Muscle Responsible for Forward Protrusion of the Mandible
The lateral pterygoid muscle is the primary muscle responsible for forward protrusion (protraction) of the mandible, with both its superior and inferior heads working synergistically to drive this movement.
Anatomical and Functional Basis
The lateral pterygoid muscle consists of two distinct heads that collaborate during mandibular protrusion:
- Both the superior head (SHLP) and inferior head (IHLP) of the lateral pterygoid demonstrate progressive increases in electrical activity that correlate directly with forward condylar movement during protrusive jaw tasks 1
- The correlation between lateral pterygoid activity and anterior condylar translation during protrusion is exceptionally high, with mean correlation coefficients of 0.91 for the superior head and 0.96 for the inferior head 1
- These correlation values are statistically significantly different from all other masticatory muscles (masseter, temporalis, digastric), confirming the lateral pterygoid as the principal driving force for forward jaw movement 1
Mechanism of Action
The lateral pterygoid achieves mandibular protrusion through specific biomechanical actions:
- The muscle fibers attach to both the mandibular condyle and the articular disc, allowing them to draw the disc and condyle anteriorly during protrusive movements 2
- The inferior head is particularly active during opening, protrusion, and contralateral jaw movements, while the superior head also participates in protrusive tasks 3, 4
- The muscle provides fine control of horizontal jaw movements, with irregularities in condylar movement correlating temporally with prominent bursts of lateral pterygoid activity 1
Clinical Relevance
Understanding the lateral pterygoid's role has important clinical implications:
- The lateral pterygoid plays a crucial role in parafunctional excursive jaw movements and generation of side-to-side and protrusive jaw forces 3
- The preservation and reattachment of the lateral pterygoid muscle within the glenoid fossa during temporomandibular joint reconstruction may sustain normal TMJ functionality 5
- Mandibular advancement devices used for obstructive sleep apnea work by mechanically advancing the mandible forward, effectively mimicking the action of the lateral pterygoid muscle to maintain airway patency 5
Common Misconceptions
Contrary to classical teaching that assigns completely separate functions to each head, recent evidence demonstrates that both heads of the lateral pterygoid work together during protrusive movements, with the superior head also participating in opening and protrusive tasks 3, 4