24 Questions
What is the maximum average opening of the mouth during yawning or singing?
50 mm
What is the primary movement of the condyle during the early phase of opening the mouth?
Rotation within the concave inferior surface of the disc
What happens to the mandible during elevation?
It closes the mouth
What is the primary movement during lateral excursion?
Side-to-side translation of the condyle and disc within the fossa
What is the function of bilateral contraction of the masseter muscle?
Elevation of the mandible and slight protrusion
What happens to the mandibular condyle and disc during protrusion?
They translate anteriorly and slightly downwards
What is the direction of the axis of rotation during the later phase of opening the mouth?
Inferiorly
What is unique about the TMJ joint in terms of movement?
It involves a combination of rotation and translation
What is the result of unilateral contraction of the temporalis muscle?
Slight ipsilateral excursion of the mandible
What happens to the left condyle during left lateral excursion?
It forms a pivot point within the fossa as the right condyle rotates anteriorly and medially
What is the function of bilateral contraction of the medial pterygoid muscle?
Elevation and slight protrusion of the mandible
What is the movement of the condyle and disc during the late phase of opening the mouth?
Translation in a forward and inferior direction
What is the amount of opening required during mastication?
18 mm
What is the result of bilateral contraction of the masseter and temporalis muscles?
Elevation and protrusion of the mandible
What is the movement of the mandibular condyle and disc during retrusion?
They translate posteriorly and slightly upwards
What percentage of the ROM does the early phase of opening the mouth consist of?
35% to 50%
What type of movement occurs during protrusion of the mandible?
Anterior translation without significant rotation
What is the average normal movement of the mandible during lateral excursion?
11mm translation
What is the opposite movement of protrusion?
Retrusion
What type of movement involves the upward movement of the mandible?
Elevation
What is the function of the articular disc in the TMJ?
To add stability to the joint and guide the condyle of the mandible during movement
What is the movement that involves the downward movement of the mandible?
Depression
What structure provides lateral stability to the capsule and assists in guiding the movement of the condyle during opening of the mouth?
Lateral temporomandibular ligament
What is the term for the side-to-side translation of the mandible?
Lateral excursion
Study Notes
Osteokinematics of the TMJ
- Depression causes the mouth to open, with maximum opening occurring during yawning or singing, averaging 50mm
- Elevation of the mandible closes the mouth, used to grind food during mastication, requiring about 18mm of opening
- Mastication requests about 36% of maximum opening
TMJ Arthrokinematics
- Movement of the mandible involves bilateral action of the TMJs
- Abnormal function in one joint interferes with the function of the other
- During rotational movement, the mandibular condyle rolls relative to the inferior surface of the disc
- During translational movement, the mandibular condyle and disc slide together
- The disc usually moves in the direction of the translating condyle
Protrusion and Retrusion
- Protrusion: Mandibular condyle and disc translate anteriorly and slightly downwards relative to the fossa
- Retrusion: Mandibular condyle and disc translate posteriorly and slightly upwards relative to the fossa
Lateral Excursion/Deviation
- Primary: side-to-side translation of the condyle and disc within the fossa
- Secondary: Slight rotational components
- During left lateral excursion, the left condyle forms a pivot point within the fossa as the right condyle rotates slightly anteriorly and medially
TMJ Arthrokinematics: Depression and Elevation
- Combination of rotation and translation among the mandibular condyle, articular disc, and fossa
- Rotation and translation occur simultaneously, hence the axis is constantly moving
- Early phase of opening (35-50% of ROM): primarily rotation of the mandible relative to the temporal
- Late phase of opening (50-65% of ROM): gradual transition from primary rotation to primary translation
Kinetics of the TMJ
- Masseterus:
- Deep and superficial heads with similar function
- Bilateral contraction elevates the mandible to bring teeth into contact and slightly protrudes mandible
- Unilateral contraction causes slight ipsilateral excursion
- Temporalis:
- Bilateral contraction elevates the mandible and slightly retrudes it
- Unilateral contraction causes slight ipsilateral excursion of the mandible
- Medial pterygoid:
- Two heads with the same function
- Bilateral contraction elevates the mandible and slightly protrudes it
Anatomy of the TMJ
- Articular disc:
- Provides stability to the joint and helps guide the condyle of the mandible during movement
- Slides with the translating condyle in a healthy TMJ
Stability of the TMJ
- Passive stability:
- Fibrous capsule provides more stability with lateral movements
- Articular disc provides stability
- Lateral temporomandibular ligament provides lateral stability to the capsule
- Retrodiscal tissue contains both elastic and collagenous fibers
- Active stability: musculature
Learn about the osteokinematics of the TMJ, including depression and elevation movements, and their roles in opening and closing the mouth.
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