Simply right click on any animation and select "save as" to your computer.
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 (3 "chews" per side, then a functional shift)  |
The image to the left is demonstrating normal
reciprocal
functioning of the Lateral Pterygoids and
Masseters/Med.Pteygoids/Temporalis'.
The Lateral Pterygoids advance the condyles, thereby opening the mouth (depressing the mandible), with the assistance of the Digastric (next webpage). The oblique orientation of the Masseters and Medial Pterygoids create a sling. The non-working side Medial Pterygoid contacts simultaneously with the opposide side working Masseter. It is this oblique orientation of the Med.Pterygoids and
Masseters that
create the functional "shift" of the mandible, not an unilateral
contraction of a Lateral Pterygoid. In normal chewing function, the
mandible opens, and then, while initiating closing, there is a shift
slightly to the side of the bolus, due to the orientation of the
masseter and medial pterygoid. There is no "canine rise" during
normal chewing fuction. Canine rise is mechanism to combat
parafunction.
The moving yellow dot in the jaw tracing to the left
shows the tracking of the gingival margin of a lower incisor during the
left "working" movement of chewing. The red lines are jaw
movements with the teeth in contact (excursive grinding to each
side). The outter most line is the envelop of maximum movements. Notice how the during normal masticatory function, the teeth
do not contact, but may occasionall glance off each other. |
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animations above show the effect of the contractions of the lateral
pterygoids: the advancement (translation) of the condyles. A
voluntary opening of the mandible requires the LPs to contract, thus
the immediate translation upon attempted opening. However, a voluntary attempt at closing requires the immediate retrusion of the condyles by the posterior temporalis, thereby "un-translating" the condyles. At the final arc of closure, the condyle is braced against the eminance, while the anterior temporalis rotates the mandible closed. |
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 The animation above and to the right demonstrate how the condyle immediately translates upon opening during masticatory function, due to the contraction of the lateral pterygoid. As closing ensues, the LPs relax, and the elevators contract. The tension of the posterior segment of the temporalis "un-translates" the condyle. During last portion of closing, the anterior temporalis and masseters brace the condyles against the eminance (seating to "CR"), referred to as "rotation". |
 The blue dot is the position of the gingival margin of the central incisor. The condyle translates immediately upon opening, and is rotating during the final phase of closure. The superior head of the lateral pterygoid is bracing the disc against the eminance as the elevators rotate the mandible closed against the resistance of the bolus. |
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Just as the anterior temporalis
can sustain considerable contaction intensities over extended periods,
so it may be with the posterior temporalis. The result would not
be the clenching of the teeth, but of the blockage of the airway.
It is this possiblity that makes for the varying reports of tooth
soreness from the use of anit-snoring/anti-apnea devices, that attempt
to hold the jaw forward. The reason why there is difficulty in
holding the jaw forward for some patients is their intensity of
retrusion by the posterior temporalis. |
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Bruxism can not be
casually described as "hyperactivity of the lateral pterygoid".
Each of the graphics below displays identical degreess of LP
"hyperactivity":
 Only the graphic to the far left can be considered to NOT be bruxism, although there IS hyperactivity of the LPs. The definitive component of bruxism is the degree of parafunctional elevation, that is, the clenching component. An accurated definition of bruxism is: Jaw clenching, with or without forcible excursive movements, where the intensity of the clenching dictates the severity (or lack of) grinding (neither the graphic at the far left or the far right would display tooth wear, yet the graphic at the far right is the most extreme form of bruxism). |
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 Above: "Protusive Clenching" (click here for an animation depicting the progression of bruxism) |
In the event the Temporalis' do not cease their active
contractions,
scenarios of varying degrees of parafunction result, as the Lateral
Pterygoids
encounter resistance to their attempts at condylar advancement, thereby
increasing their intensity of contraction and strain on their origins
and
insertions: the pterygoid plates of the sphenoid bone, and the condylar
neck and disc.
The degree of frequency, duration and intensity of the contractions of a Lateral Pterygoid is a function of the resistance provided by the parafunction ipsilateral and/or contralateral Temporalis. For example, in the animation to the left, as a Lateral Pterygoid attempts to translate its condyle, it is met with resistance provided by the contralateral Temporalis, thereby causing the Lateral Pterygoid to pull its condyle in a medial direction toward the contralateral contact. |
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