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Distraction osteogenesis 1 /certified fixed orthodontic courses by Indian dental academy


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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Distraction osteogenesis 1 /certified fixed orthodontic courses by Indian dental academy

  2. 2. INDIAN DENTAL ACADEMY Leader in continuing dental education
  3. 3. INTRODUCTION Distraction Osteogenesis is a biologic process that leads to bone formation between two bony segments that are mechanically separated at a constant rate. New bone is generated in an osteotomy gap in response to tension stresses placed across the bone gap. It enables the clinician to lengthen and widen bone and fill in gaps between bones without the need for bone or soft tissue grafts. The simultaneous expansion of the soft tissues, including muscles, ligaments , fat and skin produces excellent aesthetic and functional results and minimizes the skeletal relapse. Distraction Osteogenesis applied to the craniofacial skeleton has proven to be a major advance in the treatment of congenital deformities. The patient population for distraction includes those with craniofacial microsomia , Nager’s syndrome, Treacher Collins syndrome, Pierre Robin syndrome, Temperomandibular joint ankylosis and post traumatic growth disturbances
  4. 4. DEVELOPMENT   The first bone distraction was performed by Codivilla in 1905 for the treatment of a shortened femur. Subsequently, Ilizarov introduced distraction osteogenesis technique for limb lenghthening. The procedure was initiated by surgical bone division with maximum preservation of periosteum and endosteum-a technique called corticotomy. Ilizarov divided two-third of the bony cortex with a narrow osteotome followed by completion of bone separation with rotational osteoclasis
  5. 5.   His distraction protocol used a 5 to 7 day latency period ( the time frame between bone division and initiation of traction forces). Bone segments were then gradually separated at a rate of 1 mm per day in four equal increments of 0.25 mm. On completion of distraction ,the consolidation period( the time required for remodeling of the regenerate tissue) began and continued until the newly formed bony tissue in the distraction gap had remodeled.
  6. 6.     Snyder et al in 1973 used Ilizarov’s principle to the mandible. He resected a unilateral 15 mm bone segment from a dog mandible , creating a crossbite. An extraoral distraction appliance was placed. After 7 day latency period ,device was activated at a rate of 1 mm per day for 14 days at which time occlusion was restored. Reestablishment of mandibular cortex and medullary canal across the distraction gap was noted after 6 weeks of fixation.
  7. 7.  In 1976 Michieli and Miotti, reproduced Snyder’s work,using an intra oral device and in 1984 Kutsevliak and Sukachev took the experiment a step further by lenghthening a normal dog mandible 1.2 cm using Ilizarov principle.
  8. 8.  Panikarovski et al in 1982 performed the first significant histologic evaluation of mandibular distraction regenerates in 41 days.    A fibrous interzone was observed in the central region of the distraction gap with collagenous fibres and capillaries oriented parallel to the direction of distraction. Newly created bone ,in the form of longitudinally oriented trabeculae ,originated from the residual mandibular segments and progressed towards the fibrous interzone. Results of these studies demonstrated that the mechanism of new bone formation ,during gradual mandibular distraction was similar to that during limb lenghthening.
  9. 9.    Karp et al conducted a similar experimental study with a more comprehensive analysis of distraction regenerates at different stages of formation. Histomorphologically, the distraction gap was represented by four zones-a central zone of fibrous tissue; a zone of extending bone formation; a zone of bone remodeling and a zone of mature bone. These studies provided a scientific basis for clinical adaptation of the distraction osteogenesis technique to craniofacial complex.
  10. 10.   In 1989, McCarthy et al were the first to clinically apply the technique of extraoral osteodistraction on four children with congenital craniofacial anomalies. They used a Hoffman Mini Lengthener attached to the osteotomized bone segments with two pairs of pins.
  11. 11.    Bone division was initiated by placing a series of drill holes along the osteotomy line, which were then connected with a narrow osteotome. After a latency of 7 days, lengthening began at a rate of 1 mm per day performed in two increments of 0.5 mm. After 18 to 24 days of distraction, external fixation was maintained for an additional 8 to 10 weeks
  12. 12.     G.Altuna et al in 1995,performed distraction osteogenesis of maxilla in adolescent female macaca cynamolgus monkeys. An orthodontic appliance was constructed with a Glen Ross screw oriented antero posteriorly . Anterior sub apical osteotomies of the maxilla were carried out. Anterior segment was advanced 4 mm in two and 6 mm in one monkey and was repaired by well organized alveolar bone at the end of the retention period.
  13. 13.     Histologically the osteotomy site in the lenghthened maxilla showed complete regeneration of the alveolar crest. The height of the alveolar crest in the lenghthened osteotomy site was just apical to cementoenamel junction. The buccal plate of the lenghthened osteotomy site was intact consisting entirely of bone and regeneration of the osteotomy site was mediated by trabeculae of cancellous bone. The study showed for the first time that distraction osteogenesis can be successfully applied to maxilla.
  14. 14. DEVICES USED IN DISTRACTION OSTEOGENESIS OF THE CRANIOFACIAL SKELETON  Distraction devices can be classified into Intraoral devices  Extraoral devices   Extraoral devices can be Unidirectional  Bidirectional  Multidirectional   Intraoral devices can be Tooth borne  Bone borne  Hybrid (Tooth borne and Bone borne) 
  15. 15. EXTERNAL UNIDIRECTIONAL DISTRACTION DEVICES  In 1992,McCarthy et al introduced an external unidirectional distractor to successfully lengthen the mandible unilaterally in three children and bilaterally in one child.  The amount of distraction varied from 18 mm to 24 mm.  The distractor consisted of a single calibrated rod with two clamps.  Each clamp holds two 2 mm half pins that are placed on either side of the osteotomy.  Approximately 20 mm to 24 mm of bone stock posterior to the last tooth bud is necessary to place this device.  By turning the bolt at the end of the rod ,the distance between the clamps can be changed to provide expansion or compression at the level of the bone.
  16. 16.      Ortiz-Monasterio and Molina modified the Ilizarov technique by performing an incomplete corticotomy. They leave the internal cortical plate and the cancellous layer intact and use a semi rigid external distractor. Molina built into his distractor the capability to further exploit the secondary soft tissue expansion associated with osteodistraction. By leaving the lingual cortical plate intact,initial distraction of the device causes the pins to diverge and the expansion rod to bow out. At some critical point,the inner cortical plate snaps and elongation of the bone proceeds.It is believed that the change in shape of the mandible with this technique more closely follows the curve of mandibular growth.
  17. 17.     Despite the fact that the Molina distractors are unidirectional,changes in three dimensions have been documented. A criticism of this technique is the predictability of how and when the inner cortical plate will break. In situations where there is minimal bone posterior to the last tooth bud,a single pin in the proximal segment may be an advantage over double pins. If there is inadequate bone for even a single pin, polley and Figueroa advocate the removal of a tooth bud or an interdental osteotomy.
  18. 18. EXTERNAL BIDIRECTIONAL DISTRACTION DEVICE   A bidirectional distraction appliance provides an additional degree of freedom over the unidirectional device. More severe mandibular hypoplasias, such as Treacher Collins syndrome and bilateral micrognathia, involve deficiencies in more than one plane.
  19. 19.    Klein and Howaldt developed an external bi-directional device capable of achieving controlled changes in angulation. (KLSMartin LP). Changes can be made in the gonial angle which is often obtuse in case of mandibular deficiency. The device consists of two geared arms 5 cm in length connected to a middle screw that enables the arms to be moved up or down to change angulations.
  20. 20.   Molina offers an external bi-directional distractor(Wells Johnson Co)based on same principles as his unidirectional device. Two external corticotomies which preserve the internal cortical plate and cancellous bone are performed on either side of the gonial angle.
  21. 21.     A pin is placed in each bony segment for a total of three pins. The combination of an intact lingual cortical plate,the position of the pins and the flexibility of the device result in closing of the gonial angle and an increase in the convexity of the mandible and overlying soft tissue. The change in gonial angle cannot be precisely controlled because the middle pin only functions as a pivot. A criticism of the double osteotomy procedure is the risk for avascular necrosis of the intervening segment and damage to tooth buds during pin placement.
  22. 22. MULTIPLANAR DISTRACTION DEVICE   The ability to make transverse changes was the final step in achieving three diamensional control. Building on their previous work, McCarthy et al reported their experience using an external multiplanar device(Stryker Leibinger) to correct the asymmetry in a child with unilateral craniofacial microsomia.
  23. 23.         The multiplanar device consists of a central housing with two work gears in different planes. Two arms extend from the housing with pin clamps at either end. Each quarter turn of the wheel results in 0.25 mm of expansion. There is 20 mm of length on each arm for a total of 40 mm of linear expansion. Two activation screws enable changes in the transverse and vertical angulations. Each turn of the screw results in 3 degrees of rotation KLS-Martin LP also offers a multidirectional distractor that they recommend for older children. The two arms are connected to a middle section by a ratchet and ball joint combination that allows the arms to move independently of one another. Each arm is approximately 60 mm in length.
  24. 24. INTERNAL DISTRACTORS      In response to criticism of the external distractors, internal devices were developed to eliminate the problems of facial scarring, pin tract infections and high visibility. It should be kept in mind that at this time,internal devices are capable of unidirectional distraction only. In 1995,McCarthy et al introduced an intraoral distraction appliance tested on the canine model. After performing an osteotomy,the device was placed on the buccal surface of the mandible and the lenghthening rod was extended into the buccal vestibule. A drawback of the appliance was that it could only accommodate 20 mm of expansion.
  25. 25.     Drs Vasquez and Diner, from the Armand-Trousseau Childrens Hospital in Paris,developed two internal distractors,one for lenghthening the mandibular body and the other for lenghthening the ramus (Stryker Leibinger). Each device comes in two sizes to enable 18 mm or 28 mm of expansion and is held in place by four 1.6 mm self-drilling pins. The rod attachment used to activate expansion is available in sizes varying from 83 mm to 123 mm in length. The rod extends into the buccal sulcus and rests between the lips for easy access.
  26. 26.     Synthes Maxillofacial(Paoli,PA) manufactures a partially internalized distractor capable of 30 mm of distraction. The distractor is held in place by four 2 mm self tapping screws, and the expansion rod is fully enclosed to provide comfort and to minimize any soft tissue interference. KLS-Martin LP manufactures a miniaturized intraoral mandibular distractor with a flexible arm that exits percutaneously. There are three sizes,allowing 10 mm, 15 mm, or 20 mm of distraction and they are held in place by a total of six 1.5 mm screws.
  27. 27. TOOTH-BORNE APPLIANCES     In 1997,Razdolsky et al introduced a completely tooth-borne intraoral distractor capable of making linear changes (Oral Osteodistraction LC). Current technique starts by fitting preformed stainless steel crowns to one tooth on either side of the anticipated osteotomy site( usually the second molar and first bicuspid teeth). Rubber base impression is taken of the entire arch, and the distractor is fabricated on the cast by the laboratory. The stainless steel crowns are cemented before surgery. An osteotomy is made between the selected teeth,and the expanders are placed to complete the ROD (Razdolsky Osteogenesis Device) appliance.
  28. 28.   There are several ROD appliances available, with sizes enabling 11 mm to 15 mm of distraction. In addition to the ROD 1 used to distract between teeth to increase arch length, the ROD 2 ( partially tooth borne/partially bone borne) advances the mandible posterior to the last molar; the ROD 3 widens the mandible; ROD 4 is designed for maxillary distraction and ROD 5 is designed for ridge augmentation.
  29. 29. MANDIBULAR WIDENING DEVICE     Early application of distraction osteogenesis to widen the mandible was described by Guerrero and Contasti. Bands were fitted on the lower first bicuspids and molars, and a jackscrew was soldered at the midline for expansion. Harper et al and Bell et al performed mandibular midline osteotomies in adult monkeys employing cemented Hyrax-type expansion appliances. Guerrero et al reported their findings after redesigning the mandibular midline distractor to provide bony anchorage(Dynaform Intraoral Distraction Device; Stryker Leibinger)
  30. 30. RIDGE AUDMENTATION    Chin and Toth performed vertical alveolar distraction in a 17 year old girl with a Knife-edged ridge that made placement of implants impossible without augmentation. The distractor (LEAD System, Stryker Leibinger) was placed and after a latency period of 5 days, distraction proceeded at a rate of 1 mm per day for 9 days. The device was retained for 10 days, at which time it was removed. After 6 weeks, Osseointegrated implants were placed in the greatly increased mass of bone
  31. 31. MIDFACE DISTRACTION   After the successful application of distraction osteogenesis in the human mandible, it was only a matter of time before the technique was applied to the midface. In 1993,Rachmiel et al reported their findings on midface advancement in sheep using external distractors.
  32. 32. Molina and Ortiz-Monisterio reported using an orthodontic face protraction mask combined with a Le Fort I osteotomy to achieve distraction osteogenesis.  After attempting this technique,Polley and Figueroa realized that the facemask with elastics was not sufficiently rigid to achieve the desired amount of forward movement.  They developed an adjustable rigid external fixation (RED;KLS-Martin LP) system for maxillary advancement. 
  33. 33.      The distraction device is symmetrically positioned and secured with two to three scalp screws. Tracing wire is connected from the extraoral hooks extending from the splint to the horizontal bar on the distractor. The horizontal bar of the device can be adjusted up and down to allow multiplanar control of the vertical as well as the horizontal movements. Retention is continued by wearing an orthodontic facemask with elastics at night for 4 to 6 weeks. They reported using the RED appliance in a 10 year old child with severe maxillary hypoplasia as a result of bilateral cleft lip and palate.The device was simple to use and the scalp screws did not cause any problems.
  34. 34.     Molina designed a unidirectional orbital malar distractor that is used in conjunction with a Le Fort III osteotomy(Wells Johnson Co). The self contained rod is smooth and facilitates function and comfort. The active portion of the rod exits percutaneously behind the ear and can be expanded up to 25 mm. The anterior point of the device has a point pivot that allows flexibility in placement behind the malar bone.
  35. 35.      Chin and Toth custom designed their own internal distraction devices for use in the maxillofacial complex. Models of the skeleton are milled from computed tomographic data to plan the surgery and design their distractors. Chin and Toth,s approach to distraction departs from the principles outlined by Ilizarov in several ways. In their surgical technique for midface advancement Toth et al create proximal boxes to seat the device. The forces of distraction are transmitted directly against the bone,rather than creating a torturing force that may dislodge the retention screws.
  36. 36. DISTRACTION IN INFANTS   In 1994,McCarthy suggested that distraction could be performed in children as young as 2 years of age. As the knowledge of distraction osteogenesis has increased, the technique has been successfully applied to infants with severe deficiencies that require immediate intervention.
  37. 37.     Cohen et al introduced a system of miniature distractors that could be customized for use anywhere in the craniofacial complex. Facial moulages of the infant were taken to aid in the design of the device. A modified Le Fort III osteotomy with internal orbital osteotomies and a mandibular osteotomy were performed. The distraction devices were placed to correct the sagittal and vertical maxillary deficiency,expand the orbit and increase mandibular body length. Each vector was chosen independently,the devices were custom modified and multiple distractions proceeded simultaneously.
  38. 38.   Cohen further developed his miniature distraction devices,called the Modular Internal Distraction(MID) system(Stryker Leibinger) This is the first internal distraction system approved by the Food and Drug Administration for marketing. Two distractor frames are available to provide 15 mm or 30 mm of distraction.
  39. 39.     The frames are attached to 1.7 mm mini Wurzburg three dimensional mesh plates of varying sizes using 1.6 mm connecting screws. There is a flexible activation cable that exits percutaneously; preauricularly or postauricularly, through the scalp or intraorally. It is recommended that a complete osteotomy be performed with a latency period of 5 to 7 days, followed by 1 mm per day of distraction and a consolidation period of 8 to 12 weeks. These devices can also be used in older children.
  40. 40.        Molina(Wells Johnson Co) offers a unidirectional Baby Mandibular Distractor designed for infants. It is 50% smaller and lighter than the standard unidirectional distractor. Bilateral corticotomies are performed at the mandibular angle behind the most posterior tooth bud. A long continuous pin is used to penetrate both proximalsegment to provide increased strength and stability across the arch. Individual pins are placed in the distal segments and the devices are mounted. Rodrigues and Dogliotti described mandibular lenghthening with a simple custom designed appliance to bring the base of the tongue forward in three newborn infants with glossotosismicrognathic association. The surgical technique was the same as outlined by Molina ,but Rodriguez and Dogliotti used a long K-wire in place of the continuous pin.
  41. 41. PRINCIPLES OF DISTRACTION OSTEOGENESIS   (ILIZAROV PRINCIPLES) 1. BONE CUT: It is important to preserve the osseous blood supply. Because of the abundant vascular supply of the craniofacial skeleton,either an osteotomy or corticotomy may be performed. It is common to initially create a corticotomy in deficient mandible which then can be converted to an osteotomy. It is also important to preserve the integrity of the overlying periosteal envelope during surgery. 2. LATENCY : After bone cut is performed,a latency period of 5 to 7 days is observed before device activation. This allows for the formation of an adequate fibrovascular bridge between the bone edges. Additionally ,the surgical site passes into Phase II of wound healing, promoting a regenerative environment. Latency period may be shortened (1 to 2 days) if the patient is young.
  42. 42.   3. RATE: A regenerate can best be generated when the tensile stress is applied and bone edges separated 1.0 mm per day. For young child,the rate may be increased upto 1.5 to 2 mm per day. Advancing the bone segments more than 2 mm per day may exceed the limit of vascular supply of the overlying soft tissue. 4. RHYTHM : Continuous application of distraction force is ideal. Clinically, application of the distraction is best performed by activating the device twice a day(0.5 mm twice a day). If the patient experiences discomfort ,then the rhythm should be altered to allow for a smaller incremental application(0.25 mm for four times a day)
  43. 43.     5. CONSOLIDATION : Once the regenerate has been created,the distraction device is held in neutral fixation allowing the neomandible to ossify. The timing of the ossification process is similar to that of fracture healing(6 to 8 weeks). For younger children ,ossification can occur quicker. It is best to observe a cortical outline on the radiograph of the regenerate before device removal. Jason Cope et al in Int.J.Oral &Maxillofacial surgery in 2001 used digital subtraction radiography for monitoring distraction regenerate formation. Subtraction radiography is a method by which two virtually identical serial radiographs, taken under the same conditions, can be superimposed, common anatomical structures subtracted, and the difference quantified in terms of net gain(increased mineralisation) or net loss(decreased mineralisation). They showed Digital Subtraction Radiography to be highly sensitive and accurate for detecting bone mineral changes
  44. 44. STAGES IN THE DEVELOPMENT OF BONY REGENERATE 1. The “Stage of fibrous tissue” consisting of highly organized, longitudinally oriented parallel strands of collagen with spindle shaped fibroblasts and undifferentiated mesenchymal precursor cells throughout the matrix.
  45. 45. 2. 3. 4. The “Stage of extending bone formation” in which fibroblasts and undifferentiated precursor cells of the matrix were in continuity with osteoblasts. The osteoblasts had a longitudinal orietation. The osteoblasts arouse from transformed spindle shaped fibroblastic cells located between the collagen bundles. The “Stage of bone remodeling” consisting of advancing fields of bone resorption and apposition. There were increased numbers of osteoclasts. The “Stage of mature bone” in which compact cortical bone was located adjacent to the mature bone in the nondistracted areas.The bone spicules were thicker and less longitudinal than in the remodeling stage
  46. 46. MAXILLARY DISTRACTION   Alvaro.Figueroa et al in AJO 99 reported of maxillary distraction osteogenesis in cleft patients with severe maxillary deficiency, with the use of a rigid external distraction (RED) device. Patients are evaluated employing a comprehensive clinical examination, facial and intraoral photographs, cephalometric and panoramic radiographs, dental casts, video imaging, computerized axial tomographic scans and a comprehensive speech evaluation.
  47. 47.  A patient having the following characteristics is considered for maxillary advancement through distraction osteogenesis with the use of RED system Transverse,vertical and horizontal maxillary deficiency needing an advancement greater than 6 mm to 8 mm  palatal clefts with severe scarring  normal mandibular morphology and position  normal neck/chin angle  patients in the full primary dentition or older  patients with an intact cranium 
  48. 48.    To deliver the distraction forces to the maxilla, a custom made semirigid intraoral splint is fabricated. The orthodontic maxillary bands with 0.050 inch headgear tubes are fitted on the first permanent molar teeth, or on the second primary molars in young children. An impression is obtained of the maxillary arch and the bands are transferred from the mouth to the impression to prepare a working dental cast.
  49. 49.     If the arch is small or irregular ,a custom made device has to be fabricated. Labial and palatal 0.045 or 0.050 stainless steel wires are bent around the perimeter of the dental arch as close as possible to the labial or palatal aspect of the teeth. If orthodontic appliances are present ,the wires must be bent to clear the brackets, thereby facilitating the path of insertion. The wires are then soldered to the molar bands. If additional rigidity is required, stability wires can be soldered between the labial and palatal wires across the dental embrasures, usually distal to the lateral incisors on both sides or a trans palatal bar added.
  50. 50.   Two straight pieces of heavy rigid stainless steel orthodontic wires(0.060 inch or heavier) are soldered perpendicular to the labial wire just distal to the lateral incisors or medial to both lip commisures. The gingival intraoral aspect of the wire is cut short and bent like a hook to be used for face mask elastic traction
  51. 51.      This gingival hook will be used during the retention phase after the distraction has been completed. The occlusal or caudal aspect of the wire is left long so it can be bent over and anterior to the upper lip for comfort. The end of this external wire is eventually bent into an eyelet from which the splint and the distraction screw of the RED device are connected by means of a surgical wire. The traction hook is usually located at or above the approximate center of mass of the osteotomized maxilla. In patients without osteotomies, the center of resistance of the maxilla has been estimated to be at the level of the apices of the second bicuspids.
  52. 52.       This guideline can be used to determine the position of the traction hooks. A force vector through the centerof maas of the maxilla will advance it linearly, whereas a force vector above the center of mass will create a clockwise rotation and one below it a counterclockwise rotation. If the arch form is fairly symmetrical, an orthodontic Facebow can be used for making the splint. Expansion procedures are better to be carried out before or after distraction. Once the splint is completed,it is tried on the patient for appropriate fit,any adjustments are made, and then it is cemented in place with orthodontic glass ionomer cement. This is usually performed the day before surgery.In young or uncooperative chidren,it may be necessary to cement the splint in the operating room after anaesthesia.
  53. 53.       Before the osteotomy intraoral splint is secured with multiple circumdental wires to create a completely rigid appliance so that the distraction forces are transmitted to various teeth and not only to the molars on which the bands have been cemented. The maxillary hypoplasia in cleft patients is usually not restricted to the dento-alveolar segment,but includes the paranasal, infraorbital and malar regions. For this reason a high Le Fort I osteotomy is usually performed for patients undergoing maxillary distraction. The transverse osteotomy is performed high,extending laterally across the maxilla below or circumventing the infraorbital foramen. The lateral aspect of the transverse osteotomy can be extended to a variable degree to include the zygomatic or malar projection. In children sufficient bone is left cranial to the tooth buds to avoid disturbing them.
  54. 54.     The osteotomy is complete with septal and pterygoid dysjunction,but in children ,minimal downfracturing is performed to avoid damage to developing tooth bud . Complete down fracturing of the maxilla is not necessary . Following intraoral soft tissue closure,the cranial halo component of the RED device is placed. The halo is placed parallel to the Frankfort horizontal plane and just above the temporalis muscle. Two to three scalp screws on each side are used for fixation.
  55. 55.    Three to five days after surgery, the vertical bar of the RED device is placed in the center of the face , sufficiently anterior and also parallel to the facial plane. and the distraction system are connected to the halo. The distraction screws ,mounted on the horizontal bars, are placed at the apprapriate level to obtain the necessary vectors for the desired maxillary movement. A 25 gauge surgical wire is used to connect the traction hook from the intraoral splint to the distraction screws.Distraction is performed at home by turning the activating screw at a rate of 1 mm to 1.5 mm per day.
  56. 56.     Force levels may have to be increased during the later stages of distraction because consolidation of callus provides resistance to the advancement. Once the appropriate maxillary advancement has been achieved,the RED system is left in place for 2 to 3 weeks to permit bone consolidation. After the RED device is removed ,the external traction hooks are cut with a rotating disk. The retention after distraction consists of nightly use of face mask elastic traction (12 to 16 oz) for 6 to 8 weeks.
  57. 57.       Maxillary advancement using distraction osteogenesis has several advantages which include the ability to treat skeletal dysplasias at a young age without having to wait until skeletal maturity. It also treats only the affected maxilla without having to operate on the normally positioned or even small mandible. The surgical procedure is simplified with minimal morbidity and no need for blood transfusions,bone grafts or rigid fixation hardware. The design of the RED device is such that it allows for adjustments of the distraction force vectors during the distraction process. Limitations of the technique relates to patients with complete absence of teeth or lack of adequate bone in the cranial vault. In patients without a healthy dentition or with multiple missing teeth,it may be necessary to use osseointegrated implants or skeletal anchorage for traction hooks.
  58. 58. BIOMECHANICAL CONSIDERATIONS      After a complete Le Fort I osteotomy, the dentomaxillary complex is no longer a constrained skeletal structure and therefore the location of its center of resistance is not applicable in forecasting protractive movement. Rather,the dentomaxillary complex has been altered to a relatively free structure. Consequently,the point of application and line of action of distraction forces relative to its center of mass becomes important. The center of mass of the dentomaxillary complex is significantly influenced by the disparity in density(mass per unit volume) between its osseous and dental structures. Location of center of mass will be affected by size (maturation) of the osseous structures,the number of teeth present and surgical design of the osteotomy
  59. 59.  Experiments by Gyn Ahn et al in AJO 99 on an osteotomised dentomaxillary structure from an adult cadaver showed the center of mass in the sagittal view as being located on a line along the mesial aspect of the maxillary first molar root 14.66 mm superior to its occlusal surface
  60. 60.    If linear protraction of the osteotomised dentomaxillary complex is desired parallel to the functional occlusal plane, the line of action of the distraction forces would pass through the center of mass and be parallel to the functional occlusal plane. On the other hand,if downward and forward rotation is desired then the line of action of applied forces would be placed superior to center of mass and parallel to functional occlusion. The position of traction hooks and the direction of traction wires determines the point of application and line of action of applied forces relative to its center of mass.
  61. 61. MIDFACE DISTRACTION     In 1993 ,at Scottish Rite Chidren’s medical Centre,Steven Cohen et al performed a buried midface distraction in a child with anophthalmia and left craniofacial microsomia.Cephalograms and three dimensional computed tomographic scans,showed excellent results. Later in 1994 and early 1995 Cohen et al performed buried modified Le Fort III midface advancement in two children who had cleft lip and palate with midface hypoplasia and Class III malocclusion. In each case transverse maxillary expansion was performed simultaneously with sagittal distraction and in one case serial distractors were used to provide both vertical and horizontal distraction vectors. This represented the first case of multidirectional midface distraction.In 1996,using specially designed buried midface distraction devices Cohen et al performed a subtotal cranial vault reshaping and monobloc facial advancement in a child who had Pfieffer’s syndrome and corneal exposure.
  62. 62.       In 1997,in the journal of Craniofacial Surgery, Polley and Figueroa discussed the management of severe maxillary deficiency in childhood and adolescence,performing distraction osteogenesis with an external adjustable,Rigid Distraction Device. Their results in patients with cleft lip and palate and severe midface retrusion were impressive. The Modular Internal Distraction (MID)system allows the surgeon to fabricate custom internal distraction devices for virtually any region of the craniofacial skeleton. The first generation system contains expansion screws capable of 15 mm to 30 mm of distraction. Depending on the distraction site and osteotomy, any configuration of titanium plates can be attached to the distraction screw to permit uniplanar and possibly biplanar internal distraction. A flexible activation cable is brought out through a distant, inconspicuous stab wound in the hair behind the ear.
  63. 63. CLINICAL INDICATIONS      When patients with Cleft lip and palate and severe midface retrusion are present at the age of 6 years, distraction osteogenesis can be used in combination with early rapid palatal expansion to correct both sagittal and transverse maxillary deficiencies. Because internal devices require a second operation for removal, the treatment plan of Cohen et al in chidren with cleft lip and palate has centered around the timing of alveolar bone grafting. Simultaneous with distraction,a palatal expander is placed and, if possible, orthodontic appliances are applied. A high Le Fort I osteotomy is performed and distraction devices are placed intraorally. The distraction device is placed completely within the maxilla through an upper buccal sulcus incision
  64. 64.   If there is insufficient room for fixation of the posterior plate,a temporal incision can be made and the plate anchored to the temporal bone. The distraction vector can be varied from horizontal to oblique to provide both vertical and horizontal distraction vectors. Cohen et al prefers to use orthodontic appliances with surgical hooks,as well as hooks attached to the molar bands,for application of both dental elastics and reverse headgear in the event that      Distraction with internal devices cannot be technically performed After distraction,additional stabilization and maintainance are required. The newly formed bone undergoes a consolidation period of 2 to 3 months. Because the devices are internal and the activation cables are largely hidden in the hair,patients are quite comfortable during the consolidation phase. At the time of bone removal,alveolar bone grafting is performed with iliac bone
  65. 65.       Conventional monobloc osteotomies produce an immediate retrofrontal dead space,which fills with blood and is prone to infection. When distraction osteogenesis is used for monobloc osteotomy,the frontofacial segment is mobilized,but not advanced. Beginning on days 5 through 7 ,distraction devices are activated 1 mm per day. This latency period seems to permit remucosalisation of the nasofrontal area. Also, gradual distraction is not associated with the development of an immediate retrofrontal dead space,which is prone to infection. Other possible indications for midface distraction include     Correction of maxillary canting in hemifacial microsomia and other asymmetry malformations Apnea with associated midface retrusion Treacher Collins syndrome for zygomatic advancement Midface retrusion of any cause,depending on severity.
  66. 66. TIMING OF SURGERY      Addition of distraction osteogenesis to the surgical armamentarium has altered timings of surgical interventions. In children with syndromic craniosynostosis and severe midface retrusion,monobloc osteotomies can be performed safely at younger than 1 year of age. Overcorrection of the deformity may also eliminate the need for some future surgeries.In chidren age 4 to 7 years undergoing monobloc or Le Fort III subcranial osteotomy, operative morbidity is also reduced. According to Cohen et al distraction should be performed at 6 years of age to correct severe midface retrusion in patients with cleft lip and palate. Distraction can be used in older children with cleft lip and palate, midface retrusion and severe Class III dentoskeletal relations.
  67. 67. TREATMENT PLANNING      A surgical and orthodontic work up is necessary to develop the appropriate treatment plan. Clinical photographs,computed tomographic scans,clinical orthodontic and surgical evaluation and orthodontic records including cephalometric interpretation and mounted casts are obtained. Speech evaluation is obtained preoperatively and after removal of the distraction device because patients undergoing midface distraction are at risk for developing velopharyngeal insufficiency. Special consideration is given to the dentition and the ability to place orthodontic appliance. In children undergoing midface distraction, ideally an acrylic bite block attached to the mandible can be used to simulate the increased vertical dimensions of the maxilla that will occur with distraction
  68. 68.       By repositioning mandible in this fashion the muscles of mastication are retrained at the anticipated new vertical maxillary dimension. Orthodontic appliances are attached to the teeth.Surgical hooks are incorporated on at least the anterior dentition. In addition, hooks are placed on the molar bands for application of reverse headgear, if internal distraction cannot be performed or for retention at the conclusion of distraction. When orthodontic appliances cannot be placed,arch bars are ligated to the dentition with the assistance of piriform suspension and circummandibular wires. In patients who develop an open bite deformity, dental elastics can be placed at the conclusion of distraction, but before consolidation, to manipulate the callus and close the anterior open bite. Patients in whom dental midline rotates during distraction can also be corrected simultaneously with elastics before consolidation
  69. 69. SURGICAL TECHNIQUES LE FORT I DISTRACTION  The LeFort I osteotomy is performed in a stair step fashion to provide adequate posterior bone for attachment of the distraction device.  Because the MID system provides flexibility, the types of titanium plates selected for posterior and anterior distraction vary.
  70. 70.      To maintain a direct sagittal distraction vector, the anterior plate is generally bent with a step. In patients with insufficient maxillary bone, it may be necessary to attach the posterior plate to the temporal bone. This is done by simply making a temporal incision and retrieving the plate from below. Cohen et al believes it is necessary to make a complete osteotomy and ,therefore the osteotomy is kept just below the level of the inferior orbital foramen and nerve. In this manner the erupting dentition is also avoided.
  71. 71.   LE FORT III DISTRACTION A standard Le Fort III osteotomy is performed. In younger children who are at risk for fracturing the zygomatic-maxillary suture region, the anterior plate is configurated and rigidly fixed after the osteotomy, but before downfracture. In this fashion, inadvertent fracture across the zygomaticmaxillary suture is prevented.
  72. 72.       The anterior plate wraps around the malar eminence and extends along the inferior orbital rim. The anterior plate also is attached along the lateral orbital rim and superiorly. The posterior plate is stabilized to the temporal bone underneath the temporal muscle A 30 mm distraction frame is chosen and attached to the anterior and posterior plates. A flexible cable is brought through a stab wound posterior to the coronal incision. In Le Fort III osteotomy ,typically 2 mm to 4 mm of distraction is performed in the operating room.
  73. 73.      Distraction is then begun on the fifth postoperative day at a rate of 1 mm per day. Once the appropriate porion to orbitale distance has been reached or mild enophthalmos has been produced with overcorrection of the malocclusion, distraction is stopped and the distraction gap allowed to consolidate over a period of 2 months. Lateral and posteroanterior cephalograms are taken to ensure that the distraction device has opened symmetrically. At the conclusion of distraction dental elastics are used to correct occlusal abnormalities. After the consolidation period, the devices are removed.
  74. 74. MONOBLOC DISTRACTION (FRONTO-ORBITAL-FACIAL ADVANCEMENT)      Monobloc distraction is applicable in children aged younger than 1 year ,but can be used in any age group. A bilateral coronal incision with elevation of the anterior scalp flap was performed. Dissection was extended in a subperiosteal plane over the midforehead region and in a superior,lateral and medial direction around the orbits, and continued deep to the superficial layer of the deep temporal fascia, exposing the zygomatic arches laterally and the anterior maxilla. Through a subciliary incision of the lower lids,exposure was obtained of the inferior orbital rim and the medial orbital wall. Subperosteal mobilization of the orbital contents was completed.
  75. 75.   A bifrontal craniotomy was performed with seperation of the cranial bones from the dura;the zygomatic arches were divided and a circular orbitotomy ensued. Separation of the bony nasal septum from the anterior cranial base,seperation of the pterygomaxillary junction and midface advancement were performed.
  76. 76.      The main advantage of midface distraction appears to be the reduction of infectious complications. Children tolerate distraction extremely well and typically require postoperative ventilation for only one day. Distraction is begun on the fifth postoperative day. In contrast to Le Fort III distraction technique, no advancement is performed in the operating room After the nasofrontal region has been allowed to remucosalise, distraction is initiated at 1 mm per day. The cranial defect produced by the advancing monobloc segment can be palpated to determine when consolidation has been completed
  77. 77. MANDIBULAR DISTRACTION   Mandibular distraction is a safe and effective surgical technique. For patients with Treacher Collins, Pierre Robin, Nager and Craniofacial microsomia syndromes undergoing surgical reconstruction of the hypoplastic mandible by distraction, the length of hospitalization and operating time has been drastically reduced. It has obviated the need for autogenous bone grafting and because of the expansion of the associated soft tissues, there is a resulting multidirectional expansion of the skeletal and soft tissue envelope.
  78. 78.     Patients with mandibular growth disturbances can present at any age. If the patient is under 2 years of age, mandibular distraction is not usually performed . Soft tissue treatments such as cleft closure or preauricular skin tag removal ,are initiated. Cranial vault remodeling procedures are also performed at this age. Mandibular surgery is avoided for several reasons   It is difficult to identify tooth buds at this age ,therefore permanent dental injury is a likely occurance. The bone stock is soft,making satisfactory fixation of the distraction apparatus difficult and loss of device(because of pin loosening ) a strong possibility. Distraction at this age can be a daunting experience for the patient and the parents.
  79. 79.     From the age of 2 to 6 years,mandibular distraction osteogenesis can be considered in severe conditions with associated sleep apnea or tracheostomy. However if distraction occurs at this age interval,it is likely that a secondary distraction will be required after post pubertal facial growth, because it is unlikely that the mandibular development will keep up with the growth of the remainder of the facial skeleton. Mandibular distraction during the teenaged years should be post poned until the patient has reached skeletal maturity. In girls, this typically occurs around 15 years of age and in boys around the age of 17 years.
  80. 80. Indications for surgery in the teen years include      Residual postsurgical relapse or abnormal growth unsatisfactory bone contour Malocclusion In patients with minimal mandibular deformities, classic orthognathic procedures are indicated. Mandibular distraction should be considered in patients with moderate to severe skeletal deficiency or bilateral disease in whom pressure from the soft tissues would significantly increase the risk for post operative graft resorption or relapse of bony fixation.
  81. 81.     PREOPERATIVE CLINICAL EVALUATION The patient should be examined with the head in an upright position and submental vertex position. In patients with unilateral craniofacial microsomia,the position of the oral commissure should be documented,and the distance between it and the external auditory canal recorded. The position and contour of the chin ,inferior border,and angle of the mandible are recorded. In intraoral examination the occlusal plane or transverse cant should be related to the transorbital plane.
  82. 82.    The functional clinical examination should include documentation of mandibular excursions, including maximum interincisal opening, because a transient limitation to opening can occur at the end of distraction. It is, therefore, important to record the original interincisal opening for use as an objective goal during postdistraction physical therapy. The function of TMJ is documented,and the motor and sensory nerve functions are recorded
  83. 83. DIAGNOSTIC RECORDS     Cranial pathology and asymmetry should be documented by standard medical photographs.Lateral and posteroanterior cephalograms with the head in the correct vertical or midsagittal plane is obtained. The ear rod is positioned in the ear canal on the unaffected side but is placed on the calvaria on the affected side. Midsagittal plane is perrendicular to the floor and the lateral borders of the orbital rims are symmetrically positioned in relation to the lateral borders of the calvarium. This precise head positioning is duplicated in all subsequent recordings.In addition a three diamentional computed tomographic scan, panoramic roentgenogram and dental study models are made.
  84. 84. TECHNIQUE       Patients who require unidirectional lenghthening and have adequate mandibular bone stock are candidates for intraoral distraction. Patients in whom mandibular deficiency is more severe and who also require distraction in the vertical and horizontal dimensions are best treated with an extraoral device. In addition,patients who have previous external scars from other procedures are treated with an extraoral device.The intraoral mucosal incision along the oblique line of the ramus is used for placement of both intra oral and extra oral devices. Currently, subperiosteal dissection is used to elevate the entire lateral periosteal surface with a sharp ended elevator. After the region of the osteotomy is exposed, the reciprocating saw is used to create lateral,anterior and posterior corticotomies. Before converting the corticotomies into an osteotomy,the pins are placed.
  85. 85.       If the intraoral device is used,a single percutaneous stab incision is made for the placement of the screwdriver. For the extraoral device,a two-holed trocar is used for percutaneous placement of the posterior pins. The second anterior pair of pins is placed so that the skin between the two pin sites is compressed,thereby reducing the amount of tension on the wound and the length of the scar. The device is attached to the pins. A 3 mm osteotome completes the medial wall osteotomy , liberating the mandibular segments for distraction. The wounds are closed in layers with absorbable sutures.
  86. 86.        A careful cleaning regimen is followed in which the pin tracks are cleaned four times a day,and as needed,of any blood or serous discharge. After a latency period of 5 to 7 days ,distraction commences at a rate of 0.5 mm twice a day. This rate is continued until the mandibular length is overcorrected by several millimeters. Orthodontic intermaxillary elastics may be used to mold the regenerating new bone and optimize the occlusion. The device is left in place to serve as an external fixator for 8 or more weeks, until there is radiographic evidence of mineralisation.This stage is known as the consolidation phase. In patients with unilateral craniofacial microsomia undergoing distraction,it is important that a dental impression be taken and a bite block placed in the surgically created posterior open bite when the device is removed. This will allow the orthodontist to level the maxillary occlusal plane by allowing for eruption of the ipsilateral maxillary dento alveolar complex.
  87. 87.   VECTORS OF DISTRACTION The biological and mechanical forces that shape the regenerate(newly formed bone)during the active period of distraction osteogenesis are key elements in determining appliance position. The desired mandibular change in shape and function can be achieved by selecting and controlling the force vectors that operate during active distraction. The biologic forces arise from the surrounding neuromuscular envelope.
  88. 88.   The mechanical forces originate from activation of the distraction devices, their specific orientation to skeletal anatomy, the application of intermaxillary elastics during the active phase of distraction ,and the intercuspation of the dentition. Device placement can be vertical, horizontal or oblique described in relation to the long axis of the mandibular body.
  89. 89. VERTICAL DEVICE PLACEMENT   Vertical device placement results in an increase in the vertical dimension of the mandibular ramus. During activation, a change occurs in appliance orientation caused by the nonlinear molding effect of the neuromusculature on the regenerate as it is formed.
  90. 90.     The mandible autorotates in a counterclockwise direction and the lower incisors take a more advanced position. A posterior openbite may occur on the side that has undergone vertical distraction in the ramus. Unilateral vertical ramal lenghthening is usually associated with transverse correction of chin position and the cant correction of mandibular occlusal plane. Young patients with greater future growth potential requires a greater amount of overcorrection than is required for older patients.
  91. 91. HORIZONTAL DEVICE PLACEMENT     This is the most efficient approach for achieving sagittal projection of the mandibular body and symphysis. There is a tendency in horizontal distraction of the mandibular body to rotate in a clockwise direction resulting in an open bite due to the suprahyoid musculature in balance with the muscles of mastication and the distraction device itself. The gonial angle has been observed to open between the ramus and the body when activating the device. However,there was a return of the predistraction gonial angle with subsequent mandibular growth. Overcorrection in young, growing, severely retrognathic patient is needed to compensate for reduced growth potential.
  92. 92. OBLIQUE DEVICE PLACEMENT   Results in an increase in both vertical and horizontal dimensions of the ramus and body. Overjet and both ramal and body size deficiency may be addressed by oblique device placement.
  93. 93. ROLE OF FUNCTIONAL MATRIX      This also appears to influence the clinical outcome of Distraction Osteogenesis. Multidimensional changes in mandibular skeletal form is achieved with a unidirectional distraction device. Masticatory muscles work on the bony regenerate and thus significantly modify changes in mandibular form. Bony remodeling occurs predominantly during and after distraction while the patient is functioning with deglutition, mastication and speech. Gradual distraction or lenghthening,not only of the skeleton,but also the muscular and cutaneous tissues, probably accounts for the absence of relapse.
  94. 94.   According to Cope and Samchukov The distraction gap was occupied by fibrous tissue at the second week of consolidation period, bone trabeculae formation began from the osteotomised end by the fourth week after osteotomy, and the calcified matrix was gradually modeled and finally replaced by trabecular bone by the eighth week.
  95. 95.   Nakamoto et al in AJO 2002 in a study on dogs verified the influence of tooth movement into mature well organized and mineralized regenerate bone and into immature,fibrous and less mineralized bone. They performed a bilateral mandibular distraction with an intraoral bone borne distractor and moved the teeth into the regenerate bone after 2 weeks in one group and after 12 weeks in another
  96. 96.   Nakamoto et al showed that the rate of movement was much faster when the teeth were moved into immature bone regenerates than into mature ones. They also showed that application of heavy forces and early orthodontic tooth movement are not recommended when teeth are moved through bone regenerate to avoid tipping and severe root resorption.
  97. 97. MID SYMPHYSEAL DISTRACTION  Guerrero and Contasti pioneered the use of mandibular midsymphyseal distraction osteogenesis, calling it ”surgical rapid mandibular expansion”. The protocol consisted of vertical osteotomy in the symphyseal area and a tooth borne appliance to achieve the mandibular expansion, similar to the rapid maxillary expansion technique.
  98. 98.    Marinho Del Santo et al in AJO 2002 showed adequate mandibular basal bone expansion may be achieved with a combination of midsymphyseal distraction osteogenesis, a tooth borne expander and orthodontic appliance. Distraction appliance was constructed on Facebow mounted models on a semiadjustable articulator so that acrylic covering the lower occlusal surfaces formed a flat plane to articulate against upper teeth. Acrylic portion of the device covered the canine and posterior teeth .The incisors were not incorporated in the splint.The lingual and occlusal surfaces of the posterior mandibular teeth were etched and an acrylic resin was used for bonding the distraction appliance.
  99. 99.       An anterior horizontal incision was made in the mandibular vestibule from canine to canine and a sub periosteal dissection exposed the labial and inferior aspect of the symphysis. The soft tissue above the incision was carefully undermined between the central incisors to provide access for superior portion of the osteotomy. A (no.701) tapered fissure bur was used to create a corticotomy from just below the crestal ridge, extending inferiorly to the inferior border of the mandible. A modified extra thin reciprocating saw blade was used to complete the vertical osteotomy beginning at the inferior border and extending upward between the root tipsof central incisors. A periosteal elevator was inserted in the osteotomy site and gently torqued to complete the osteotomy up through the crestal bone. Incision was closed in 2 layers to complete the procedure.
  100. 100.          Immediately after surgery , expansion appliance was activated 2 mm . One week after surgery the expansion appliance was activated at a rate of 1 mm per day for 7 days. The appliance was maintained for an additional 3 months during the consolidation period and then it was removed. Immediately after the distraction appliance was removed, fixed orthodontic appliance was placed. By a total of 2 years treatment 6 mm of transverse arch length deficiency and a bilateral buccal cross bite was corrected. Some proclination of the mandibular incisors was observed but the arch form was significantly improved. Expansion by distraction osteogenesis with a tooth borne device can result in greater expansion of the teeth as compared with the basal bone. This can incorporate some transverse dental relapse potential, negating some of the expansion achieved. Bone borne device may minimize this effect.
  101. 101.     Transverse mandibular deficiency may manifest itself in a unilateral or bilateral buccal cross bite(Brodie bite) occurring in 1 to 1.5 % of population. John.W.King in AJO 2004 used distraction osteogenesis to correct the mandibular transverse problem. A midsymphyseal osteotomy was performed followed by gradual stretching of the callus in the treatment of a true unilateral Brodie bite of the left side.Preadjusted appliance(.018x.022 in)were placed in the maxillary arch for leveling and alignment. Three months later a bite plate was constructed and the mandibular appliance were also placed. Brackets on the mandibular central incisors were angulated to create a root divergence
  102. 102.      This reduced the chances of root and periodontal ligament damage during osteotomy. Central and lateral incisors and canine on either side were tied together with ligature and an .016 x .022 in stainless steel wire was placed before osteotomy. Archwire was cut at osteotomy site at initiation of distraction providing segmental anchorage during distraction phase. A full coverage maxillary splint stabilized the occlusion on the right side and flat occlusal plane allowed for transverse widening on the left. Before distraction surgical hooks were placed in both arches between the brackets on the right side
  103. 103.    A hybrid distractor ( bone borne and tooth borne) was constructed before midsymphyseal osteotomy. After 7 days latency period with antibiotics and mouth rinses,distraction was initiated by 0.5 mm turns twice a day till ideal canine transverse relation was achieved. Total distraction was 6 mm.
  104. 104.        Maxillary splint and right side intermaxillary elastics was worn during distraction. A denture tooth was placed in the distracted site. Surgical hooks were added on the left side and splint was discontinued. Bilateral intermaxillary elastics were worn for an additional week. Consolidation period was for 10 weeks after which distractor was removed. Bony bridge was observed radiographically before removal. After consolidation period, roots were realigned and power chain used to close distraction space. Nearly parallel distraction of the skeletal and dental componenets was observed from dental casts and cephalometric radiographs. A post distraction skeletal relapse of only 0.21 mm was observed after 1.5 years. Immediate post distraction TMJ symptoms of clicking disappeared when distractor was removed and was distraction. present a year after
  105. 105.    Reha Kisnisci et al in AJO 99 reported distraction osteogenesis of the midsymphysis in patient with Silver Russell Syndrome. Low birth weight and short stature are consistent features of the syndrome. The syndrome may be manifested as facial disproportion, limb asymmetry, normal or slightly smaller calvarium, triangular facies, a small and pointed chin with a hypoplastic mandible and high arched palate. Microdontia, crowding, congenital absence of lateral incisors ,second premolar and dental abnormalities have also been reported.
  106. 106.    In the reported case,the patient had a transverse discrepancy of the mandible in relation to maxilla and severe crowding. An intraoral, tooth-borne mandibular expansion appliance was used to widen the mandible in concert with sagittal ramus osteotomies to lenghthen the mandible. The treatment created significantly increased arch length in the mandible to facilitate patients orthodontic treatment.
  107. 107.    Samchukov et al presented a computer model of a mandible undergoing widening and lenghthening with distractors in which it was assumed that each half of the mandible rotated about the centers of each condyle during symphyseal distraction ,and that the symphyseal distractor was not rigidly fixed to the bone. They suggested that hinged devices or condylotomies should be considered to compensate for the assumed condylar rotation. Histologic changes in the TMJ were minimal.
  108. 108.  Stanley Braun et al in AJO 2002 in a study on mandibular symphyseal distraction with tooth borne distractors (Hyrax type) and bone borne distractors (Dyna form appliance) showed that each mandibular half was displaced linearly irrespective of the type of distractor used.
  109. 109.       In tooth borne distractors,there was an extremely small initial bucally directed displacement of the teeth in the periodontal ligament spaces when the distractors were activated. After this the teeth and the mandible acted as a unit to reach the targeted distraction dimension. There was no opportunity for a cellular response in the periodontal ligament within this time increment. Thus if the condyles are to be displaced angularly,the ramus and the posterior portion of the body of the mandible have to undergo complex compound bending. The muscular and soft tissue attachments to the mandible cannot bend the mandible in this manner. They conclude that the TMJ appears to accommodate these displacements because symptoms were not introduced or if present before treatment,symphyseal distraction did not exacerbate them.
  110. 110. ALVEOLAR DISTRACTION      Vertical distraction osteogenesis as described by Chin and Toth enables partial,continuous lifting of the alveolar process to promote osteogenesis between the segments. Alveolar process augmentation might be indicated for treating atrophy, trauma induced defects or ankylosed teeth. Advantages of vertical callus distraction over conventional surgical technique are that no bone is removed and that the blood supply is maintained via the lingual periosteum and the mucosa. Dental vitality is preserved. Hard and soft tissues are gradually expanded simultaneously over a period of several days and this normally results in a clear cut gain in alveolar mucosa. Drawbacks are that the distractor projects temporarily into the vestibule and the need for increased oral hygiene.
  111. 111.    A clinical study by Krafft showed that in alveolar crest distraction especially in maxilla,the palatal mucosa followed the distraction to only a minor extent, thus producing a deviation of distraction axis to the palatal. The fibrous palatal mucosa exert an influence on the direction of distraction,which vary widely from patient to patient. Intraorally applied distractor has only a unidirectional impact ,and lenghthening occurs only in a linear direction, with no possibility of 3 dimensional alignment of the osteotomised segment.
  112. 112.   Kinzinger et al in AJO 2003 used a ‘floating bone effect’ after vertical callus distraction of an ankylosed central incisor. After segmental osteotomy, a single tooth distractor was placed surgically.
  113. 113.     After a 7 day latency period, distraction was applied to change vertical incisor position, with activation during the 8 day distraction phase at a rate of 2 activations/day. Total distraction distance achieved was 4.5 mm with a marked palatal deviation clinically. The consolidation phase was reduced. Seventeen days later, before final consolidation of the newly formed bone, the distractor is removed. The tooth supporting bone segment and callus could be visualized from the vestibular aspect after removing the distractor.
  114. 114.   Four days postoperatively, a bracket was bonded onto the tooth and in addition to a passive bypass archwire, a superelastic 0.016x0.022 inch coppernickel-titanium segmented archwire was placed. After 18 days, 3 dimensional positioning of the tooth supporting segment had been achieved and the anterior region was sufficiently leveled to allow a continuous 0.016x0.022 inch stainless steel archwire for stabilization.
  115. 115.   Hanson and Melugin regard immobilization during the consolidation stage is fundamental. Here the ‘floating bone effect’ was confined to a small area ,the mobilization period was brief and the 3 dimensional alignment of tooth supporting segment was completed quickly. In general,the vertical callus distraction of an ankylosed tooth should not be attempted until growth is over.
  116. 116. CANINE DISTRACTION    In 1998, Liou and Huang demonstrated rapid distraction of 26 canine teeth in humans using distraction of periodontal ligament. They achieved an average of 6.5 mm distraction of the canines and called this technique “Dental distraction”. Seher Sayin et al in Angle 2004 did canine distraction with a tooth borne , semirigid device. The device consisted of an anterior section, a posterior section, a screw and a hex wrench to advance the screw
  117. 117.   The posterior section included a round sliding rod(1.5 mm), a retention arm for the first molar tube, a grooved screw socket. The anterior section included a retention arm for canine tube and two non grooved slots for sliding rod and screw.
  118. 118.       Vertical osteotomies were carried out after premolar extraction at the buccal and lingual sites of interseptal bone adjacent to canine tooth. The vertical osteotomies were connected with an oblique osteotomy extending towards the base of the interseptal bone to weaken the resistance. Distractors were cemented in place after surgery. An advancement of 0.25 mm was performed 3 times a day until each canine tooth was distracted into desired position. Class I canine relation was attained after an average of 3 weeks with controlled distal tipping. After a 2 week consolidation period ,the distractors were removed and edgewise mechanism started. Currently, the canine distractors are bulky, unidirectional and unavailable on market.
  119. 119. TRANSPORT DISTRACTION OSTEOGENESIS   Transport distraction osteogenesis is the technique of regenerating bone and soft tissue in a discontinuity defect. An osteotomy is made 1.5 cm from the end of the distal stump of bone adjacent to the discontinuity defect creating a transport disc
  120. 120.    Using a distraction device,the transport disc is advanced through the soft tissue discontinuity defect, creating new bone within the distraction gap, as the leading edge becomes enveloped by a fibrocartilagenous cap. This cap is then surgically removed at the end of the distraction process to establish osseous continuity. All soft tissues are also recreated including a buccal and lingual sulcus, as well as attached and unattached gingival.
  121. 121.   Transport distraction technique have been used to recreate the mandibular articulation in the form of a neocondyle. The transport disc is created from the ramus by making a reverse-L osteotomy extending from the sigmoid notch to 1 cm above the inferior border, preserving the angle of mandible
  122. 122.     This transport disc is now advanced superiorly 0.5 mm twice a day,towards the glenoid fossa using an internal or external distraction device. The segment is then held in neutral fixation until a cortical outline is seen on plain radiographs, and the distractor is then removed. Unlike mandibular reconstruction, the fibrocartilagenous cap of the leading edge of the transport disc is not removed.Rather,it acts as the new pseudo-disc. This technique has been applied for the correction of ramal height secondary to degenerative joint disease, condylar resorption after orthognathic surgery, and bony ankylosis.
  123. 123.       For cases of bony ankylosis,a gap arthroplasty is performed without the placement of intervening tissue, boneor synthetic material. A reverse-L osteotomy is performed. The segment is advanced superiorly until contact is made with the glenoid fossa. Patients are again encouraged to open and close widely to allow for the effect of functional remodeling and the formation of a neocondyle. A new cortical surface is generated with the intervening tissue acting as a pseudodisc. The patient then returns to a normal range of motion and is able to masticate regular diet.
  124. 124.    For the success of distraction osteogenesis for condylar reconstruction, it is incumbent on the patient to actively participate in physical therapy because the secondary gains at the level of the mandibular condyle occur primarily as a consequence of the patients opening wide and maintaining a soft diet, especially during the period of neutral fixation when functional remodeling occurs. Physical therapy should be continued for several months post distraction because the process of functional remodeling will continue after the distraction device is removed. Patients are encouraged to wear a flat plane occlusal splint at night while sleeping for a minimum of 6 months post distraction
  125. 125. ORTHODONTIC MANAGEMENT OF THE PATIENT  The role of orthodontics in treatment using distraction osteogenesis falls into three temporal phases: Predistraction treatment planning and orthodontic preparation  Orthodontic/orthopedic therapy during distraction and consolidation  Postconsolidation orthodontic/orthopedic management 
  126. 126. PRESURGICAL PREPARATION     Orthodontic appliances are selected and treatment is initiated that is consistent with the overall goals of the distraction treatment plan. Dental malrelationships must be eliminated that would mechanically interfere with the movement of the toothbearing segment during the gradual distraction (eg; retroclined or extruded maxillary incisors) The patients with severe mandibular retrognathia may have a transverse maxillary deficiency. It is appropriate to expand the maxilla either before or during distraction to accommodate the width of the advanced mandible
  127. 127.   Another component is the fabrication and use of distraction stabilization appliances. These interarch appliances are routinely inserted before surgery and facilitate vector control during distraction by maintaining mediolateral dental interarch relationships
  128. 128.      By maintaining transverse relationship of the maxillary to mandibular dentition, the tooth bearing segment cannot be displaced laterally; hence all the length introduced by distraction is maintained in a vertical and anterior direction. This is used for patient population - who do not require specific tooth movement before distraction ;are not in full orthodontic bands and brackets ; are very young ; have limited teeth present or may require maximum segment anchorage. Appliance consists of a banded maxillary expansion appliance and a mandibular lingual holding arch attached to two bands on each side. All eight bands on the appliance have symmetrically placed buccal and lingual ball hooks. The appliances are placed before distraction and provide multiple opportunities for the use of inter arch elastics to control mandibular position during distraction, consolidation and postconsolidation phases.
  129. 129. DURING DISTRACTION AND CONSOLIDATION       Active orthodontics/orthopedics may continue throughout the distraction and consolidation phases. This include the use of bands,brackets,distraction stabilization appliances,elastics,headgear ,acrylic guidance appliances,maxillary expansion appliancesfunctional appliance etc. This improves the quality of the surgical/orthodontic result by directing the tooth bearing segment towards its planned post distraction position. Neuromusculature affects the path of the tooth bearing segment. Patient will posture their mandible anteriorly or laterally to pick up occlusal contacts that have been lost during distraction to aid them in masticatory function. In addition,orofacial musculature and soft tissue envelope exert forces on the tooth bearing segment that may alter the direction in which this segment moves.
  130. 130.      The orthodontist must recognize the presence of these influences and compensate for them with orthodontic or orthopedic measures. External forces consisting of angular, transverse or linear activation of the distraction device affects the position of the tooth bearing segment. The adjustment capabilities of the multi directional distraction device allow for the distraction vector to be changed in all three planes When affecting the position of the tooth bearing segment,the clinician may also be affecting a change in the proximal segment position. This may create unfavourable positional changes of the condyle/ramus segment that must be monitored and controlled
  131. 131.   Interarch elastic traction applied during distraction has been shown to influence the vectors of distraction in the vertical, anteroposterior and transverse directions. The most important use of elastic traction during the active phase is to control laterognathism.
  132. 132.  Distraction osteogenesis results in a unilateral posterior open bite as the corrected mandibular plane diverges from the noncorrected (canted) maxillary occlusal plane.  The patients inability to find suitable masticatory surfaces also increases.  This results in a functional shifting of the mandible manifested by a dental midline shift away from the distracted side,a posterior buccal crossbite on the distracted side and a crossbite on the unaffected side.This laterognathism often masks the vertical lenghthening of the ramus and prevents formation of the desired unilateral open bite.
  133. 133. POST CONSOLIDATION MANAGEMENT       After consolidation,the distraction device is removed.Post distraction orthodontics/orthopedics is instituted at this time to accomplish the original treatment goals. The postdistraction orthodontic needs vary depending on whether the mandibular distraction was unilateral or bilateral. In the growing bilateral distraction patients,an anterior crossbite may have been a temporary treatment objective in anticipation of future deficient mandibular growth. Additional treatment objectives would include eruption guidance and alignment of the dentition over alveolar bone. Orthodontic treatment for growing children may need to take into consideration future distraction or orthognathic surgery. In nongrowing bilateral distraction patients,orthodontic finishing is completed at this time.
  134. 134.   In unilateral distraction the crossbite resulting from mandibular shift across the midsagittal plane may be corrected by a combination of transpalatal arches, lingual arches, intermaxillary cross elastics and a palatal expansion device. The open bite is at first maintained by the placement of a unilateral posterior bite plate.
  135. 135.    Over several months ,the posterior superior surface of the appliance is serially reduced under individual teeth to achieve eruption of the maxillary teeth and alveolar process down to the level mandibular occlusal plane. Occlusal plane management can also be achieved using a functional appliance with lingual shields to provide lateral control of mandibular position. A biteplane is included that is adjusted one tooth at a time for passive eruption of the maxillary teeth.
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