Mechanics of Mandibular Movements Flashcards
Terminal hinge axis represents what mandibular movement?
rotation - in the very beginning and anything beyond this point the mandible starts to translate as well
Five factors of mandibular movement
- initiating position (centric relation)
- types of motion - rotation and translation
- direction of motion (planes)
- degree of movement
- clinical significance of movements
clinical importance of CR?
START POINT -where you start with any restorative procedures
Rotation
definition and where
process of moving around an axis - motion of a body around its center
around horizontal axis
around frontal (vertical axis)
around sagittal axis
translation
definition and where
Motion of a body in which all of its points move in the same direction at the same velocity
*functional border starts where?
MIP
how far open when just doing rotation? what axis?
only the horizontal hinge axis
opens approx. 20-25 mm as measured between incisal edges
Direction of movement of mandible when translate and condyles when translate (in sagittal plane)
Condyles : move anterior and inferior
Mandible: moves inferior and posterior (40-60 mm)
center of rotation when go into translation?
moves from condyle to the body of ramus
when is condyle in most anterior position?
when the mandible is in maximum opening
how is maximum protrusion limited?
in part by the stylomandibular ligaments, which when close, produce a posterior movement of the condyle
posterior opening border in sagittal plane
Rotation (terminal hinge axis) and translation into MO
Anterior opening border in sagittal plane
maximum opening o maximum protrusion
superior contact border in sagittal plane
start – finish and what is in between
CR to maximum protrusion
- CR (posterior to MIP)
- anterior to MIP
- in presence of anterior guidance there is INFERIOR movement of mandible
- In protrusion, as incisal edges contact - EDGE to EDGE there is HORIZONTAL movement
- as pass each other from edge to edge - mandible moves superior and posterior teeth contact
- Continued protrusive movement is affected by the cuspal height of posterior teeth and limited by the ligaments
sagittal plane functional border
STARTS at MIP *
“clinical rest position” is found within this functional border, usually 2-4 mm below MIP
amount of normal vertical overlap?
horizontal?
2-3 mm
horizontal want to limit this
*5 things that affect the superior contact border?
- amount of variation between centric relation and maximum intercuspation (freeway space)
- steepness of the cuspal inclines of the posterior teeth
- amount of vertical and horizontal overlap of the anterior teeth
- lingual morphology of maxillary anterior teeth (relationship with anterior guidance)
- general inter-arch relationships of the teeth
does functional movement look the same if the patient has flat teeth?
no - flat more movement side to side
4 anatomic determinants of mandibular motion
- Right condyle
- left condyle
- Dentition (occlusion of permanent dentition)
- R/L TMJ joints and muscles
Frontal plane border movement : left lateral superior
Starts?
determined by?
Starts in CR
Nature of movement is determined by the morphology and interarch relationship of the opposing posterior teeth
the maximum extend of the movement is determined by the ligaments of the relating joint
Frontal plane border movement : left lateral opening
Starts?
what happens at max opening?
Starts at the maximum left lateral movement
jaw will take a convex path towards the midline (at bottom of drop near max opening)
at maximum opening the ligaments tighten and the mandible moves to midline
horizontal plane border movement
starts?
name all positions and locations within border
BORDER STARTS AT CR - which is posterior to the MIP
looks like a diamond
- left lateral
- continued left lateral with protrusion
- right lateral
- continued right lateral with protrusion
posterior intersection in horizontal plane?
marked centric relation
left lateral in horizontal plane
Number in picture?
Number 1.
Left condyle = rotating
Right condyle = orbiting
Goes from CR – left lateral and as it does the INFERIOR PTERYGOIDS ON THE RIGHT BRING THE RIGHT CONDYLE INFERIOR ANTERIOR AND MEDIAL
continued left lateral in horizontal plane
Number in picture?
Number 2.
With continued lateral there is also protrusion occuring so now the LEFT INFERIOR LATERAL PTERYGOID IS CONTRACTING TOO - along with the continued contraction of the right lateral pterygoid
overall – the left condyle will begin to move anteriorly and to the right (to follow the motion of the border we see)
so duel * contraction of the inferior lateral pterygoids
action of the inferior lateral pterygoids
active during opening in conjuction with the mandibular depressors and also active in protrusion
UNILATERAL contraction is responsible for mediotrusive movements
how to trace horizontal plane movement>
Gothic arch tracing
tracing made using static plate attached to maxilla and a stylus point attached to mandible
ask patient to make protrusive RL and LL movements
how to find centric relation position for complete denture patients?
gothic arch tracing
relationship to opening and size of the gothic arch tracing?
as the mandible is opened more – the ability of the jaw to move side to side decreases - thus the tracing becomes smaller at maximum opening
- limited/ restricted by ligaments in excessive motions
what is H in sagittal view?
Terminal hinge axis