test and also were calculated clinical significance (OR, CI = 95%). The average insertion of SHLP was 71.14% (SD 14.13) in controls and 67.80% (SD.16.23) in cases group. The only relationship that presented a significant association (OR 5.61) was found when comparing subjects with a percentage of inserting the disc into the SHLP at ≤ 50% with those who had higher levels of insertion (50%). Our results suggest that the highest percentage of insertion serves as a protective factor for anterior disc displacement, probably due to greater control of neuromuscular activity.