Prevalence of temporomandibular joint sideways disc displacement in symptom-free volunteers and comparison of signal intensity ratios of masticator muscles on magnetic resonance images

The objectives of this study were to figure out the prevalence of sideways disc displacement of the temporomandibular joint (TMJ) in symptom-free volunteers and to compare signal. The study was based on bilateral Magnetic Resonance Images (MRI) of 112 joints in 56 symptom-free volunteers. Sideways displacements were identified as medial disc displacement (MDD) and lateral disc displacement (LDD). The signal intensity ratios (SIR) of masticator muscles for both normal joints and pure sideways displacements were measured with elliptic ROI on T1 and T2 weighted MRIs. Of the 112 TMJ images, one showed LDD and two showed MDD. The signal intensity ratios increased for pterygoid lateral and temporal muscles in sideways disc displacements. The results of this study suggest that the temporal muscle fibres are also inserting into the TMJ disc like the pterygoid muscle. Therefore, sideways disc displacements have direct effect on pterygoid lateral and temporal muscles.