Magnets in ortho dontics

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Magnets in Orthodontics:

Magnets in Orthodontics

Introduction:

Introduction Magnetic fields can be either Natural or artificial. These fields were tested and proven to have no adverse effects on humans. These test results have made possible the use of magnets in the field of dentistry.

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The first use of magnets in Dentistry was by Behran and Egan in the year 1953. They used it as implants for denture retention. First use of magnets for tooth movement was described by Blechman and Smiley by experimenting on cats. Becker in 1970 introduced rare earth magnets having properties superior to previously used magnetic alloys.

Properties of magnets:

Properties of magnets Magnetic field can be either Static or Time varying. Static field produced by Direct current Time varying field by alternating current Static field characterized by flux lines which start at the north pole and following a smaller or wider curved path,return to the magnet at the south pole.

Properties……..:

Properties…….. COULOMBS LAW : States that the force between two magnetic poles is proportional to their magnitudes and inversely proportional to the square of the distance between them. CURIE POINT : Pierre Currie observed magnets to loose their properties if subjected to a specific temperature which is called Curie point.

Properties……...:

Properties……... High force to volume ratio: Introduction of rare earth magnets has led to the use of smaller magnets delevering a higher force than the bulkier ones. An increase in the force to volume ratio{miniaturizing effect}makes the use of magnets in Dentistry a beneficial modality.

Properties……..:

Properties…….. Maximal force at short distances: Rare earth magnets give maximal force at short distances in comparison to elastics,which attain maximum force at longer distances. Three Dimensional Centripetal orientation of attractive magnetic forces gives the operator a complete tooth control on precise engagement.

Properties……….:

Properties………. No interruption of magnetic force lines by intermediate media. When using attractive forces frictional forces are excluded. Rare earth magnets can maintain energy if protected against corrosion, thermal and other biologic pertuberances unlike other force delivery systems that deteriorate over a short time.

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A study by J.A Von Fraunhofer in 1992 found that magnets with a seperation of less than 2mm obeyed coulombs law 0 -2mm seperation effective forces were reduced Seperation beyond this created values which are lesser than those required for physiological tooth movement

Properties …...:

Properties …...

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Types of Magnetic materials : In various dental applications the following materials have been used. 1. Platinum-cobalt 2. Aluminium-Nickel-Cobalt 3. Ferrite 4. Chromium-Cobalt-Iron 5. Samarium-Cobalt 6. Neodymium-iron-Boron.

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SAMARIUM -COBALT MAGNETS A powdered metallurgically processed inter-metallic alloy of Cobalt and rare earth metals when compared with other rare earth magnets. Required force obtained from a small size of the magnet making it ideal for orthodontic use. Have high resistance to demagnetization with time. High Curie point-680 centigrade They are Parylene coated to prevent leaking of toxic substances.

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Biologic concept of Magnetic force and Histologic changes. It was found that magnetic forces inflicted a minimum of stress that induces various bio-chemical changes in a patient during orthodontic tooth movement. No subcutaneous changes as inflammation or adverse reaction under the magnets. Resorption of bone occurred under magnets after 3-4 weeks. Reduced chances of necrosis of bone as magnets make erythrocytes thinner.

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Lars Bondemark and Jure Kurol studied changes in human pulp and gingival tissue on exposure to magnetic field and found no changes. Mac Donald 1993 reported an increased proliferation and systemic activity in fibroblasts on the use of static magnetic fields. Astudy by Cerny and Sandler found no bioharzardous effect with rare earth magnets.

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A study by Lars Bondemark &Alf Wennberg in 1994 showed Uncoated Samarium Cobalt magnets showed severe toxicity Parylene coated Samarium magnets showed mild toxicity Coated &uncoated Neodymium magnets showed negligible toxicity Short term exposure to magnet fields did not cause any cytotoxic effect on cells

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Magnetic Force systems in Orthodontics 1.Relocating impacted teeth 2.Expansion of arch 3.Distal/mesialization of molars 4.Intrusion of posterior teeth in open bite cases 5.Class 11 correction with functional appliances 6.Skeletal correction with functional appliances 7.Closure of diastema 8.Retainers

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9. Uprighting and Derotation of teeth 10. Magnetic Brackets 11. Class 11 correction with Magnetic Twin block 12.Magnetic appliance for treatment of snoring patients with and without sleep apnoea 13. Extrusion of fractured teeth 14.Extraction and Non-extraction cases 15.Treatment of hemifacial microsomia

Magnetic Appliances:

Magnetic Appliances

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Magnetic Appliance for an extraction case Attractive magnetic forces are used to bring about orthodontic tooth movement Magnetic Appliance for a non-extraction case Derived from magnets in attraction or repulsive mode

Magnetic Activator Devise:

Magnetic Activator Devise Magnetic functional appliance developed by Darendilier in 1993 for correction of mandibular deviations Active vertical correcter introduced by Darendilier in in 1986 as a non surgical alternative treatment for Skeletal open bite

Fixed Magnetic Appliance:

Fixed Magnetic Appliance Introduced by Varun Kalra &Charles Burstone in 1989 Appliance has the magnets in repelling mode embedded in the upper and lower acrylic splints

Magnetic Twin Blocks:

Magnetic Twin Blocks Clark used magnets in his Twin Block Magnets were embeded in the inclined surface of the twin block in attractive mode When used in the repelling mode it reduces the need for reactivation Used in different ways for treating Class 11 and Class111 malocclusion

Magnetic Brackets:

Magnetic Brackets Introduced by Kawata et al in 1987 Samarium Cobalt magnets with an edgewise bracket on one surface to receive the archwire and a mesh on the inferior surface for direct bonding Designed to deliver 250gms force Complex lab procedures&dimensions of the brackets to obtain necessary force levels were seen as maximum disadvantages

Propellent Unilateral Magnetic Appliance:

Propellent Unilateral Magnetic Appliance Introduced by Chafe 1995 for stimulating an autogenous costochondral graft in hemifacial microsomia Consists of Samarium - Cobalt magnets embedded in upper & lower acrylic bite blocks in the repelling mode

Magnetic Appliance For treatment of Snoring Patients:

Magnetic Appliance For treatment of Snoring Patients Introduced in 1998 by Mars Bernhold & Bondemark Two intraoral occlusal splints each with four parylene coated Neodynium magnets are used Full tooth coverage is required to prevent unwanted tooth movements

Deimpaction with Magnets:

Deimpaction with Magnets Used by Vardimone et al in 1991 He used a magnetic bracket bonded to an impacted tooth & intraoral magnet linked to a Hawley type retainer to guide the erupting tooth Darendeliler in 1994 used a small bonded magnet on an impacted Canine Sandler 1991used a similar method

Functional Orthopedic Magnetic Appliance :

Functional Orthopedic Magnetic Appliance Developed by Vardimon in 1989 for Class 11 & class 111 malocclusion FOMA 11 consists of upper magnet located anterior to lower magnet in a non displaced jaw relationship FOMA 111 consists of upper and lower plates with magnets all magnets kept in an attractive mode

Autonomous Fixed Appliance:

Autonomous Fixed Appliance Darendelier &Jobor in 1992 used this to treat a Class 11 Bimaxillary protrusion Samarium Cobalt were bonded to individual teeth at an appropriate level forming the Autonomous Fixed Appliance

Magnets for closing Diastemas:

Magnets for closing Diastemas Muller in 1984 bonded rectangular magnets delivering 117.5 gms of force of attraction on each maxillary central incissor to close a midline diastema

Expansion with magnets:

Expansion with magnets A study on Facicularis monkeys proved that repelling magnets delivered ideal forces for expansion compared to a jack screw appliance Darendililer et al in 1993 used mid palatal repelling magnets and showed both dental and skeletal expansion in his report

Magnets For Molar Distalization:

Magnets For Molar Distalization Molar Distalization was reported by Gianelly et al in 1998,Bondemark et al 1990,Takami et al 1991 and Steger et al 1975 they used repelling magnets between upper premolar and molar Bondemark et al 1994 compared push coils versus magnets for molar distalization

Molar Distalization:

Molar Distalization

Extrusion of fractured teth:

Extrusion of fractured teth Bondemark &Kurol in 1997 used magnets to extrude the fractured root Magnets used were in the attractive mode with a minimum gap of 2mm after the desired extrusion the tooth can be restored

Extrusion of crown-root fractured teeth:

Extrusion of crown-root fractured teeth

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Advantages of magnetic appliances Eliminates patient co-operation Produces less pain and discomfort Continous force exerted Treatment time reduced Reduced periodontal disturbance No friction Less chair side time Better force Better directional control

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Disadvantages Tarnish &corrosion Cytotoxic effects Bulk of the magnets Taste - Bitter Costly

Recycling of Magnets:

Recycling of Magnets Bondemark &Kurol conducted extensive studies on recycling of rare earth magnets concluded that the biocompatability &force stability is not effected Darendililer felt that magnets should not be recycled for ethical reasons

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Summary & Conclusion Magnets can be used to give predictable forces in either attraction or repelling mode & can be made small enough to suit most dental applications. The evidence currently available from biological safety testing would suggest that the risk of harmful biological effects are negligible.The high cost can be overcome by reusing it after sterilization & recycling.

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