1. The document discusses jaw movements and positions, focusing on the temporomandibular joint and mandible. 2. It describes the temporomandibular joint in detail, including its components like the condyle, articular disc, and fossa. It also discusses the different types of mandibular movements like protrusion, retrusion, and lateral movements. 3. Mandibular movement is classified as rotational or translational depending on the dimensions involved. The main types of rotational movement are hinge, protrusive, and retrusive movements.

1. GROUP 5 ASSIGNMENT

2. OBASANYA Adedotun Augustine-DEN/2007/051 (CHAIRMAN) OGUNLOLA OmowumiAbosede-DEN/2007/057 (SECRETARY) DADA Babatunde- DEN/2007/036 OKUNOLA Ibukunoluwa Esther- DEN/2007/063 IWEGBU Samuel Enere -DEN/2007/046

3. JAW MOVEMENTS AND POSITIONS

4. Introduction MANDIBLE It is the largest and strongest bone of the face. It develops from the first pharyngeal arch. It has a horse - shoe body which lodges the teeth, and a pair of rami which projects upwards from the posterior ends of the body and provide attachments to muscles To study mandibular movement one should have knowledge about anatomy of temporomandibular joint, function and neurophysiology of masticatory system and mechanism of mandibular movement.

5. Temporomandibularjoint The temporomandibular joint, or TMJ, connects the lower jaw called the mandible, to the temporal bone at the side of the head. There are two temporomandibularjoints, one on each side of the jaw. Since TMJ are flexible, the jaw can move smoothly up and down and side to side, allowing us to talk, chew and yawn. Muscles attached to, and surrounding the joint, control its position and movement

6. Temporomandibular joint When opening the mouth, the rounded ends of the lower jaw joint, called condyle, glide along the joint socket of the temporal bone The condyle slide back to their original position when we close our mouth

7. Articular disc divides the joint cavity into upper and lower cavities Mandibular notch

8. Temporomandibular joint Movements Protrusion or protraction, Retraction, Depression, Elevation Muscles involved are known as muscles of mastication. Muscles of mastication are –temporalis, masseter, lateral pterygoid (L Pt), Medial pterygoid( M Pt)

9. Temporomandibular joint Protraction is brought about by lateral pterygoid assisted by medial pterygoid

10. Retraction by posterior fibers of temporalis •Elevation-temporalis , masseter and medial pterygoid

11. Lateral chewing movements-alternately protruding and retracting the mandible on each side with a certain amount of rotation

12. Determination of mandibular movements Factors that determine mandibular movements are: 1. Condylar guidance 2. Incisal guidance 3. Neuromuscular factors

13. Condylar guidance(posterior determinant) It can be defined as the mandibular guidance generated by the condyle and articular disc traversing the contour of the glenoid fossa. The condyle moves along the glenoid fossa during mandibular movements . Hence, the surface of the glenoid fossa determines the path of movement of the condyle. The slope of the glenoid fossa is a S-bend, hence the condyle moves along a S-shaped path.

14. Incisal Guidance(anterior determinant) It is defined as the influence of the contacting surfaces of the mandibular and the maxillary teeth during mandibular movements. During protrusion, the incisal edge of the lower anteriors slide along the slope of the lingual surface of the upper anterior teeth before reaching edge-to-edge contact. The incisal guidance is absent in a completely edentulous patient. It is reproduced in the complete denture by arbitrarily setting the anteriors using a standard incisal guide value and modifying to suit the patient during aesthetic anterior try-in.

15. Neuromuscular factors The muscles of mastication are the most important determinants of mandibular movements. Many neurological disorder like parkinsonism produce muscle dysfunction Each muscle has a specific action on the mandible The movement of the mandible in any direction is predominantly controlled by one particular muscle and is coordinated by the remaining. When there is hypertrophy or dysfunction of one group of muscles, the movement of the mandible is un-coordinated and asymmetrical.

16. MECHANISM OF MANDIBULAR MOVEMENT

17. Mandibular movement occurs as a complex series of interrelated three dimensional rotation and transitional activities. It is determined by combined and simultaneous activities of both temporomandibular joints. Although the TMJ is cannot function entirely independent of each other, they also rarely function with identical concurrent movement.

18. Types of mandibular movement A. Based on the dimension involve in the movement. Rotation Translation B. Based on the type of movement Hinge Protrusion Retrusion Lateral movement C. Based on the extent of movement Border movement Intra-border movement

19. CLASSIFICATION Mandibular movement occur as a complex series of interrelated 3-D ROTATIONAL and TRANSLATION activities.

21. In the masticatory system, rotation occurs when the mouth opens and closes around a fixed point or axis within the condyles.

22. In TMJ, rotation occurs as the movement within the superior surface of the condyle and the inferior surface of articular disc.

24. Mandibular movement in horizontal axis is an opening and closing motion. Know as hinge movement (example of mandibular activity In which a pure rotational movement occurs ) a) Horizontal

25. b) Frontal

26. c) Saggital Occurs when one condyle moves inferiorly while the other remains In the terminal hinge position.  because the ligaments and musculature of TMJ prevent an inferior displacement of the opposite condyle movements.

28. Protrusive movement It occurs while incising and grasping food. This movement occurs after the condyle rotates for more than 13⁰ in the temporomandibular joint. When the mandible slides forward and the mandibular and maxillary anterior teeth are in edge to edge relation, the protrusive movement is said to be complete.

29. Retrusive movement It occurs when the mandible is forcefully moved behind its centric relation. It is usually not a common movement and the patient cannot voluntarily produce it.

30. Lateral movements They are of two types Lateral rotation or laterotrusion Bennett movement Lateral rotation:- This is said to occur when the mandible moves away from the mid-sagittal plane either on the left or the right. It should be noted that when the mandible moves laterally, the condyles on both sides do not share the same path of movement.

31. Simply put Lateral movement of mandible occurs when one condyle rotates within TM fossa and the other condyle translates forward and inward. The translating condyle is called the non-working condyle and the rotating condyle is called the working condyle. The direction of lateral movements is determined by external – pterygoid muscle on the non-working side and by deep capsular ligaments of the condyle on working side. The right condyle is allowed only a small rotatory movement because its lateral pole is limit by TM ligament and cannot move backwards for more than 1mm.

32. Bennett in 1908 studied the working condylar path and called it ‘Bennett movement’ now referred to as laterotrusion. Bennett movement is a bodily side shift of mandible that occurs during lateral movement. During lateral movement working condyle rotates and moves slightly outward. This movement is between 2-4 mm. If the TM ligament of rotating condyle is very tight, there is no bodily side ship of the mandible and there fore no Bennett movement occurs. Bennett movement

33. BENNETT ANGLE It is defined as the saggital plane and the path of the advancing condyle during lateral mandibular movements as viewed in the horizontal plane. This is the angle formed between the path of the non-working condyle and the saggital plane It therefore moves forwards and medially in an arc around the opposite condyle while moving over the temporal bone

34. OVERBITE AND OVERJET The majority of patients with natural dentitions have upper anterior teeth which overlap their opposite number in the lower jaw both horizontally (‘overjet’) normal is 2mm and vertically (‘overbite’), normal is 2mm

35. Base on the extent of movement Border movement The maximum amount of movement in any plane or direction is termed the border movement. Within the confines of the border movements there is an extremely wide range of movement called intra-border movement. Most mandibular movement occurs as intra-border movements. Function at the border limits is usually demonstrated during Para-functional activities such as bruxism or wide opening yawning.

36. Base on the extent of movement The border positions are limited by nerves muscles and ligaments. Border movement demonstrates the movement from centric occlusion backward to centric relation and forward to protrusive border movement. The lowermost point in the point of maximum opening from where the mandible can be taken to all border movements. Border movements are recorded and measured because they are repeatedly reproducible.

37. Single Plane Border Movement Sagittal plane border and functional movement Horizontal plane border and functional movement Frontal (vertical) border and functional movement

38. Sagittal Plane Border Movement

39. Sagittal Plane Border Movement Posterior open border Anterior open border Superior contact border Functional movements

40. Sagittal Plane Border Movement Posterior open border movement

41. Sagittal Plane Border Movement Anterior open border movement

42. Sagittal Plane Border Movement Superior contact border movement

43. Sagittal Plane Border Movement Superior contact border movement(cont.)

44. Sagittal Plane Border Movement Superior contact border movement (cont.)

45. Sagittal Plane Border Movement Superior contact border movement (cont.)

46. Sagittal Plane Border Movement Functional movements

47. Horizontal Plane Border Movement Left lateral border Continued left lateral border with protrusion Right lateral border Continued right lateral border with protrusion Functional movements

48. Horizontal Plane Border Movement Left lateral border

49. Horizontal Plane Border Movement Continued left lateral border with protrusion

50. Horizontal Plane Border Movement Right lateral border

51. Horizontal Plane Border Movement Continued right lateral border with protrusion

52. Horizontal Plane Border Movement Functional movements

53. Envelope of motion The “Full Envelope” of Hinge and TranslatoryMovements as viewed in the mid-saggital reference plane appears as a special “envelope-like figure” known as: POSSELTS ENVELOPE

55. Swallowing

56. Yawning

58. Bruxism

60. Mastication Mastication is defined as the act of chewing. This act is made up of rhythmic and well controlled separation and closure of maxillary and mandibular teeth. Each opening and closing of mandible represents a chewing stroke. The chewing movement in the frontal view has tear shaped pattern. It can be divided into opening phase and closing phase. Closing phase is further divided into crushing phase and grinding phase. While chewing, adults open their mouth to a comfortable distance and move the mandible in a forward direction until the edges of maxillary and mandibular teeth meet. The food bolus is then transported to the centre and mandible goes to its original position. Children below 10 years begin their chewing stroke with lateral movement but after 10 years of age the chewing pattern varies and the stroke is more vertical.

61. Deglutition Deglutition or swallowing is an innate function. It is starting point of peristaltic transport of food to stomach. This activity may be divided into-oral, pharyngeal and esophageal phases of which first is voluntary and other two one reflex. In order that deglutition may be initiated, the air passage through mouth must be closed. The anterior seal is normally accomplished by the lips, but the edge and apex of the tongue may substitute in some cases. During deglutition mandible is generally stabilized against maxilla by contraction of masseter and temporalis muscle. This results in contact of the upper and lower teeth.

62. Respiration The role of mouth in respiration is secondary to that of nasal cavity. If there is nasal obstruction, mouth becomes a primary respiratory passage. The mouth remains open, mandible depresses and the air passes through the mouth instead of the nose.

63. Speech The teeth, tongue, lips, floor of mouth and soft palate form the resonance chamber that effects pronunciation. During speech the teeth are generally not in contact although the anterior teeth may come very close together. During speech the various mandibular movements take place.

64. Para-functional Movements Para-functional movements of the mandible are activities that serve no useful function and are potentially harmful to the dentition and its contagious structures. They can result in tooth mobility, migration, excessive wear or fracture, PDL widening. TMJ pain, muscle pain, restricted mandibular movements.Bruxism Normal person masticate with chewing strokes that are well rounded, within definite borders, and less repeated.In bruxism the strokes are much shorter and slower and have an irregular but repeatable pathway appear to relate to the altered functional movement of the condyle which the disorder is centered.Bruxism may be due to habit, general stress, pain, exertion, anger, occlusal interference.

65. Clenching In vertical affort (clenching in centric occlusion), most of the elevator muscles are activated maximally. In some subjects the medial pterygoid muscle activity is low. The variation between subjects related to occlusal contacts and musculoskeletal morphology. The inferior head of the lateral pterygoid produces little activity or only 25 percent of maximum activity compared to the superior head.

66. Clenching Muscle activity decreases when less posterior teeth only the incisors in contact The digastric muscle slightly active during vertical effort with intercuspal clenching more active during vertical incisive clenching.

67. Jaw positions Physiologic rest position The position assumed by mandible when the head is in an upright position, the muscles are in equilibrium in tonic contraction and condyles are in a unstrained neutral position is the physiologic rest position of mandible. The mandibular resting position is one of the earliest postural positions to be developed. The jaws are not clamped together but, they are separated by rather constant distance, even before there are any teeth in the mouth. Even though the muscles are not in active function, a limited number of fibers are apparently still contracting to maintain the relaxed position of the mandible and posture of the head.

68. Jaw positions The postural position can be altered by conditions in the masticatory system as well as by systemic factors. Factors influencing the postural rest position are 1) Body and head posture.2) Sleep 3) Psychic factors influencing muscle tonus.4) Age 5) Proprioception from dentition and muscles6) Occlusal changes, such as attrition.7) Pain8) Muscle disease and muscle spasms.9) Temporomandibular joint disease.

69. Free-way space This is referred to the space between the at rest.free -way space exist only at rest. During occlusion,the teeth come in contact with one another and the space is lost. Denture js fabricated in vertical dimension at occlusion so that the free-way space js formed

70. Rest Vertical Dimension(RVD) It is defined as the length of the face when the mandibule is at rest This is the position of the mandibule in relation to the maxilla when the maxillofacial musculature are in a state of tonic equilibrum. This position is influenced by the muscles of mastication,muscles involved in speech, deglutition and breathing.

71. Rest vertical dimension acts as reference point during recording the occlusal vertical dimension(ovd) Vd at rest=VD at occlusion+free-way space Moving the head backwards tends to increase RVD, while tilting it forward has the opposite effect

72. Factors to consider when recording RVD 1. The position of the mandible is influenced by gravity and the posture of the head. Hence while recording the patient should be asked to sit upright with his/her head upright and eyes looking front. 2. when recording all muscles affecting this record should be relaxed. 3. presence of any neuromuscular disease in the patient can influence at rest position.

73. Method used to measure RVD 1. Facial measurements after swallowing and relaxing 2. tactile sense 3. measurement of anatomical landmarks 4. speech 5. facial expression

74. Occlusal vertical dimension(OVD) OVD is the length of the face when the teeth are in contact and the mandible is in centric relation When the teeth are fully intercuspidated, the position is known as intercuspal position(IP) The free-way space is at zero and the RVD is equal to the OVD.

76. Pre-extraction record

78. Physiological rest position

79. Phonetics

80. Aesthetics

81. Swallowing threshold

82. Tactile sense or neuromuscular perception

84. Centric Occlusion Centric occlusion is relation of opposing occlusal surfaces that provides maximum intercuspation or planned contact. Centric relation is bone to bone relationship where as centric occlusion is a relationship of upper and lower teeth to each other. Once CR is established centric occlusion can be built to coincide with it or to provide a broad area of tooth contact in this position.

85. CHRISTENSEN PHENOMENON When an edentulous patient protrudes the mandible with record rims in place, a space opens between them at the back of the mouth (Christensen phenomenon). This gap is proportional to the condylar angle, and a wax wafer recording it may subsequently be used to set the condylar angle on an adjusted articulator. When making this record the mandible should not be protruded so far as to bring the condyles over the articular eminences.

86. IMPORTANCE OF THE JAW POSITIONS IN EDENTULOUS PATIENTS Edentulous patients have lost the proprioceptive feedback from the oral cavity. Hence the dentist’s only landmarks are an estimate of the patient’ RVD and a determinant of the position of the RCP/RCA. To build the occlusion for complete dentures these two landmarks are considered, any other observation being pure conjecture.

87. It is conventional to provide the patient with an IP on the RCP/RCA at vertical dimension slightly less than the RVD. While in the natural dentition IP is often slightly in front of the RCP/RCA, it has been found that this system works well clinically. Some dentists prefer to adjust the artificial dentition so that the patient may glide the mandible slightly forwards from the RCP with the teeth still evenly in contact.

88. CONCLUSION The mandibular movement is considered as the chewing apparatus of masticatory system. It should be borne in mind that mandibular movements occurs besides mastication like biting, chewing swallowing, vomiting, breathing, speaking, singing, yawning, facial expressions. In other words, it plays life promoting roles and other important roles in the digestive and respiratory acts, vocal performances and more or less every day human activities and behaviors.