Factors affecting normal occlusion

A deeper insight into the development of occlusion, and the various concepts associated with it

1. Factors affecting Normal Occlusion Presented by: Kritika Suroliya , 1 st year Post Graduate Student, Department of Orthodontics and Dentofacial Orthopaedics.

2. Learning objectives At the end of the seminar, the learner must be oriented with: Concept of normal occlusion Development of Concept of Normal Occlusion Various factors affecting normal occlusion

3. Contents Introduction Definitions Development of concept of Normal Occlusion: 1) Fictional Period 2) Hypothetical Period 3) Factual Period Factors affecting Normal Occlusion (A) Bone Relation (B) Tooth Relation (C) Eruption (D) Intra-oral forces (E) Occlusal Forces Temporomandibular Joint Andrew’s six keys Summary Conclusion References

4. Introduction S. Davies, R.M.J Gray ; What is Occlusion? British Dental Journal, Volume 191, No.5

5. Introduction S. Davies, R.M.J Gray ; What is Occlusion? British Dental Journal, Volume 191, No.5

6. Introduction Evaluation, Diagnosis and Treatment of Occlusal Problems – Peter E. Dawson, 3 rd edition

7. Introduction Evaluation, Diagnosis and Treatment of Occlusal Problems – Peter E. Dawson, 3 rd edition

8. Introduction Evaluation, Diagnosis and Treatment of Occlusal Problems – Peter E. Dawson, 3 rd edition

9. Introduction Evaluation, Diagnosis and Treatment of Occlusal Problems – Peter E. Dawson, 3 rd edition

10. Introduction Evaluation, Diagnosis and Treatment of Occlusal Problems – Peter E. Dawson, 3 rd edition

11. Introduction Evaluation, Diagnosis and Treatment of Occlusal Problems – Peter E. Dawson, 3 rd edition

12. Determinants of Occlusion Evaluation, Diagnosis and Treatment of Occlusal Problems – Peter E. Dawson, 3 rd edition

13. Introduction Evaluation, Diagnosis and Treatment of Occlusal Problems – Peter E. Dawson, 3 rd edition

14. Introduction Clusion - “closing” Oc - “up” Occlusion- Closing up

15. Definition Occlusion refers not only to contact of arches at occlusal interface but also to all those factors concerned with development and stability of masticatory system and with use of teeth in oral motor behaviour. (Wheeler’s) Occlusion is an act of closure or a state of being closed. (Dorland)

16. Definition Angle, in the 7 th edition of “Malocclusion of the teeth”, defined normal occlusion as: “Normal relations of the occlusal inclined planes of the teeth when the jaws are closed”.

17. Normal Occlusion Normal occlusion of the teeth may be defined as that structural composite consisting fundamentally of the teeth and the jaws and characterized by a normal relationship of the so-called occlusal, inclined planes of teeth that are individually and collectively located in architectural harmony with their basal bones and with cranial anatomy, exhibit correct proximal contacting and axial positioning and have associated with them normal growth, development, location and correlation of all environmental tissues and parts. (Strang)

18. Dynamic Occlusion Dynamic Occlusion refers to the occlusal contacts that are made whilst the mandible is moving relative to the maxilla. The mandible is moved by the muscles of mastication and the pathways along which it moves are determined not only by these muscles but also by two guidance systems. Posterior guidance is provided by TMJ. Anterior guidance is by canine guided occlusion or group function. (Davies & Gray ) S. Davies and R.M.J. Gray ; What is Occlusion? British dental Journal

19. Functional Occlusion Functional occlusion refers to the occlusal contacts of the maxillary and mandibular teeth during function, i.e., during speech, mastication and swallowing. J.R. Clark, R.D. Evans; Functional Occlusion: A review. Journal of Orthodontics Vol.28

20. Ideal Occlusion This is given in established texts as: The co-incidence of Centric Occlusion in Centric Relation (CO=CR), when there is freedom for the mandible to move slightly forwards from that occlusion in the same sagittal and horizontal plane. (Freedom in Centric Occlusion) When the mandible moves there is immediate and lasting posterior disclusion (anterior guidance on front teeth) Ash M M , Ramjford S P. Occlusion 4 th edition

21. Line of occlusion Angle in 1906, described the Line of Occlusion as “the line of greatest normal occlusal contact”. But in 1907, he redescribed it as, “the line with which in form and position according to type, the teeth must be in harmony if in normal occlusion.” Ricketts in 1997 redefined the line of occlusion to its contemporary definition as, “A distinctively individual line at the bucco -incisal contact, with a location, position and form to which the teeth must conform to be in normal occlusion.”

22. Development of the concept of occlusion Fictional period (before 1900) Hypothetical Period (1900-1930) Factual Period (1930-present) Orthodontic Principles and Practice - T.M. Graber, 3 rd edition. P

23. Fictional Period First of the three periods in the development of a concept of occlusion Pioneers like Fuller, Clark or Imrie talked of “antagonism”, “meeting” or “gliding” of teeth Creation of a normal standard was lacking Kingsley wrote in 1880: “Peculiarities of the permanent teeth are recognized by everyone of extended observation…because they are a greater or less departure from a normal standard… Such a standard cannot…be one shape to which all must conform… The standard of normality of the dental arch is a curved line expanding as it approaches the ends, and all teeth standing on that line.” Orthodontic Principles and Practice - T.M. Graber, 3 rd edition.

24. Hypothetical Period Edward H. Angle: 1899- Edward Hartley Angle, crystallized the orthodontic thinking on occlusion and brought the concept out of the realm of fiction. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition.

25. Hypothetical Period Matthew Cryer and Calvin Case: Angle’s adversaries Cryer suggested that the concept of occlusion would have to take into consideration individual variation. Case’s concept of apical base divided the dentofacial area into four segments or zones of movement The first suggestion of a functional analysis or a dynamic approach to occlusion came with some experiments by Bennett in 1908. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition.

26. Hypothetical Period The constant battles among Angle, Case and Dewey, in the contemporary literature, and in and out of society meetings, only served to enhance interest in Orthodontics and increase dedication and devotion of their disciples.

27. Hypothetical Period E. Lischer and Paul Simon: Lischer took a more functional approach and introduced the act of mastication as a requisite part of the definition. Simon made strong representations against the acceptance of an arbitrary norm standard in occlusion. Recognition of the interdependence of teeth and occlusion, jaw relationships, craniofacial morphology and their effect on the ultimate concepts of occlusion formed the basis of the science of orthodontics. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition.

28. Hypothetical Period Milo Hellman: Showed racial variations in so-called normal occlusions Hellman and others studied the prognathism of the human denture in relation to a cranial base. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition.

29. Factual Period Holly Broadbent and Hans Planer emerged bringing a broader physiological approach. The factual period was to become the functional period. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition.

30. Factors affecting Normal Occlusion

31. Factors affecting Normal Occlusion The position, size and relationship of the bone in which the tooth develops (bone relation) The position and relationship of the tooth within that bone (tooth relation) The path which the tooth follows to reach the mucous membrane before eruption (eruption) The forces which guide its course after eruption (intra oral forces) The forces which start to operate when the tooth makes contact with its opponent (occlusal forces) Orthodontics for Dental Students - White & Gardiner, 3 rd edition

32. (A) Bone Relation The relationship of the maxilla or mandible to other bones and to each other is probably determined by heredity, congenital hormonal imbalance, traumatic and pathological conditions which interfere with bone growth. These bone relationships have marked effect upon the nature of the ultimate occlusion. Orthodontics for Dental Students - White & Gardiner, 3 rd edition

33. (A) Bone Relation

34. (A) Bone Relation A. Hereditary or racial influences: Most dental and facial characteristics are inherited from the parents, though these may be modified by environmental factors like prenatal and postnatal influences, pressure habits, nutritional disturbances etc. Horawitz S.L. 1958 stated that heredity is significant in determining the following characteristics and thus influence the development of normal occlusion. Width, height and length of the palate Crowding and spacing of the teeth Position and conformation of perioral musculature to tongue size and shape Soft tissue peculiarities – character and texture of the mucosa, frenum size, shape and position

35. (A) Bone Relation B. Congenital Influences: The development and growth of the craniofacial skeleton with associated soft tissues and the primary teeth, and a few permanent teeth begin prenatally and an interference with this development, either due to nutritional, metabolic, or other systemic influences, drugs or trauma, may all result in malocclusion. Example: TMJ Ankylosis, Cleft Lip and Cleft Palate, Cerebral Palsy

36. (B) Tooth Relation Effect due to developmental position of tooth The developmental position may be modified by the presence of other tooth germs; this is likely to occur where there is insufficient space or extra teeth are present. Orthodontics for Dental Students - White & Gardiner, 3 rd edition

37. (B) Tooth relation Permanent incisors: They develop lingual to the roots of their predecessors Canines: Maxillary canines develop high in the maxilla close to the floor of the orbit Mandibular canines develop near to the inferior border of the mandible Orthodontics for Dental Students - White & Gardiner, 3 rd edition

38. (B) Tooth relation Premolars: Its crowns develop below and between the roots of the deciduous molars. Molars: The lower permanent molars develop at the root of the coronoid process, oriented with a mesial inclination which in the course of eruption takes a curved path in a upward and forward direction. Upper permanent molars which develop in the tuberosity of the maxilla, have their occlusal surfaces facing distally at first, and swing downwards and forwards as they erupt through an arc of a circle whose centre should be somewhere in the region of the next tooth mesially . Orthodontics for Dental Students - White & Gardiner, 3 rd edition

39. (C) Eruption Latin, erumpere – “to break out” It means the axial or occlusal movement of the tooth from its developmental position within the jaw to its functional position in the occlusal plane. Physiologic tooth movement is described as consisting of the following: Pre-eruptive tooth movement Eruptive tooth movement Post-eruptive tooth movement Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

40. (C) Eruption Pre-eruptive tooth movement: Pre-eruptive tooth movement can be considered as the movement positioning the tooth and its crypt within the growing jaws, preparatory to tooth eruption. When deciduous tooth germs first differentiate, they are very small and there is a good deal of space in between them. This space is soon used because of the rapid growth of the tooth germs, and crowding results. This crowding is then relieved by growth of the jaws in length, which permits drifting of the tooth germs. Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

41. (C) Eruption Pre-eruptive tooth movement: Permanent teeth with deciduous predecessors also move before they reach the position from which they will erupt, but it involves a lot of other factors such as: Body movement of the tooth germ, growth of the tooth germ, or a relative change in position of associated deciduous and permanent tooth germs. The permanent molars, which have no deciduous predecessors also exhibit tooth movement. Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

42. (C) Eruption Eruptive tooth movement: During this phase, the tooth moves from its position within the bone of the jaw to its functional position in occlusion. The principal direction of movement is occlusal or axial. Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

43. (C) Eruption Post-eruptive tooth movement: Post-eruptive tooth movements are those that 1) Maintain the position of erupted tooth while the jaw continues to grow 2) Compensate for occlusal and proximal wear Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

44. (C) Eruption Theories of eruption: Bone remodelling theory Root formation theory Vascular Pressure theory Periodontal ligament traction theory Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

45. (C) Eruption Bone Remodelling Theory: Bone remodelling clearly is important to permit tooth movement. However, whether bony remodelling that occurs around teeth causes or is the effect of tooth movement is not known, and both circumstances may apply. Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

46. (C) Eruption Root formation theory: Root formation follows crown formation and involves cellular proliferation and formation of new tissue that must be accommodated by either movement of the crown of the tooth or resorption of bone at the base of its socket. Advocates of the root growth theory of eruption postulated the existence of a ligament, the cushion hammock ligament, straddling the base of the socket from one bony wall to the other like a sling. Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

47. (C) Eruption Vascular pressure theory: It is known that teeth move in synchrony with arterial pulse, so local volume changes can produce limited tooth movement. Ground substance can swell by up to 50% with the addition of water, and a differential pressure is produced sufficient to cause tooth movement between the tissues below and an erupting tooth above. Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

48. (C) Eruption Periodontal Ligament traction theory: There is a good deal of evidence that eruptive force resides in the dental follicle-periodontal ligament complex. Periodontal ligament fibroblasts have the ability to contract and transmit a contractile force. Thus the fibroblasts possessing contractile filaments, are in contact with one another to permit summation of contractile forces, and exhibit fibronexuses by which such forces can be transmitted to the collagen fibre bundles. These not only remodel but are also inclined at the correct angle to bring about eruptive tooth movement. Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar

49. (C) Eruption

50. (C)Eruption Applied aspects: The path of eruption is likely to be modified by the presence of adjacent tooth roots and teeth. The presence of teeth mesially and distally is important in determining the mesio -distal limits of the path of eruption. Very little limitation is set bucco -lingually before eruption, unless the space for eruption has been invaded by some other tooth. This is likely to occur when the deciduous predecessor has been lost some time before the eruption of its successor. Failure of absorption of roots of deciduous teeth may cause a deflection in the path of eruption of the succeeding permanent teeth.

51. Applied aspects: The apical arch, or positions assumed by the tooth apices, is determined by the developmental positions of the teeth in the jaws and the form and relations of the jaws themselves. The morsel arch, or arch of tooth crowns, which must conform to the apical arch, is additionally under the influence of those factors which operate on the tooth crown after their eruption. These are for the most part, physical pressures rising from muscular function. The remoteness from other teeth especially upper canine, as it develops high in maxilla, releases this teeth from limitations imposed by neighbouring teeth ; as a result ectopic eruption or failure of eruption is commonly seen. Orthodontics for Dental Students - White & Gardiner, 3 rd edition

52. (D) Intra-oral forces Physical forces encountered by teeth: Buccolingual forces – arises from the musculature of the lips, cheeks and tongue, and; Mesiodistal forces – exerted through adjacent teeth. Orthodontics for Dental Students - White & Gardiner, 3 rd edition

53. (D) Intra-oral forces Muscles have two physical properties which are important in their kinetic activity. They are: Elasticity: Extensibility within certain limits is accomplished by an external force, but the muscle returns to its exact original shape after being stretched. Contractility: It is the ability of a muscle to shorten its length under innervational impulse. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

54. Principles of Muscle Physiology All or None Law: Sherrington has pointed out that individual muscle fibres have no variable contraction status, but are either relaxed or going into maximum contraction by virtue of adequate stimulus. The strength of a muscle contraction depends upon: The frequency of the stimuli The number of fibres involved Muscle Tonus: It is a state of slight constant tension which is a characteristic of all healthy muscles and which serves to obviate the muscle taking up slack when it enters upon contraction. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

55. Principles of Muscle Physiology Resting Length: It is a rather constant and predeterminable relationship, permitting the maintenance of postural relations and dynamic equilibrium by contraction of minimal number of fibres, consistent with the demands of the moment. Stretch or Myotactic reflexes: It is the reflex contraction of a healthy muscle which results from a pull on its tendon. Reciprocal Innervation and Inhibition: The inhibition of tonus of the muscle may be brought about by the excitation of its antagonist. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

56. (D) Intra-oral forces Orthodontics for Dental Students - White & Gardiner, 3 rd edition

57. Passive Forces The muscles which have a direct effect on the jaws are those of deglutition, expression and mastication. The tongue within the lingual vestibule is applied to the lingual surfaces of the teeth and the hard and soft palate. The lips and cheeks are applied to the labial and buccal surfaces. Orthodontics for Dental Students - White & Gardiner, 3 rd edition

58. Active muscle forces Active muscle forces exert pressure only intermittently. The degree of force is greater than that of muscle tonus. Both the degree of force and the frequency with which it is exerted varies greatly. Orthodontics for Dental Students - White & Gardiner, 3 rd edition

59. (D) Intra-Oral Forces Orthodontics for Dental Students - White & Gardiner, 3 rd edition

60. Buccinator Mechanism Although bone is the hardest tissue in the body, it is one of the most responsive to change when there is an alteration in the environmental balance. The major factor in this environmental balance is the musculature. Environmental factors are the constant relationship and resistance afforded by the buttressing effect of the contiguous teeth, occlusal interdigitation and the bone-building resorption balance maintained in the periodontal membrane. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

61. Buccinator Mechanism Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

62. Buccinator Mechanism Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

63. Buccinator Mechanism Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

64. Buccinator Mechanism Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

65. Applied Aspects

66. (E) Occlusal Forces The movement of the mandible from its rest position to its position of maximum contact is under voluntary control; this is modified by a discharge of impulses arising from the proprioceptive nerve endings situated in the Temporomandibular Joint, tendons, muscles and periodontal membranes of the teeth. The path taken by the mandibular teeth from the rest position to that of maximum occlusal contact is known as “Path of closure”. Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

67. (E) Occlusal forces Intra-arch tooth alignment/ Approximal contact: Intra-arch tooth alignment refers to the relationship of the teeth to each other within the dental arch. Imagine that a line is drawn through all the buccal cusp tips and incisal edges of the mandibular teeth. Further imagine that this line is broadened into a plane that includes the lingual cusp tips and continues across the arch to include the opposite side buccal and lingual cusp tips. The plane that is established is called the plane of occlusion. Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

68. (E) Occlusal Forces Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

69. (E) Occlusal Forces Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

70. (E) Occlusal Forces Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

71. (E) Occlusal Forces Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

72. Curve of Spee If from the lateral view, an imaginary line is drawn through the buccal cusp tips of the posterior teeth, a curved line following the plane of occlusion will be established that is Convex for the maxillary arch Concave for the mandibular arch. These convex and concave lines match perfectly when the dental arches are placed into occlusion. This curvature was first described by Von Spee . Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

73. Curve of Wilson If a line is drawn through the buccal and lingual cusp tips of both the right and left posterior teeth, a curved plane of occlusion is observed. The curvature is convex in the maxillary arch and concave in the mandibular arch. This curvature of occlusal plane observed from the frontal view is called the Curve of Wilson. Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

74. Bonwill’s triangle Bonwill noted that an equilateral triangle existed between the centres of the condyles and the mesial contact areas of the mandibular central incisors. He depicted this as having 4-inch sides. In other words, the distance from the mesial contact area of the mandibular central incisor to the centre of either condyle was 4 inches, and the distance between the centres of the condyles was 4 inches. Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

75. Monson’s curve Monson used Bonwill’s triangle and proposed a theory that a sphere existed with a radius of 4 inches whose centre was an equal distance from the occlusal surfaces of the posterior teeth and from the centres of the condyles. Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

76. Occlusal Table The area of the tooth between the buccal and lingual cusp tips of the posterior teeth is called the occlusal table. The occlusal table represents 50-60% of the total buccolingual dimension of the posterior tooth and is positioned over the long axis of the root structure. Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

77. (E) Occlusal Forces Inter-arch alignment: Inter-arch tooth alignment refers to the relationship of the teeth in one arch to those in the other. When the two arches come into contact, as in mandibular closure, the occlusal relationship of the teeth is established. Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

78. (E) Occlusal Forces Inter-arch alignment Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

79. Inter-arch tooth alignment The buccal cusps of the mandibular posterior teeth and the lingual cusps of the maxillary posterior teeth occlude with the opposing central fossa areas. These are called the supporting cusps or centric cusps. They are primarily responsible for maintaining the distance between the maxilla and mandible. This distance supports the vertical facial height and is called the vertical dimension of occlusion Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

80. Inter-arch tooth alignment The buccal cusps of the maxillary posterior teeth and the lingual cusps of the mandibular posterior teeth are called the guiding or non centric cusps. The major role of non-centric cusps is to minimize tissue impingement. The non centric cusps also give the mandible stability so that when the teeth are in full occlusion, a tight definite occlusal relationship results. This relationship of the teeth in their maximal intercuspal position. Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

81. Cusp-Fossa Relationships Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

82. Cusp-Fossa Relationships Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

83. Cusp-Fossa Relationships Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

84. Cusp-Fossa Relationships Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

85. Applied Aspects Posterior cross bite exists when the mandibular lingual cusps occlude in the central fossae of the maxillary teeth and the maxillary buccal cusps occlude in the central fossae of the mandibular teeth. Tight occlusal contacts between opposing arches prevent supra-eruption or extrusion of teeth. Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition

86. Temporomandibular Joint In the analysis of any occlusion in relation to TMJs, the condition and position of TMJs must be determined before the occlusion can be analysed. Much of the movement of the mandible is determined by the two TMJs, which rarely function with identical simultaneous movements.

87. Positions of Mandible Postural resting position (physiologic rest) The mandible is suspended from the cranial base by the cradling musculature. The postural position can be altered by conditions in the masticatory system as well as by systemic factors. Factors influencing postural position are the following: Body and head posture Sleep Age Proprioception from the dentition and muscles Occlusal changes, such as attrition Pain Muscle disease and muscle spasm Temporomandibular joint disease Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

88. Freeway space When an individual is at rest, the mandible is held in such a position that the upper and lower teeth are normally separated a little. Orthodontics for Dental Students - White & Gardiner, 3 rd edition

89. Positions of Mandible Centric Relation: It may be defined as the unstrained, neutral position of the mandible in which anterosuperior surfaces of the mandibular condyles are in contact with the concavities of the articular disks as they approximate the posteroinferior third of their respective articular eminentia . Centric Occlusion: With maximal contact of the inclined planes of the opposing teeth, there must be a bilaterally symmetrical activity, a balanced and unrestrained relationship of the temporomandibular structures, etc. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

90. Positions of Mandible Habitual resting position: Habitual resting position may not be the same as the physiological resting position. Certain pathological conditions may disrupt the establishment of a normal postural position of the mandible, example, Mouth breathing Selective paralysis induced by poliomyelitis Markedly enlarged adenoids Pain TMJ pathology Habitual occlusal Relation: In a normal occlusion, habitual occlusion and centric occlusion should be the same. But the habitual occlusion position or intercuspal position is often an abnormal one. Malposition of individual teeth and tooth guidance due to premature contacts produce traumatic disturbances that are injurious to the teeth and investing tissues. Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

91. Positions of Mandible Most Retruded position (terminal hinge axis position) Most Protruded position Orthodontic Principles and Practice - T.M. Graber, 3 rd edition

92. Andrew’s six keys of Occlusion I. Molar relationship: The distal surface of the disto -buccal cusp of the upper first permanent molar occludes with the mesial surface of the mesio -buccal cusp of the lower second permanent molar. II. Crown angulation ( mesio -distal tip): The gingival portion of each crown is distal to the incisal portion and varied with each tooth type. III. Crown inclination (labio-lingual, bucco -lingual): Anterior teeth (incisors) are at a sufficient angulation to prevent overeruption Upper posterior teeth – lingual tip is constant and similar from 3–5 and increased in the molars Lower posterior teeth – lingual tip increases progressively from the canines to the molar

93. Andrew’s six keys of Occlusion IV. No rotations V. No spaces VI. Flat occlusal planes

94. Summary The designation of normal depends upon the assessment of all the factors discussed in today’s seminar. Teeth, that are healthy, even if malaligned , with healthy investing tissues, normally functioning musculature and no temporomandibular joint pathology, go a long way toward being normal.

95. Conclusion The interplay of all these groups of influence produces an arrangement of teeth which is infinite in its variety and, from the point of view of aesthetics and function, may or may not be acceptable.

96. References Orthodontic Principles and Practice - T.M. Graber, 3 rd edition. Orthodontics for Dental Students - White & Gardiner, 3 rd edition A Textbook of Orthodontia – Strang Evaluation, Diagnosis and Treatment of Occlusal Problems – Peter E. Dawson, 3 rd edition Management of Temporomandibular Disorders and Occlusion – Jeffrey P. Okeson, 4 th edition S. Davies and R.M.J. Gray ; What is Occlusion? British dental Journal J.R. Clark, R.D. Evans; Functional Occlusion: A review. Journal of Orthodontics Vol.28 Orban’s Oral Histology and Embryology (13 th edition) – G S Kumar