Biomechanics of the TMJ

Question 1

Biomechanics

Describe the arthrokinematic movements of the following mandible motions: protrusion, retrusion, lateral excursion, depression, elevation

Temporomandibular Joint

Answer 1

Protrusion: condyle and disc translate anteriorly following the slope of the articular eminence.
Retrusion: condyle and disc translate posteriorly following the slope of the articular eminence.
Lateral excursion: side to side translation of disc and condyle in fossa; occurs with slight rotation in horizontal plane
Depression: when the mouth begins to open the condyle rolls posteriorly in the inferior cavity; then the disc moves and the condyle slides anteriorly in the superior cavity; limited by the superior retrodiscal laminae
Elevation: reversal of depression.

Question 2

Biomechanics

Describe the arthrokinematic sequence of mouth opening at the TMJ.

Temporomandibular Joint

Answer 2

Roll in the inferior cavity followed by a slide in the superior cavity

Question 3

Biomechanics

List the muscles involved in the following motions:
* Protrusion
* Retrusion
* Lateral excursion
* Depression
* Elevation

Temporomandibular Joint

Answer 3

Protrusion: masseter, temporalis, medial and lateral pterygoids
Retrusion: temporalis; suprahyoids
lateral excursion: masseter, temporalis, medial and lateral pterygoids
Depression: lateral pterygoid; suprahyoid
Elevation: masseter, temporalis, medial pterygoid

Question 4

Biomechanics

Explain how a forward head posture affects the TMJ.

Temporomandibular Joint

Answer 4

Forward-head posture stretches the infrahyoids. Also, the mandible is depressed and retruded, which changes the position of the condyles