Biomechanics of tooth movement /certified fixed orthodontic courses by Indian dental academy

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Biomechanics of tooth movement /certified fixed orthodontic courses by Indian dental academy

  1. 1. BIOMECHANICS OF TOOTH MOVEMENT INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. CONTENTS www.indiandentalacademy.com
  3. 3.  Introduction What is Biomechanics  Center of gravity  Center of resistance  Center of rotation Various Terminologies and laws FORCE MOMENT COUPLE MOMENT TO FORCE RATIO STATEOF EQUILIBRIUM   www.indiandentalacademy.com
  4. 4. Begg Mechanotherapy  INTRODUCTION  Objectives of Stage-I Biomechanics of incisor intrusion Degree of anchor bend Role of Class II elastics  o o o Biomechanics of Incisor Tipping  Objectives of Stage-II Biomechanics of space closure  Conclusion  Bibliography www.indiandentalacademy.com
  5. 5. The literature on orthodontic biomechanics usually concerns either specific applications of interest to clinicians or basic questions primarily of interest to researchers. Few articles have attempted to explain biomechanical principles by an approach that would allow the clinician without a background in engineering to understand the concepts and their potential for clinical relevance. In this article, we attempt to review for the clinician the basic relationships between forces and tooth movement. www.indiandentalacademy.com
  6. 6. BIOMECHANICS www.indiandentalacademy.com
  7. 7. Biomechanics is the study of mechanics as it affects the biologic systems. It is the application of mechanics to the biology of tooth movement. Biology + Mechanics = Biomechanics www.indiandentalacademy.com
  8. 8. Physical properties such as distance, weight, temperature and force are treated mathematically as either SCALARS or VECTORS. www.indiandentalacademy.com
  9. 9. SCALARS include temperature and weight, they have a definite magnitude but do not have a direction. They are completely described by their magnitude. www.indiandentalacademy.com
  10. 10. VECTORS include force, these have both magnitude and direction. In case of force, along with magnitude and direction, point of application must be taken into account. www.indiandentalacademy.com
  11. 11. Various terminologies and laws: FORCE MOMENT COUPLE MOMENT TO FORCE RATIO www.indiandentalacademy.com
  12. 12. FORCE: It is defined as an act upon a body that changes or tends to change the state of rest or motion of the body. Force is a vector it has both magnitude and direction. www.indiandentalacademy.com
  13. 13. The forces are indicated by straight arrows www.indiandentalacademy.com
  14. 14. In case of understanding the magnitude and direction of tooth movement, point of application of force is important www.indiandentalacademy.com
  15. 15. CENTER OF MASS Each body has a point in its mass, which behaves as if the whole mass is concentrated at that single point, which we call the CENTER OF MASS in a gravity free environment. www.indiandentalacademy.com
  16. 16. Center of Gravity: The same is called center of Gravity in an environment where gravity is present. www.indiandentalacademy.com
  17. 17. The center of gravity of the tooth is located more towards the crown of the tooth as the mass of the tooth is concentrated more coronally www.indiandentalacademy.com
  18. 18. Since the tooth is partially restrained as its root is embedded in bone its center of gravity moves apically and this is known as CENTER OF RESISTANCE (Cres) www.indiandentalacademy.com
  19. 19. Center of Resistance Center of Resistance Center of Gravity www.indiandentalacademy.com
  20. 20.  In case of single rooted tooth center of resistance is on the long axis of tooth between one third and one half of the root length apical to alveolar crest. www.indiandentalacademy.com
  21. 21.  For a multirooted root, the center of resistance is probably between the roots 1-2 mm apical to furcation. www.indiandentalacademy.com
  22. 22. Center of Resistance Varies (Cres): Length of root: Maxillary canine have long root than maxillary lateral incisor. Thus center of resistance of canine will be more apically placed as compared with center of resistance of lateral incisor. Alveolar bone height: Center of resistance shifts apically as with the alveolar bone loss.  www.indiandentalacademy.com
  23. 23. Periodontal status: The center of resistance shifts apically in periodontally compromised patients. Size and shape of the crown and root. www.indiandentalacademy.com
  24. 24. The center of resistance for a single rooted tooth estimated by different authors as; At 50% of root length – Proffit, Nikoli  Between 50% to 30% of root length – Smith and Burstone.  At 33% of root length – Burstone  Between 25% to 33% root length – Nanda  www.indiandentalacademy.com
  25. 25. Moment Is defined as a tendency to rotate www.indiandentalacademy.com
  26. 26. Moments can be symbolized by curved arrows. www.indiandentalacademy.com
  27. 27. MOMENT is the product of the force times the perpendicular distance from the point of force application to the center of resistance. M=Fxd It is measured in grams – millimeters. d www.indiandentalacademy.com F x d(X) = M(X) F
  28. 28. MOMENT OF FORCE: Moment is a measure of the turning tendency produced by a force. When a force is applied at any point other than through the center of resistance in addition of moving the center of resistance in direction of the force, a moment is created. www.indiandentalacademy.com
  29. 29. In case of tooth, since it is embedded in the alveolar bone, we cannot apply force directly on Cres, but can apply force on the exposed part of the tooth, which is at a distance from Cres. Therefore with a single force we invariably create a moment called as moment of force. www.indiandentalacademy.com
  30. 30. A MOMENT may be referred as Rotation Tipping Torquing. www.indiandentalacademy.com
  31. 31.  Rotation  Tipping  Torquing www.indiandentalacademy.com Flash Player Movie Flash Player Movie Flash Player Movie
  32. 32. If a line of action does not pass through the center of resistance the force will produce some rotation. The potential for rotation is measured as moment. www.indiandentalacademy.com
  33. 33. The direction of a moment can be determined by continuing the line of action of the force around the center of resistance. F www.indiandentalacademy.com x d(X) = M(X)
  34. 34. CENTER OF ROTATION: It may be defined as a point about which a body appears to have rotated as determined from its initial to final position. www.indiandentalacademy.com
  35. 35. A simple method of determining a Center of rotation - Draw the long axis of the tooth in its initial and final positions; we will see that both these lines intersect at a point. This is the point around which the tooth rotates and is called Center of rotation. www.indiandentalacademy.com
  36. 36. Center of Rotation www.indiandentalacademy.com
  37. 37. Center of rotation could be at the center of resistance, apical or incisal to Cres or at infinity. Its position will determine the type of tooth movement. The moment to force ratio controls the center of rotation for the intended tooth movement. www.indiandentalacademy.com
  38. 38. TYPES OF MOVEMENT TOOTH POSITION OF THE CENTER OF ROTATION A. Translation Lies at infinity B. Uncontrolled tipping Slightly apical to center of resistance C. Controlled tipping Apex of root D. Root movement or Torquing Incisal or occlusal edge www.indiandentalacademy.com
  39. 39.  Uncontrolled tipping: In this situation, when force is applied the crown moves in one direction and root moves in the opposite direction. Here Center of rotation lies near to center of resistance. This is referred as uncontrolled tipping. www.indiandentalacademy.com
  40. 40. Uncontrolled tipping www.indiandentalacademy.com
  41. 41.  Controlled Tipping: In this situation, crown moves in the direction of force but the root position remains the same or get minimally displaced. Here Center of rotation lies at apex of the root. www.indiandentalacademy.com
  42. 42. Controlled tipping www.indiandentalacademy.com
  43. 43.  Translation : In this situation tooth moves bodily e.g. both crown and root portion of tooth moves bodily in the direction of force. Here Center of rotation lies at infinity. All the points in the tooth move by same distance in the same direction in translation. www.indiandentalacademy.com
  44. 44. Bodily Movement Center of Rotation at infinity www.indiandentalacademy.com
  45. 45.  Root movement: In this situation, root moves in the direction of force but the crown position remains the same or get minimally displaced. Here Center of rotation lies at incisal edge of the crown. www.indiandentalacademy.com
  46. 46. Root Movement www.indiandentalacademy.com
  47. 47. COUPLE: Two equal and opposite, non collinear forces are called a couple. Couple consists of two forces of equal magnitude, which are parallel to each other but not coincident and they face in opposite direction. www.indiandentalacademy.com
  48. 48. The moment of this couple is equal to the magnitude of one of the forces multiplied by the perpendicular distance between the two lines of action of force. www.indiandentalacademy.com
  49. 49. If the two forces of the couple act on opposite sides of the center of resistance, their effect is additive. However, if they are on the same side of the center of resistance, their effect is subtractive www.indiandentalacademy.com
  50. 50. F2 d + F1 M1= F1Xd M2=F2Xd M=F X D Additive www.indiandentalacademy.com
  51. 51. F1 F2 D1 - D2 M1=F1XD1 M2=F2XD2 M= F X (D1-D2) Subtractive www.indiandentalacademy.com
  52. 52. DIFFERENCE BETWEEN THE MOMENT OF A FORCE AND MOMENT OF COUPLE: www.indiandentalacademy.com
  53. 53. Moment is a measure of the turning tendency produced by a force.  Moment of force is always relative to point of application. It means moment of a force will be low relative to a point (point of application) close to line of action and high for a point (point of application) with a large perpendicular distance to line of action.  In case of Couple moment, it is not relative to any point. www.indiandentalacademy.com
  54. 54. MOMENT TO FORCE RATIO: www.indiandentalacademy.com
  55. 55. It seems that type of movement exhibited by a tooth is determined by the ratio of the counter-balancing moment produced to the net force that is applied to a tooth . This is called as the moment to force ratio . www.indiandentalacademy.com
  56. 56. In terms of direction, the counterbalancing moment is always going to be in the direction opposite the moment of force. www.indiandentalacademy.com
  57. 57. Counter-balancing moment Moment of force Force www.indiandentalacademy.com
  58. 58. The ratio of the counter-balancing moment to the force applied determines the type of tooth displacement, brought about by the combined application of a force and counter-balancing moment. As the counter-balancing moment increases, the center of rotation moves apically. www.indiandentalacademy.com
  59. 59. At one specific level of M/F the moment which arises from the force and the applied counter-balancing moment cancel out each other i.e. there is no rotational component, and hence only a translation takes place under the effect of force . www.indiandentalacademy.com
  60. 60.  M/F Ratio values normally quoted of various types of displacements are M/F ratio less than 5:1 causes uncontrolled tipping in which the crown and the root apex move in opposite directions. M/F ratio between 5:1 and 8:1 causes controlled tipping in which the root apex remains stationary and only the crown moves. www.indiandentalacademy.com
  61. 61. M/F ratio of 10:1 causes translation. The crown and the root apex move to same extent in the same direction of force. M/F ratio of 12:1 causes root movement. The crown remains stationary while only the root moves. www.indiandentalacademy.com
  62. 62. It is important to note that the differences between the M/F Raito for controlled tipping, translation and root movement are small. In other words, even small alterations in the magnitude of the applied force or the counter-balancing moment will alter the type of tooth movement brought about. www.indiandentalacademy.com
  63. 63. STATE OF EQUILIBRIUM www.indiandentalacademy.com
  64. 64. When an appliance is fitted in the mouth, it assumes a state of equilibrium. The active elements in the appliance generate certain forces or moments. Other forces or moments arise automatically in the system to balance these forces or moments. Some of them may be beneficial while others may be undesirable. www.indiandentalacademy.com
  65. 65. For example, tip back bend (like the bite opening bend in Begg appliance) generates a moment which tends to tip the molar tooth crown distally. This is balanced by an automatic creation of another moment in the overall system in opposite direction comprising of two forces an intrusive force at the anterior end and on extrusive force on the molar. www.indiandentalacademy.com
  66. 66. www.indiandentalacademy.com
  67. 67. BEGG MECHANOTHERAPY www.indiandentalacademy.com
  68. 68. Begg mechanotherapy is very efficient in opening the deep anterior overbites. It is generally agreed that Begg mechanics bring about bite opening by a combination of molar extrusion (especially of lower molars) and some intrusion of lower anteriors. Upper anteriors may not change in their position in vertical direction (i.e. they are prevented from erupting) or may intrude slightly or may even extrude slightly. www.indiandentalacademy.com
  69. 69. There are three basic movements in the Begg mechanotherapy Incisor intrusion  Tipping of teeth  Root uprighting.  www.indiandentalacademy.com
  70. 70. The mechanism of intrusion is understood by considering the net intrusive force magnitude and direction. While tipping of teeth and root uprighting is explained on the basic of M/F ratio. www.indiandentalacademy.com
  71. 71. OBJECTIVES OF STAGE I: www.indiandentalacademy.com
  72. 72. Open the anterior bite : Proper amount of bite opening bends or curves in the arch wire. Continuous wearing of Class II (intermaxillary) elastics as required.  Eliminate anterior crowding : Vertical loops between crowded anterior teeth, with bracket areas modified for desired overcorrection.  www.indiandentalacademy.com
  73. 73. Close anterior spaces : Plain arch wire with latex elastic or elastomeric chain from cuspid to cuspid.  Over correct rotated cuspids and bicuspids : Rotating springs Elastomeric traction into the arch wire  www.indiandentalacademy.com
  74. 74. Over correct the mesiodistal relationship of the buccal segments Continuous wearing of class II elastics. Proper bite opening bends in both upper and lower arch wires.  www.indiandentalacademy.com
  75. 75. BIOMECHANICS OF STAGE I www.indiandentalacademy.com
  76. 76. As we understand today the Begg appliance is a good example of single couple system. Stage I arch wire www.indiandentalacademy.com
  77. 77. The orthodontic environment created during stage I is conducive to rapid movement of anterior teeth under the light forces generated by the arch wires and intermaxillary elastics www.indiandentalacademy.com
  78. 78. MECHANISM OF INTRUSION: www.indiandentalacademy.com
  79. 79. Lack of true intrusion of the maxillary incisors was one of the major weaknesses of traditional Begg. Bite opening occurred mainly on account of molar extrusion and some intrusion of the lower incisors. www.indiandentalacademy.com
  80. 80. Stage I arch-wire www.indiandentalacademy.com
  81. 81. Whether the upper incisors intruded is a debated issue. The round archwire derives bite opening force from the anchor bends. www.indiandentalacademy.com
  82. 82. A anticlockwise moment generated by the anchor bend in the molar tube (upper) is automatically balanced by the generation of clockwise moment in the anterior segment along with intrusive force on the anterior and extrusive force on the molars in order to establish state of equilibrium. www.indiandentalacademy.com
  83. 83. This flaring tendency of upper incisors can be resisted by using Class II elastics during stage I. But class II force along with horizontal component have vertical component of force which reduces the magnitude of the intrusive force of the arch wire on the upper anteriors. www.indiandentalacademy.com
  84. 84. vertical problem www.indiandentalacademy.com
  85. 85. Thus the interplay between the intrusive force from the archwire and the retractive force from the elastics determines both the magnitude and direction of the net resultant force acting on anterior teeth. www.indiandentalacademy.com
  86. 86. VARIOUS TYPES OF BITE OPENING BENDS: The Anchor bend the conventional bite opening bend causes more intrusion of canines while the lateral and central incisors progressively lag behind.  www.indiandentalacademy.com
  87. 87.  A Gable bend causes a progressively more intrusion of central and lateral incisor, as compared to canine Mollenhouer’s bite opening curve – Mollenhouers especially recommends it with use of 0.018 wire.  www.indiandentalacademy.com
  88. 88. www.indiandentalacademy.com
  89. 89.  Swain modification: Mild gingival curve is incorporated in the anterior section, from mesial of cuspid to mesial of other side cuspid. www.indiandentalacademy.com
  90. 90. CONSIDERATION OF THE MAGNITUDE OF INTRUSIVE FORCE. www.indiandentalacademy.com
  91. 91. OPTIMAL INTRUSIVE FORCE VALUE: www.indiandentalacademy.com
  92. 92. Many authors have suggested optimum intrusive force values ranging from 15-30 grams per upper incisor and slightly higher values for upper canines. www.indiandentalacademy.com
  93. 93. For active intrusion the upper anteriors should receive approximately 60 grams net force in the midline, after negating the extrusive component of Class II elastics. www.indiandentalacademy.com
  94. 94. ROLE OF LIGHT CLASS II ELASTICS: www.indiandentalacademy.com
  95. 95. Hocevar stated that 120 grams of archwire generated intrusive force in conjunction with 60 grams of Class II elastics pull on either side is “efficient for intrusion” www.indiandentalacademy.com
  96. 96. According to Dr.Jayade net intrusive force of 60 grams can be obtained by a combination of 75 grams of intrusive force generated by arch wire and some modification in wearing of elastics that is by using light elastic forces for longer periods from 2-5 days. Very light Class II force is delivered as the elastic force diminishes rapidly in oral environment. www.indiandentalacademy.com
  97. 97. Sims states the use of 3/8” ultra light elastics instead of routinely used 5/10” light elastics. He said continue the same elastic for 4-5 days till they break. www.indiandentalacademy.com
  98. 98. Role of Class I Elastic Forces www.indiandentalacademy.com
  99. 99. Modifying the force system to achieve simultaneous intrusion and retraction using Class I elastic instead of Class II elastics was first illustrated by Shin Yang Liu (1981). www.indiandentalacademy.com
  100. 100.  In pure begg technique the direction of the intrusive vector of the maxillary arch wire and the extrusive vector of the class II elastics are opposite . This accounts for the difficulty in obtaining anterior maxillary teeth intrusion. www.indiandentalacademy.com
  101. 101.  In this technique modification, of using Class I elastics , it solve the problem of lack of intrusion of the maxillary anteriors. www.indiandentalacademy.com
  102. 102.  In this arrangement the vectors are in the same direction as the elastic pull and the archwire force are unidirectional and hence synergistic www.indiandentalacademy.com
  103. 103. Dr. Jyothindra Kumar introduced concept of power arms as a point of attachment high up in the vestibule for the engagement of Class I elastics. CLA SS IE LAS TI CF ORC E www.indiandentalacademy.com
  104. 104. Dr. Jayade has been using Class I elastics, which were worn from transpalatal arch (TPA) to the canine hooks/loops. CLA SS IE LAS TI CF ORC E www.indiandentalacademy.com
  105. 105. It is impossible to precisely calculate the required intrusive force every time, for every patient, since it is dependent on various variables.  Different root sizes and tooth inclination. Different arch sizes, which affect the length of the wire spans and stretch of the elastics.  www.indiandentalacademy.com
  106. 106.  Individual biomechanical response Difference in the archwire sizes. Normally .018” wire will produce more intrusive force as compared to 0.016” wire when some degree of anchor bend is given.  www.indiandentalacademy.com
  107. 107. THE CONCLUSION IS, “TO USE HIGHER INTRUSIVE FORCES IN COMBINATION WITH VERY LIGHT CLASS II ELASTIC FORCES FOR ACTIVE UPPER INCISOR INTRUSION” www.indiandentalacademy.com
  108. 108. CONSIDERATION OF THE DIRECTION OF THE RESULTANT FORCE: www.indiandentalacademy.com
  109. 109. Teeth respond only to the resultant of the forces which are applied and not to the individual components of the force system. www.indiandentalacademy.com
  110. 110. During Stage I, the upper anteriors are subjected to two forces i.e. the retractive force of class II elastics and the intrusive force generated by the anchor bend in the arch wire. The resultant of these two will determine how the upper anterior teeth respond to the intrusion. www.indiandentalacademy.com
  111. 111. THE INTERPLAY BETWEEN THE ANCHOR BEND AND CLASS II ELASTICS INTRUSION FORC TIC S LA CE R FO II E S AS www.indiandentalacademy.com CL
  112. 112. The direction and magnitude of resultant force both depend upon the interplay between.  Magnitude of Intrusive Force: Whose direction remains constant i.e. tangential to the arc that the anterior segment of the archwire would subscribe, if released from the brackets.  Magnitude and the direction of the elastic force. www.indiandentalacademy.com
  113. 113. Different inclinations of the anterior teeth would require different combinations on of the intrusive and elastic forces. Hocevar states, that the teeth are not affected by the magnitudes of various components of force systems, they experience only the total resultant force www.indiandentalacademy.com
  114. 114. For example, in case severely proclined upper anteriors a low magnitude of intrusive force along with high class II force would give a desired resultant force, passing palatal to Cres, this will help correcting the proclination of incisors . Once the inclination of upper incisors is corrected then the class II elastics force is reduced helping in keeping the resultant force close to Cres . www.indiandentalacademy.com
  115. 115. 60 gms 45gms 30gms 60gms www.indiandentalacademy.com
  116. 116. In Class II Division 2 cases , where the upper centrals are retroclined , only intrusive force should be used (Avoiding the Class II elastics) The intrusive force acts labial to Cres and corrects the retroclination. Once the inclination is corrected then we can use Class II elastics . www.indiandentalacademy.com
  117. 117. 40gms 50gms 20gms www.indiandentalacademy.com
  118. 118. MECHANICS OF BEGG TIPPING: www.indiandentalacademy.com
  119. 119. The concept of tipping back the teeth in the first stage & further in stage II … INTRUSION FORC T AS L II E S AS www.indiandentalacademy.com CL IC C OR F E
  120. 120. Generally, uncontrolled tipping is undesirable because it leads to root resorption as stated by Reitan. There is more resorption when uncontrolled tipping is in labio-lingual direction. www.indiandentalacademy.com
  121. 121. Intrusion and tipping are intimately related not only because they are carried out simultaneously but also, when both are balanced judiciously it help in overcoming uncontrolled tipping of incisors. www.indiandentalacademy.com
  122. 122. This is achieved by manipulating the intrusive force generated by wire and retractive component of force from the Class II elastics. www.indiandentalacademy.com
  123. 123. BOTH THE ANCHOR BEND IN THE WIRE AND CLASS II ELASTICS PRODUCE MOMENTS IN THE SAME LABIO-LINGUAL PLANE BUT ACT IN OPPOSITE DIRECTIONS. www.indiandentalacademy.com
  124. 124. The intrusive force produces crown labial-root lingual moment e.g.. anticlockwise moment on the upper anteriors. While the retractive force produced the Class II elastics generates clockwise moment e.g. crown lingual-root labial moment www.indiandentalacademy.com
  125. 125. The moment from the intrusive force can act as the counter balance moment against the moment produced by the elastic force. The ratio of the former to the retraction component of the elastic force is the M/F ratio which governs the type of tipping while retracting the anterior teeth. www.indiandentalacademy.com
  126. 126. The most important consideration is to keep light Class II elastic and use adequate amount of intrusive force so that correct M/F ratio (8:1) is obtained to have a controlled tipping. www.indiandentalacademy.com
  127. 127. PREVENTING UNCONTROLLED TIPPING OF UPPER INCISORS www.indiandentalacademy.com
  128. 128. In the refined Begg mechanics, use of MAA which provides a moment in the labio-lingual plane by creating a couple. This couple moment is an anti-clockwise moment. www.indiandentalacademy.com
  129. 129. S AS CL IC ST A EL II www.indiandentalacademy.com F E RC O
  130. 130. Once the bite is opened in the first stage, the intrusive force level is reduced which inturn reduces M/F ratio. This leads to greater likelihood of uncontrolled tipping of upper anterior teeth during later part of the first stage and whole of second stage. Thus the anticlockwise moment produced by anchor bend on anterior is supplemented by with the moment of couple produced by MAA www.indiandentalacademy.com
  131. 131. Flaring occurs as lower incisors are subjected to crown labial root-lingual moment from the intrusive force generated in arch wire, while there is no restraining force on these teeth as similar to Class II elastic force on Upper incisors. www.indiandentalacademy.com
  132. 132. PREVENTING UNCONTROLLED TIPPING OF LOWER INCISORS: www.indiandentalacademy.com
  133. 133. The flaring can be avoided by two means; Minimizing the clockwise force moment by reducing the intrusive force. Secondly, cinching tightly the distal ends of the arch wire.   www.indiandentalacademy.com
  134. 134. Lastly by producing counter moment using a MAA for labial root torque or a reverse torquing auxiliary (Udder arch)  www.indiandentalacademy.com
  135. 135. www.indiandentalacademy.com
  136. 136. In case of severely lingually tipped lower anteriors, Cres will be lying buccal to the point of application of the intrusive force generated by the anchor bend so there is more chances to tip the lower anteriors more lingually. www.indiandentalacademy.com
  137. 137. So in that case we give a By pass arch wire in order to upright the lower incisors . www.indiandentalacademy.com
  138. 138. www.indiandentalacademy.com
  139. 139. www.indiandentalacademy.com
  140. 140. BEGG STAGE II www.indiandentalacademy.com
  141. 141. Amongest the traditionally described stages of Begg technique, the second stage of treatment involves closure of extraction spaces. This is thought to be the easiest phase of treatment www.indiandentalacademy.com
  142. 142. During Stage II all the corrections achieved during Stage I should be maintained.  Maintain Edge to Edge relationship of anterior teeth: Reduce the anchor bend in arch wire and wear intermaxillary elastics as required . www.indiandentalacademy.com
  143. 143.   Maintain anterior space closure : To give cuspid ties either by elastomeric rings or steel ligatures. To maintain overcorrected or normal mesiodistal molar relationship : Keep wearing of intermaxillary elastics as required during posterior space closure. www.indiandentalacademy.com
  144. 144.  In addition to the above, the stage II of the refined Begg aims are Controlled tipping of the incisors, when space closure is to be mainly achieved by the anterior retraction. www.indiandentalacademy.com
  145. 145. OBJECTIVES OF STAGE II: www.indiandentalacademy.com
  146. 146. When all the objectives of Stage I are met stage II mechanics can be instituted. The sole or main purpose of II stage is closure of extraction spaces. www.indiandentalacademy.com
  147. 147. The extraction space can be closed by either retraction of the anteriors or protraction of the posteriors or combination of both. www.indiandentalacademy.com
  148. 148. BIOMECHANICS OF STAGE II www.indiandentalacademy.com
  149. 149. The anchor bend should be sufficient as to produce a counter clockwise moment greater than the clockwise moment produced by the Class I and Class II elastics in upper arch. www.indiandentalacademy.com
  150. 150. The M/F ratio should be sufficient or around 8/1 so as to have a controlled tipping movement. www.indiandentalacademy.com
  151. 151. If anticlockwise moment is less than clockwise moment produce by Class I and Class II elastics on upper anterior, then M / F ratio will less and it will uncontrolled tipping of upper anterior teeth. www.indiandentalacademy.com
  152. 152. Class I Elastic Forces INTRUSION FORC CLASS I ELASTIC FORCE At the end of Stage II www.indiandentalacademy.com
  153. 153. Same way in lower arch the clockwise moment should be greater than anticlockwise moment produced by Class I elastics. So as to have controlled tipping movement. www.indiandentalacademy.com
  154. 154. Normally 0.016 upper and lower arch wires with reduced bite opening bends are used. Some authors say use of heavy arch wire 0.020” as it will function as retainers to maintain arch form and bite opening achieved during stage I. www.indiandentalacademy.com
  155. 155. Dr. Swain advocated the use of lingual attachments on molars and cuspids to allow the use of lingual space closing elastics to aid the traditionally used buccal vector of intra maxillary elastic force during stage II known as half strength elastics. www.indiandentalacademy.com
  156. 156. Two distinct advantages in using intra maxillary (Half strength) space closing elastics  It gives a better positional control over the anchor molar thus obviating the need for a mandatory compensate toe in bend when using elastic force only from buccal side.  Closure of extraction spaces becomes easier. www.indiandentalacademy.com
  157. 157. www.indiandentalacademy.com
  158. 158. USE OF BRAKING MECHANICS www.indiandentalacademy.com
  159. 159. When further retraction of anterior teeth into the remaining extraction space is deemed undesirable clinically , then the posterior teeth are brought forward, that is posterior teeth are mesialized. www.indiandentalacademy.com
  160. 160. To achieve mesialization of posterior teeth heavy elastic forces are required with concurrent use of brakes in the anterior region. www.indiandentalacademy.com
  161. 161.  Various brakes are:  Using uprighting springs (passive springs) Reverse torque to incisor roots (Udder arch and MAA)  Using T pins www.indiandentalacademy.com
  162. 162. Passive Uprighting Springs UDDER ARCH T PINS MAA www.indiandentalacademy.com
  163. 163. The brakes reverse the anchorage site from the posterior to anterior segment by allowing bodily movement rather than the tipping of anterior teeth, this bodily movement provides more resistance hence acting as a anchorage. www.indiandentalacademy.com
  164. 164.  He summarized that the direction of resultant force should pass through the center of resistance of anterior teeth (or close to it).  Therefore, substituting Class II elastic forces by Class I elastic forces would orient the resultant force more vertically passing nearer to the center of resistance of anterior teeth. www.indiandentalacademy.com
  165. 165. Stage I arch-wire www.indiandentalacademy.com
  166. 166. www.indiandentalacademy.com Leader in continuing dental education www.indiandentalacademy.com

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