Magnets in orthodontics


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Magnets in orthodontics

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. INTRODUCTION  Magnetic fields in the environment can either be natural or artificial. We are exposed to either of these fields at homes, in automobiles, by wearing wrist watches and walking under high power lines. These magnetic fields were tested and proven that they had no adverse effects on humans. The tests and reports have given entry to magnets in the field of Medicine and Dentistry several decades ago.
  3. 3.  The first use of magnets in Dentistry was by Behran and Egan in 1953. Who used it as implants for denture retention. The use of magnets for orthodontic tooth movement was first described by Blechman and Smiley who bonded earth magnets made of Aluminum- Nickel - Cobalt to the teeth of adolescent cats to produce tooth movement. Other rare earth magnets, Samarium. - Cobalt, introduced by Becker in 1970 .
  4. 4. Neodymium - Iron - Boron (Nd2Fe14B) have been of special interest as these alloys have properties superior to previously used magnetic alloys like Al – Ni-Co, Ferrite and Platinum - Cobalt magnets, which had their limitations, particularly in relation to their size, high cost and risk of demineralization. Rare earth magnets which have exceptionally high maximum energy product values and high resistance to demagnetization permit their use in devices where small size and superior performance are desired, as in the field of orthodontics.
  5. 5. PHYSICS OF MAGNETS  In biomagnetic experiments, three parameters need to be considered: 1. Gradient: The gradient usually characterizes the inhomogeneity of the field. The physical difference between an inhomogeneous field and a homogeneous field is that, an inhomogeneous field exerts an accelerating force upon particles which are more para-or more dia-magnetic than their surroundings, and this accelerating force apparently accounts for all observed biomagnetic
  6. 6.  2. Field intensity: (H). To compute the field B produced by a permanent magnet in the surrounding environment, the relationship used is: B = µH, where H = field intensity, or magnetomotive force (oersteds), and B = field flux density (gauss) and µ= 1, for air and most other biologic material. Therefore, B = H for any magnetic operation. For the most efficient use of magnetic material (i.e., the smallest size magnet for a given output), a magnet should be designed to operate at the point of maximum
  7. 7.  3. Direction of field vector: The direction of electron spin in the third shell of the atom produces a magnetic moment, which accounts for the magnetic field. A limited volume of these tiny electromagnets form domains of internal field energy, which can be reoriented in direction to establish external field energy. (Once magnetized, a permanent magnet requires no further energy to maintain the field.) .
  8. 8. PROPERTIES OF MAGNETS  Where ever there is an electric current flowing there is always a magnetic field. In principle, the magnetic field can either be static or time varying. A static field is formed in the case of direct current, and time varying field is produced by altering current sources. A time varying magnetic field which has periodic variations in intensity induces Eddy current within the body.
  9. 9.  In dentistry, hard magnetic materials or Ferro, magnetic materials with magnets of static constant field are used. The static kind of magnetic field is usually characterized by lines. In the case of a bar magnet with north pole at one end and south pole at the other, the flux lines start from the north pole and following a smaller or wider curved path, return to the magnet at the south pole.. However, as some orthodontic situations when intrusion of posterior teeth is not only static, but depending on mandibular movements the field will become more like a time varying field.
  10. 10. COULOMB’S LAW  All magnets obey this law which states that the force between two magnetic poles is proportional to their magnitudes and inversely proportional to the square of the distance between them.
  11. 11. CURIE POINT  Rare earth magnets tend to loss their magnetism at room temperature. Pierre Currie observed that magnets tend to lose their properties if subjected to a specific temperature which causes their domain to return to random distribution. This point of temperature is called Currie Point. In Orthodontics, this has been overcome by using magnets which are combined with other elements so that they can be incorporated in appliances and also be heat sterilized.
  12. 12. HIGH FORCE TO VOLUME RATIO  Introduction of new magnetic alloys allowed the use of permanent magnets in dentistry. These rare earth magnets, which belong to Lanthinide series, are 20 times stronger than , , Aluminium- Nickel - cobalt. Thus for the same force magnitude a 20 time smaller magnetic unit can be applied with rare earth magnets because the oral cavity dictates the size of the appliance, the increase in F/V ratio (also known as Miniaturizing Effect) makes the use of magnets in dentistry a beneficial modality.
  13. 13.  In physical forms, the new magnetic alloys are characterized by a high coercive force (high magnetic field strength) which indicates their ability to encounter demagnetization forces, a high reminence of magnetic induction, which indicate the extent of spontaneous magnetization and high energy product thus their ability to attract or repulse
  14. 14. MAXIMAL FORCE AT SHOR DISTANCES  Conventional appliances such as coils, springs, elastics etc, react according to Hookes Law, where, force (f) is proportional to a constant such as the elastic modulus(µ), time and the distance (d). Magnetic forces react according to Coulombs law where the force is proportional to the inverse square of the distance (F X- 1/d2). The rare magnets give maximal force at short distance in comparison to elastics, which attain maximum force on more distance for example on mouth opening.
  15. 15. THREE DIMENSIONAL CENTRIPETAL ORIENTATION, OF ATTRACTIVE MAGNETIC FORCE  When two magnets are displaced in all three planes they attract to a complete overlap centripetal attraction in all three spatial dimensions, as this is called, therefore gives the operator complete tooth control on precise engagement. No interruption of magnetic force lines by intermediate media.  Another unique feature of magnetic forces is that any media interposed between two magnets cannot bar the passage of magnetic force lines. Intra oral magnets are attracted to each other even if soft and hard tissues are interposed in the gap between the two magnets
  16. 16. NO FRICTION IN ALTERNATIVE FORCE CONFIGURATION  Attracting magnets are useful in controlling the three spatial dimensions. This feature is called Centripetal Orientation. when an attractive force configuration is used, friction forces like arch wire in the slot are excluded. But in the use of repulsive forces, Muller Prongs guiding elements are used for centripetal orientation. But these may induce friction in the appliance and may call for increase in force threshold to compensate for the loss of friction.
  17. 17. NO ENERGY LOSS  Elastics are the best examples of force systems that deteriorate over a short time. The viscoelastic properties of elastics are prone to relaxation. In contrast, rare earth magnets can maintain energy if protected against corrosion, thermal and other biologic disturbances.
  18. 18. TYPES OF MAGNETIC MATERIALS In various dental applications the following materials have been used:  Platinum - Cobalt (Pt - Co)  Aluminium - Nickel - Cobalt (Al - Ni - Co)  Ferrite  Chromium - Cobalt - Iron  Samarium - Cobalt (Sin - Co)  Neodymium –Iron-Boron (Nd Fe B)
  19. 19.  The first three above mentioned magnets were expensive and bulky and were used with their limitation till rare earth magnets were developed in 1970.  Finally, Samarium Cobalt rare earth magnets were found to be suitable for orthodontic use due to various reasons.Neodymium- Iron - Boron was introduced which are 70% more powerful than a same size Sm - Co, magnets but are susceptible to corrosion and very brittle.
  20. 20. ADVANTAGES OF MAGNETS  It eliminates patient co-operation as it is totally operator controlled.  It produces less pain and discomfort  Continuous force is exerted  Treatment time is reduced.  Magnetic tooth movement is biologically more acceptable with reduced periodontal disturbance, root resorption and caries.
  21. 21.  No friction  Appliance adjustments are minimal, therefore it takes less chair time  Better force, working range control is achieved by maintaining the distance between magnets.  Better directional force control
  22. 22. DISADVANTAGES  Magnets suffer from tarnish and corrosion  These tarnish and corrosion products are cytotoxic  Concerns have been expressed on the biological effects of static magnetic field.  Bulk of magnets is still a concern in space limiting applications.  It is bitter to taste and not very cost effective.
  23. 23. SAMARIUM - COBALT MAGNETS (SmCo5 & Sm2Co17 )  It is a powdered metallurgically processed inter- metallic alloy of Cobalt and rare earth metal.  Superior magnetic properties when compared to other rare earth magnets except Neodymium - Iron Boron magnets,  Even with a flat shape there is hardly any demagnetization making it ideal and small for orthodontic use.  The force necessary in orthodontics can be obtained from a small size of the magnet measurable in millimeters.
  24. 24.  Magnetic properties are invariable in course of time i.e. have high resistance to demagnetization with time.  High Currie Point, of 680ºC allowing heat sterilization and manipulation with heat up to 200ºC without demagnetization  Corrosion resistance is comparatively high since they are parylene coated to prevent leaking, of toxic substances. They can also be encased in stainless steel jackets.  They should be handled with care as they are brittle but are stronger than Neodymium- Iron - Boron magnets. Hence they are difficult to process but can be filed slightly with dental tools
  25. 25. NEODYIUM-IRON-BORON MAGNETS  These are the latest rare earth magnets they are materials of choice because of the following ADVANTAGES  High energy product value 260 Kj/ m³as compared to 190Kj/m³ of the samarium cobalt magnets  Better bio compatibility  High energy product implies stronger forces of attraction
  26. 26. DISADVANTAGES  Very susceptible to corrosion  Risk of destroyed magnetic properties and forces  To avoid liberation of cytotoxic product into the oral cavity it is necessary to coat these magnets with parylene and then embed them into the acrylic blocks
  27. 27. BIOLOGICAL CONCEPT OF MAGNETIC FORCE AND HISTOLOGIC CHANGES  Treatment with traditional orthodontic appliances in human subjects has shown a decrease from normal in the levels of citric acid and calcium in the blood. It was suggested by these findings that the movement may cause a stress that induces various bio-chemical changes.
  28. 28.  . In studying the methods of reducing stress induced by traditional orthodontic appliances,it was found that there were no subcutaneous changes as inflammation or adverse reaction under the magnets. There was an apparent inhibitory effect of magnets on the epithelial recycling evidenced by the reduced thickness of epithelium under attracting or repelling magnets.
  29. 29.  Resorption of bone accessed under magnets after 3-4 weeks, as evidenced by the increased number of Howship lacunae, containing osteoblasts. There was inhibitory effect on the bone lining osteoblasts, which by feed back system promoted osteoblasts differentiation. Magnets made the erythrocytes thinner and longer enabling them to pass through the compressed capillaries in the periodontal ligament during orthodontic loading. This reduces the chances of necrosis of bones and tooth surfaces..
  30. 30.  It was found that a biologically optimal intrusive force was 450 gms a study by Serny and Sandler found no bio-hazardous effect with rare magnets  Lars Bondemark and Jude Kurol studied changes in human dental pulp and gingival tissue on exposure to magnetic field. They found no difference in clinical gingival condition  Encouraging result like increased proliferation and systematic activity in fibroblasts on the use of static magnetic field has been reported by Mac Donald (1993). Also a doubling in the Alkaline Phosphate in osteoblasts like cells were noted.
  31. 31. MAGNETIC FORCE SYSTEMS IN ORTHODONTICS Magnetic force systems are now popularly used for:  Relocating impacted teeth (Vardimon et. al. 1991)  Expansion of arch (Alexander 1987)  Distalization / Mesialization of teeth  Intrusion of posterior teeth in open bite cases  Class II correction with functional appliances  Skeletal correction with functional appliances
  32. 32.  Closure of diastema  Up righting and derotation of teeth  Retainers  Magnetic Brackets  Puma hemi facial microsomia.  Class II correction with magnetic twin block  Non extraction and extraction cases  Magnetic appliance for treatment of snoring patients with and without sleep apnoea.  Extrusion of fractured teeth
  33. 33.
  34. 34. MAGNETS FOR CANINE RETRACTION  According to a study conducted by John Daskalogiannaskis and Kenneth Roy Mclachlan (1996). They used an assembly of magnets for retraction of canines as these magnets provided higher rate of orthodontic translation by delivering a constant force to the tooth.
  35. 35. APPLIANCE DESIGN  Cases in which the first premolars had been extracted canine were retracted by having a  A Nance /Transpalatal arch for reinforcing anchorage  A vertical loop was made in 0.017x 0.025 inch TMA wire with a helix between the premolar and the molar for receiving a magnet.  Another wire 0.018x0.025 SS arch wire was fabricated as vestibular wire which was inserted in the auxiliary tube( this assembly is for 0.18slot appliance)this vestibular wire receives two 2x3x5 mm in size Neodymium-Iron –Boron magnet and the magnet on the helix with the loop comes in between these two magnet such that the mesial magnet and the middle magnet are in repelling mode where as the distal magnet and the middle magnet are in attractive mode
  36. 36.  Thus this appliance with magnets provided a constant force for the retraction of the canines and this method is two times faster than the conventional methods of retraction as they use interruptive force which degrades after sometime
  37. 37.  If there is a need to close premolar spaces simultaneously, another three magnet arrangements may be used. The upper magnetic force system is arranged as previously described. The magnets are arranged so as to permit the upper magnets to fall between the lower two magnets, with a 2 mm wire gap between all the attractive poles. As usual the base arch wires are used to guide tooth movement and reinforce anchorage.  Also intramaxillary magnetic forces can be applied in order to close spaces
  38. 38.
  39. 39.  This magnetically active functional appliance was developed by Darendilier (1993).  It can be used for the correction of mandibular deviations (MAD I).  Class II malocclusions (MAD II).  Class III corrections (MADIII).  For skeletal open bite cases (MAD IV).
  40. 40.  He had used Samarium Cobalt magnets in attractive and repelling mode to achieve orthodontic and orthopedic correction.  In MADII, attracting magnets are used on a two piece upper and lower activator. This allows freedom for mandibular movement.  In class II malocclusions with open bite it is combined with posterior repelling magnets on the maxillary plate for expansion of' the arch which is called magnetic expansion device (MED).  MAD IV is used for skeletal open bite cases with posterior repelling magnets and also anterior attracting magnets.  He had also used Neodymium - Iron - Boron magnets in MAD IV
  42. 42.  The MAD IV-a is used in cases where the anterior segment of the maxilla is vertically correct or overdeveloped (gummy smile)., the posterior and anterior magnets are placed in full contact (Fig A).  The MAD IV-b is used when an additional extrusive effect is needed in the maxillary anterior region. The anterior magnets are positioned with a vertical opening of 2-3mm, while the posterior magnets are placed in full contact. (Fig B).  The MAD IV-c is used when only anterior extrusion is needed. The posterior magnets are omitted, and the anterior magnets are placed with an opening of 1- 2mm, (Fig C).
  43. 43. A:MAD IVa B:MADIVb,C:MADIVc
  44. 44. A. Combined MED and MAD III appliance. B. Bonded upper plate, with two mid palatal samarium cobalt magnets forming MED. C. Removable lower plate with magnets.
  45. 45.
  46. 46.  It was introduced by Dellinger in (1986) as a non-surgical alternative treatment for skeletal open bite. It consists of upper and lower bite blocks with Samarium Cobalt magnets in Stainless Steel cases embedded in them. The “ energised bite blocks" extended only in the posterior segment with a lingual heavy wire connecting bite blocks of each arch. Lateral flanges were incorporated in the lower split to resist shearing forces and development of bite results in autorotation of the mandible, closure of anterior open bite and reduction of lower anterior facial height were reported.
  48. 48.
  49. 49.  A fixed magnetic appliance was introduced by Varun Kalra and Charles Burstone (1989).  The appliance consists of an upper and lower acrylic splints with Samarium Cobalt magnets in stain less steel casting embedded in them in the repelling mode.  The acrylic blocks are bonded and extended along, the posterior segment only with a wire continuing from these splints to the incisor surfaces which are also bonded lingually to these teeth.  Thus the repelling force is transmitted to the entire arch. .
  50. 50. Hypothesis for this appliance (1) If all erupted teeth in the upper and lower arches could be intruded with an appliance, the mandible would auto-rotate upward and forward into the interocclusal space created. (2) If this appliance could displace the condyle downward and forward, away from the posterior part of the glenoid fossa, stimulation of condylar growth might occur. Both these effects, an increase in length of the mandible and an upward and forward autorotation of the mandible, would be beneficial in treating Class II malocclusions associated with increased lower facial height and a retrusive mandible.
  51. 51. APPLIANCE FABRICATION  The working bite was taken with the mandible in centric relation and opened 7 to 8 mm in the permanent first molar region.  The appliance consisted of upper and lower acrylic splints that were bonded on the occlusal halves of the permanent first molars, deciduous molars or premolars, and canines. .
  52. 52.  Samarium cobalt magnets measuring 20 x 8 x 2 mm were encased in a stainless steel case 0.007-inch thick and embedded into the upper and lower acrylic splints in a repelling mode.  In addition a 0.028-inch wire was embedded in the acrylic. This wire rested on the lingual surfaces of the four permanent incisors and was individually bonded to them; thereby intrusive forces were transmitted to the entire arch
  53. 53.
  54. 54.  Clark used Samarium Cobalt and neodymium-Iron- Boron in his well acclaimed and accepted twin block. These magnets were embedded in the inclined surfaces of the twin blocks. In attractive mode they ensured the twin blocks are always in contact even at night when usually the masticatory slackness causes the twin blocks to go out of contact. When the magnets are used in the repelling mode it reduces the need for reactivation,by including an additional forward posture of the mandible. These were used in different ways for treating Class II and Class III malocclusions and also for correction of facial asymmetry.
  55. 55.
  56. 56.  They were introduced by Kawata et al., in 1987. They consisted of Samarium - Cobalt magnet with an edge wise brackets on one surface to receive arch wires and a mesh on the inferior surface to facilitate direct bonding to teeth. The magnets were coated with Nickel and Chromium to prevent corrosion. They were designed to deliver 250 gms of force and to form an ideal arch in both maxilla and mandible on completion of treatment  Though shorter treatment time and good bio- compatibility were seen, dimensions of the brackets to obtain necessary force levels and complexity of laboratory preparation were seen as main disadvantage.
  57. 57.  Maxillary magnetic brackets (frontal view).  . Rear view of maxillary magnetic brackets.
  58. 58.  Mandibular magnetic (frontal view).  Rear view of mandibular magnetic brackets
  59. 59.  Clinical application of magnetic brackets in crowded dental arch.  Moving mandibular teeth by use of magnetic force.
  60. 60.
  61. 61.  A new appliance introduced by Chafe (1995) for stimulating an autogenous costochondral graft in hemi facial microsomia consists of Samarium Cobalt magnets embedded in upper and lower acrylic bite blocks in the repelling mode. The long axis of the magnets were perpendicular to the blocks interface encouraging results were reported.
  62. 62.
  63. 63.  This appliance was reported by Mars Bernhold and Bondemark in 1998. During sleep when the masticatory muscles are physiologically relaxed, there is an obvious risk that the mandibular complex moves backward and closes the air flow in the upper air way space.  Two intra oral occlusal splints, maxillary and mandibular each with four parylene coated Neodymuim - Iron - Boron magnets are used. Full tooth coverage is required for the splints to prevent unwanted tooth movements.
  64. 64. It was also reported that this appliance increased the hypo pharyngeal airway space ,tongue base was lowered and the contact between the tongue and the soft palate reduced significantly .
  65. 65.
  66. 66. Maxillary permanent canines are the most commonly impacted tooth in 0.9 - 2.2% of the patients. Orthodontic movement of the impacted canine after surgical exposure is most commonly carried out.  DISADVANTAGES OF SURGICAL EXPOSURE 1. Infection 2. Gingival Inflammation 3. Bony recession 4. Apical migration of epithelial attachment
  67. 67. 5. Exposure of cemento enamel junction 6 .Communication of the impacted tooth with the oral cavity can cause periodontal tissue damage 7. Painful 8 .Root resorption 9. Ankylosis
  68. 68. MAGNETS USED  Samarium Cobalt magnets  Neodymium - Iron - Boron magnets
  69. 69.  Sandler in 1992 described a user and patient friendly method of treating unerupted teeth. Neodymium - iron - Boron magnet is attached to the unerupted tooth and a second larger magnet is incorporated in a removable appliance.
  70. 70. TECHNIQUE  Preparation of' magnet involves tying a thin stainless Steel ligature around it and then coating this unit with unfilled resin. The ligature acts as a handle for the magnet at operation and also ensures that the magnet is bonded to the tooth in correct orientation
  71. 71.  Magnet prepared for bonding
  72. 72.  Composite resin provided an impermeable barrier, preventing any ionic diffusion that would lead – to corrosion as well as facilitating the attachment of the magnet to the unerupted teeth at operation.  The second larger magnet 5 x 5 x 2mm is incorporated into a removable appliance. It is completely surrounded by the acrylic of the appliance, which again will prevent ionic diffusion.  The only adjustment that is sometimes required is the repositioning of the larger magnet 2 - 3mm occlusally, once the two magnets are in apposition.
  73. 73. Fig. 4. Appliance in place. Fig. 5. Upper left canine just erupting through the mucosa. Fig. 6. Larger magnet repositioned to allow further movement. Fig. 7. Sufficient eruption to allow attachment to be placed.
  74. 74. Sufficient eruption for bracket attachment
  75. 75. ADVANTAGES OF THIS TECHNIQUE 1.No unpleasant or uncomfortable manipulation of wires, springs or elastics. 2.A low continuous force that increase over time. 3.Since a palatably directed force is possible, the health of the labial plate and zone of attached gingiva are optimized.
  76. 76. TECHNIQUE PROPOSEDBY Vardimon et al  Vardimon et al., in 1991 introduced a new magnetic attracting system, with a magnetic bracket bonded to an impacted tooth and an intra oral magnet linked to a handy type retainer. Horizontal and vertical magnetic brackets were designed with the magnetic axis magnetized perpendicular and parallel to the base and bracket respectively.
  77. 77. Modified twin bracket to receive a nonmagnetized prism-shaped magnet.
  78. 78.  In a deep impaction case, the surgical mucoperiosteal flap was sutured over the bonded magnetic bracket. Attraction was initiated 1- 2 weeks after healing. Thus the tooth emergence into the oral cavity replicated normal eruption condition. The attracting force level was in the range of 0.2 - 0.5N. Adjustment was accomplished by temporarily interposing a magnetic space between the two magnetic units. No side effects were
  79. 79. Non eruption of maxillary canines.
  80. 80. A, Before surgery view. B, Raising a mucoperiosteal flap. C, Bonding the magnetic brackets and suturing back the flap partially over the brackets.
  81. 81. A, Vacuum-molded maxillary appliance with intraoral magnets attached by self-curing acrylic, no clasp attachments are required because of the attractive force system.  B, At progressed stage, acrylic has to be removed from the removable appliance to eliminate interferences with the erupted canines.
  82. 82. D,Canines emerged into the mouth with no mucosal recession.
  83. 83. ADVANTAGES  Less invasive procedure.  Effective attractive forces at short distance.  Controlled spacial guidance
  84. 84. TECH NIQUE PROPOSED BY Darendelider  Ali Darendelider in 1994 showed a different approach to the use of fixed and removable magnets in treatment of impacted canine. He used it on a 12-year old girl with palatally impacted upper right canine; the root of the impacted tooth was completely developed. Space gaining was achieved using conventional appliances. A partial cast of the erupted upper left canine was made for controlling a magnet to fit the palatal surface of the impacted canine.
  85. 85.  The pre-shaped 3mm. x 4mm. x 5mm Samarium Cobalt magnet was then coated with a thermoplastic material and a mesh was bonded to the tooth side.  The deciduous canine was extracted prior to surgery,
  86. 86.  A. Magnet contoured to cast of erupted left canine. B. Mesh bonded to tooth side of magnet.
  87. 87. A. Surgical exposure of impacted canine. B. Magnet bonded to exposed crown. C. Passive removable plate in place after closure of flap over impacted tooth and magnet.
  88. 88. Magnet mounted to acrylic plate, 6.5mm from bonded magnet.
  89. 89. Impacted canine visible under palatal mucosa; removable plate discontinued.
  90. 90. Ballista spring" sectional arch wire with attached magnet tied to continuous arch wire.
  91. 91. Eruption of impacted canine crown
  92. 92. Button bonded to impacted canine for conventional traction After fixed appliance treatment.
  93. 93.
  94. 94.  Hyeon –shik Hwang and Ki-Heon Lee (2001) reported a case study in which the over erupted molars were intruded with corticotomy and magnets  A molar can over erupt due to a lost antagonist and this antagonist cannot be replaced because of the over eruption of the molar.  The use of conventional fixed appliance can cause undesirable extrusion of adjacent teeth and also it takes longer time.  Molars can be intruded quickly using corticotomy and magnets without side effects and also in adult patients in whom the growth is already over.
  95. 95.  Corticotomy is performed under LA muco gingival flaps are raised on both buccal and lingual side and the cortical bone is exposed beyond the apical region. After the corticotomy the flaps are returned to their original position.  Appliance is fabricated on working models with orthodontic bands on the over erupted molar; wires are soldered onto the buccal and lingual side of the band to make room for the magnet. A removable appliance is fabricated with Adams and cantilever springs for retention
  96. 96.  .The cantilever spring are placed facing the molar band  A disk shaped Neodymium-Iron-Boron magnet is used on the band and the spring in the repelling mode  This assembly of the magnets brings about faster intrusion and eliminates the need for any kind of grinding of the opposing teeth for the replacement of the missing teeth.
  97. 97.
  98. 98.  These functional appliances were developed by Vardimon (1989)  For class II and class III malocclusion. They are called FOMA II and FOMA III respectively.  FOMA II consists of an upper magnet located anterior to a lower magnet in a non-displaced fair relationship. Both magnets are, incorporated in upper and lower plates.  The FOMA Ill consists of an upper and lower plates with magnets incorporated into each plate. The upper magnet is retracted periodically to stimulate maxillary development/advancement and mandibular retardation. All magnets are kept in an attractive mode.
  99. 99. The upper plate of a FOMA III , Upper plate of a FOMA III in an experimental animal
  100. 100.
  101. 101.  The FMS incorporates some principles of the Schwartz appliance and was introduced by Vardimon and his associates. It consists of upper and lower removable plate that each contain an magnetic unit; both units are arranged in an attractive pole orientation.  . The upper magnetic unit comprises a stainless steel magnetic housing with a single prong attached to it. The magnetic housing incorporates two cylindrical rare earth magnets (SmCo5). If expansion of the maxillary, arch is required, an expansion screw is linked to the magnetic housing and prong.
  102. 102.  The lower magnetic unit consists of a magnetic housing that encompasses two cylindrical rare earth magnets (SmCo) corresponding to those in the upper magnetic housing .The lower magnetic housing has a posterior inclined wall that forms an oblique plane. Guidance of the mandible into the CPCP is provided by the sliding of the mandibular oblique plane along the maxillary, prong on mouth closure. In accordance with therapeutic requirements, an expansion screw can be linked to the lower unit. The anchoring units of the plates include Adams, Triangular (Arrowhead) and Elastic Clasps
  103. 103. Almost all class II malocclusions can be treated clinically by one of the following four types of FMS:
  104. 104. Type1 An upper magnetic unit with an expansion screw combined with a lower magnetic unit with no expansion screw.
  105. 105. Type II an upper unit with an expansion screw combined with a lower magnetic unit with an expansion screw.
  106. 106. Type III An upper magnetic unit with expansion and protraction screws combined with a lower magnetic unit with no expansion screw.
  107. 107. Type IV An upper magnetic unit with expansion and protraction screws with a lower magnetic unit with expansion screw.
  108. 108. MODE OF ACTION OF FMS Two definitions are important in understanding the mode of action of the FMS. SPATIAL MAGNETIC FORCE SYSTEM  This refers to the dissociations of the attractive magnetic, force into its three vector components:  The vertical force(fx)acting along the craniofacial axis(x)causing jaw closure  The lateral shearing force (fy) acting along the transverse axis (y), producing medial mandibular shift from any lateral excursion.  The sagittal shearing force (fz) acting along the posteroanterior axis, generating mandibular advancement in protrusive excursions.
  109. 109. CENTRIPETAL SPATIAL ORIENTATION  This describes the attraction of a mobile mandibular magnet by a stationary, maxillary magnet toward a full overlap of their magnetic interfaces at the CPCP[constructive protrusive closure position] from any point within a spatial domain of mandibular movements confirmed by attractive force system.  A maximal vertical attractive force (fx) of almost 3 Newton acts between the upper and lower magnetic units at occlusion which enables normal physiologic oral activity during active periods and constraints of the mandible in the CPCP during rest
  110. 110.  The FMS is designed for all three force components of the attractive magnetic force system and the mechanical component (prong, oblique plane) act synergistically to guide and constrain the jaw in the CPCP. Regardless of the anteroposterior displacement or other movement of the mandible which it undertakes, it always moves to the CPCP in the shortest three dimensional way. This centripetal spatial orientation feature extends the duration the mandible is located in the most functionally efficacious corrective position and thus increases the function performance.
  111. 111.
  112. 112.  A class II bimaxillary protrusion case treated with magnets was reported by Darendelier and Jobor (1992).  They used full bonded upper and lower magnets of SmCo, bonded to individual teeth at the appropriate level forming the autonomous fixed appliance. The individual Magnets delivering, a force of 20 - 30 gins to close all the diastemas present. The magnets were coated with composite resin to prevent corrosion. It was also coated to prevent toxic damage. After the diastemas were, closed the patient was treated with magnetic activator device (MAD II) for full correction of skeletal and dental class II relationship.
  113. 113. Lower magnets temporarily affixed to cast for indirect bonding. MAGNETS IN ARCHES
  114. 114.
  115. 115.  This was reported by Muller (1984), who bonded rectangular magnets (SmCo) delivering 11.7 gms of force of attraction on each maxillary central incisor to close a midline diastema. She also mentioned the possibility of bonding the magnets palatally for better aesthetics. Absence of friction and no reactivation were needed, which were advantageous.
  116. 116.
  117. 117.  Magnetic expansion studies conducted by Vardimon et a, on female macala facicularis monkeys. He then compared with conventional jackscrew expansion and concluded that repelling magnetic (SMC05) expansion from tooth bonded or palatally pinned appliance delivered ideal forces compared to the jackscrew appliance which caused atrogenic features.  Darendileder et al., (1993) used mid palatal repelling magnets (SMC05) expansion device (MED). He showed both dental and skeletal expansion in his case report.
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  119. 119.  Springate (1991) used micro magnets made of Neodymium - Iron – Boron as a fixed retainer palatally in a patient with persistent midline spacing. No hindrance in maintaining oral hygiene was an added advantage to this successful treatment.
  120. 120.
  121. 121.  One of the effective methods to resolve a Class II malocclusion is the distal movement of upper molars to establish a class I relationship. The premolars and canines are subsequently moved back to class I positions and finally the incisors are retracted.  Repelling magnets can provide continuous force need to establish a class I molar relationship in the early mixed dentition.
  122. 122.  Gianelly et al., 1998 used intra arch repelling magnets to distalize the maxillary molars. The repelling surfaces of the magnets were brought into contact by passing 014” SS wire through the loop on the auxiliary wire, then tying back a washer anterior to the magnets. Force extended by the magnets began at 200-225gm then as the space opened, with 1mm of space between magnets, the applied force was only 75 gms.  After 7 weeks, the molars were in class I relation
  123. 123. Magnet therapy for distalization  Right and left lateral views with repelling magnets in position.
  124. 124. Upper and lower occlusal views 7 weeks after magnet distalization. Lingual arch wire in mandible will be extended distally to retain distalized lower right molar
  125. 125. Takami itoli et al in 1991 reported a clinical study designed to measure the molar distalization achieved with repelling magnets in molar distalization system. concluded that  There was some amount of labial movement of the anterior teeth approx 30-50% of the distal movement of the molars  Initial discomfort to the buccal mucosa till the patient got accustomed to the appliance  There was difficulty in brushing and there was food lodgement between the teeth and magnets  The molar distalization seen was almost entirely a bodily movement, with slight distal tipping and rotation.
  126. 126. THE EFFECT OF PULSATING ELECTROMAGNETIC FIELDS ON CONDYLAR GROWTH(PEMF)  A study conducted by John A.Gerling and Peter M Sinclair on guinea pig for the growth of the mandibular condyles under the effect of 100 hertz for 8 hrs in day indicated that there was increase in vascularity , secretion of cartilaginous inter cellular matrix and woven bone formation but no significant increase in the length of the mandible  But they suggested that these electromagnetic fields with functional appliance can be used for mandibular condylar modulation.
  127. 127. EXTRUSION OF FRACTURED TEETH  A sub gingival crown root fracture presents the clinician with a difficult restorative problem including reaching the fracture line and is complicated by the need to maintain the periodontal tissues in good health. The treatment available till now was extraction and replacement with a bridge.  A new method has been reported by Bondemark and Kurol (1997) by using magnetic force to extrude the fractured root.
  128. 128.  The magnetic system consisted of either one or two cylindrical parylene or stainless steel coated, Neodymium. - Iron - Boron magnets placed in the coronal part of the remaining tooth with a thin layer of composite axially over the root.  Another larger parylene coated Neodymium - Iron - Boron magnet was embedded in the acrylic of a removable appliance.  They were arranged in attractive mode with a minimum gap of 2mm.  After the desired extrusion, the tooth can be restored
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  130. 130.  Bondemark and Kurol conducted extensive studies on recycling of  Rare earth magnets used in orthodontics. They concluded that recycling does not affect the biocompatibility and force stability of the magnets even though the recycling process involved autoclaving.  They also recommended that new partially encased Samarium Cobalt magnets be stored in water for 24 hours before use to reduce the release of cytotoxic components.  Cernyl (1979, 1980) showed high cytotoxicity for Neodymium - Iron - Boron magnets. However Darendililer, felt that magnets should not be recycled for ethical reasons and also because they demagnetize during the recycling process.
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  132. 132.  Magnets can be used to give predictable forces in either attraction or repelling mode. They can be made small enough to suit most dental applications.  The orthodontic stimuli provided by the magnetic appliance has reduced the systemic stress reaction seen with conventional orthodontic mechanotherapy .  Treatment time is shorter ,no periodontal problem and foremost no discomfort
  133. 133.  Conceivable risks of harmful biological effects are negligible with magnets.  Their high cost can be overcome by reusing it after sterilization and recycling  The static magnetic fields control mobility by accelerating the osteogenic rate and control pain by blocking sensory neuron action potential. These properties of static magnetic field promise a pain free and mobility free orthodontics.
  134. 134. For more details please visit