This document provides an overview of the biology of orthodontic tooth movement. It discusses physiologic tooth movement including eruption, migration, and movement during mastication. It then covers the theories of tooth eruption and details migration/drift of teeth. The document outlines the periodontium including its cellular elements and fibers. It explains orthodontic tooth movement through pressure-tension theory and the effects of light versus heavy forces. It also discusses the potential deleterious effects of orthodontic forces and factors that can enhance or impede tooth movement.

1. BIOLOGY OF ORTHODONTIC TOOTH MOVEMENT Prepared By JEAN MICHAEL Final Year - RDC 1 JM Widescreen (16:9) Guided By Dr. Hariprasad MDS Dr. Sarath MDS Dr. Shaji MDS Dr. Yohan Varghese MDS, PhD

2. Physiologic Tooth Movement It is the naturally occurring tooth movements that take place during and after tooth eruption Tooth eruption Migration or drift of teeth Changes in tooth position during mastication 2 JM

3. Tooth Eruption Axial or occlusal movement of the tooth from its developmental position within the jaw to its functional position in the occlusal plane 3 JM

4. Theories Of Tooth Eruption Vascular pressure theory Root formation Bone Remodeling Periodontal ligament traction This theory states that the periodontal ligament is rich in fibroblasts that contain contractile tissue. The contraction of these periodontal fibers (mainly the oblique group) result in tooth eruption. 4 JM

5. Migration Or Drift Of Teeth Teeth have the ability to drift through the alveolar bone Human teeth have a tendency to migrate in mesial or occlusal direction This maintains the inter-proximal and occlusal contact Aided by bone resorption and deposition by osteoclasts and osteoblasts respectively 5 JM

6. Mesial - due to proximal caries (loss of tooth structure) Occlusal - Due to premature exfoliation or absence of opposing tooth (supra-eruption) 6 JM

7. Tooth Movement During Mastication Normal force of mastication – 1 to 50 kg It occurs in cycles of 1 secondduration Teeth exhibit slight movement within the socket and return to their original position on withdrawal of the force Whenever the force is sustained for more than 1 second, periodontal fluid is squeezed out & pain is felt as the tooth is displaced within the periodontal space 7 JM

8. PERIODONTIUM 8 JM

9. 9 JM

10. Thickness of normal PDL – 0.5 mm Collagenous fibres of PDL connects the cementum and lamina dura The fibers run at an angle attaching farther apically on the tooth than on the adjacent alveolar bone PDL space is filled with fluid derived from vascular system 10 JM

11. Periodontal Ligament 11 JM

12. Cellular Elements in the PDL Fibroblasts – produce and destroys collagen fibers Osteoblasts –produce new bone Osteoclasts – aids in bone resorption Cementoblasts – forms new cementum Cementoclasts – removes cementum PDL is vascular and contains nerve endings which aid in proprioception 12 JM

13. 13 JM

14. FIBROBLAST 14 JM

15. OSTEOCYTE JM 15

16. OSTEOBLASTS JM 16

17. OSTEOCLASTS JM 17

18. Is orthodontic movement possible for a tooth that has undergone endodontic treatment ? YES (the PDL is intact in this case) Is it possible to move an ankylosed tooth ? NO (here there is complete absence of the PDL) JM 18

19. Piezoelectric Effect When a force is applied to a crystalline structure (like bone or collagen), a flow of current is produced that quickly dies away When the force is released, an opposite current flow is observed The piezoelectric effect results from migration of electrons within the crystal lattice 19 JM

20. Response to Normal Function Teeth and periodontal structures are subjected to forces up to 50 kg during mastication Force is transmitted to the alveolar bone which bends in response Generation of piezoelectric currents It acts as an important stimulus to skeletal regeneration and repair resulting in adaptation of bony architecture to functional demands 20 JM

21. Response to Continuous Pressure < 1 second: Fluid in the PDL is incompressible 1 – 2 seconds: PDL fluid expressed, Tooth moves within PDL space 3 – 5 seconds: PDL fluid squeezed out, Tissue compressed and immediate pain is felt if force is heavy 21 JM

22. Force for Orthodontic Tooth Movement Forces that bring about orthodontic tooth movement are continuous and should have a minimum magnitude (threshold) Below this threshold limit, the PDL has the ability to stabilize the tooth by active metabolism The minimum pressure required is 5 to 10 gm/cm2(current concept) 22 JM

23. Resting Pressure from Lip & Tongue Upper Anteriors Force exerted by LIP > Tongue Lower Anteriors Force exerted by TONGUE > LIP Teeth remain stable in their position as the unbalanced forces acting on them, are below the threshold limit tolerated by the metabolism in PDL 23 JM

24. Magnitude of Force VS Tooth Movement 24 JM

25. ORTHODONTIC TOOTH MOVEMENT 25 JM

26. Modes of Orthodontic Tooth Movement Forces created by orthodontic appliances bring about tooth movement by 2 mechanisms. FRONTAL Resorption UNDERMINING Resorption 26 JM

27. Frontal Resorption Accomplished by Light Orthodontic Forces least painful least harmful to the periodontium Most desirable 27 JM

28. UnderminingResorption Caused by Heavy Orthodontic Forces Painful More harmful to the periodontium Occurs in a small scale even in the most careful orthodontic treatment The dentist should always try to minimize this 28 JM

29. Role of Piezoelectric Current Piezoelectric currents produced on application of force on tooth and alveolar bone dies off quickly and play little role in orthodontic tooth movement Orthodontic tooth movement requires sustained forces which does not produce continuous piezoelectric current But these signals which are produced while normal chewing are required for proper maintenance of normal bony architecture 29 JM

30. The Pressure – Tension Theory When force is applied on the tooth, PDL is compressed on one side and stretched on the other side Blood flow is decreased on the pressure side where PDL is compressed Blood flow is increased on the tension side where PDL is stretched 30 JM

31. The process of initiation of tooth movement has 3 stages Alternation of blood flow associated with pressure within the PDL The formation and release of chemical messengers Activation of cells which causes deposition and resorption of bone 31 JM

32. BONE RESORPTION (osteoclastic activity) takes place at the side of the PDL where there is PRESSURE BONE FORMATION (osteoblastic activity) takes place at the side where there is TENSION 32 JM

33. Maintenance of Thickness of Alveolar Bone In an ideal treatment, the attachment level is maintained Resorption and deposition of bone maintains its thickness in the facial and lingual side irrespective of the type of movement the tooth has undergone on the alveolar bone 33 JM

34. Chemical Regulation of OTM Within the 1st hour Increase in Prostaglandin E & Interleukin – 1 Increase in Cytokines & Nitric oxide (NO) After 4 hours of pressure application Increase in cAMP (chemical mediator for differentiation) PROSTAGLADINS can stimulate formation of both OSTEOBLAST & OSTEOCLAST 34 JM

35. It takes a minimum of 4 to 6 hours of continuous force to initiate orthodontic tooth movement So removable appliance worn for less than this minimum period of time is of no use Maximum efficiency is obtained if the appliance is worn for 24/7 35 JM

36. Types of Orthodonic Forces LIGHT Force – Frontal resorption HEAVY Force – undermining resorption 36 JM

37. Effect of Magnitude of Force on PDL 37 JM

38. Application Of Continuous Light Force < 1 second: PDL fluid is incompressible, alveolar bone bends, piezoelectric signal generated 1 – 3 seconds: PDL fluid expressed & tooth moves within the socket 3 – 5 seconds: Blood vessels within PDL partially compressed on pressure side & dilated on tension side. PDL fibers and cells are mechanically distorted 38 JM

39. Minutes: Blood flow altered & oxygen tension begins to change. Prostaglandins and cytokines released Hours: Metabolic changes ocures. Chemical messengers affects cellular activity. Enzyme levels change 4 Hours: Iincreased cAMP levels are detectable & cellular differentiation begins within PDL 2 Days: Tooth movement begins as osteoclasts & osteoblasts remodel bony socket 39 JM

40. No pressure – Normal perfusion of blood vessels 40 JM

41. Light pressure – blood vessels constricted 41 JM

42. Tension side – Fibers stretched & Vessels open wide 42 JM

43. Result of Continuous Light Force Osteoclasts initiates resorption of lamina dura from the side of PDL The osteoclasts arrive in 2 waves 1st wave derived from the PDL itself 2nd wave (larger) from distant areas via blood flow All these events lead to FRONTAL RESORPTION 43 JM

44. Application of Continuous Heavy Force < 1 second: PDL fluid is incompressible, alveolar bone bends, piezoelectric signal generated 1 – 3 seconds: PDL fluid expressed & tooth moves within the socket 3 – 5 seconds: Blood vessels with in PDL occlude on the pressure side 44 JM

45. Minutes: Blood flow gets cut off to compressed PDL area Hours: Cell death in compressed area 3 to 5 days: Cell differentiation in adjacent marrow spaces; undermining resorption begins 7 to 14 days: Undermining resorption removes lamina dura adjacent to compressed PDL & tooth movement occurs 45 JM

46. Heavy Pressure – Blood flow totally cut off 46 JM

47. Compressed PDL after Sterile Necrosis 47 JM

48. Cellular Changes Loss of blood flow causes sterile necrosis of the PDL A “Hyalinized” area devoid of cells and vasculature develops Osteoclasts appear within the adjacent bone marrow spaces and begins an attack on the underside of the bone immediately adjacent to the necrotic PDL area An initial delay in tooth movement ocures 48 JM

50. A considerable thickness of bone has to be removed from the underside before any tooth movement can take place49 JM

51. Undermining Resorption 50 JM

52. Frontal Resorption VS Undermining Resorption 51 JM

53. Centre Of Resistance It is the point on the tooth when a single force is passed through it, would bring about its translation along the line of action of the force JM 52

55. ANCHORAGE It is the Resistance to Unwanted Tooth Movement Or It is the nature and degree of resistance to displacement offered by an anatomic unit for the purpose of effecting tooth movement JM 54

56. Absolute Anchorage Appliances gaining anchorage from extraoral structures – Extraoral appliances (eg – Head Gear) JM 55

57. 2. Titanium screws implanted into the alveolar bone through the gingiva to act as anchorage JM 56

58. Intraoral Anchorage Anchorage value of a tooth is proportional to the surface area of the root The tooth with larger root surface area requires greater force to move JM 57

59. Anchorage Value Of Each Tooth JM 58

61. JM 61 ROTATION ROOT UPRIGHTING

62. JM 62 EXTRUSION INTRUSION

63. Optimum Forces For OTMs JM 63

64. Forces Delivered by Appliances Continuous Force (ideal spring) Interrupted Force (removable active plates) Intermittent Force (removable appliances) 64 JM

65. Continuous Force 65 JM

66. Interrupted Force 66 JM

67. Intermittent Force 67 JM

68. Deleterious Effects of Orthodontic Force Pain Allergic reactions Mobility Gingival Inflammation Loss of vitality of pulp Root Resorption JM 68

69. Pain If appropriate force (not heavy) is applied, the patient feels little pain immediately Pain develops after several hours The patient feels mild aching sensation and the teeth are quite sensitive to pressure The pain usually lasts for 2 – 4 days and disappears until the appliance is reactivated JM 69

70. For most of the patients, the pain associated with the initial activation of the appliance is most severe Pain is due to the development of ischemic areas in the PDL The pain is directly proportional to the area of PDL that has undergone sterile necrosis (hyalinization) So heavier forces produce larger areas of hyalinization and greater pain Pain can be managed using analgesics like ACETAMINOPHEN JM 70

71. Allergic Reactions Some patients may develop allergic reactions to Stainless steel which contains NICKEL Allergic reactions manifest as widespread erythema and swelling of oral tissue which develops 1 – 2 days after starting the treatment In such patients, Stainless steel appliances (brackets, bands, wires etc) should be substituted with TITANIUM appliances JM 71

72. Mobility Mobility is due to Widening of PDL space during orthodontic treatment Temporary disorganization of the fibers in the PDL Moderate increase in mobility is an expected response of orthodontic treatment JM 72

73. Heavier Force causes greater degree of Undermining Resorption which leads to Excessive mobility Excessive mobility indicates that there is heavy force acting on the tooth If the tooth becomes extremely mobile, force should be discontinued until the mobility decreases to moderate levels Excessive mobility will usually correct itself without permanent damage JM 73

74. Insults to the Pulp There will be a modest inflammatory response within the pulp at the beginning of the treatment It may cause an initial mild pulpitis which has no long term significance JM 74

75. Loss of Vitality of Pulp Loss of vitality may be encountered if there is History of previous trauma to the tooth Poor control of orthodontic forces Heavy forces cause abrupt movement of root apex causing obstruction of the blood flow to the pulp Relatively heavy forces applied for intrusion can also give rise to the same situation JM 75

76. Root Resorption Cementum adjacent to the hayalinized PDL undergo resorption by cementoclast cells This can progress to the extend of dentin destruction Once orthodontic forces are removed, repair occurs by the deposition of new cementum in the area of previous destruction Dentin once lost will not be replaced JM 76

77. Craters of Root Resorption in Dentin JM 77

78. Types of Resorption Slight Blunting Moderate resorption – up to ¼ of the root length Severe resorption – more than ¼ of the root length Moderate Generalized Resorption Severe Generalized Resorption Severe Localized Resorption JM 78

79. Slight Blunting JM 79

80. Moderate Resorption JM 80

81. Severe Resorption JM 81

82. Moderate Generalized Resorption Most of the teeth show some loss of root length Greater in patients whose treatment duration was longer Shortening of root length is more for maxillary incisors In most cases, this type of resorption is clinically insignificant JM 82

83. Severe Generalized Resorption This is mostly of unknown etiology In case of patients with thyroid deficiency, chances of developing severe generalized resorption is high To prevent this, thyroid supplementation is indicated JM 83

84. Severe Localized Resorption Caused by excessive forces and prolonged duration of treatment Risk of severe resorption is much greater for maxillary incisors Very high risk is noted if roots of maxillary incisors are forced against the lingual cortical plate JM 84

85. Effect of DRUGS on OTM JM 85

86. Drugs which Enhance OTM Vitamin D administration Direct injection of Prostaglandin into PDL (disadvantage – It is very painful) JM 86

87. Synthesis of Prostaglandins JM 87 PHOSPHOLIPIDS PROSTAGLADINS CORTICOSTEROIDS ARACHIDONIC ACID NSAIDS

88. Drugs which Impede OMT BISPHOSPHONATES – for Osteoporosis Alendronate PROSTAGLADIN INHIBITORS Indomethacin TETRACYCLINES Doxycycline JM 88

89. TRICYCLIC ANTIDEPRESSANTS Doxepine Imipramine ANTIARRHYTHMIC agents Procaine ANTIMALARIALS Drugs Quinine Chloroquine JM 89

90. Patient with Osteoporosis This condition is encountered in case of post-menopausal females The patient may be using BISPHOSPHONATES which binds to Hydroxyapatite in bone and inhibits Osteoclast mediated Bone Resorption BEFORE ORTHODONTIC TREATMENT, Consult the patient’s physician and temporarily switch to estrogen therapy (Evista) JM 90

91. Pain killers – Do they Inhibit OTM ? Common analgesics used during treatment IBUPROFEN ASPIRIN At the dose level used during orthodontic treatment, they do not impede tooth movement Acetaminophen is a better option as it is a centrally acting agent which does not reduce inflammation JM 91 NSAIDS

92. Prostaglandin Inhibitors in Microspheres If Prostaglandin Inhibitors were placed in mini-spheres and could be maintained in the sulcus around tooth (like antibiotics in periodontal therapy) which has to serve as anchorage, the efficiency of the orthodontic treatment can be improved. JM 92

93. Conclusion A dentist should thoroughly understand the biological factors and principles behind Orthodontic Tooth Movement. He should achieve the desired aesthetic and functional result using the optimum amount of force. He should also give consideration to the health of the periodontium and thus try to minimize the deleterious effects of the treatment. JM 93

94. REFERENCE Contemporary Orthodontics 4/e Orban’s Oral Histology and Embryology 11/e Ten Cate’s Oral Histology 7/e Orthodontics – The Art and Science 4/e JM 94

95. THANK YOU jean_michael@hotmail.com jean_michael@hotmail.com