intrusion_seminar.pptxghajkzfajjdbdfhhdh

Dipika

1. BIOMECHANICS OF INTRUSION

2. SYNOPSIS INTRODUCTION DEFINATION AND CLASSIFICATION OF INTRUSION. PRINCIPLES OF INTRUSION MORPHOLOGICAL CHARACTERISTICS OF DEEPBITE. INTRUSION MECHANICS IN BEGGS. INTRUSION MECHANICS IN PEA. TRUE INTRUSION . A. 2 X2 AND 2 X4 APPLIANCE(UTILITY ARCH) B. BURSTONE’S CONTINUOUS INTRUSION ARCH. C. BURSTONE’S THREE PIECE INTRUSION ARCH.

3. 8. INTRUSION WITH ALPHA AND BETA MOMENTS 9. K-SIR (KALRA SIMULTANEOUS INTRUSION AND RETRACTION. 10. CONNECTICUT INTRUSION ARCH. 11.INTRUSION MECHANICS OF TADS APPARENT INTRUSION A. REVERSE CURVE NiTi B. ANTERIOR BITE PLANE. 11. CONCLUSION.

4. Definition True intrusion is achieved by moving the root apices of the anteriors closer to the bony base. Relative intrusion is achieved by keeping them where they are, while the mandible grows and the posterior teeth erupt. Apparent intrusion is achieved by extrusion of the posterior teeth

5. Planning for intrusion Natural plane of occlusion – original axial inclination and alignment of the posterior teeth Anterior aesthetics – the relationship of the incisor to the upper lip The amount of attached gingiva present in the mandibular incisor region A – B discrepancy

6. Deep bite can be either skeletal or dentoalveolar Skeletal deep bite is due to - upward rotation of mandible - downward rotation of maxilla - combination Dentoalveolar deep bite is due to - overeruption of anteriors - infra occlusion of the molars - combination

7. Deep bite correction Intrusion of anteriors Extrusion of posteriors Worsening of Class II Profile

8. Improves the Class II Profile Intrusion of the anteriors Control of the vertical dimension Forward rotation of the mandible

9. Intrusion Intrusion Bio Mechanical Histological

10. According to Burstone the average force values for intrusions are : Moment values are based on 30 mm distance from incisors to the center of resistance of posterior segment. Teeth Force / Side Total force in midline Moment / side (gm- mm) Upper Central incisors. Central & lateral incisors. Central & lateral incisors & canine. 25 50 100 50 100 200 750 1,500 3,000 Lower Central & lateral incisors. Central & lateral incisors & canines. 20 80 40 160 600 2,400

11. Factors affecting intrusion Controlling force magnitude and constancy Anterior single point contacts Point of force application Selective intrusion Control of reactive units Avoid extrusive mechanics

12. TRUE INTRUSION Lowest magnitude of force Force level increased No intrusion Root resorption Reciprocal effect on posterior segment Experience a vertical force Worsening of the Class II Profile Force magnitude and constancy

13. Anterior single point of contact Possible to determine the exact amount of force exerted by the appliance system No moment introduced into the wire TRUE INTRUSION

14. Point of application Perpendicular to the distal extension of the anterior segment Passing through center of resistance Intrusion of incisor segment Apply a distal force – changes the direction of the resultant force

15. Point of Application Point of application as close to the distal of the lateral incisor bracket, anterior to the center of resistance Force of application is redirected with a distal force Force of application is more anterior The force is passing through the center of resistance and is parallel to the long axis of the tooth True intrusion and no retraction

16. Point of application Force passing through the center of resistance Line of action is lingual to center of resistance and parallel to the long axis of the tooth Combination of intrusion and tipping of anteriors Force of application is redirected with a distal force

17. Control of the reactive unit Minimize the intrusive force As many teeth as possible joined to form the posterior segment Transpalatal arch BEST CONTROL OVER POSTERIOR TEETH Anchor loss Moment arm is large from the anterior to posterior segment Head gear

18. Pressure Side On side towards which force is applied Resorption of the cortical bone Resorption of the fibres embedded in the alveolar bone DETACHMENT Histological aspect of intrusion

19. Histology of the tension side Tension Side On side from which force is applied The fibre straightened as the tooth moves away from the alveolar bone Bony wall not resorbed fibres remain attached to the cortical and the cementum Lengthening of the fibre in the intermediate plexus DETACHMENT

20. Intrusion BEGG PAE

21. Intrusion mechanics in Begg Posterior Distal tipping Mesial in rotation Extrusion Anchor bend Anterior Class II elastics Extrusion of anteriors Retraction of the anteriors Prevents the crown lingual – root labial movement Intrusion of anteriors Crown labial, root lingual of the anteriors Anterior Posterior Extrusion

22. Intrusion mechanics in Begg Consideration of the magnitude of the intrusive force Optimal intrusive force value Role of class II elastics Consideration of the direction of the resultant force Magnitude of the intrusive force Magnitude and direction of the elastic force Arch wire size for generating higher intrusive force

23. Factors affecting intrusive force Intrusive force varies with Different root sizes and tooth inclination Different arch sizes which affect the length of the wire span and stretch of the elastics Change in the dental arch sizes during treatment Individual biomechanical response Changing elastic force during rest and function

24. DIFFERENTIAL MOMENT When wire is engaged in bracket slot and anti-clockwise moment is generated in anterior as the force is labial to the center of resistance and reciprocal clockwise moment of greater magnitude on molar. This is referred to as differential moment .

25. TRADITIONAL BEGGS We apply forces from the archwire and the class II elastics. Thus we have two vectors of force acting at a point. The resultant of these forces will be applied on the tooth or the direction in which the tooth will move. As the force is passing behind the COR thereby, causing a moment resulting in uncontrolled tipping.

26. Bite opening bends Begg Technique is universally acknowledged for its efficient bite opening mechanics, which is indeed one of the strength of the technique . This is the procedure where there is incorporation of bends in the arch wire so that it helps in the intrusion of the anterior teeth and extrusion of the molars. Many authors have proposed different sites for the bite opening bends in the arch wire.

27. Anchor bends First in the conventional begg’s , anchor bend is placed 3 mm mesial to the molar tube in such a way that there is gingival displacement of the anterior part of the arch wire therefore when the arch wire is placed in the bracket, there is a intrusive force acting on the anterior segment.

28. Gable bend This is a modified bite opening bend given in the arch wire distal to the canine. This tends to cause extrusion of the canines and the intrusion of the central and laterals

29. Hocevar’s modification In a modification given by Hocevar , bite opening bends are placed on either side of canine, which results in more intrusion of central incisors and relative extrusion of lateral incisors and canine.

30. Kameda’s modification In this modification both the anchor bends and gable bends are given, there is extrusion of the canine and intrusion of the incisors

31. Swain s modification Swain advocates giving a mild gingival curve in the anterior region which starts from mesial side of one canine to the mesial side of the other canine for the better intrusion of the anteriors .

32. In a modification given by Mollenhauer , where a bite opening curve is given, it will result in extrusion of the canine and intrusion of central and lateral incisors Mollenhauer’s

33. Vertical step up bend This intrusive action can be further augmented by incorporating a vertical step up bend 3mm in height mesial to the molar tube . After giving this bend, anchor bend of required degree can be given in the upper end of the step up bend.

34. Power arm with class I elastics. Now at present we switch from class II to class I elastics, keeping the force constant, the resultant passes close to the center of resistance. Consequently, the moment is reduced and rotational effect is decreased. REFINED BEGGS

35. If we use power arm and engage class I elastics, the resultant force passes even closer to center of resistance of the tooth, resulting in controlled tipping and intrusion.

36. The Begg appliance works to our satisfaction in cases of bidental protrusion. This is because in most of cases the bite is shallow and class I or horizontal force is delivered right from the beginning. This causes the resultant to pass close to the CORe of the teeth, leading to controlled tipping of the upper and lower anteriors .

37. Buccolingual control, a round archwire in a round tube cannot control the molars buccolingually and the anchor bends which we incorporate in the archwire produce a number of side effects. There is extrusion as the force is buccal to the CORe of molar, the molars tend to roll lingually. This can be overcome by TPA or lingual arch.

38. The intrusive force generated by the archwire converges the teeth more because it is passing mesial to the center of resistance. So the net intrusive effect is almost nil.

39. The intrusive force passes distal to the center of resistance. The moment created causes the teeth to tip further distally.

40. Therefore, the intrusive force generated by the archwire used in Begg is effective only where the anterior teeth are upright mesiodistally, as the force will pass through the center of resistance.

41. Continuous and segmental arch Deep bite correction Extrusion of molars Intrusion of anteriors Flaring of the incisors Genuine intrusion with minimal extrusive movement in the molar area Evaluation of continuous arch and segmented arch leveling technique in adult patients 1996 AJO

42. INTRUSION IN PEA INTRUSION ARCH WIRES Intrusion can be accomplished in two ways with intrusion arches. 1 . With continuous archwire that bypasses the premolars and canine teeth. 2. With segmented base archwire . So that there is no connection along the arch between the anterior and posterior segments and an auxiliary depressing arch.

43. UTILITY ARCH (2X4 APPLIANCE ) This auxiliary archwire was developed and refined by Ricketts for bioprogressive therapy. The utility arch engages only two molars and the four incisors. It is commonly known as a 2 X 4 appliance.

44. Types of Utility arches Passive arch Intrusion arch Retraction arch Protraction arch 44

45. Dimensions 45

46. Incisal segment Posterior vertical segment Vestibular segment Molar segment Anterior vertical segment PARTS OF UTILITY ARCH

47. Basic components of utility arches Molar segment extends into tube, cut flush or bent gingivally Posterior vertical segment formed by making a 90 degree bend with 142 arch forming plier 3-4 mm – md, 4-5 mm – mx 3 rd order bend at junction with molar segment to avoid impingement on gingiva Vestibular segment Formed by placing 90 deg bend at inferior portion of vertical segment Wire passes anteroinferiorly along the gingival margin without interfering with any other components 47

48. Anterior vertical segment 4-5 mm – md, 5-8 mm – mx, specific lengths determined by depths of vestibules in individual patient and by type of fixed appliance Incisal segment Final 90 deg bend creates it, lies passively in brackets after leveling with sectional arches Wire selection – blue elgiloy – RMO 018 – mx – 016x022 md – 016x022 / 016x016 022 – mx – 019x019 md – 019x019 48

49. Function of utility arch Position of lower molar to allow for cortical anchorage – only uprighting and buccal torquing Manipulation and alignment of lower incisor segment Stabilization of lower arch – allowing segmental treatment of buccal segments – round tripping avoided Physiological roles of lower utility arch – early removal of incisal interferences Overtreatment - not necessary to link overbite control to overjet control 49

50. MATERIAL FOR UTILITY ARCH Blue elgiloy of 0.016" x 0.016" 0.016" x 0.022 ” Dimension in an 0.022" slot. A utility arch can even be made with 0.014" or 0.018" round wires.

51. It produces 60-100 gms on the lower incisors for intrusion . The overall effect is intrusion and possible torquing of the lower incisors as well as tipping back of the molars. 5 mm space between the anterior border of the auxiliary tube and the posterior vertical segment of the utility arch allows tying back the utility arch.

52. Intrusion of the anterior teeth can be produced in one of the two ways: After ligating the utility arch into the anterior brackets, an intrusive force can be produced by placing an occlusally directed gable bend in the posterior portion of the vestibular segment of the archwire . 2. Other type of activation involves placing a tip back bend in the molar segment. The tip back bend causes the incisal segment of the archwire to lie in the vestibular sulcus. The intrusive force is created by placing the incisal segment of the utility arch into the bracket of the incisors. This activation creates a moment that allows for the long action of the lever arm of the utility arch to intrude the incisors.

53. The tip back bend in the molar segment leads to posterior tipping of the first molars. Which can be avoided by placing a gable bend in the posterior aspect of the vestibular segment or a transpalatal arch can be used.

54. Passive arch Mixed dentition Maintains arch length during transition by preventing mesial migration of molars Influences the eruption of posterior teeth by holding cheek musculature away from erupting teeth Spontaneous arch widening Permanent dentition Maintenance of anchorage – incorporates anteriors Non extraction cases – anchorage after distalization of molars, to allow for premolar driftodontics in combination with TPA or extra oral devices Extraction cases –placed for anchorage control prior to canine retraction

55. Intrusion arch Posterior vertical segment 5 mm anterior to auxiliary tube – intrusion with retraction – prevents labial tipping during intrusion Intrusion produced in two ways Occlusally directed gable bend in posterior portion of vestibular segment Tip-back bend in molar segment – sometimes tips molar back – avoided with TPA 55

56. Retraction arch Fabrication similar to Intrusion Utility Arch Incorporation of loop allows for longer range of activation Uses – most commonly during final stages of comprehensive edgewise treatment for space closure via retraction of incisors Provides necessary intrusion that must often precede retraction In mild anterior crossbite cases with spacing and proclination With bonded orthopedic appliances (Herbst, bonded RME) To grasp the extension posterior to the auxillary tube. The wire is pulled 3-5 mm posteriorly and them bent upward at an angle. An occlusally directed gable bend in the vestibular segment is used to produce intrusion.

57. Protraction arch Mixed dentition Prior to functional jaw orthopedic appliance therapy in cl II patients with retruded upper incisors. Only upper arch strapped with TPA and utility arch Permanent dentition Proclining and intruding incisors in cl II div II cases Presurgical orthopedic phase of treatment for mandibular advancement, to decompensate position of upper incisors

58. Fabrication Vertical segment flush with tube Loop distal to anterior segment and occlusal to vestibular segment Anterior leg lies 2-3 mm anterior to ultimate position when passive Activation tying into anterior brackets gable bend for intrusion Re-activation Bending posterior vertical segment from 90 to 45 58

59. These springs are made of 0.017”x 0.025” TMA wire. The upper and lower arches have to be leveled and aligned and a rigid stainless steel wire, preferably 0.017”x 0.025” dimension is engaged. Anchor is reinforced by TPA and lingual holding arch. The intrusion springs can be made with or without helix. The wire is bent gingivally mesial to the molar tube and then helix is formed. The mesial end is bent in hook and is engaged onto the main archwire distal to the lateral incisors. The mesial end of the spring lies passively at the height of the mucobuccal fold and the spring is activated by pulling the hook down and engaging in onto the archwire . BURSTONE’S INTRUSION SPRING

60. Continuous intrusion arch The basic mechanism for intrusion consists of three parts: 1. The posterior anchorage unit. 2. The anterior segment. 3. The intrusion arch itself . Initial alignment of anterior teeth is not necessary when performing intrusion. The intrusion arch itself is fabricated from 0.017" x 0.025 " TMA or 0.016" x 0.022" TMA.

61. POSTERIOR ANCHORAGE UNIT Early in treatment the posterior teeth are aligned and joined together with a buccal stabilizing segment of heavy wire Right and left posterior segments are joined together by transpalatal arch in the maxilla and lingual arch in the mandible whenever possible at least the first molar and second premolar should be used and the addition of other teeth would further enhance the anchorage potential

62. Intrusive arch spring The intrusive arch consist of 0.016 x 0.022 inch or 0.017 x 0.025 inch TMA A step down bend is placed at the canine bracket to avoid this bracket upon activation of the intrusion arch

63. Anterior segment Initial alignment of anterior teeth is not necessary when performing intrusion Intrusive spring is tied to the wings of the brackets of incisor not into the slot Formed to fit the teeth to be intruded.

64. Burstone’s Three piece Intrusion Arch The basic mechanism for intrusion consists of three parts: 1. The posterior anchorage unit. 2. The anterior segment. 3. The intrusion spring itself .

65. Intrusion cantilever Posterior anchorage unit Anterior segment with posterior extension

66. The anterior segment is bent gingivally distal to the laterals and then bent horizontally creating a step of approximately 3mm. The distal part extends posteriorly to the distal end of the canine bracket where it is formed into a hook. The anterior segment should be made of 0.021”x0.025” stainless steel wire to prevent side effects created by bending of the wire during force application .

67. The intrusion cantilevers are made from 0.017" X 0.025 " TMA wire. The wire is first bent gingivally mesial to the molar tube and then a helix is formed. On the mesial end the cantilever, hook is bent through which the intrusion force can be applied to the anterior segment. The cantilever is then activated by the making a bend mesial to the helix at the molar tube, and then cinched back.

68. The anterior segment which is extended till the distal end of the canine bracket, i.e., 2-3 mm distal to the center of resistance of the anterior segment of teeth allows distal placement of the intrusive force, which is desired in a case of flared incisors. A small distal force can be added by placing an elastomeric chain extending form the molars to the anterior segment of wire on each side. This force facilitate simultaneous intrusion and retraction by redirecting the force parallel to the incisor long axis.

69. The center of resistance of the four incisors is usually estimated to be halfway between the crest of the alveolar bone and the apex of the lateral incisors root in the sagittal plane. An intrusive force through the centre of resistance of the four incisors will cause pure intrusion of these incisors along the line of action of the force. This same effect can be produced in a three piece intrusion arch with force passing perpendicular to the distal extension of the anterior segment and through the center of resistance.

70. It is possible to change the direction of the net intrusive force by applying a small distal force. Thus, if intrusion along the long axis of the incisors in indicated, the point of intrusive force. can be moved anteriorly and a small distal force will help to direct the intrusive force along the long axis of the incisors . If the intrusive force is placed distal to the centre of resistance and an appropriate small distal force is applied, intrusion and simultaneous retraction of the anterior teeth occurs. This is because of the clockwisemoment created around the centre of resistance of the anterior segment. The overall force system includes an anterior intrusive force and a posterior extrusive force and a tip back moment.

71. LOOP MECHANICS When a offset bend is placed in the wire like anchor bend in Begg a differential moment is created, with a greater clockwise moment in the posterior and anticlockwise moment in the anterior segment. The side with the greater moment shows extrusion and there is intrusion on the side with the lesser moment.

72. Alpha moment :- this is the moment acting on the anterior teeth (often termed anterior torque).

73. Beta moment :- this is the moment acting on the posterior teeth. Tip-back bends placed mesial to the molars produce an increased moment.

74. Horizontal forces :- these are the mesio -distal forces acting on the teeth.

75. Vertical forces :- These are intrusive – extrusive forces acting on the anterior or posterior teeth. These forces generally result from unequal alpha and beta moments.

76. Alpha and beta bends. 15 25 If the beta moment is greater than the alpha moment, anchorage is enhanced by the mesial root movement of the posterior segment, and there is a net intrusive force on the anterior teeth.

77. The K-SIR (Kalra Simultaneous Intrusion and Retraction) archwire is a modification of the segmented loop mechanics of Burstone and Nanda K-SIR archwire : .019“x.025" TMA archwire with closed U-loops 7mm long and 2mm wide. K- SIR APPLIANCE

78. 90° bends placed in archwire at level of U-loops. Centered 90° V-bend creates two equal and opposite moments (red) that counter tipping moments (green) produced by activation forces.

79. Archwire with off-center 60° V-bend placed about 2mm distal to U-loop. Off-center V-bend creates greater moment on molar, increasing molar anchorage and intrusion of anterior teeth.

80. Trial activation performed on each loop. Archwire after trial activation. The archwire is inserted into the auxiliary tubes of the first molars and engaged in the six anterior brackets.It is activated about 3mm , so that the mesial and distal legs of the loops are barely apart. The second premolars are bypassed to increase the interbracket distance between the two ends of attachment. This allows the clinician to utilize the mechanics of the off-center V-bend.

81. Neutral position of loop determined with mesial and distal legs extended horizontally. In neutral position, loop is 3.5mm rather than 2mm wide. The archwire is inserted into the auxiliary tubes of the first molars and engaged in the six anterior brackets.It is activated about 3mm , so that the mesial and distal legs of the loops are barely apart. The second premolars are bypassed to increase the interbracket distance between the two ends of attachment. This allows the clinician to utilize the mechanics of the off-center V-bend.

82. The K-SIR archwire exerts about 125g of intrusive force on the anterior segment. There will initially cause controlled tipping of the teeth into the extraction sites. As the loops deactivate and the force decreases, the moment-to-force ratio will increase to cause first bodily and then root movement of the teeth. The archwire should therefore not be reactivated at short intervals, but only every six to eight weeks until all space has been closed. ACTIVATION IN THE MOUTH IS 3MM every 6-8 weeks

83. THE CONNECTICUT INTRUSION ARCH The CTA is fabricated from a nickel titanium alloy. It incorporates the characteristics of utility arch as well as those of the conventional intrusion arch. Two wire size are available 0.016” x 0.022” and 0.17” x 0.25”.

84. The maxillary and mandibular versions have anterior dimensions of 34mm and 28mm, respectively. In most cases, the wire is not directly ligated into the bracket slots, the anterior wire dimension is adequate to allow for it. The bypass, located distal to the lateral incisors, is available in two different lengths to accommodate for extraction, nonextraction , and mixed dentition cases.

85. Dimensions of preformed CONNECTICUT INTRUSION ARCHES Maxillary CTA Mandibular CTA Anterior dimension 34mm 28mm Posterior dimension: long (non-extraction 22mm 22mm Posterior dimension: short (extraction and mixed dentition) 15mm 15mm

86. MECHANICS The CTA’s basic mechanism for force delivery is a V bend lies just anterior to the molar brackets. When the arch is activated, a simple force system results, consisting of a vertical force in the anterior region and a moment in the posterior region.

87. Incisor intrusion requires 50g of force directed apically along the center of resistance. The moment created at the molar will also vary, according to the amount of force at the incisor multiplied by the distance at the molars. These minor changes can be made to ensure proper force delivery.

88. A pure intrusion arch would have a point contact at the incisors. Insertion of the wire into the incisor brackets, however, will tend to flare the incisors, which may or may not be desirable. The CTA’s point of force application is anterior to the center of resistance, which will flare the incisors. A tight cinch-back—a sharp bend distal to the molar tube, preventing forward slippage of the wire—will prevent incisor flaring during intrusion and produce some retraction of the incisors during molar tipback .

89. Connecticut intrusion arch Advantages The intrusion arch will tip the molars back and simultaneously bring about intrusion Single design can correct multiple problems with no wire changes Minimal chair side time Niti wire delivers light continuous forces under large activation These alloys have high memory and low load deflection rate producing small increments of deactivation over time and thus reducing the number of reactivation

90. ANTERIOR BITE PLANE In growing patient an efficient method of overbite reduction is the use of an anterior bite plane. Anterior plane inhibits the vertical development of the lower incisors and allows differential eruption of the posterior teeth to take place. The lower incisors are not intruded. The anterior bite plane should be just thick enough to disengage the posterior teeth by 2-3 mm.

91. Motivate the patients to wear the appliance 24 hours especially during eating so that the efficiency of the appliance is enhanced. Within about two months the posterior teeth will be in occlusion and the overbite will be reduced Maintenance of overbite reduction will require a lower fixed appliance before the bite plane is removed; the lower arch should be fully bonded and an archwire should be fitted with sufficient dimension to maintain control of the vertical positions of the incisors.

92. REVERSE CURVE NITI

93. When a reverse curve NiTi wire is introduced with the concept that two equal and opposite moments will be produced as it is two couple system. If the moments are not equal, as the system to come into equilibrium vertical forces are created. Extrusion in the posteriors and intrusion in the anterior will take place

94. Extra oral forces in intrusion High pull head gear

95. High pull head gear SHORT OUTER BOW Angulated high to create head gear force line of action anterior to the center of resistance Intrusive component Distal component Large moment that Tends to flatten the Occlusal plane Anticlockwise Moment

96. High pull head gear OUTER BOW Angulated such that head gear force line of action passes through the center of resistance Intrusive component Distal component No moment that Tends to alter the Occlusal plane Equal to the inner bow

97. High pull head gear LONG OUTER BOW Angulated to create head gear force line of action posterior to the center of résistance Intrusive component Distal component Large moment that Tends to steepen the Occlusal plane Clockwise Moment

98. Vertical pull head gear The main purpose of this headgear is to produce an intrusive direction of force to maxillary teeth with posteriorly directed forces

99. Maxillary intrusion splint Full coverage heat cured palatal plate and both anterior and posterior capping carried into the labial surface of the teeth Kloehn bow at 60 to the occlusal plane and high pull head gear Force of about 600 grams 14 hours wear per day Reduces incisor proclination and overjet together with the distal movement of the first molar and intrusion of the molar

100. PRECAUTIONS BEFORE MOLAR INTRUSION Vertical change in the molar position may affect the alveolar bone height. Thus the existing infra bony pockets can be aggravated by molar intrusion hence elevation of the alveolar bone contour around the target tooth can be levelled along with the levelling of the crown It is therefore important to check the alveolar bone level before intrusion

101. SIDE EFFECTS AFTER INTRUSION The main problem encountered during molar intrusion is buccal crown tipping. Application of a vertical force to the elastic hook on a molar tube at a distance from the center of resistance generates a moment that can produce such tipping. Additional anchorage from extra implants or extensions to other teeth may be needed to avoid these side effects

102. Passive or active applianes can be used to control the moment of the intrusive force. FIRST OPTION: Use of a large, stainless steel transpalatal arch. DISADVANTAGE: Moment of the intrusive force may be difficult to counteract despite the rigidity of the TPA. SECOND OPTION: Place an additional TAD on the opposite side of the tooth. * The intrusive force applied to the new TAD should be of equal magnitude to achieve a pure translator movement of the molar.

103. THIRD OPTION: 0.036 X 0.036 Beta titanium Transpalatal arch. * This TPA applies a buccal crown torque in the stationary molar and ties the other end of the arch occlusally or gingivaly to the lingual attachment of the tooth to be moved. * An intrusive lingual force is generated that counteracts the moment of the intrusive force in the buccal area.

104. INTRUSION OF SINGLE MOLAR An extruded molar requires pure molar intrusion along its long axis of the tooth without the extrusion of the adjacent tooth. It is important to provide a line of force passing through the centre of resistance both on the lateral view and on the frontal view to prevent possible buccolingual or mesiodistal tipping during intrusion. Cres of the upper first molar is expected to be at the center of the occlusal table close to the palatal root. RECOMMENDED INSERTION POINT: Mesial interdental area on the buccal side and the distal interdental area on the palatal surface or vice versa. In this way, the combined bilateral force from the buccal and palatal sides will produce a line of force passing through the Cres of the molar inducing pure intrusion without tipping.

105. Additional miniscrews can be placed on either side of the alveolar slope to enhance the adjustablility of the force direction Three or four miniscrew implants are useful to prevent or correct the tipping of molars especially if the molars are severly intruded.

106. INTRUSION OF BUCCAL SEGMENT Patients with anterior open bite caused by an excess of dentoalveolar posterior segments have been successfully treated with TAD’s. The anterior open bites is often found with occlusal planes diverging anteriorly from the first premolars. Intrusion of the buccal segment not only corrects the occlusal problem, but Reduces the lower anterior facial height Reduces the facial convexity as the mandible autorotates anteriorly and superiorly in a counterclockwise direction.

107. The intrusion of the buccal segment or occlusal plane can be either a level or canted intrusion. If the occlusal planes diverge from the molar anteriorly a canted intrusion is indicated and accomplished by differentialy intruding a larger amount posteriorly. In canted intrusion a force passing distal to the center of resistance is needed to intrude differentially more on the molar than on the premolar. Cres of the buccal segment(first molar to first premolar): BETWEEN THE FIRST MOLAR AND SECOND PREMOLAR.

108. When canted intrusion of the buccal segment is desired it is easier to achieve with a plate system than with miniscrews . With the plate system the buccal segment can be moved in any direction without concerns of root damage to the teeth. Moreover the line of action of force can easily be altered by adding a power arm to a miniplate system.

109. If the occlusal plane diverge anteriorly from the canine , a level intrusion may be indicated. In level intrusion a force passing through the center of resistance of the buccal segment is necessary to produce pure translation.

110. Miniscrews are a viable option if a level intrusion of the occlusal plane is to be corrected. Because the intereradicular space is limited however any force not passing through the estimated center of resistance will cause a moment that might tip the roots into the miniscrew . It can be prevented by: 1) Initially intruding the molar separately and then the premolar intruded directly or indirectly after rigidly connecting the molar to the miniscrew . 2)Another alternative to add another miniscrew between the roots of the premolar.

111. TECHNICAL ASPECTS In intrusion of the buccal segment for correction of the open bite, the upper arch is et up by placing a rigid 0.017x0.025 stainless steel wire segment bilaterally from the second molar to first premolar. The anterior segment includes the upper incisor with the same wire dimensions. The canine should not be connected to either segments initially but rather connected to the archwires after the buccal segment has intruded. Connecting the canine to the buccal segment may cause extrusion of the canine if the intrusive force is applied to the first or second molar.

112. Conclusion Though this tooth movement has been the topic of discussion regarding the possibility a thorough study of the clinical situation, diagnosis and treatment planning can definitely help in achieving intrusion of the anterior or posterior segment. Nevertheless it is important to understand the biomechanical and histological basis of the tooth movement.

113. References Steven J. Lindauer, “Basics of mechanics” semin orthod , 7, 2001: 1-15 Charles J. Burstone “ Biomechanics of deep overbite correction” semin orthod 2001: 7: 26-33 Bhavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biomechanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136-43. Jayade “ Refined beggs ” Richard J. Smith, Charles J. Burstone , “ Mechanics of tooth movement” vol 85, 294-307 Mcnamara A J and Brudon WL, Orthodontic and dentofacial orthopedics. Needham press, 2001.