Inferior Head Of Lateral Pterygoid Research Articles

TMJ Disc Displacement Angle Analysis in MRI: A New Proposal

Objective: To evaluate the co relation of clinical symptoms and MRI findings of TMJ in symptomatic Temporomandibular Dysfunction (TMD) patients. Material and Method: MRI TMJ scan of 25 patients were evaluated. The subjects had clinical evidence of reciprocal TMJ clicking or restricted mouth opening. This study determined the variability of temporomandibular joint (TMJ) disk position in antero-posterior aspect of the joint using magnetic resonance imaging (MRI). Disk position was evaluated on MRI by measuring the angle formed by a line through the middle of the condyle and tangential to the posterior-most aspect of the disk. Joint effusion was checked using T2 weighted image sequence. Thickness of superior and inferior head of lateral pterygoid muscle was measured. These MRI findings were then correlated statistically to clinical findings. Results: Out of 50 TMJ's (25 patients); 40% had biconcave shape (no deformity), 16% cases showed lengthened disc, 12% cases showed a flattened disc, 12% cases showed thick posterior band. Varying degrees of disc displacement was associated with disc shape deformity. Increased thickness of Inferior head of lateral Pterygoid had statistically strong association with pain. Conclusion: A strong positive co relation was seen between the clinical and MRI findings in symptomatic TMD patients. Further using this, a new Disc Displacement angle measurement method and classification of disc shape was proposed for better disc evaluation.

A working-side change to lateral tooth guidance increases lateral pterygoid muscle activity

The inferior head of lateral pterygoid (IHLP) is thought to play a critical role in the generation and control of lateral jaw movements. The aim was to test the hypothesis that a change to the lateral tooth guidance (working-side occlusal alteration, OA) results in a significant change in the electromyographic (EMG) activity of the IHLP during standardised lateral jaw movements (laterotrusion) tracked by a jaw-tracking system. Ten trials of right laterotrusion were repeated under: control 1 (before occlusal alteration), OA (after occlusal alteration placement), and control 2 (after occlusal alteration removal) conditions in 14 subjects while recording left IHLP, bilateral anterior and posterior temporalis, masseter and submandibular muscles. IHLP activity was significantly (p<0.05) increased with the occlusal alteration during the outgoing (movement from intercuspal position to approximately 5mm right) and return phases of laterotrusion. The other muscles demonstrated no change or a significant decrease in activity. These findings suggest that a change to the occlusion on the working-side in the form of a steeper guidance necessitates an increase in IHLP activity to move the mandible down the steeper guidance. It must be emphasised that these data cannot be used as justification for occlusal therapy.

Activity in the inferior head of the human lateral pterygoid muscle with different directions of isometric force

The aim was to test the hypothesis that this head of the muscle plays a part in the generation and fine control of horizontal mandibular forces in a range of directions. Electromyographic activity was recorded from the inferior head of the lateral pterygoid of eight individuals during the generation such forces to a target in contralateral, ipsilateral and protrusive directions, and in two intermediate directions (contralateral–protrusive, ipsilateral–protrusive). The mean electromyographic activity and the mean firing rates of 21 single-motor units were significantly affected by direction, with the highest activity being contralateral, and graded decreases occurring as the direction shifted to the ipsilateral. Firing rates were significantly correlated with force magnitude. The data suggest that the inferior head of the human lateral pterygoid is involved in the creation and fine control of mandibular forces in different horizontal directions.