Mandibular Movements

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MANDIBULAR MOVEMENTS:

MANDIBULAR MOVEMENTS Dr. Sahil Sarin J.R.1 Deptt . of Prosthodontics

CONTENTS:

CONTENTS Introduction Definitions Types of movements Bennet movement Sagittal border and functional movements Frontal border and functional movements Vertical border and functional movements Envelope of motion Determinants of mandibular movements

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Chewing stroke Methods for recording mandibular movements Limitations of TMJ movements Clinical significance of mandibular movement Conclusion References

INTRODUCTION:

INTRODUCTION Mandibular movement occurs as a complex series of inter-related 3 dimensional rotational and translational activities. It is determined by combined and simultaneous activity of both temporomandibular joints.

DEFINITIONS:

DEFINITIONS Centric relation: (terminal hinge position, / ligamentous position) A maxillomandibular relationship, in which the condyle articulate with thinnest avascular portion of their respective discs with the complex in the anterior- superior position against the slopes of articular eminences. This position is clinically discernible when the mandible is directed superiorly anteriorly and restricted to purely rotational movement about a transverse horizontal axis.

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Maximum intercuspation: Maximum intercuspal position (ICP) / centric occlusion. The complete intercuspation of teeth independent of condylar position, sometimes referred to as the best fit of the teeth regardless of condylar position

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Centric relation occlusion: It is said when centric relation and maximum intercuspation are at same position.

TYPES OF MOVEMENTS OCCUR IN THE TMJ:

TYPES OF MOVEMENTS OCCUR IN THE TMJ Rotational Translational

Rotational movement:

Rotational movement In the masticatory system, rotation occurs when the mouth opens and closes around a fixed point / axis within the condyles . In TMJ, rotation occurs as a movement within inferior cavity of the joint. It can occur in: Horizontal plane Frontal plane Sagittal plane

Axis of rotation::

Axis of rotation: Horizontal axis of rotation (hinge movement) : Mandibular movement around the horizontal axis is an opening & closing motion. The hinge movement is probably the only example of Mandibular movement activity in which “pure” rotational activity occurs.

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Vertical axis of rotation: This movement occurs in horizontal plane when mandible moves into lateral excrusion . The centre of this rotation is a vertical axis extending through the rotating or working side condyle.

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Sagittal axis of rotation: When the mandible moves to one side, the condyle on the opposite side from the direction of movement travels forward. As it does, it encounters the eminentia of glenoid fossa and moves downward simultaneously. When viewed in the frontal plane, this produces a downward arc on side opposite the direction of movement, rotating about an anteroposterior (sagittal) axis passing through the condyle.

TRANSLATIONAL MOVEMENT:

TRANSLATIONAL MOVEMENT In this each point of the moving object has a simultaneously same velocity and direction. It occurs when mandible moves forward, as in protrusion. The teeth, condyles and rami all move in same direction and same degree. Translation occurs within the superior cavity of joint.

BENNET MOVEMENT::

BENNET MOVEMENT: Dr. Norman Bennet (1908) studied working condylar path and called it Bennet movement, presently referred to as lateral translation. It is defined as “ the bodily lateral movement / lateral shift of mandible resulting from movements of the condyles along lateral inclines along the Mandibular fossa in lateral jaw movement”

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During a lateral excursion the orbiting condyle moves downward, forward and inward in mandibular fossa around axis in the opposite condyle. The movement of orbiting condyle is determined by: Morphology of medial wall of Mandibular fossa Inner horizontal portion of temporomandibular ligament which attaches to the lateral pole of rotating condyle.

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The lateral translation movement has three attributes: Amount Timing Direction

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The more medial the wall from the medial pole of the orbiting condyle, the greater the amount of translation movement. The looser the TM ligament attached to the rotating condyle, the greater the lateral translation movement. The direction of lateral translation movement depends primarily on direction taken by the rotating condyle during the bodily movement.

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Side shift of non-working condyle may be: Immediate, Precurrent , Progressive . When the lateral translation movement occurs early, a shift is seen even before the condyle begins to translate from the fossa , it is termed an immediate or early side shift.

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Lateral translation that occurs during the first 2-3mm movement of the non-working condyle is called the precurrent side shift. Lateral translation that continues linearly after 2-3mm of forward movement of the non-working condyle is termed as progressive side shift.

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Bennet angle: The angle formed between the sagittal plane and the average path of advancing condyle as viewed in the horizontal plane during lateral Mandibular movements. Studies have shown Bennet angle to be about 7.5- 12.8 0 To calculate the Bennet angle, Hanau proposed the following equation: Bennet angle (L) = (H/8) + 12 H  horizontal condylar inclination.

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Significance of Bennett movement: This movement is responsible for the lateral chewing stroke It is a movement during which the greater lateral force is exerted For this reason it is extremely important that the articulating surfaces are in strict harmony with this side shift.

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It is important to record the path of the Bennett movement and arrange the cusps of the teeth so that they can pass each other without clashing or climbing upon each other during function. At the same time we want to maintain a proximity of contact of these surfaces in order that they can perform their function of chewing without damage to the supporting structures.

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Effect on cusp height and fossa depth: Greater the side shift of the mandible, shorter the cusps must be. Lesser the side shift of the mandible, longer the cusps may be. Lundeen et al 1978 : Amount of lateral movement in horizontal plane -0.75mm On an average 80% of patients had a Bennett movement of 1.5mm or less. (J Prosdent , Vol 40,no 4, 1978, 442-452)

BORDER MOVEMENTS IN SAGITTAL PLANE:

BORDER MOVEMENTS IN SAGITTAL PLANE Mandibular motion viewed in sagittal plane can be seen in four distinct movement components: Posterior opening border Anterior opening border Superior contact border Functional movement

BORDER AND FUNCTIONAL MOVEMENTS (SAGITTAL PLANE):

BORDER AND FUNCTIONAL MOVEMENTS (SAGITTAL PLANE)

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Limiting factors for the movement: Posterior & anterior opening border movement is determined or limited primarily by ligaments and morphology of the TMJ. Superior contact border movements are determined by occlusal and incisal surfaces of the teeth.

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Posterior opening border movement 1 st position : condyle stabilized in terminal hinge position The mandible can be lowered in a pure rotational movement without translation of the condyle. In CR, the mandible can be rotated around horizontal axis to a distance of only 20-25 mm between the incisal edges of maxillary and Mandibular incisors.

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Posterior opening stage one - early rotational movement around the horizontal axis

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2 nd position: After 1 st stage, anterior & inferior translation of condyle occurs. Now axis of rotation of mandible shifts into body of ramii . During this, condyle moves anteriorly and inferiorly. Maximum opening  40-60 mm between incisal edges.

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Posterior opening stage two- translational down the eminence

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Anterior opening border movement: with mandible maximally opened, closure accompanied by contraction of lateral inferior pterygoid will generate closing border movement. Because the maximum protrusive position is determined in part by stylomandibular ligament, as closure occurs tightening of ligament produces posterior movement of condyle. Therefore it is not pure hinge movement.

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Anterior opening in sagittal plane

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Superior contact border movement Throughout this entire movement, tooth contact is present. In CR position, tooth contacts are normally found on one or more opposing pairs of posterior teeth. If muscular force is applied to the mandible, a superoanterior movement or shift will result until the intercuspal position (ICP) is reached. In ICP the opposing anterior teeth usually contact when mandible is protruded from maximum intercuspation

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The contact between incisal edges of mandibular anterior teeth & lingual inclines of maxillary result in anterioinferior movement of mandible  edge to edge relationship  horizontal movement continues

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Incisal edges of Mandibular teeth pass beyond incisal edges of maxillary teeth  mandible moves in superior direction until the posterior teeth contact.

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The occlusal surface of posterior teeth then dictates the remaining pathway to maximum protrusive movement. This then joins with most superior position of anterior opening border movement.

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Functional movement It occurs during activity of the mandible. Takes place within border movements & thus considered as free movement. Most functional activities require maximum intercuspation & therefore typically begin at/ below ICP. When the mandible is at rest, it is found to be located approximately 2- 4 mm below ICP( clinically rest position).

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In this position teeth can be quickly & effectively brought together for immediate function. If the chewing stroke is examined in sagittal plane, the movement will be seen to begin at ICP & drop downward & slightly forward to position of desired opening. It then returns in straighter pathway slightly posterior to opening movement.

HORIZONTAL PLANE BORDER & FUNCTIONAL MOVEMENTS:

HORIZONTAL PLANE BORDER & FUNCTIONAL MOVEMENTS A rhomboid shaped pattern Has four distinct movement components Left lateral border Continued left lateral border with protrusion Right lateral border Continued right lateral border with protrusion

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left lateral border movements With condyle in CR position, contraction of right inferior lateral pterygoid will cause right condyle to move anteriorly and medially. If left lateral pterygoid stays relaxed, the left condyle will remain situated in CR and result will be left lateral border movement. Left condyle: rotating/ working condyle Right condyle: orbiting condyle/ non-working condyle

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continued left lateral border movement with protrusion Contraction of left inferior lateral pterygoid muscle along with continued contraction of right, will cause left condyle to move anteriorly and to right. The movement of left condyle to its maximum anterior position will cause a shift in Mandibular midline back to coincide with the midline of the face.

Continued left lateral border movement: :

Continued left lateral border movement:

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Right lateral border movement: The mandible is returned to CR Contraction of left inferior lateral pterygoid muscle will cause left condyle to move anteriorly and medially. If right pterygoid stays relaxed, the right condyle will remain situated in CR position  cause right lateral border movement.

Right lateral border movement: :

Right lateral border movement:

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continued right lateral border movement with protrusion: With mandible in right lateral border position, contraction of right inferior pterygoid muscle along with continued contraction of left inferior pterygoid muscle will cause the right condyle to move anteriorly and to the left. The movement of right condyle to maximum anterior position will cause a shift back in Mandibular midline to coincide with midline of face.

Continued right lateral border movements :

Continued right lateral border movements

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Functional movement: Functional movements in horizontal plane most often occur near ICP. During chewing the range of jaw movement begins some distance from maximum ICP. But as food is broken down into smaller particle size, jaw action moves closer and closer to ICP.

FRONTAL (VERTICAL) BORDER & FUNCTIONAL MOVEMENT:

FRONTAL (VERTICAL) BORDER & FUNCTIONAL MOVEMENT It has shield shaped pattern Left lateral superior border Left lateral opening border Right lateral superior border Right lateral opening border.

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Left lateral superior border movement: With mandible in maximum intercuspation, a lateral movement is made to the left. A recording device will disclose an inferiorly concave path being generated. Path is primarily determined by: the morphology and inter-arch relationships of maxillary and Mandibular teeth. Secondarily by: condyle disc fossa relationships and morphology of working or rotating side TMJ.

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Left lateral opening border movement: From maximum left lateral superior border position an opening movement of mandible produces a lateral convex path. As maximum opening is approached, mandible moves medially causing Mandibular midline to coincide with midline of the face.

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Right lateral superior border movement: Mandible is returned to maximum intercuspation lateral movement is made to the right

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Right lateral opening border movement: From the maximum right lateral border position, an opening movement of mandible produces a laterally convex path. With maximum opening, mandible moves medially that causes a shift back in Mandibular midline to coincide with midline of face to end this movement.

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Functional movement It begins and ends at ICP. During chewing, the mandible drops directly inferiorly until desired opening is achieved. It then shifts to the side on which the bolus is placed and rises up. As it approaches maximum intercuspation, the bolus is broken down between the opposing teeth. In the final millimeter of closure, the mandible quickly shifts back to ICP.

ENVELOPE OF MOTION:

ENVELOPE OF MOTION By combining Mandibular border movements in three planes, a 3-D envelope of motion can be produced that represents the maximum range of movement of the mandible. The superior surface of the envelope of motion can be produced that represents the maximum range of movement of the mandible.

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The superior surface of the envelope is determined by tooth contacts whereas the other borders are primarily determined by ligament and joint anatomy that restricts or limits movement.

DETERMINANTS OF THE MANDIBULAR MOVEMENT:

DETERMINANTS OF THE MANDIBULAR MOVEMENT Mandibular movements are determined by: Anterior determinant Posterior determinant Neuromuscular determinant These determinants are the anatomic structures that dictate or limits the movement of the mandible.

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The anterior determinant  dental articulation Posterior determinants are temporomandibular articulation and their associated structures.

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Anterior determinants Vertical and horizontal overlap Maxillary lingual concavities of anterior teeth A greater vertical overlap  more vertical opening during early phase of protrusive movement & creates a more vertical pathway at end of chewing stroke.

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Increased horizontal overlap  allows more horizontal jaw movement Anterior determinants can be altered by orthodontic treatment.

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Posterior determinants Shape of articular eminences Anatomy of mesial walls of Mandibular process Configuration of Mandibular condylar process These can not be controlled.

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With Steeply sloped eminences, there is large downward component of condylar movement during lateral & protrusive excursion. The anatomy of medial wall allows condyle to move slightly medially as it travels forward. The side shift becomes greater as extent of medial movement increases.

MASTICATORY MANDIBULAR MOVEMENTS:

MASTICATORY MANDIBULAR MOVEMENTS The major function of mandible is to exert, via teeth, the force necessary to break down food into smaller particles. The range of masticatory Mandibular movements were 1 st described by Ulrich & Bennett at the turn of 20 th century. They showed that there was no fixed axis of rotation.

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Chewing stroke: The complete chewing stroke has a tear shaped movement pattern It has 2 phases: Opening phase Closing phase

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Opening phase Condyle moves forward along sagittal course for at least one quarter of time period of one complete opening closing cycle. The condyle then begins to move laterally and then posteriorly rapidly. After about ¾ of time period of one chewing cycle, the condyle is posterior, inferior and lateral to its ICP.

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Closing phase: Crushing phase Grinding phase Now the condyle moves anteriorly , medially & superiorly during final one quarter time frame of chewing cycle.

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1 st phase of closure traps the food between the teeth and is called as crushing phase . As teeth approaches each other ,the lateral displacement is lessened so that when the teeth are only 3mm apart the jaw occupies a position only 3-4mm lateral to the starting position of the chewing stroke. At this point teeth are so positioned that the buccal cusps of mandibular teeth are almost directly under buccal cusps maxillary teeth on the side to which the mandible has been shifted.

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As mandible continues to close, the bolus of food is trapped between the teeth which begin the grinding phase of closure stroke. Grinding phase -the mandible is guided by the occlusal surfaces of teeth back to the intercuspal position, which causes the cuspal inclines of teeth to pass across each other permitting shearing and grinding of bolus of food.

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Although mastication occurs bilaterally, about 78% of people have a preferred side where the majority of chewing occurs. This is normally the side with greatest no. of teeth contact in lateral glide. Persons with no such preference simply chew alternately. (J PROSTHET DENT 55: 498-500, 1986)

  FACTORS AFFECTING MANDIBULAR MOVEMENTS DURING CHEWING STROKE:

FACTORS AFFECTING MANDIBULAR MOVEMENTS DURING CHEWING STROKE Amount of lateral movement is greater when food is introduced and then becomes less as the food is broken down. Consistency of food- Hard foods –greater amount of lateral movement. Soft foods-lesser lateral movement eg.chewing on a carrot creates a broader stroke than while chewing on a cheese.

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Tall cusps and deep fossa -promote predominantly vertical chewing strokes where as flattened cut worn out teeth encourage a broader chewing stroke. Malocclusion produces an irregular and less repeatable chewing stroke Normal persons with good occlusion masticate with chewing stroke that are well rounded that have definite borders.

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Persons with TMJ disorders-strokes are shorter and slower & have an irregular pathway but repeatable pathways related to altered functional movement of the condyle around which the pain is centered.

METHODS USED FOR RECORDING MANDIBULAR MOVEMENTS:

METHODS USED FOR RECORDING MANDIBULAR MOVEMENTS Various graphic methods can be used to record Mandibular movements like: Gothic arch tracing Pantographs Kinesiographs

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Gothic arch tracing/ arrow point tracing: Also termed as central bearing tracing

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Gothic arch tracer:- the device that produces a tracing that resembles an arrowhead / gothic arch. The device is attached to opposing arches. The shape of tracing depends on relative location of marking point and the tracing table. The apex of a properly made tracing is considered to indicate the most retruded , unstrained relation of mandible to maxilla that is centric relation.

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Intra- oral arrow point tracing: The central bearing device is located intra-orally and is more simple. It consist of a recording plate attached to the maxillary teeth and a recording stylus attached to the mandibular teeth. As the mandible moves, the stylus generates a line on the recording plate that coincides with this movement Disadvantage: Tracer is not visible during the procedure and size of tracing is very small making it difficult to determine the apex of tracing.

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Extra-oral arrow point tracing: Same central bearing device as that of intra oral technique is used with additional attachments that project outside the mouth. An extra-oral tracing pointer and plates are situated extra-orally, tracing can be examined as it is made. Size of tracing pattern is also larger, thus apex can be identified easily.

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Pantographic tracings: It is an extra oral technique of recording jaw movements by graphical methods. The extra oral technique was pioneered by GYSI.

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It is defined as “a graphic record of Mandibular movement in 3 planes as registered by the styli on the recording tables of a pantograph; tracings of mandibular movement recorded on plates in horizontal and sagittal planes.”

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These equipments are very sophisticated and are generally not used for fabrication of complete denture. These tracers are generally used for full mouth rehabilitation of dentulous patients. Instrument used to do a pantographic tracing is called a pantographic tracer. It resembles a complicated face bow.

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Flag  the surface over which tracing is done. Stylus  a stylus is present for each flag. The styli draw tracing pattern on the flag. The pantographic tracer has 6 flags: 2 flags located perpendicular to one another near each condyle . Totally there are 4 flags adjacent to the right and left condylar guidance. They locate true hinge axis. 2 flags are placed in anterior region. They record the anteroposterior movement.

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Advantages of pantograph: This system can be used in diagnosis & treatment monitoring in TMJ-muscle dysfunction by assessing pantograph tracing reproducibility. Graphical data can be kept as permanent record

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Kinesiograph The Mandibular movements can be measured with a kinesiograph ( sirognathograph ) It does not interfere with jaw motion and can analyze spatial displacement of mandible. It uses magnets and magnetometers to sense the magnetic field as mandible moves in space. (J Prosthet Dent –Vol:68, No.4, 1992, 672- 676)

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Modification of magnetic fields are transferred into electrical potentials and fed directly to a computer that analyze mandibular movement in 3 spatial planes and records spatial coordinates: Sagittal Frontal Horizontal

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Other methods which can be used to measure Mandibular movement: Electro myographic analysis of jaw movements Study is conducted to determine the range of variability of muscular activity in jaw movements.

LIMITATION OF MANDIBULAR MOVEMENT:

LIMITATION OF MANDIBULAR MOVEMENT Trismus limits the mandibular movement and restricts opening of mouth. Limited oral opening restricts mastication, impairs speech and deglutition and limits access for dental treatment. ( J Prosthet Dent –Vol:59, No.3, 1988,330-333)

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Etiology: Acute factors Chronic factors Treatment related factors

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Acute factors: Trauma Infection Trauma can occur during an inferior nerve block injection  muscle inflammation  limits mandibular movement and pain. Infection can occur as a sequel of pericoronitis or oral surgery. Tetanus is specific infection of bacterial origin that results in progressive muscular rigidity with restricted mandibular movement and dysphagia . (J Prosthet Dent –Vol:59, No.3, 1988,330-333)

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Chronic factors: Most common- TMJ dysfunction It can result from: - poor joint architecture, -mal-position of the disk - occlusal disharmony Rheumatoid arthritis can also be a cause of TMJ pain and restricted mandibular movement. (J Prosthet Dent –Vol:59, No.3, 1988,330-333)

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Pathologic process in the TMJ space or surrounding area can mechanically limit mandibular movement. These processes include: - osteoma of mandibular condyle or zygoma - chondroma -fibrous dysplasia -cysts -overgrowth of condyle or coronoid process of the mandible.

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Intracapsular (true) or extracapsular ankylosis (false) of the TMJ can restrict mandibular motion. False ankylosis usually occurs as a result of zygomatic fracture.

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Treatment related factors: Limited mandibular movement often follows surgical treatment. After orthognathic surgery, it may be due to muscular atrophy as a result of fixation. Surgical resection of maxilla & mandible can also result in restricted movement of mandible. Radiation therapy may limit mandibular movement if the muscles of mastication are included in the treatment fields. It occurs due to muscle fibrosis caused by effect of radiation on the blood supply.

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TREATMENT: These include: physical therapy pharmacotherapeutics Surgery These modes can be used alone or in combination with other modes of treatment (J Prosthet Dent –Vol:59, No.3, 1988,330-333)

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Physical therapy: It includes: Exercise Use of mechanical devices Aids to improve circulation

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Exercise is the least invasive treatment and is especially helpful during radiation therapy, following orthognathic surgery and for scleroderma patients. An acceptable technique includes opening of mouth as wide as possible 20 times at least 3-4 times per day. In addition 8-10 actively assisted lateral excursions should be done to exercise the pterygoid muscles.

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Mechanical devices can be used to increase mouth opening on a slow, incremental basis. Tongue depressor can be lubricated with petroleum jelly or glycerine & placed between the arches for 1 min to increase opening. Additional depressors can be added one at a time to increase opening. A tapered, threaded acrylic screw can also be placed and turned between the teeth to apply an opening force to the mandible.

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The tongue depressor, clothespin and tapered screw produces a unilateral force. The dynamic opening device, the inflatable bite opener, and an intraoral prosthesis with inter-arch springs can also be used-these produce bilateral forces.

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Moist heat and ultrasound are used to improve circulation. Moist heat packs which contain silica gel and are covered with canvas can be placed in water and heated to 170 0 F. The packs are then wrapped in a towel and applied directly to the region. Moist heat stimulates circulation, lowers muscle tension, and has a sedative effect.

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Ultrasound applied to the pre-auricular region for 5-7 min to stimulate circulation, decrease inflammation and increase elasticity in muscle tissue.

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Pharmacotherapeutics : When limited mandibular movement is cause by infection, antibiotics are the treatment of choice. Penicillin V, 500 mg four times daily, is the drug of choice unless patient is allergic to penicillin. Alternatively erythromycin can be prescribed.

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Arthritic inflammation can be treated with NSAIDS, which ease pain and result in some improvement in motion. Muscle relaxants may help in acute cases of limited mandibular movement.

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Surgery: The primary purpose of surgery in treating limited mandibular movement is to expose and remove an irritant or growth that physically restricts mandibular movement. Surgery is the treatment of choice for removal of tumors, cysts or foreign bodies. Surgery may also be indicated in TMJ therapy, ankylosis , and scleroderma. (J Prosdent Dent –Vol:59, No.3, 1988,330-333)

CLINICAL SIGNIFICANCE OF MANDIBULAR MOVEMENTS::

CLINICAL SIGNIFICANCE OF MANDIBULAR MOVEMENTS: A prosthodontist designs a prosthesis to replace the lost teeth for replacement of missing teeth and restoring function. Knowledge of mandibular movements is essential as it may help the dentist in: understanding the occlusion treating TMJ disorders development of tooth for dental restorations arranging artificial teeth

CONCLUSION :

CONCLUSION Mandibular movement occurs as a complex series of inter-related 3 dimensional rotational and translational activities. It is determined by combined and simultaneous activity of both temporomandibular joints. Mandibular movement depends on certain anatomic limitations. The extremes, called border movements, are subject to restriction by the TMJs and ligaments and the teeth.

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Speech and mastication are examples of functional movements Bruxism and clenching are examples of parafunctional movements. These accomplish no purposeful objective and are potentially harmful. Knowledge of mandibular movements is very essential for prosthodontists as it helps in understanding the occlusion and arranging artificial teeth.

REFERENCES:

REFERENCES Mosby, management of temporomandibular disorders & occlusion, jeffrey P.Okeson Elsevier, Gray’s Anatomy, Susan Standring , 40 th edition Jaypee , textbook of oral and maxillofacial surgery, Neelima Anil Malik , 2 nd edition Textbook of complete dentures – Elsevier, Arthur O. Rahn & Charles M. Heartwell , 5 th edition Elsevier, contemporary fixed prosthodontics , Rosenstiel , Land, Fujimoto, 4 th edition

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Quintessence books, fundamentals of fixed prosthodontics , Herber T. Shillingburg , 3 rd edition J Prosthet Dent –Vol:59, No.3, 1988,330-333 J Prosthet Dent –Vol.4, No.5, 1954, 611-620 J Prosthet Dent –Vol:17, No.1,1967, 44-48 J Prosthet Dent –Vol:68, No.4, 1992, 672- 676

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J Prosthet Dent –Vol.13, No.3, 1963, 480-484 J Prosthet Dent –Vol.27, No.5, 1972, 524-532 J Prosthet Dent –Vol.25, No.3, 1971, 287- 298

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