TEMPOROMANDIBULAR JOINT & IT'S BIOMECHANICS.pptx

The temporomandibular joint (TMJ) is a pivotal component in prosthodontics due to its complex biomechanics and role in mandibular function. The TMJ consists of the mandibular condyle and the temporal bone, with an articular disc in between, facilitating smooth movement. Its biomechanics involve a combination of rotational and translational movements, essential for mastication, speech, and other mandibular activities. Understanding TMJ function is crucial in prosthodontics for diagnosing and treating disorders, designing prostheses, and ensuring proper occlusion and jaw alignment. Accurate assessment and management of the TMJ can significantly impact the success and comfort of prosthetic treatments

1. TMJ & IT’S BIOMECHANICS DR. SATVIKA PRASAD MDS DEPT. OF PROSTHODONTICS

2. INTRODUCTION The temporomandibular joint is unique in both structure as well as function. Structurally, the mandible is a horse shoe shaped bone that articulates with the temporal bone at each posterior superior end and produces 2 distinct but highly interdependent articulations. Each TMJ contains a disc that separates the joint into upper and lower articulations Functionally, mandibular movement involves concurrent movement in the four distinct joints, resulting in a complex structure that moves in all planes of motion to achieve normal function

3. WHAT IS BIOMECHANICS ? It is the study of structures and function of biologic system. WHAT IS BIOMECHANICS OF TMJ ? It is a complex combination activity, in which both right and left joints most function together in coordination of jaw movement. This is important to understand the function and dysfunction in masticatory system.

4. TEMPOROMANDIBULAR JOINT It is a diarthoridal , ginglymus , bicondylar variety of compound synovial joint where the condyloid process of the mandible and the articular disk articulates with the mandibular fossa of temporal bone. SYNONYMS OF TMJ- Craniomandibular joint Jaw joint Mandibular joint Synovial joint Ginglymus joint Diarthroidal joint Complex joint

5. Therefore it is called as GINGLYMOARTHROIDAL JOINT

6. COMPONENTS OF TMJ By definition, Compound joint is formed of 3 bones. However TMJ is formed of 2 bones- Mandibular condyle Temporal bone Articular disc Ligaments Capsule Associated muscles Bony Surfaces Separate these 2 bones and function as non ossified bone

7. GLENOID FOSSA – ARTICULAR EMINENCE The glenoid or mandibular fossa , is the concavity in the temporal bone that houses the mandibular condyle. Its, Anterior wall is built by the articular eminence of the squamous part of temporal bone Posterior wall- by tympanic plate of temporal bone {which also forms anterior wall of Ext. Acoustic Meatues } MANDIBULAR CONDYLE The articular surface of the mandible is the upper and the anterior surface of the condyle.

8. ARTICULAR DISC It is BICONCAVE firm, oval, fibrous plate that is positioned between the mandibular condyle and the articular fossa and eminence and divides the joint in upper and lower compartment It’s a non ossified bone which permits complex movements of the joint Consists of dense collagenous tissue devoid of blood vessels and nerve fibres. Its has 3 zones- [in sagittal plane] Anterior part - about 2mm Intermmediate part – thinnest – 1mm Posterior part – about 3mm Normally, the joint is placed in the intermediate zone.

9. FUNCTIONS OF ARTICULAR DISC Accommodate hinge and gliding action Act as shock absorber Shape and thickness- governed by muscle forces controlling position of mandible and condyle. Stabilizes condyle within TMJ Reduces wear of TMJ Aids lubrication of the joint by storing fluid squeezed out from loaded area.

10. CAPSULE The fibrous capsule is attached above to the articular tubercle, the circumference of the mandibular fossa in front and the squamotympanic fissure behind, and below to the neck of the mandible. The capsule is loose above the intra-articular disc, and tight below it The synovial membrane lines the fibrous capsule and the neck of the mandible.

11. LIGAMENTS

12. CAPSULAR LIGAMENT- The entire TMJ is surrounded and encompassed by the capsular ligament. Function- to encompass the joint, thus retaining the synovial fluid. COLLATERAL (DISCAL) LIGAMENTS- Attach medial and lateral borders of the articular disc to the poles of condyle There are 2- Medial discal ligament – attach medial edge of the disc to the medial pole of the condyle Lateral discal ligament – lateral edge to the lateral pole of the condyle These ligaments are responsible for hinging movement of the TMJ The discal ligaments have vascular supply and are innervated LATERAL TEMPOROMANDIBULAR LIGAMENT- It reinforces and strengthens the lateral part of the capsular ligament. It is attached above to the articular tubercle , and below to the posterolateral aspect of the neck of the mandible.

13. SPHENOMANDIBULAR LIGAMENT- arises form the spine of the sphenoid bone and is directed downward and outward, inserting on the mandible at the lingula . It has NO influence on the mandibular movement. STYLOMANDIBULAR LIGAMENT- it extend from the styloid process and the stylohyoid ligament to the region of the mandibular angle. This ligament is relatively, Loose - when the jaws are closed or they are wide open Tensed - when mandible is maximally protruded Thus, apparently, this ligament can limit excessive protrusive movements

14. MUSCLES Masster muscle Temporalis muscle Medial pterygoid muscle Lateral pterygoid muscle Diagastric muscle Mylohyoid muscle Geniohyoid muscle

15. MUSCLE ORIGIN INSERTION ACTION MASSTER Zygomatic arch Lateral surface of ramus Elevates the mandible TEMPORALIS Temporal fossa Coronoid process Elevates the mandible Side to side grinding movement Posterior fibres retract the protruded mandible LATERAL PTERYGOID Lateral pterygoid plate Anterior margin of articular disc and capsule; anterior surface of neck of mandible Depress mandible Right lat. Pterygoid & right med. Pterygoid – turn chin to left side - for grinding movements MEDIAL PTERYGOID Medial surface of lateral pterygoid plate Medial surface of angle and ramus of mandible Elevates mandible DIAGASTRIC Posterior belly- mastoid process of temporal bone Ant. Belly- digastric fossa of mandible Both unite to form intermediate tendon and inserts onto hyoid bone Opens the jaw when masseter and temporalis are relaxed MYLOHYOID Mylohyoid line Body of hyoid bone Depresses mandible GENIOHYOID Inferior mental spine of mandible Hyoid bone Depresses mandible

16. 1. Depression (Opening the mouth): By Digastric, Geniohyoid & Mylohyoid muscles assisted by gravity. Because it involves forward movement of head of mandible, lateral pterygoid is also involved. 2. Elevation (Closing the mouth): By temporalis, masseter & medial pterygoid muscles. is a very powerful movement. 3. Protraction (Protrusion): By mainly lateral pterygoid muscle, with some assistance by medial pterygoid . 4. Retraction ( Retrusion ): By Geniohyoid , Digastric & posterior and deepfibers of temporalis and masseter muscles, respectively. Both head of mandibule & articular disc slide anteriorly and posteriorly on the articular surface of the temporal Bone with both sides moving together. 5. Lateral Chewing Movement (Grinding movement): By alternative protrusion & retraction of the mandible on each side. Also during chewing a certain amount of rotation occurs. MOVEMENTS

17. EXAMINATION OF TMJ

18. HISTORY QUESTIONS TO BE ASKED: Do you have pain in the face, front of ear and the temple area? Do you get headaches, earaches, neck ache, or cheek pain? When is the pain at its worst? Does your jaw ever lock or get stuck? Have you had any jaw injury? Have you had treatment for jaw symptoms? if so, what was the effect Do you experience pain when using the jaw? Do you experience pain in the teeth? Do you experience joint noises when moving your jaw or chewing? Does your jaw motion feel restricted? Do you have any other muscle, bone, or joint problem such as arthritis?

19. INSPECTION Facial asymmetry Masseter muscle hypertrophy Temporalis muscle hypertrophy Opening pattern Alignment of teeth

20. DEVIATION DEFLECTION Any shift of jaw midline during opening that disappears with continued opening Any shift of midline to one side that becomes greater with opening that does not disappear at maximal opening Due to disc derangement Due restricted movement of joint

21. Examine hands for systemic disease E.g. - Heberden’s nodes of osteo-arthrosis , ulnar deviation of rheumatoid arthritis, which may also involve TMJ

22. PALPATION Areas of tenderness or swelling Sensitivity and distribution of symptoms Range of mandibular movements, Detection of click and/or crepitus. The TMJ can be palpated by extra-auricular and intra-auricular methods. Palpation can be done standing at 10 o'clock or 11 o'clock position

23. RANGE OF MANDIBULAR MOVEMENT The maximum opening distance between the incisal edges of upper and lower incisor is measure by using scale, Boley gauge or ruler Normal opening- 40 – 55 mm It can be estimated by patient’s own or clinician’s finger Normal – 3 finger end on end 2 finger- reveals opening in reduction but NOT necessarily reduction in function 1 finger- indicates reduction in function

24. Normal lateral movement is > 7mm Measurements are made with teeth slightly separated , measuring the displacement of lower midline from maxillary midline. Any condition like tumour, muscle spasm, fracture, ankylosis etc will prevent the normal translation of one condyle will not prevent the contralateral condyle from sliding forward normally. The result is deviation of the chin toward the affected side.

25. Intra-auricular Intra-auricular palpation can be achieved by placing a little finger inside the external auditory meatus. During mandibular movement the posterior pole of the condylar head can be palpated with the pulp of the little finger. Intra-auricular palpation may also be used to elicit capsular tenderness. Extra-auricular Extra auricular examination of TMJ is done by placing index finger in the pre-auricular region about 1.5cm medial to the tragus of ear. The lateral pole of the condyle is accessible during this examination. Examination of TMJ

26. Masticatory muscle Masseter Place your palpating finger pads between the zygomatic arch and the angle of the mandible. Ask the patient to alternately contract and relax the masseter; clenching the teeth and then relaxing the jaw will accomplish this. Feel for the contraction of the masseter as the client clenches the teeth . Once the contraction of the masseter has been felt, palpate the entire muscle from the zygomatic arch to the angle of the mandible as the client continues to contract and relax it.

27. Temporalis Place your palpating finger pads over the temporal fossa on the head (superior to the ear). Ask the client to alternately contract and relax the temporalis; clenching the teeth and then relaxing the jaw will accomplish this. Feel for the contraction of the temporalis as the client clenches the teeth. Once the contraction of the temporalis has been felt, palpate the entire muscle as the client continues to contract and relax it

28. Lateral Pterygoid Wearing either a glove or a finger cot, place your palpating finger inside the vestibule of the client’s mouth (between the cheeks and the teeth) and run along the external surfaces of the upper teeth until you reach the back molars. Then press posteriorly and superiorly into a little pocket in the tissue between the gum above the upper teeth and the condyle of the mandible. You will be on the internal surface of the lateral pterygoid Now ask the client to gently either protract the mandible at the TMJs or deviate contralaterally the mandible slowly and carefully (deviate it to the opposite side of the body). Feel for the contraction of the lateral pterygoid Once felt, palpate as much of the lateral pterygoid as possible, from the condyle of the mandible to the inside wall of the mouth (above the gum of the upper teeth)

29. Medial Pterygoid Place your palpating finger along the internal surfaces of the lower teeth until you reach the back molars, then press posterolaterally until you reach the inside wall of the mouth. Now ask the client to protract the mandible. Feel for the contraction of the medial pterygoid . Once felt, palpate as much of the medial pterygoid as possible. From outside the mouth: Curl your palpating fingers around to the inside surface of the angle of the mandible. Ask the client to elevate the mandible at the TMJs by clenching the teeth. Feel for the contraction of the medial pterygoid

30. Digastric Muscle Identify the lateral margins of the hyoid, and then palpate the inferior surface of the mandible by placing the thumbs on either side of the midline To confirm the location , patient is asked to swallow A prominence of the anterior belly can be palpated under the thumb tips as the hyoid is drawn superiorly

31. AUSCULTATION There are 2 types of joint sound to look out for:- Clicks - single explosive noise of short duration. Crepitus - continuous 'grating' noise

32. Doppler Auscultation Doppler Auscultation allows to listen to patient’s joints by using a stethoscope with a microphone that incorporates the Doppler wave effect. Piper Classifications helps to assess a patient’s joint health when using Doppler Auscultation. By listening to the joint, and noting when the pop or click occurs, we can determine where the disc is off. We Diagnose the TMJ problem as classifications of 1 through 5. For example: Class 1 - denotes a normal joint. Class 2 and 3 - means that the patient has lateral pole issues if the noises occur after translation has begun. Class 4 and 5 - means the patient has medial pole issues because the pop, or click occurs during rotation and the disc is displaced.

33. RADIOGRAPHY X Ray Ultrasound can be useful in assessing the extent of disc derangement MRI is considered gold standard MRI

34. SPECIAL TESTS & OUTCOME MEASURES 1. Tongue blade test This test is used to screen the patient as to whether they require diagnostic imaging. The patient holds the tongue depressor between their teeth whilst the practitioner tries to snap it. The test is positive should this maneuver illicit a discomfort that forces the patient to let go of the tongue depressor before it snaps . 2. Oral Behaviours checklist (OBC) This checklist assists in objectively recording whether any accessory behaviors induced by circumstances such as stress and anxiety are contributing to the condition.

35. PROSTHODONTICS IMPLICATIONS OF TEMPOROMANDIBULAR JOINT WHY TMJ IS IMPORTANT FOR PROSTHODONTISTS? Muscles + joints + teeth Neuromuscular dentistry Teeth must fit into harmony of jaw relationship not vice versa

36. BIOMECHANICS OF TMJ Functional movements of TMJ Disc control Mandibular movements

37. VERTICAL DIMENSION The dimension that determines VDO is located at the elevator muscles because it is the repetitive contracted length of the muscles that establishes the jaw-to-jaw vertical position at maximum intercuspation . This dimension at maximum intercuspation is controlled by the muscles, regardless of condylar position. This means that if condyles are displaced vertically down the eminentia at maximum intercuspation , the dimension from muscle origin to insertion is shortened when the condyles are seated up into CR

38. Centric relation is the relationship of the mandible to the maxilla when the properly aligned condyle disc assemblies are in the most superior position against the eminentiae irrespective of vertical dimension or tooth position. - GPT 8 CENTRIC RELATION

39. HOW MANDIBLE GOES INTO CENTRIC RELATION A) Superficial masseter moves the condyle UP against the posterior slope B) The medial pterygoid moves the condyles UP from the lingual side of the mandible C) The temporalis attach to the coronoid process between the teeth and the TMJs and moves the condyle UP

40. JOINT SYSTEMS ONE JOINT SYSTEM- ROTATION is the only physiologic movement. As the disc is tightly bound to the condyle by lateral and medial discal ligaments. Forms a condyle disc complex.

41. SECOND JOINT SYSTEM- Free sliding movement of the disc occurs as the disc is not attached to the articular fossa between the superior surface of the joint cavity , referred to as TRANSLATION

42. Normal functional movement of the condyle and disc during the full range of opening and closing. Note that the disc is rotated posteriorly on the condyle as the condyle is translated out of the fossa. The closing movement is the exact opposite of the opening movement.

43. MANDIBULAR MOVEMENTS Acc. to Osken there are 2 types of movements - Rotational / hinge- Occurs mainly between the disc and the condyle in the lower joint compartment Translation / sliding – Occurs mainly between the articular eminence and disc (and mandible) in the upper compartment Based on the plan of border movements- Horizontal Vertical / frontal Sagittal plane movements

44. Horizontal orientation axis : opening and closing movement, referred to as a hinge, therefore it occurs around an axis called the hinge axis. It is considered the purest rotation movement Vertical axis of rotation : Also called frontal axis. It occurs when one of the condyles moves anteriorly from the position of the terminal hinge axis with the vertical axis in the opposite condyle, which remains in said axis. This type of movement does not occur normally Sagittal axis of rotation : Occurs when one of the condyles moves inferiorly while the other remains in the position of the terminal axis. This movement occurs in conjunction with other movements. Mathematical studies indicate that in this plane there is the same contact and muscle activity from one side to the other, so there are no alterations in dental occlusion that result in a joint without load

45. ECCENTRIC MANDIBULAR MOVEMENTS Any movements of the mandible apart from centric occlusal position that results in tooth contact is called as eccentric movement Types of eccentric movements – Protrusive movements Retrusive movements Laterotrusive movements

46. PROTRUSIVE MOVEMENTS A protrusive movement occurs when the mandible moves (both the condyles) forward and downward along the incline of the articular eminence. Occurs while incising and grasping food. This movement occurs after the condyle rotates about in TMJ. Posteriorly is guided by the articular eminence {condylar path guidance} Anteriorly is guided by sliding of the lower anterior teeth incisal edges on the upper anterior teeth palatal concavities { incisal guidance} In Posselt’s envelope, it occurs in the upper surface. Starting from the position 1 to edge to edge , and ending at position 5 The retrusive movement takes place by the similar movement as the protrusive but in reverse manner (upward and back ward movement) Sagittal protrusive condylar path : 5-55 ̊ and mean is 30 ̊ Sagittal protrusive incisal path range : 70 ̊ Retruded contact position Habitual intercuspal position (maximum intercuspation ) Edge to edge occlusion Anterior biting to a reverse vertical overlap Protruded contact position

47. LATERAL MOVEMENTS Sagittal lateral condylar path : When lateral movement is executed, the working condyle rotates and moves outward while other, non working condyle translates forward, medially downward orbiting around the rotating working condyle Lateral movement of the mandible is the result of contraction of one lateral pterygoid muscle. When the lateral pterygoid muscle of one side contracts the mandible moves to the opposite side. This orbiting condylar path of working condyle is called as BENNETT MOVEMENT

48. Components of lateral movement The side to which the mandible is moving is called the WORKING SIDE The side that is opposite to the working side is called BALANCING OR NON WORKING SIDE The condyle on the working side is called the WORKING OR ROTATING CONDYLE (it rotates around the vertical axis and then shift in lateroposterior direction making the Bennett's movement. The non-working condyle is called THE BALANCING OR THE ORBITING CONDYLE (it moves forward downward and medially

49. Bennett's movements ( Laterotrusion ) It is the lateral bodily shift of the mandible resulting from movements of the condyles along the lateral inclines of the mandibular fossae in lateral jaw movement. Bennett angle: the angle formed between the sagittal plane and the average path of the advancing condyle (at the balancing side) as when viewed in the horizontal plane during lateral mandibular movements. All of these movements occur within an envelope of movement called posselt's envelope Bennet angle [L] = H/8 +12 {H=horizontal condylar inclination} Avg. = 7.5 ̊ to 12.8 ̊

50. ENVELOPE OF MOTION Dr. Ulf Posselt in 1952 first described a 3D concept of mandibular movements. It was a combination of border movements in all 3 planes- Sagittal Horizontal Frontal Although it has characteristic shape it varies from person to person but it has same characteristic shape. The superior surface of the envelope is determined by the tooth contacts. The others borders are primarily determined by the TMJ anatomy and the ligaments.

51. The mandibular movements are limited by ligaments, the articular surfaces of the TMJ, and the morphology and alingment of the teeth. The outer range of movement is reproducible and called border movements The outer border of this envelope of motion is known as “ border movement ”. Any other movements occur within the border is called intra border movement, it appears as a drop of water. RCP= retruded contact position ICP= intercuspal position Pr = maximum protrusion R= maximal mandibular opening with the condylar heads in the reproducible retruded position T= maximal mandibular opening with full antero-inerior translation of the condylar heads RCP-ICP= this path is termed as slide. It has the potential for horizontal, vertical and lateral components. The lateral element to this slide cannot be seen in the sagittal plane. E= edge to edge position of incisors

52. BORDER MOVEMENTS IN SAGITTAL PLANE In Centric relation contact (CRC) we will see the condyles in the glenoid fossa and closure of the mandible along the hinge axis, until first tooth contact is made.

53. Centric occlusion (CO), or Maximum intercuspation (MI), is achieved when the patient is told to get their maxillary and mandibular teeth together in a comfortable contacting position

54. The mandible will open along the hinge axis, with the condyles rotating within the glenoid fossa. The rotational movement will terminate at the Terminal Hinge Axis Position (THA) The terminal hinge axis is the rotational movement that occurs from CR to THA position Maximum opening displays the most inferior position of the mandible, after the patient is instructed to open their mouth as wide as they can

55. Maximum protrusion depicts complete contact with the teeth as the mandible is completely protruded anteriorly. It is the most anterior of the positions, when viewed from the sagittal plane. Edge to edge contact of maxillary and mandibular incisors Mandible is protruded from MI , maintaining some type of tooth contact throughout

56. BORDER MOVEMENTS IN HORIZONTAL PLANE Characteristically described as a “DIAMOND” shape Parallel to the occlusal plane or the floor

57. CR . First tooth contact when the condyles are maximally situated in the glenoid fossa CO. Maximum intercuspation of the teeth in horizontal plane Edge to edge incisal position of the teeth in horizontal plane.

58. As the mandible opens, the size of the horizontal plane border decreases until it reaches a “point” at the maximum opening position

59. BORDER MOVEMENTS IN FRONTAL PLANE Viewing the frontal plane is described as “SHIELD” diagram

60. Maximum opening of the mandible in the frontal plane. This is the most inferior position

61. SAGITTAL PLANE FRONTAL PLANE HORIZONTAL PLANE

62. Most common conditions affecting TMJ in a prosthetic set up Occlusal discrepancies Dysharmony between centric relation & occlusion Bruxism Trauma Mal- alingment of the occlusal surfaces of the teeth due to defective crowns or other restorative procedures Excessive gum chewing and nail biting Degenerative joint diseases, e.g. osteoarthritis

63. Primary requirements for successful occlusal therapy Stable TMJ Non interfering posterior teeth Anterior teeth in harmony with envelope of function TREATMENT Restoration of the occlusal surfaces of the teeth A) selective reshaping or grinding of teeth B) crown, bridges, implants Occlusal splints (night guards / mouth guards) Orthodontic treatment / orthoganathic surgery

64. CONCLUSION Dentist must assess the oral function of patients prior to any treatment, since mastication is the most important oral function and is closely associated to TEMPOROMANDIBULAR JOINT. Therefore, examination of TMJ and thorough knowledge of its anatomy and functioning are the keys for successful PROSTHODONTIC treatment.

65. REFERENCES Oral and maxillofacial surgery – Fonseca – 4 th edition Stratmann U, Mokrys K, Meyer U, Kleinheinz J, Joos U, Dirksen D, Bollmann F. Clinical anatomy and palpability of the inferior lateral pterygoid muscle. The Journal of prosthetic dentistry. 2000 May 1;83(5):548-54. Kaur H, Datta K. Prosthodontic management of temporomandibular disorders. The Journal of Indian Prosthodontic Society. 2013 Dec;13(4):400-5. YATANI H. Clinical Consideration for Prosthodontic Approach Based on the TMJ Imaging Analysis. 日本補綴歯科学会雑誌 . 1999;43(1):27-36. Ai M, Yamashita S. Tenderness on palpation and occlusal abnormalities in temporomandibular dysfunction. The Journal of Prosthetic Dentistry. 1992 Jun 1;67(6):839-45.