Page 130 - Edited - Webster HEAD AND NECK - part 1

A SUMMARY OF MUSCLE ACTIONS ON THE MANDIBLED
HN108
(A) SIMPLE OPENING (CLOSING) (i.e. depression & elevation of the mandible) involve
SYMMETRICAL action of muscles:

OPENING
:
BOTH lateral pterygoid mm.
BOTH digastric mm. *
BOTH geniohyoid mm.*
CLOSING: BOTH masseter mm. BOTH mylohyoid mm. *
BOTH temporalis mm.
BOTH medial pterygoid mm. * HYOID BONE
MUST BE FIXED-
(B) ANTERO-POSTERIOR SHIFTS
Involve symmetrical action of
muscles. RETRACTION: Is limited by the
ARTICULAR LATERAL LIGAMENT &
TUBERCLE the tympanic bone.
BOTH temporalis mm. (posterior fibres)
BOTH digastric mm.*
PROTRACTION is limited BOTH geniohyoid mm.*
by the articular tubercle.
BOTH medial pterygoid mm.
BOTH lateral pterygoid mm.
TYMPANIC
* HYOID FIXED (SHEET 71) BONE

(C) MEDIO-LATERAL SHIFTS

Involves an asymmetrical action of the pterygoid mm.
These movements are limited largely by
the LATERAL(TEMPORO- SPINE OF SPHENOID & SPHENOMANDIBUNAR
LATERAL LIGAMENT
MANDIBULAR) LIGAMENT. MEDICAL LIGAMENT
&
LATERAL
PTERYGOID
MM.

REMEMBER that the pterygoid
muscles of one side displace the mandible
to the OPPOSITE SIDE.
RIGHT
If one set are disfunctional, operating of PTERYGOID
the pterygoid muscles in an attempted MUSCLES
SYMMETRICAL MOVEMENT will MANDIBLE
shift the mandible to the side of the MOVES TO LEFT
dysfunctional muscles. SEE TEXT

K.E.W.