Magnets in orthodontics. /certified fixed orthodontic courses by Indian dental academy


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  • Progressed maxillary and mandibular magnetic brackets designed to arrange an ideal arch by themselves.
  • Daskalo
  • Source: AJO-DO on CD-ROM (Copyright © 1998 AJO-DO), Volume 1986 May (428 - 436): A clinical assessment of the Active Vertical Corrector - Dellinger.
    Fig. 1. Example of the Active Vertical Corrector (AVC). Occlusal and tooth contact views of mandibular appliance (A) and maxillary appliance (B).
    Source: AJO-DO on CD-ROM (Copyright © 1998 AJO-DO), Volume 1986 May (428 - 436): A clinical assessment of the Active Vertical Corrector - Dellinger.
    Fig. 1. Example of the Active Vertical Corrector (AVC). Occlusal and tooth contact views of mandibular appliance (A) and maxillary appliance (B).
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  • Magnets in orthodontics. /certified fixed orthodontic courses by Indian dental academy

    2. 2. INDIAN DENTAL ACADEMY Leader in continuing dental education
    3. 3. Magnets and Magnetism Properties of Magnets Applications of Magnets in Orthodontics Biological effects of magnets and safety concerns. Conclusion.
    4. 4. MAGNETS The first known magnets were the lodestones, which were stones that were magnetized naturally. The Greeks and the Chinese were amused by the stones’ ability to attract metal over a short distance, as if by magic. Later they learnt to use lodestones in compasses to determine direction. Today magnets are used extensively.e.g. in VCR’s, audio cassettes, ATM and credit cards, and the electronics industry. The largest magnet existing on Earth is the planet Earth itself.
    5. 5. Why does magnetism occur? Magnetism occurs due to a quantum physical effect called exchange coupling, which results in the alignment of the magnetic dipole moments of the atoms. This persistent alignment of magnetic dipole moments in magnetic materials is responsible for the phenomenon of magnetism.
    6. 6. Properties of magnets All magnets have magnetic fields around them. The field emerges from one pole of the magnet conventionally known as the North Pole and returns to the other or South Pole.
    7. 7. A magnetic field induces changes in the medium surrounding the magnet, such as air. This is called the flux density of the magnet The flux produced by the magnets causes them to attract or repel other magnets, and attract other materials containing iron. The force produced by any two magnets is inversely proportional to the square of the distance between them. f α 1/d2 Thus, the force between two magnets falls dramatically with distance.
    8. 8. The development of high energy magnets in the 1970’s resulted in magnets capable of producing high forces relative to their sizes. This was due to the property of magneto-crystalline anisotropy, which allows single crystals to be preferentially aligned in one direction, thus increasing the magnetism. Recently, the development of rare earth magnets such as Samarium-Cobalt and Neodymium-Iron-boron have taken place. These have a higher ability to be magnetized, and also have high coercivity, which is the ability of the magnet to resist demagnetization.
    9. 9. Disadvantages of high energy magnets : Brittle Low corrosion resistance Irreversible magnetic loss on heating, even to modest temperatures. In case of magnets embedded in acrylic appliances to move teeth, the loss of flux due to the exothermic setting reaction of acrylic (80-90º C) is to be taken into account.
    10. 10. Applications of Magnets in Orthodontics. Magnets were initially used in dentistry for fixation of dentures. (Freedman,1953; Thompson, 1964; Winkler,1967) They were also implanted surgically into molar regions of edentulous mandibles for retention of complete dentures.(Behrman 1960,1964.) The development of rare earth magnets with improved properties resulted in growing interest in their use as an alternative to traditional force systems in orthodontics. In 1978, Blechman and Smiley were the first to report the use of magnetic force to move teeth (in a cat). Since then, a number of applications have been developed for magnets in orthodontics.
    11. 11. 1. Relocation of Unerupted teeth. The cause of impaction, in particular of the palatally impacted maxillary canine, is related to aberration in the eruption process, and not due to arch length deficiency. Thus a shorter root of the upper lateral incisor frequently can cause palatal impaction of the upper canine because of a lack of guidance. This calls for the application of a therapeutic procedure by which the normal eruption mechanism can be simulated.
    12. 12. Conventional traction methods have been found to be associated with gingiva inflammation, bone recession, reduced attached gingiva, periodontal pockets, exposed cementoenamel junction, and root resorption of the impacted and adjacent teeth. Magnetic traction can avoid these side effects. The use of two attracting magnets in the treatment of unerupted teeth was described by Sadler, Meghji and Murray ( BJO 1989). One magnet was bonded to the impacted tooth, while a second stationary magnet was incorporated in a removable acrylic appliance. The location of the stationary magnet decided the direction of force. Activation was done by repositioning the magnet on the plate occlusally.
    13. 13. Vardimon et al (AJO-DO 1991,introduced a magnetic attraction system, with a magnetic bracket bonded to an impacted tooth and an intraoral magnet linked to a Hawley type retainer. Vertical and horizontal magnetic brackets were designed, with the magnetic axis magnetized parallel and perpendicular to the base of the bracket, respectively. The vertical type is used for impacted incisors and canines, and the horizontal magnetic bracket is applied for impacted premolars and molars.
    14. 14. A B C D
    15. 15. A three-dimensional analysis of the magnetic forces found the small magnetic bracket combined with a large pole surface area of the intra-oral magnet to exhibit the most efficient convergent guidance. In deep impaction, the Nd2Fe14B magnetic bracket was coldsterilized before surgery, and the surgical flap was then sutured over the bonded magnetic bracket. Attraction was initiated 1 to 2 weeks after healing. Thus tooth emergence into the oral cavity replicated normal eruption conditioning. The system operated at an attractive force level of 0.2 to 0.5 N. Adjustment was accomplished by temporarily interposing a magnetic spacer between the two magnetic units. No side effects were observed in a restricted number of treated cases, and treatment time was reduced.
    16. 16. Advantages Better rapport with the patient. No manipulation of wires, springs or elastics. Since a palatal force is possible, health of the labial cortical plate and zone of attached gingiva are optimized in buccally erupting canines. Can be used in molar and premolar impactions with ease Less adjustments required, less pain to the patient. 3 D control over the erupting tooth. The stationary magnet on the plate can be placed eccentrically with respect to the intraoral bracket, to produce normal eruption and less need for uprighting the tooth later. As the magnet is completely sealed off from the oral cavity, there is no chance of inflammation or infection. Also, normal alveolar bone levels and epithelial attachment are maintained.
    17. 17. Pradeep CS et al (Indian Orthodontic Conference 1999) presented 2 cases in which removable acrylic appliances incorporating magnets were used to erupt impacted canines. In the first case, the patient had bilaterally impacted upper canines. Occlusal view showed them to be horizontally impacted. The left side canine was chosen as the experimental tooth.
    18. 18. Disimpaction was carried out using Samarium cobalt type magnets (4x4x2 mm), one of which was bonded to the impacted tooth after surgical exposure, and the flap replaced. The second magnet was incorporated into an acrylic removable appliance.
    19. 19. After 4 weeks of wearing the appliance, occlusal radiographs showed uprightment of the horizontally impacted canine.
    20. 20. After 6 weeks the there was a noticeable bulge in the palatal mucosa and the canine could be easily palpated under the mucosa. After 2 months of treatment, ulceration of the mucosa over the canine was visible. In the second case, an impacted upper left canine was similarly treated.
    21. 21. Pradeep et al also reported the use of parylene coated Samarium cobalt magnets bonded to lingual surface of central incisors for closing mid line diastemas in 5 cases.
    22. 22.
    23. 23. 2. Space closure with magnets. Mueller(EJO 1984) used rectangular magnets applying 117.5 grams of attracting force for median diasrema closure. In 1987, Kawata et al soldered Sm-Co magnets plated with chromium and nickel to Edgewise brackets for administration of mesio-distal magnetic forces. Progressed maxillary and mandibular magnetic brackets designed to arrange an ideal arch by themselves
    24. 24. In cases involving extraction, canines were retracted conventionally until magnetic brackets on the 2nd premolars exerted enough force on the canines. The authors reported reduced treatment time, resulting in neither pain nor discomfort, nor periodontal problems.
    25. 25. Daskalogiannakis and Mc Lachlan(AJO DO 1996) used rare earth magnets to provide continuous activation to canine retracting loops, and reported that the continuous force levels achieved by the use of magnets resulted in twice as much movement as compared to the controls where force levels decayed with time.
    26. 26. 3. Molar intrusion and correction of anterior open bite Dellinger(AJO 1986) reported on the Active Vertical Corrector, an “energized bite block”appliance, which uses Samarium cobalt magnets oriented in repulsion to produce a posterior intrusive force of 600-700 g per magnetic unit. This appliance was worn in combination with headcap and chin strap for at least 12 hours per day. It was postulated that this appliance was more efficient than usual bite block therapy due to the intermittent electromagnetic field produced by mandibular movements, which would enhance tooth movements.
    27. 27. Example of the Active Vertical Corrector (AVC). Occlusal and tooth contact views of mandibular appliance (A) and maxillary appliance (B). Seated Active Vertical Corrector (AVC).
    28. 28. The AVC intrudes posterior teeth by reciprocal action as noted by the arrows. Intrusion of posterior teeth results in closure of the open bite and autorotation of the mandible
    29. 29. Initial anterior photograph of male patient aged 8 years 11 months, taken before patient began wearing AVC Posttreatment anterior photograph of male patient aged 9 years 6 months, taken after patient wore appliance for 4½ months.
    30. 30. Woods and Nanda (Angle Orthod 1988) studied the intrusion of posterior teeth in growing baboons, with magnetic and acrylic bite blocks. They postulated that since similar responses were produced with both magnetic and non-magnetic bite blocks, it would appear that the depression of buccal teeth seen in this study could be attributed as much to the muscular response to the artificially-increased vertical dimension as to the presence of the repelling magnets. In another study done on non-growing baboons, Woods and Nanda (AJODO 1991) found significant intrusion of posterior teeth with magnets as compared to acrylic bite blocks. However, the effects of the magnets were reduced as compared to growing animals.In the absence of other evidence the authors hypothesised that electromagnetic fields might be involved in increasing the response within bone to potential intrusive forces delivered by the repelling magnets.
    31. 31. Kiliardis et al ( EJO 1990) randomly divided a 20 patients aged 9-16 years, with anterior open bite into two treatment groups: one with the Active Vertical Corrector and the other with acrylic posterior bite blocks of same thickness as magnetic appliance. In the first group, a quick response in dental and skeletal vertical relationship was seen. In all growing individuals, especially those in early mixed dentition stage, the open bite closed in less than 4 months. The cause of open bite closure was due to intrusion of posterior teeth. In the older adolescents, there were smaller changes, and relapse was observed in two cases. A major side effect of treatment with magnetic appliance was the tendency for development of unilateral cross bite (in up to half the patients), followed by a tendency for developing full scissor bite on the opposite side.
    32. 32. This was due to the lateral forces that are normally developed when repelling magnets move toward each other. In the Bite Block group, main improvement occurred in the first weeks after insertion, followed by a plateau period. Though the improvement was neither as rapid or extensive as with the first group, no transverse problems were noticed. The major difference in their modes of action is that magnets continuously transfer forces to the posterior teeth depending on the distance between the repelling magnets. Bite block on the other hand, transfers intermittent forces to the teeth, only when it is in contact with them. Transverse problems with magnetic appliance could be diminished by using less powerful magnets, or decreasing treatment time, or by providing a guiding flange to counteract lateral forces.
    33. 33. Kuster and ingervall (EJO 1992) compared the effects of stainless steel spring loaded and cemented magnetic bite blocks for correction of anterior open bite in children. There was significantly greater improvement in the group treated with magnetic bite blocks (average improvement of 3mm in overbite) as compared to spring loaded group. This was due to intrusion of posterior teeth resulting in anterior mandibular rotation, as well as eruption of incisors. Interestingly, the authors did not report any development of cross bite in their magnetic cases. The authors however cautioned that there was a tendency for relapse following correction, and advised active retention for a long period. They suggest a regime of cemented bite blocks followed by a longer period of removable bite blocks.
    34. 34. Noar et al (AJO-DO 1996) carried out lab based experiments to examine the effect of orientation of magnets on the force levels achieved.
    35. 35.
    36. 36. The results showed there that there was a reduction in repulsive force in the tilted alignment as compared to perfect alignment of magnets. In addition, the skewed and edge to edge alignment cases actually showed attractive forces at close distances. This study highlights that the orientation of the magnets is of the utmost importance. In the mouth, when the mandible moves, the magnets will frequently be misaligned and will rarely be producing their maximum reported repulsive force. It was concluded that the claims that bite-block appliances containing magnets enhance the intrusion of buccal segments in cases with Anterior open bite, because of the force produced between the repelling magnets could not be supported by the results of this lab based study.
    37. 37. Hwang and Lee (AJODO 2001) reported the use of magnetic force in conjunction with a corticotomy procedure, to intrude over erupted molars following loss of their antagonist. Corticotomy is a surgical technique in which a fissure is made through the cortical bone that surrounds a tooth so that the tooth is embedded within a bone block that is connected to the adjacent blocks through only the medullary bone. In this way, the tooth acts like a handle by which the bands of the less dense medullary bone are moved as a block. The bone blocks are moved with the teeth, rather than moving the teeth within the bone. In these situations, a heavier force of more than 90 g was applied on the molar because it was necessary to move the bone block with the tooth. Although there was no discomfort or root resorption, further research is needed to determine an optimal force value for use after corticotomy.
    38. 38. Pretreatment Corticotomy Magnetic appliance Post intrusion
    39. 39. 4. Molar distalization: Gianelly et al ( JCO 1988, AJO DO 1989) reported the intra-arch placement of repelling magnets against the maxillary molars in conjunction with a modified Nance appliance cemented on the first premolars, to distalize the Class II molars. The modified Nance appliance was anchored to the first premolars to encourage the distal drift of the second premolars. Bilateral distal extensions (0.045inch wire) with loops at the end were soldered to the labial aspect of the premolar bands so that the loops approximated the molar tubes.
    40. 40. An 0.014-inch ligature wire was placed through the loop and extended anteriorly to encircle a tieback hook mesial to the magnets. When tightened, the repelling magnets are held in contact. When second molars were not present, the fastest molar movement was observed and Class I molar relationships were attained within 2 to 5 months. When second molars were present, treatment time increased as there were 2 teeth to move distally. When magnets were used in the treatment of adults, the results were less predictable and the time factor increased. The appliances were well tolerated by patients and were used successfully to move molars distally with relatively minor anchorage loss. Consistently, 80% of the space created represented distal movement of the molars. Thus for every 5 mm of space opened, the molars were moved posteriorly 4 mm while the premolar-incisor segment moved forward 1 mm Significantly, patient co-operation was dispensed with.
    41. 41. Itoh et al (JCO 1991) described an appliance called the Molar Distalization System, which also made use of repelling magnets. The mesial magnet of each pair is mounted so that it can move freely along a sectional wire. A sliding yoke, with ligation hooks mesial to the mesial magnet, brings the repelling magnets together to activate the magnetic force. A primary molar or premolar in good condition is selected as the anchor tooth in and a Nance holding arch is placed to reinforce anchorage. The distal end of the MDS terminates in a three-pronged fork, with the middle prong sized for insertion into the headgear tube.
    42. 42. Ligating around the two outer prongs secures the MDS to the molar tube. The constant magnetic force of about 8oz results in rapid distal movement of the first molars. This movement separates the magnets, which must be reactivated by being placed back in contact every two weeks. Bondemark and Kurol (EJO 1992) carried out distalization of 1st and 2nd molars simultaneously, in a group of 10 patients, using a similar appliance, but including the second premolars as anchorage. They reported that all maxillary molars were distalized into Class I relationship during a mean time of 16.6 weeks. Whereas the mean molar crown movement was 4.2 mm, anchorage loss in anterior region was about 1.8 mm. Mean distal tipping of the 1st and 2nd molars was 8 and 5.6 degrees respectively.
    43. 43. The disadvantages of the method as reported by the authors were: Time consuming and expensive construction. Chances of relapse due to tipping component of molar movement. Loss of anchorage anteriorly in the form of increased inclination and overjet. The effectiveness of magnets for distalization of molars has been compared with that of Ni Ti coil springs in a number of studies, by Bondemark et al (Angle Orthod 1994), Erverdi et al (BJO 1997, split mouth study), and by Bondemark (EJO 2000). All of these studies show Ni Ti Coil springs to be more efficient in molar distalization as compared to magnets.
    44. 44. 5. Maxillary expansion Repulsive magnetic forces for maxillary expansion were first described by Vardimon et al in monkeys, AJO DO 1987. Repulsive magnetic force was applied using direct as well as indirect placement of magnets. These were also compared with expansion through conventional jackscrew, by means of the implant method. The feasibility of magnetic force to produce orthopedic changes was unequivocally demonstrated. Advantages in the use of magnetic forces are a predetermined force range with upper and lower limits (for example, 435 to 80 g) and thus the elimination of potential iatrogenic sequelae in the form of uncontrolled force levels
    45. 45. Indirect placement of magnets in acrylic housing Expansion achieved with the directly placed magnets Direct placement of magnets with telescopic element
    46. 46. A clinical study on maxillary expansion with a Magnetic Expansion Device (MED) has been reported by Darendeliler, Strahm and Joho, (EJO 1994). Using a bonded and a banded variety of the MED in 2 and 4 patients respectively, exerting 200-250 grams of force, they found more pronounced skeletal expansion with the banded appliance. Stability was adequate after a post-retention period of 12.5 years. The authors indicated that the use of light continuous forces (250-500 grams) could generate dental and skeletal movements, the degree depending on the patient’s status.
    47. 47. 6.Functional appliances for correction of Class II malocclusion The rationale for introducing magnets to the arsenal of functional appliances is based on the unique characteristics of magnetic forces,which are: High force to volume ratio. Maximal force at short distances. 3D centripetal orientation of attractive magnetic forces. No interruption of forces by intermittent media. No energy loss. In addition, functional magnetic appliances may act more effectively in propelling dormant genetic tendencies than conventional functional appliances. E.g. a locked mandibular growth pattern caused by Class II div 2 Malocclusion.
    48. 48. One of the major reasons for failure of conventional functional appliances is incompetent sagittal displacement. Normally interjaw tooth contact totals between 8 minutes and 20 minutes during a 24-hour period, but only 1 to 2 minutes during nighttime. Furthermore, Witt and Komposch found a physiologic limitation in providing adequate vertical support to an activator during sleeping time. These facts indicate a possible limited effective duration— that is, the patient might wear the appliance but in a completely unproductive position. Logically, increasing the construction bite beyond the habitual posture position might provide vertical support.However, increased bite clearance decreases the protrusion performance.
    49. 49. Vardimon et al (AJO-DO 1989) introduced a new functional appliance to correct Class ll dentoskeletal malocclusions,called the functional orthopedic magnetic appliance (FOMA) II. This uses upper and lower attracting magnetic means (Nd2Fe14B) to constrain the lower jaw in an advanced sagittal posture. In a study done with this appliance in monkeys, it was found that the functional performance of the FOMA and the FOMA+FA was superior to that of FA alone. Also, there was greater increase in mandibular length and less proclination of incisors
    50. 50. Kalra et al (1989) described the use of repelling magnets in patients with Class II div1 malocclusion in association with increased lower face height. After 4 months treatment with intrusive force of 90 gms per tooth in 10 patients, the authors reported significant increase in length of mandible and decrease in mandibular plane angle.
    51. 51. Another functional appliance introduced by Darendeliler and Joho, (AJO-DO 1993) known as the MAD II, consists of an upper and lower removable appliance, carrying magnets in both buccal segments. In Class II cases with normal vertical proportions, the magnets are placed distal to the upper canine and distal to the lower first premolar.
    52. 52. In deep bite situations, the inclination of the magnets and subsequent magnetic force orientation is chosen in such a way to produce dental extrusion in the premolar-molar area. The magnets are placed to produce an attracting force between them and located more posteriorly
    53. 53. In Class II open bite situations, two pairs of lateral magnets in a repelling configuration can be used posteriorly, with the objective that they will produce molar and premolar intrusion, with some distal movement in the upper arch, while pushing the mandible downward and forward. An additional pair of attracting midline magnets located at the retroincisal area will help to achieve symmetry and alignment of upper and lower midlines
    54. 54. Joho and Darendeliler (EJO 1993) compared Class II deep bite patients treated with the MAD II appliance with untreated controls. They found the appliance to augment the lower facial height, and it was accompanied by almost immediate functional adaptation. The Functional Magnetic System, described by Vardimon et al, incorporates some of the principles of the Schwarz appliance. It consists of upper and lower removable plates that each contain a magnetic unit, both of which are in attractive configuration.
    55. 55. The upper magnetic unit comprises a stainless steel magnetic housing incorporating two SmCo5 magnets, with a single prong attached to it. Expansion screw may be incorporated if required. The lower magnetic unit also has a magnetic housing with two cylindric rare earth magnets corresponding to those in the upper.
    56. 56. The lower magnetic housing has a posterior inclined wall that forms an oblique plane. Guidance of mandible into constructive protrusive contact position (CPCP) occurs by sliding of mandibular oblique plane along the maxillary prong on mouth closure. This is further enhanced by a groove in the oblique plane.
    57. 57. Anchoring units of the plates include Adams, triangular and elastic clasps. Depending on the severity of Class II malocclusion, any of 4 modifications of the FMS can be used, depending on incorporation of expansion and protraction screws.
    58. 58. William J Clark has also reported a modification of the Twin Block appliance that incorporates magnets for Class II correction. However, he states that the question of whether to use attracting or repelling magnets is yet to be resolved.
    59. 59. 7.Functional Appliances for Class III malocclusions: Vardimon et al (AJO-DO 1990) developed an intraoral intermaxillary appliance for the treatment of Class lll malocclusions that exhibit midface sagittal deficiency with or without mandibular excess. The functional orthopedic magnetic appliance (FOMA) III consists of upper and lower acrylic plates with a permanent magnet incorporated into each plate. The upper magnet is linked to a retraction screw and is retracted periodically (e.g., monthly) to stimulate maxillary advancement
    60. 60. The upper plate of a FOMA III consists of a 0.031-inch stainless steel arch wire forming the metal substructure (a). The arch wire bypasses the premolar-canine segment to permit eruption and crosses the occlusal plane at the M1-M2 embrasure. The upper magnetic housing (b) is linked to a retraction screw (c). The magnetic unit (b + c) is positioned along the midpalatal line
    61. 61. The attractive mode neodymium magnets used in this study produced a horizontal force of 98 gm and a vertical force of 371 gm. The ratio of horizontal to vertical force vectors is dictated by inclination of magnetic interface in the sagittal plane. The more perpendicular the magnetic interface is to the occlusal plane (sin 90° = 1), the greater is the horizontal force vector (Fh = attractive force ´ sin a).
    62. 62. Six female Macaca -fascicularis monkeys were treated with FOMA IIIs. After 4 months of treatment, the following results were found: The growth pattern of the cranial base (saddle angle) was not altered. Midfacial protraction did occur along a recumbent hyperbolic curve with a horizontal maxillary displacement and an anterosuperior premaxillary rotation. Cumulative protraction of the maxillary complex was initiated at the pterygomaxillary fissure with an additional contribution provided by other circummaxillary sutures (zygomaticomaxillary s., transverse s., premaxillary s.) Inhibition of mandibular length was minimal, but a tendency toward a vertical condylar growth pattern was observed.
    63. 63. The interaction between sutural and condylar growth sites appeared biphasic, characterized by an immediate and rapid excitation of the circummaxillary sutures followed by a delayed and slow suppression of the condylar cartilage. A later radiographic and histologic study by Vardimon et al (AJODO 1994), again on monkeys, revealed the following data: Maxilla: The target area of the protractive force was found to be localized in the pterygomaxillary fissure. Three dimensionally, the separation of the sutures at the PMF was found to diminish in inferosuperior and lateromedial directions. Radiographically, the horizontal and vertical displacements of the lower PMF point were three and five times greater than the corresponding displacements of the upper PMF point, respectively. Mandible: Radiographically, mandibular length was unaffected after 4 months of treatment, and the distance condylion-pogonion was equally increased in the treated (0.75 ± 0.78 mm) and the control animals (0.77 ± 0.32 mm).
    64. 64. Histologically, the condylar cartilage demonstrated increased osteoclastic activity at the zone of endochondral ossification and a decreased apposition rate at the adjacent bony trabeculae. Conceivably, the two target areas (PMF sutures versus condylar cartilage) demonstrate two diverse time-related responses that are either unrelated or interrelated to each other. An unrelated tissue response suggests that tissue stimulation (sutural) is always superior to tissue suppression (condylar). Another possible unrelated tissue reaction implies diverse response velocity (high sutural, low condylar). An interrelated mechanism suggests that an applied force will dissipate initially at the less resistant target area (sutures), and will subsequently affect the more resistant target area (condyle) once the sutural resistance exceeds a certain threshold. The fact that no pathologic change was found in the condylar cartilage encourages a long-term use of the FOMA III appliance, initiating treatment at an early skeletal age.
    65. 65. Darendeliler et al (JCO 1993) reported a case of a 7.5 years old female with Class III dental malocclusion and bilateral cross bite who was treated with a combined MAD III and MED appliance. Upper and lower buccally placed magnets were used for correction of A-P discrepancy. The upper and lower magnets had a tendency to move toward a fully centered contact, thus creating a forward force against the maxilla and a backward force against the mandible. When combined with an MED, the MAD III offers an alternative in the early correction of Class III malocclusions.
    66. 66. 8. Treatment of obstructive sleep apnea, snoring. The OSAS is characterized by a number of symptoms: Intermittent upper airway obstruction during sleep Socially handicapping snoring, Daytime sleepiness In long-standing cases of the syndrome, headache, hypertension, cardiac, and pulmonary complications often ensue. The automobile accident rate in OSAS patients is reported to be two to three times higher. Work performance, family and social interaction, and other aspects of quality of life also appear to be compromised 10% of men and 5% of women in the 30- to 40-year age group are habitual snorers,
    67. 67. The precise cause and pathogenesis of upper airway occlusion during sleep remains uncertain. Factors reported are: Retrognathism of the maxilla and mandible, Increased lower facial height, Reduced anteroposterior size of the bony pharynx Elongated soft palate, Enlarged tongue, Decreased posterior airway space, Inferior position of the hyoid bone. The treatment is directed toward improving the air flow by various surgical and nonsurgical methods.
    68. 68. Non-surgical methods have included treatment with dental appliances, usually removable functional appliances. The mandible is supposed to advance forward, and it is assumed that widening of the upper airway space is created and breathing during sleep enhanced. 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 airway space. In such situations, a magnetic appliance may be more effective than the conventional passive functional appliance, because the magnet forces prevent the closing by providing direct and continuous mandibular advancement.
    69. 69. Bernhold and Bondemark (AJO-DO 2001) used a magnetic appliance to treat 25 male patients with handicapping snoring or obstructive sleep apnea It consistedof a maxillary and a mandibular occlusal acrylic splint. In each splint, four cylindrical neodymiumiron-boron magnets were embedded and oriented to produce intermaxillary forces that pulled the mandible forward.
    70. 70. All patients easily accepted the magnetic appliance. The main symptoms, snoring and daytime sleepiness, decreased significantly. The blood oxygen saturation during sleep was also improved. No aberrant effects on TMJ status. The appliance made the mandible rotate downward and backward, mean 7.8°, and this rotation mostly camouflaged the forward movement of the mandible.
    71. 71. There was no significant influence on the hyoid bone position, but the hypopharyngeal airway space increased, the tongue base was lowered, and the contact between the tongue and soft palate was reduced significantly. Gavish et al (AJO-DO 2001) used the FMS (functional magnetic system) to treat 28 patients with OSA After 8 weeks of FMS treatment, it was found that the respiratory disturbance index decreased significantly; minimal oxygen saturation increased significantly, reaching a normal value; day time tiredness improved; snoring declined; the oral cavity anterior region increased significantly, and the pharyngeal airway passages did not change. The functional magnetic system operated by increasing the anterior region of the oral cavity, mainly vertically, with no change in the posterior oral cavity region and pharyngeal airway passages. . They concluded that the functional magnetic system is a
    72. 72. 9. Extrusion of crown-root fractured teeth A subgingival 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. Bondemark et al AJODO 1997 described the use of magnets to extrude such teeth with excellent periodontal results.
    73. 73. Other Uses: Springate and Sandler (BJO 1991) reported the use of Nd-Fe-Bo micro-magnets as a fixed retainer which does not hinder oral hygiene. Two such micro magnets bonded to central incisors mesio-lingual surface were used to retain closure of mid-line diastema. RAC Chate (EJO 1995) has reported the development of the PUMA or Propellant unilateral magnetic appliance, which uses magnets incorporated in unilateral bite blocks for correction of hemifacial microsomia.
    74. 74. Biological effects of magnets and safety concerns: Though magnets have been widely used in orthodontics , there have been concerns regarding their safety and possible harmful effects. These are particularly attributed to corrosion products of magnets and their cytotoxic effects, as well as the possible harmful effects of the magnetic fields themselves. Bondemark et al (AJODO1994) showed that there is a release of water-soluble cytotoxic components from Sa-Co magnets. Hence, it is very important to use non-cytotoxic or coated magnets .
    75. 75. A study by Bondemark et al (EJO 1995) to investigate the biological effects of magnets on human tissues, showed that weak static fields below 0.09T in commercially available orthodontic magnets did not cause any histologically detectable changes in human dental pulp or gingiva. This study is in agreement with a number of previous studies in animals and supports the claim that weak static magnetic fields are harmless to oral tissues. It is important to note that the WHO report of 1987 states that static magnetic fields upto 2T show no significant health effects.
    76. 76. Conclusion The development of powerful, rare earth magnets has resulted in their application in many areas of orthodontics. However, at present the most promising clinical uses for these magnets are mainly confined to tooth movement for impacted teeth, and Class II and Class III malocclusions, as well as for treatment of open bite cases. In particular the long term effects of correction of open bite with magnetic appliances has to be evaluated. Also smaller, thinner magnets are to be developed for better results.
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    83. 83. Thank you Leader in continuing dental education