Tmj muscles &movements / fellowships in orthodontics


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Tmj muscles &movements / fellowships in orthodontics

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  3. 3. ANATOMY OF TMJ • It is synovial joint of condylar variety • It consists of two components 1. Osseous components 2. Soft Tissue components Osseous components - Glenoid Fossae - Articular eminence - Head of the mandible - Condylar Process - Neck - The convex superior surface of the condyle articulates with the concave inferior surface of the articular
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  5. 5. SOFT TISSUE COMPONENTS • Articular disc :: Flat, circular or dense fibrous tissueFlat, circular or dense fibrous tissue connective tissue plateconnective tissue plate • Concavo convex superior surface and concaveConcavo convex superior surface and concave inferior surface.inferior surface. • Superior surface permits gliding movements andSuperior surface permits gliding movements and inferior surface permits rotation and glidinginferior surface permits rotation and gliding movementsmovements • The presence of articular disc differentiates a TMJThe presence of articular disc differentiates a TMJ from any other joint in the body making it a bonefrom any other joint in the body making it a bone to tissue and tissue to bone tissue and tissue to bone articulation.
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  7. 7. ARTICULAR CAPSULE • Loose thin, sack of fibrous connective tissue • Attached to the border of articulating surface of temporal bone and (neck) condyloid process • Lateral surface of the capsule is strengthened by temporomandibular ligament. • Sphenomandibular ligament: – Spine of sphenoid-inserts into mandibular ligament • Stylomandibular Ligament: – Styloid process- mandibular angle • Temporomandibular ligament
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  9. 9. MUSCLES OF TMJ • Muscles involved in functioning and stabilizingMuscles involved in functioning and stabilizing of the TMJ are:of the TMJ are: 1.1. Masticatory musclesMasticatory muscles 2.2. The suprahyoid musclesThe suprahyoid muscles • Muscles of Mastication: – MasseterMasseter – TemporalisTemporalis – PterygoidsPterygoids – LateralLateral –
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  11. 11. ROLE OF MASCULATURE IN MANDIBULAR MOVEMENT Lateral Pterygoid • Consists of Superior head and Inferior head • Muscle which runs in a horizontal direction • Chief muscle for the protraction of mandible • As it relaxes, the posterior fibres of temporalis muscle pull the condyle back to its centric position • When it contracts it draws forward the condyle along with the disc. • If this muscle contracts one side and remains relaxed on other side then the mandible will be moved laterally on other side
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  14. 14. Superior head • Superior head is active only on closing. It braces the disc against the posterior slope of articular eminence Inferior head of the lateral • Active only on opening movement Harmonious Contraction • When both the heads contracts there is synchronization of superior and inferior head during protraction thus permitting the condyle and disc to move forward. Simultaneously when there is relaxation of these two heads the muscle permit the condyle disc assembly to go back to centric position
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  17. 17. MEDIAL PTERYGOIDMEDIAL PTERYGOID • The external pterygoid moves the condyle forward and the internal pterygoid on one side moves the body of the mandible laterally to the opposite side. • Acting together it elevates the mandible, acting alone it draws the mandible laterally Masseter: • Superficial fibres- elevate mandible • Deep fibres – horizontal in direction – assist in retraction of mandible
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  22. 22. TEMPORALISTEMPORALIS • Posterior fibres are forward and towards the ascending ramus when they contact, retrade the mandible • Middle fibres – vertical elevate the mandible • Anterior fibres- protrudes the mandible • When all fibres contract simultaneously elevate the mandible Temporalis and Masseter • Are closing muscles and also retrude mandible. It is interesting to observe that the temporalis is attached to the anterior upper part of ascending ramus and the masseter is inserted down below on the outer surface of ramus. So this pattern of insertion stabilizes mandible in position during function.
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  24. 24. SUPRAHYOID MUSCLESSUPRAHYOID MUSCLES These muscles help the mandible to depress they are Diagastric Stylohyoid Mylohyoid Geniohyoid Blood Supply:: Superficial temporal artery Deep part of maxillary artery Nerve supply: Sensory – Auriculotemporal Motor – Messentric
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  26. 26. MANDIBULAR MOVEMENTSMANDIBULAR MOVEMENTS Significance of understanding mandibular movements Knowledge of mandibular movements is essential to develop 1. Tooth forms 2. Understanding occlusion 3. For arranging artificial teeth 4. Treating TMJ disturbances 5. Preserving periodontal health 6. Designing, selecting and adjustment of articulators
  27. 27. The major structures to be observed in the TMJ movement are: 1. The fossa with articular tubercle 2. Articular disc 3. Mandibular condyle The two basic movements – Rotation – Translation
  28. 28. • Rotation: Rotational movement is the one in which all the points within a body describe concentric circles around a common axis, i.e., the body changes its position but not place. • Translation: This is the one in which all the points within a body are moving at the same velocity and in same direction.
  29. 29. • The mandibular movements are related to three planes of the skull – horizontal, frontal and Sagittal and are usually described as three dimensional • Dimension is defined as magnitude measured in a particular direction or along a diameter or principle axis.
  30. 30. Schematic representation of TMJSchematic representation of TMJ movementmovement The line A – A represents a line of reference drawn vertically through the tissues to changes in position of the related structures as they refer to centric occlusion.
  31. 31. The tissues have been changed in position as the mandible separates teeth from centric occlusion. There has been essentially a rotatory movement of the condyle head
  32. 32. Represents purely translatory movement
  33. 33. Mandible has been extended beyond the respiratory rest position. Joint has a combination of small degree of both translatory and rotary movement.
  34. 34. Marked translatory and additional rotary movements of all element of the joint.
  35. 35. Axis of RotationAxis of Rotation • Rotational movements of mandible are made around three axis: 1. Transverse 2. Vertical 3. Sagittal
  36. 36. Transverse axisTransverse axis • During opening and closing the mandible moves in the Sagittal plane around a transverse axis • Passes through or near both the axis •Transverse axis can be located when opening and closing occur with the mandible in its most position • Transverse axis moves as the mandible is moved in lateral, protrusive and latero protrusive movement • If the mandible is in a forward position and opening and closing occurs, the rotation will still take place about the same transversal axis, however since the mandible cannot be fixed in space in the forward position, the transverse axis will be instantaneous for any given location and will move & tilt the
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  38. 38. Vertical AxisVertical Axis • In lateral excursion the mandible around a vertical axis passing through or near the condyle on the working side and condyle on the balancing side moves forward and medially.
  39. 39. Sagittal AxisSagittal Axis • During lateral mandibular movement, the condyle on the balancing side that is moving forward and medially also moves downward movement of the condyle on the balancing side causes the mandible to rotate around a Sagittal axis passing through or near the condyle on the working side As the condyle on the working side rotates around the vertical axis the Sagittal moves in a corresponding manner
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  41. 41. Border movementsBorder movements • Border movements of mandible in any direction in which it moves • The envelope of motion of the mandible in the border positions has been recorded in three planes – Horizontal, Frontal, and Sagittal • Different types of border movements: – Opening and closing – Protrusion – retrusion – Lateral shift • The envelope id the locus of the ultimate intersections of a series of curves or surfaces
  42. 42. Envelope of motion in SagittalEnvelope of motion in Sagittal planeplane • The mandibular movements tracings were made with a head attached to lower central incisors and the envelope of motion was plotted • The diagram shows the envelope of motion I.e., maximum border movements in the Sagittal plane. • The tracing starts at P (most protruded position). As the mandible is moved posteriorly while tooth contact is maintained, a dip in the top line of the tracing occurs as the incisor pass across one another • Centric occlusion (Co0 is reached when there is maximum interruption. • When the mandible is further retruded, posterior position of the mandible in the Glenoid fossa is depicted by centric relation (CR)
  43. 43. Envelope of motion in SagittalEnvelope of motion in Sagittal plane (Contd.)plane (Contd.) • As the teeth separate from CR the mandible and the patient continue to open this retruded, with no apparent condylar translation to MHO (Maximum hinge opening) • CR + MHO Terminal hinge movement • As the patient further open the mouth the mandibular condyle moves anteriorly in the Glenoid fossa depicting translation till MO (Maximum opening) • At this point the condyle are in an near their most anterior downward position in fossae • The most forward line on the tracing, running from MO to P, represents the pathway of the mandible as it is moved from its most opening position upward to its most protruded position.
  44. 44. • Any mandibular movementAny mandibular movement observed from the side will fallobserved from the side will fall within this envelope of motionwithin this envelope of motion since it represents all extremesince it represents all extreme positionposition • When the patient is relaxed andWhen the patient is relaxed and the jaws in the resting position.the jaws in the resting position. Rest position occursRest position occurs somewhere downward slightlysomewhere downward slightly forward of CR.forward of CR.
  45. 45. Envelope of motion in frontalEnvelope of motion in frontal planeplane
  46. 46. Bennett MovementBennett Movement • Bennett movement is the bodily side shift of the mandible which when it occurs may be recorded in the region of the rotating condyle on the working side • Demonstrated by Bennett in 1908 • Bennett studied working condylar path moved outwards during sideward movement of mandible in frontal plane, where as the non-working condyle moved inward or medially • The orbiting condylar path consists of two components namely, ISS PSS ISS: Occurs when non working condyle moves from centric relation straight inward
  47. 47. • PSS: Is translatory portion of lateral movement – Cause of Bennett movement is connection of external pterygoid muscle Importance of Bennett Movement : – Its direction and timing influence the freedom of movement to and from centric and eccentric jaw positions. – Balanced gliding occlusion will be difficult to achieve if the direction and timing of Bennett movement is not recorded and transferred to articulator Bennett Angle : Angle formed by the horizontal lateral condylar path and sagittal plane (mean value 160 )
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