Mandibular Movements

Fundamentals of Occlusion

Masticatory system as a functional unit Jaws Teeth Temporomandibular joints (tmjs) Associated ligaments Muscles of mastication Tongue Cheeks Lips Sensory motor innervation (and vasculature)

Ideal occlusion That are harmonious with the existing tmjs and masticator)1 muscles Stable occlusal contacts Vertical dimension of occlusion

Complexity of mandibular movements Many different mandibular movements occur during Mastication Speech Swallowing Respiration Facial expression Parafunctional movements Bruxism Clenching

Peripheral influences Jaw reflexes

Centric Relation

components of the temporomandibular joint A, articular eminence C, condyle; D, articular disc E, external auditory meatus L, lateral pterygoid muscle R, retrodiscal tissue

Condyle movements

In a dysfunctional joint with an internal derangement the condyle is displaced posterior to the disc at the intercuspal position

In a dysfunctional joint with an internal derangement In translation of the mandible to After initial rotational opening, the condyle is still posterior to the disc

In a dysfunctional joint with an internal derangement In translation of the mandible to maximum opening, the condyle recaptures the disc, clicking into position as it does

In a healthy joint the condyle is in a superoanterior position in the fossa with the articular disc interposed when the teeth are in maximum intercuspation

In a healthy joint In the initial stage of opening, the condyle rotates in position, with the disc remaining stationary

In a healthy joint In maximum opening, the condyle translates forward, with the disc still interposed

Mandibular Movement

The mandible moves about a horizontal axis, as seen in a hinge axis opening.

Mandibular movement occurs around a vertical axis during a lateral excursion.

The mandible also rotates around a sagittal axis when one side drops down during a lateral excursion.

A protrusive movement occurs when the mandible moves forward

When the mandible moves into a left lateral excursion the right condyle (A) moves forward and inward while the left condyle (B) will shift slightly in a lateroposterior direction.

Bennett angle (S'PB) The Bennett angle used in articulators with an immediate lateral translation capability is measured from the sagittal plane after the (I) immediate or early lateral translation has occurred.

Bennett angle In the nonworking condyle (NW) The "traditional" Bennett angle (SCB) measures the angle from the sagittal plane to the endpoint of the movement of the condyle center.

The farther anterior a tooth the less the influence of the temporomandibular joint (TMJ) the greater the influence of the anterior guidance (AG).

Envelop of motion

The Envelope of Motion limits of possible motion and certain mandibular reference positions

Envelope of motion (mandibular border movement area) in the sagittal plane. CO, Centric occlusion; CR, centric relation; MHO, maximum hinge-opening position MO, point of maximum opening of the jaws P, most protruded position of the mandible with the teeth in contact Rest, postural rest position

Envelope of motion (mandibular border movements) in the frontal plane CO, Centric occlusion MO, point of maximum opening of the jaws Rest, postural rest position.

Occlusal Interferences

Normal Versus Pathologic Occlusion

centric occlusal interference often occurs during mandibular closure between maxillary mesial-facing cusp inclines and mandibular distal-facing inclines. As a result, the mandible is deflected anteriorly.

A working interference may occur between maxillary lingual-facing cusp inclines and mandibular buccal-facing cusp inclines on the working side.

A nonworking interference results when there is contact between maxillary buccaI-facing cusp inclines and mandibular lingual-facing cusp inclines on the nonworking side

A protrusive interference occurs when distal-facing inclines of maxillary posterior teeth contact mesial-facing inclines of mandibular posterior teeth during a protrusive movement.

TILL HERE

The criteria for such an occlusion have been described by Okeson 1- In closure condyles posterior teeth anterior teeth 2. Occlusal forces in the long axes of the teeth. 3. lateral excursions working-side disocclude or nonworking 4. protrusive anterior tooth disocclude posterior 5. upright posture posterior heavier than anterior

Occlusal disharmony and threshold

Organization of the Occlusion Bilateral Balanced Occlusion Unilateral Balanced Occlusion Mutually Protected Occlusion

Effects of Anatomic Determinants

Molar Disocclusion

Condylar Guidance

A shallow protrusive condylar inclination requires short cusps

while a steeper path permits the cusps to be longer (B).

A pronounced immediate lateral translation requires that the cusps be short (A), while a gradual lateral translation allows the cusps to be longer (B).

The angle between the working (W) and nonworking (NW) paths is greater on teeth located farther from the condyle.

A pronounced vertical overlap of the anterior teeth permits posterior teeth to have longer cusps (A) . A minimum anterior vertical overlap requires shorter cusps (B).

A pronounced horizontal overlap of the anterior teeth requires short cusps on the posterior teeth (A). A minimum anterior horizontal overlap permits the posterior cusps to he longer (B).

Anterior Guidance

While a shallow protrusive path would require short cusps in the pres­ence of minimal anterior guidance (A) the posterior cusps can be lengthened if the anterior guidance is increased (B).

A pronounced immediate lateral translation would dictate short cusps where there is little anterior guidance (A . However, the cusps can be lengthened if the anterior guidance is increased (B).