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Distraction Osteogenesis
Dr. Waqar Jeelani
Resident - Orthodontics
1
Distraction Osteogenesis
“A biological process of new bone formation between
the surfaces of osteotomized bone segments that are
separated gradually by incremental traction”
Distraction Histogenesis :
– Adaptive regenerative changes in surrounding soft
tissues
Historical Overview
Alessandro Codiwilla (1905)
– First report of surgical limb lengthening
– Oblique osteotomy and external traction pins
– Complications: infections, overstretching, poor blood
supply, and inadequate fixation
Historical Overview
G.A. Ilizarov (1950’s)
– Lengthening limbs through gradual distraction of
fracture callus
– Rhythm and rate of distraction
– Minimal complications
Historical Overview
McCarthy (1992)
– DO to lengthen congenitally hypoplastic mandible
Historical Overview
• Rachmiel et al (1993) and Blocks et al (1995)
– Maxillary distraction
• Polley et al (1995)
– Midface distraction with externally fixed cranial halo frame
Historical Overview
Chin and Toth (1996)
• Mandibular alveolar distraction osteogenesis to increase the
height of the alveolus
Chin M, Toth BA. Distraction osteogenesis in maxillofacial surgery using internal devices:
review of five cases. J Oral Maxillofac Surg. 1996 Jan;54(1):45-53.
Distraction Techniques
Physeal
Distraction
• Distraction of
growth plate
• Endochondral
bones
Callotasis
• Distraction of
healing callus
• Membranous
bones
Types of Distraction Osteogenesis
• Defined on the number of foci at which osteogenesis
occurs:
– Monofocal elongation DO
– Bifocal distraction
– Trifocal distraction
9
Biology of Distraction
1. Osteotomy/Corticotomy phase
2. Latency phase
3. Distraction phase
4. Consolidation phase
5. Remodeling phase
Osteotomy Phase
• Divides the bone into two segments
• Triggers process of bone repair
– Angiogenesis
– Fibrogenesis
– Osteogenesis
Latency Phase
• Period from bone division to onset of distraction
• Inflammation and soft callus formation of the fractured bone
• Soft callus formation begins 3-7 days and lasts 2-3 weeks
• Latency period = 5-7 days
Distraction Phase
• Characterized by the application of traction forces to
osteotomized segments
• Rate : 1 mm/day
• Rhythm : 0.25 mm every 6 hours
0.5 mm twice a day
• Duration : 1-3 weeks
Consolidation Phase
Cessation of traction forces to removal of distractor
• Newly formed bone mineralizes and increases in bone density
and strength
Duration: 3- 4 months
Remodeling Phase
• Removal of distractor to application of functional
loading
• Formation of lamellar bone
Indications
• Congenital retrognathic syndromes
• Severe mandibular deficiency > 10-15 mm
• A short mandibular ramus
• TMJ degenerative disease
• Obstructive sleep apnea
• A narrow, V-shape mandible
• Maxillary deficiency in CLP or Craniosynostosis
• Post-traumatic growth disturbance
• Atrophy of edentulous segments
• Oncologic mandibular osseous defects
Advantages
• Safe and effective surgical technique can be
performed on outpatient basis
• Can be done in children as young as 2 years
• Distraction histogensis results in growth of
associated functional matrix
• Long term improvement in condylar morphology
• Greater degree of correction can be achieved
• Grafts are not required
• Minimal skeletal relapse
17
Disdvantages
• Requires second surgery to remove distractor
appliances
• Risk of infection at surgical site is greater
• Pain and discomfort during distraction
• Required meticulous planning
• Results are not as precise as orthognathic surgery
18
Treatment Planning
• Extraoral Examination
– Forehead, orbit, zygoma, external ear
– Oral commissure, chin, mandibular angles
• Intraoral Examination
– Occlusion
– Occlusal plane
• Function
– Maximum interincisal opening
– Mandibular deviation or deflection
– TMJ evaluation
– Sensory nerve function
19
Treatment Planning
• Diagnostic Records
– Standard extraoral and intraoral photographs
– Dental models articulated on a semi-adjustable
articulator
– Lateral and PA cephalograms
– OPG
– CBCT
– CT Scan
– Stereolithographic models
20
Factors Affecting DO
Local Factors Systemic Factors Distraction Factors
Osteoprogenitor Supply Age Rate of Distraction
Blood Supply Metabolic Disorders Frequency of
Distraction
Infection Vitamin D Deficiency Latency Period
Soft Tissue Scarring Connective Tissue
Disease
Rigidity of Fixation
Bone Stock Steroid Therapy Consolidation Period
Prior Radiation Therapy Calcium Deficiency Length of Regenerate
21
Imola MJ, Ducic Y, Adelson RT. The secondary correction of posttraumatic craniofacial
deformities. Otolaryngol Head Neck Surg. 2008;39(5):654-60.
Treatment Planning
• Distraction Device Orientation
22
Biomechanical Considerations
• Factors related to distractor device
• Factors related to bone and surrounding tissues
• Factors related to device orientation
Properties of Distractor
• Mechanical integrity of device
• Number, length and diameter of fixation pins
• Material properties
Quality of Hard and Soft Tissues
• Shape of the bone
• Cross-sectional area
• Density of bone
• Tension of soft tissues
• Site of osteotomy and joint function
Distractor Orientation
• Transverse plane (Model I)
– Distractors oriented parallel to the lateral surface of
mandible
Distractor Orientation
• Transverse plane (Model II)
– Distractors oriented parallel to each other and to
midsagittal axis
Distractor Orientation
• Transverse plane (Model III & IV)
– Distractors placed parallel to lateral surface of
mandible (III), parallel to each other (IV)
Distractor Orientation
• Sagittal plane (Model V)
• Sagittal plane (Model VI)
Craniofacial Distractors
CraniofacialDistractors
External
Distractors
Unidirectional
Bidirectional
Multiplanar
Internal
Distractors
Tooth-Borne Distractors
Bone-Borne Distractors
Hybrid Distractors
External Unidirectional
Distractors
• Single calibrated rod with two clamps
• Each clamp holds two 2-mm half-pins
• 20-24mm of bone posterior to last tooth bud
• Limitations:
– Difficulty in predicting direction
– Inability to change direction
– Scarring
External Bidirectional Distractors
Molina and Ortiz Monasterio
• Two geared arms 5 cm in length
• Middle screw - change angulation
• Double osteotomy (horizontal in ramus and vertical in corpus)
• Two 2-mm pins in each segment of bone
External Bidirectional Distractors
Advantages:
– Additional degree of freedom
– Deficiencies in more than one plane
– Two osteotomies - flexible distraction
– Easy and optimal device placement
Potential problems
– Risk for avascular necrosis of intervening segment
– Damage to tooth buds during pin placement
External Multiplanar Distractors
• Two distraction rods with sliding clamps connected
in by multiplanar hinge in the middle
• Two arms extend with pin clamps at either end
• Each quarter turn results in 0.25 mm of expansion
Use of Intermaxillary Elastics
• Modification of distraction vectors
• Intermaxillary elastics can have skeletal effects
during distraction
– Secondary to molding of the regenerate
• “Fine tuning” of the occlusal outcome
• Elastics may be worn in Class II, III, vertical, or
transverse pattern
• Helpful in the retention of results
35
Mandibular Extra-oral
Distraction Devices
Advantages
• Small children applicability
• Simplicity of attachment
• Ease of manipulation
• Multiplanar adjustment
• Low infection rate
• Out patient surgery
Disadvantages
• Apprehension
• Bulky appliance
• Social inconvenience
• Facial scars
• Reduced consolidation
period
Internal Distractors
Advantages
Eliminate the problems of:
– Facial scarring
– Pin tract infections
• Better esthetics
• Long consolidation
period possible
Disadvantages
– Unidirectional distraction
– Difficult activation of
ramus distractors
– Poor fit
– Trauma to surrounding
tissues
Internal Tooth-Borne Distractor
Device
• Preformed stainless steel crowns
• Distractor fabricated on cast, crowns cemented
• An osteotomy made between selected teeth,
distractor placed
• Latency period: 3-4 days
• Consolidation period 5 weeks
Symphesial Distraction
• For V shape mandible
• Severe mandibular crowding
• Brodie’s syndrome
• To avoid inderdental stripping or extractions
39
Symphesial Distraction
• Osteotomy Cuts
40
Symphesial Distraction
41
Symphesial Distraction
Samchukov et al. (1998) reported 0.34-degree condylar
rotation for every 1 mm of widening
42
Samchukov, M.L., Cope, J.B. Cherkashin A.M., (2001) The biomechanical effects of distraction device
orientation during mandibular lengthening and widening. In: Samchukov, M.L., Cope, J.B.,
Cherkashin, A.M. (Eds.), Craniofacial distraction Osteogenesis. Mosby, St. Louis, pp. 131–146.
Periodontal Bone Regeneration
• Faber J, Azevedo RB, Báo SN. Distraction osteogenesis may promote periodontal
bone regeneration. J Dent Res. 2005 Aug;84(8):757-61. 43
Distraction Osteogensis for
Vertical Bone Augmentation
• McAllister BS, Gaffaney TE. Distraction osteogenesis for vertical bone augmentation
prior to oral implant reconstruction. Periodontol. 2003;33:54-66. 44
Thank you!

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Distraction Osteogenesis in Orthodontics

  • 1. Distraction Osteogenesis Dr. Waqar Jeelani Resident - Orthodontics 1
  • 2. Distraction Osteogenesis “A biological process of new bone formation between the surfaces of osteotomized bone segments that are separated gradually by incremental traction” Distraction Histogenesis : – Adaptive regenerative changes in surrounding soft tissues
  • 3. Historical Overview Alessandro Codiwilla (1905) – First report of surgical limb lengthening – Oblique osteotomy and external traction pins – Complications: infections, overstretching, poor blood supply, and inadequate fixation
  • 4. Historical Overview G.A. Ilizarov (1950’s) – Lengthening limbs through gradual distraction of fracture callus – Rhythm and rate of distraction – Minimal complications
  • 5. Historical Overview McCarthy (1992) – DO to lengthen congenitally hypoplastic mandible
  • 6. Historical Overview • Rachmiel et al (1993) and Blocks et al (1995) – Maxillary distraction • Polley et al (1995) – Midface distraction with externally fixed cranial halo frame
  • 7. Historical Overview Chin and Toth (1996) • Mandibular alveolar distraction osteogenesis to increase the height of the alveolus Chin M, Toth BA. Distraction osteogenesis in maxillofacial surgery using internal devices: review of five cases. J Oral Maxillofac Surg. 1996 Jan;54(1):45-53.
  • 8. Distraction Techniques Physeal Distraction • Distraction of growth plate • Endochondral bones Callotasis • Distraction of healing callus • Membranous bones
  • 9. Types of Distraction Osteogenesis • Defined on the number of foci at which osteogenesis occurs: – Monofocal elongation DO – Bifocal distraction – Trifocal distraction 9
  • 10. Biology of Distraction 1. Osteotomy/Corticotomy phase 2. Latency phase 3. Distraction phase 4. Consolidation phase 5. Remodeling phase
  • 11. Osteotomy Phase • Divides the bone into two segments • Triggers process of bone repair – Angiogenesis – Fibrogenesis – Osteogenesis
  • 12. Latency Phase • Period from bone division to onset of distraction • Inflammation and soft callus formation of the fractured bone • Soft callus formation begins 3-7 days and lasts 2-3 weeks • Latency period = 5-7 days
  • 13. Distraction Phase • Characterized by the application of traction forces to osteotomized segments • Rate : 1 mm/day • Rhythm : 0.25 mm every 6 hours 0.5 mm twice a day • Duration : 1-3 weeks
  • 14. Consolidation Phase Cessation of traction forces to removal of distractor • Newly formed bone mineralizes and increases in bone density and strength Duration: 3- 4 months
  • 15. Remodeling Phase • Removal of distractor to application of functional loading • Formation of lamellar bone
  • 16. Indications • Congenital retrognathic syndromes • Severe mandibular deficiency > 10-15 mm • A short mandibular ramus • TMJ degenerative disease • Obstructive sleep apnea • A narrow, V-shape mandible • Maxillary deficiency in CLP or Craniosynostosis • Post-traumatic growth disturbance • Atrophy of edentulous segments • Oncologic mandibular osseous defects
  • 17. Advantages • Safe and effective surgical technique can be performed on outpatient basis • Can be done in children as young as 2 years • Distraction histogensis results in growth of associated functional matrix • Long term improvement in condylar morphology • Greater degree of correction can be achieved • Grafts are not required • Minimal skeletal relapse 17
  • 18. Disdvantages • Requires second surgery to remove distractor appliances • Risk of infection at surgical site is greater • Pain and discomfort during distraction • Required meticulous planning • Results are not as precise as orthognathic surgery 18
  • 19. Treatment Planning • Extraoral Examination – Forehead, orbit, zygoma, external ear – Oral commissure, chin, mandibular angles • Intraoral Examination – Occlusion – Occlusal plane • Function – Maximum interincisal opening – Mandibular deviation or deflection – TMJ evaluation – Sensory nerve function 19
  • 20. Treatment Planning • Diagnostic Records – Standard extraoral and intraoral photographs – Dental models articulated on a semi-adjustable articulator – Lateral and PA cephalograms – OPG – CBCT – CT Scan – Stereolithographic models 20
  • 21. Factors Affecting DO Local Factors Systemic Factors Distraction Factors Osteoprogenitor Supply Age Rate of Distraction Blood Supply Metabolic Disorders Frequency of Distraction Infection Vitamin D Deficiency Latency Period Soft Tissue Scarring Connective Tissue Disease Rigidity of Fixation Bone Stock Steroid Therapy Consolidation Period Prior Radiation Therapy Calcium Deficiency Length of Regenerate 21 Imola MJ, Ducic Y, Adelson RT. The secondary correction of posttraumatic craniofacial deformities. Otolaryngol Head Neck Surg. 2008;39(5):654-60.
  • 22. Treatment Planning • Distraction Device Orientation 22
  • 23. Biomechanical Considerations • Factors related to distractor device • Factors related to bone and surrounding tissues • Factors related to device orientation
  • 24. Properties of Distractor • Mechanical integrity of device • Number, length and diameter of fixation pins • Material properties
  • 25. Quality of Hard and Soft Tissues • Shape of the bone • Cross-sectional area • Density of bone • Tension of soft tissues • Site of osteotomy and joint function
  • 26. Distractor Orientation • Transverse plane (Model I) – Distractors oriented parallel to the lateral surface of mandible
  • 27. Distractor Orientation • Transverse plane (Model II) – Distractors oriented parallel to each other and to midsagittal axis
  • 28. Distractor Orientation • Transverse plane (Model III & IV) – Distractors placed parallel to lateral surface of mandible (III), parallel to each other (IV)
  • 29. Distractor Orientation • Sagittal plane (Model V) • Sagittal plane (Model VI)
  • 31. External Unidirectional Distractors • Single calibrated rod with two clamps • Each clamp holds two 2-mm half-pins • 20-24mm of bone posterior to last tooth bud • Limitations: – Difficulty in predicting direction – Inability to change direction – Scarring
  • 32. External Bidirectional Distractors Molina and Ortiz Monasterio • Two geared arms 5 cm in length • Middle screw - change angulation • Double osteotomy (horizontal in ramus and vertical in corpus) • Two 2-mm pins in each segment of bone
  • 33. External Bidirectional Distractors Advantages: – Additional degree of freedom – Deficiencies in more than one plane – Two osteotomies - flexible distraction – Easy and optimal device placement Potential problems – Risk for avascular necrosis of intervening segment – Damage to tooth buds during pin placement
  • 34. External Multiplanar Distractors • Two distraction rods with sliding clamps connected in by multiplanar hinge in the middle • Two arms extend with pin clamps at either end • Each quarter turn results in 0.25 mm of expansion
  • 35. Use of Intermaxillary Elastics • Modification of distraction vectors • Intermaxillary elastics can have skeletal effects during distraction – Secondary to molding of the regenerate • “Fine tuning” of the occlusal outcome • Elastics may be worn in Class II, III, vertical, or transverse pattern • Helpful in the retention of results 35
  • 36. Mandibular Extra-oral Distraction Devices Advantages • Small children applicability • Simplicity of attachment • Ease of manipulation • Multiplanar adjustment • Low infection rate • Out patient surgery Disadvantages • Apprehension • Bulky appliance • Social inconvenience • Facial scars • Reduced consolidation period
  • 37. Internal Distractors Advantages Eliminate the problems of: – Facial scarring – Pin tract infections • Better esthetics • Long consolidation period possible Disadvantages – Unidirectional distraction – Difficult activation of ramus distractors – Poor fit – Trauma to surrounding tissues
  • 38. Internal Tooth-Borne Distractor Device • Preformed stainless steel crowns • Distractor fabricated on cast, crowns cemented • An osteotomy made between selected teeth, distractor placed • Latency period: 3-4 days • Consolidation period 5 weeks
  • 39. Symphesial Distraction • For V shape mandible • Severe mandibular crowding • Brodie’s syndrome • To avoid inderdental stripping or extractions 39
  • 42. Symphesial Distraction Samchukov et al. (1998) reported 0.34-degree condylar rotation for every 1 mm of widening 42 Samchukov, M.L., Cope, J.B. Cherkashin A.M., (2001) The biomechanical effects of distraction device orientation during mandibular lengthening and widening. In: Samchukov, M.L., Cope, J.B., Cherkashin, A.M. (Eds.), Craniofacial distraction Osteogenesis. Mosby, St. Louis, pp. 131–146.
  • 43. Periodontal Bone Regeneration • Faber J, Azevedo RB, Báo SN. Distraction osteogenesis may promote periodontal bone regeneration. J Dent Res. 2005 Aug;84(8):757-61. 43
  • 44. Distraction Osteogensis for Vertical Bone Augmentation • McAllister BS, Gaffaney TE. Distraction osteogenesis for vertical bone augmentation prior to oral implant reconstruction. Periodontol. 2003;33:54-66. 44

Editor's Notes

  1. Distraction histogenesis: A traction force applied to bony segments also creates tension in the surrounding soft tissues, initiating a sequence of adaptive changes termed as distraction hisogenesis
  2. Bone lengthening by distraction osteogenesis dates back to Alessandro Codiwilla, who in 1905 published the first report of surgical limb lengthening. He used an oblique osteotomy and external traction pins to lengthen limbs which were originally shortened by congenital deformity or trauma. The basic method of externally distracting a surgically-created osteotomy did not change much for the next 70 years. During the first half of the century, this technique did not gain clinical acceptance because every surgeon attempting leg lengthening procedures encountered serious complications such as infections, overstretching, poor blood supply, and inadequate fixation.
  3. In 1950’s, Illizarov, a Russian orthopedic surgeon defined a number of biological and mechanical factors that play a role in the process of new bone formation and began the modern era of DO, applying it primarily to lengthen limbs. He gave the law of tension stress that if steady traction is applied to bone fragments after corticotomy or osteotomy, the bone can be lengthened by formation of new bone at the surgical site by callotosis. In particular, he explained the significance of rhythm and rate of distraction, preservation of the periosteum, bone marrow and vascularity, and stable fixation to successful bone lengthening with minimal complications.
  4. McCarthy was the first who introduced the application of craniofacial distraction in mandible
  5. Maxillary distraction was reported in 1993 by Rachmiel et al who performed midface gradual advancment on five sheep. Block et al demonstrated anterior maxillary advancement using tooth borne device in Dog Polley et al used an externally fixed cranial halo frame to distract the midface
  6. Disraction technique is divided into two categories depending on the anatomic sides. Predominant method of distraction in maxillofacial region is callotasis
  7. The basic technique of DO involves five sequential steps
  8. A corticotomy is made preserving the local blood supply to both the periosteum and medullary canal. However, greater blood supply in the facial skeleton prefer osteotomy of the jaws which is more predictable and less uncomfortable for the patients
  9. The distraction device is inserted so that the two bony ends are stable during the first five days. This period is called the latency period during which initial fracture healing and callus formation occurs. If distraction begun too early, the result is decreased bone formation often with cartilaginous elements present and decreased mechanical strength of new bone. If it is too late (after the hard callus formation), the distraction device may be unable to further separate the bone.
  10. There are two important variables in the activation i.e. rate or amount of distraction per day and rhythm that is how frequently the device is activated. Ideally, Distraction of the bony ends is initiated at a rate of 1 mm/day at a rhythm of 0.25 mm every 6 hours. In majority of maxillofacial cases the most common protocol is 0.5 mm twice a day, New bone is usually visible in the distraction gap by the third week. Ossification occurs at the edges and then progresses toward the center of the stretched callus.
  11. The distraction device is left in place while the regenerate bone matures and remodels. The distractor must be rigid enough to prevent movement of bone during this period of healing. If movement occurs, either from inadequate fixation or premature removal of the appliance, a malunion or fibrous non union may occur. Ideally the consolidation period should coincide with the time required for complete mineralization of the bone
  12. Severe deficiencies of either jaw that needs to be ameliorated at an early age such as Pierre robin anomaly Severe mandibular deficinecy that requires lengtheing of mandible more than 10-15 mm. Growth modification can produe only 5 mm of diffrential growth. Orthognathic surgery becomes more difficult and less predictable when more than 8-10mm of advancement and more than 15 mm is outside of their envelope of surgical movement A short mandibular ramus that muse be lengthened. With conventional surgery the musculature of pterygomasseteric sling does not adapt to lengthening of ramus. However, distraction histogenesis could be the way to overcome this limitation.
  13. applied at a younger age (2 years) than is typical for the costochondral rib graft reconstruction It has obviated the need for autogenous bone grafting, as is often required in traditional orthognathic surgical procedures. Distraction histeogensis result in growth of associated soft tissues, such as the muscles of mastication, subcutaneous tissue, and skin (functional matrix).
  14. The patient should be examined with the head in an upright position, a goal often rendered difficult because of craniofacial asymmetry and head tilt. One should note forehead, orbital, zygomatic, and external ear position and relationships by also viewing the patient from the "bird's eye" and submental vertex positions. 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 (or ear remnant) recorded. The position and contour of the chin, inferior border, and angle of the mandible are recorded. The external ear is graded according to one of several classification protocols. The intraoral examination documents the status of the occlusion. It is important to relate the intraoral pathology to the extraoral skeletal and soft tissue abnormalities. The occlusal plane or transverse cant should be related to the transorbital plane (Fig 1A), a determination later facilitated by examination of the posteroanterior cephalogram (Fig 1B). Assessment of the transmeatal, transgonial, and midsagittal (verti
  15. The clinician must position the head so that the midsagittal plane is perpendicular to the floor and the lateral borders of the orbital rims are symmetrically positioned in relation to the lateral borders of the calvarium.
  16. The biomechanical parameters of osteodistraction can be divided into several categories Extrinsic or fixator related factors Intrinsic or tissue related factors Factor related to device orientation
  17. These parameters affect the mechanical integrity of the distraction device which in turn influence the stability of the bone fixation These parameters include number, length and diameter of fixation pins, rigidity of the device and material properties of the distractor mechanism.
  18. Intrinsic parameters affect the quality of the forming distraction regenerate. These parameters include geometric shape, crossectional area, density of distracted bone segments, the length of distraction regenerate and tension of soft tissue envelope.
  19. The effect of distractor device orientation on bilateral mandibular lengthening was evaluated first in transverse plane. Simulated osteotomy of the mandibular corpus was performed posterior to third molars bilaterally. Two linear distractors were placed parallel to the lateral surface of mandible in the Model 1. Note the intercondylar width increased during lengthening compared with predistraction phase. The magnitude of this increase was propotional to the amount of lengthening. Because of the limited lateral movement of condyles, this generate unfavorable reactive forces. Clinically, this will result in bending of distraction device, localized pressure resorption of bone around screws and rotation of proximal segments about the condyles leading to joint compression.
  20. In model II, distractors are placed parallel to the direction of distraction (parallel to each other and to midsagittal axis). No intercondylar width increase developed during lengthening. In this model, the lateral forces and the tensile and compressive strains were minimized significantly
  21. In model III and IV, bilateral mandibular corpus lengthening and midsymphyseal widening occurring simultaneously. A third osteotomy was simulated thorugh the middle of the symphysis and a third distractor was placed on bone segments of the anterior mandible with lengthening distractors placed parallel to the lateral surface of mandible in model III and parallel to the direction of distraction in model IV. Midline widening results in rotation of the mandibular condyle in both models, however, the intercondylar distance increased during lengthening only in model III. The condylar rotation seen during midline widening, if not compensated can create inappropriate loading on the articular surfaces however, the histological changes were minor and were limited to atypical morphology of one two or three of the layers of the condylar cartilage.
  22. Mandibular corpus lengthening with distractors placed parallel to the inferior border of the mandible (model V). A simulated osteotomy of the mandublar corpus ws performed posterior to the third molars bilaterally, and linear distractors were positioned on the lateral surface of the bone segments. Note the inferior translation of the distal segment resulting in increase in lower anterior facial height during lengthening. Each mm of distraction generated 0.3mm increase in LAFH when distraction vector angle was 17 degrees
  23. 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. It was recognized early on that the external linear distractor had several limitations. The disadvantages included scarring as a result of pins dragging through the skin during expansion, difficulty predicting the direction in which the distraction would proceed, and the inability to change direction once the distraction process had begun. The initial placement of the pins determines the placement of the device and, therefore, the direction of distraction.
  24. Molina and Ortiz Monasterio developed an external bidirectional device in patients with mandibular micrognathia involving both the ramus and corpus and angle of mandible and required independent corrections in two directions. 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 angulation. For adequate correction of mandibular deformities, two distraction sites were generated via double level corticotomy which enabled lengthening in both parts of the mandible simultaneously but independently
  25. 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. In the case of Treacher Collins syndrome, bidirectional distraction is essential for correction of the two-step occlusal plane and ramus deficiency. When two osteotomies are performed, distraction can be performed on both arms of the distractor, and expansion proceeds at twice the rate of a unidirectional device. 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. Pretreatment planning should address these potential problems.
  26. The ability to make transverse changes was the final step in achieving three-dimensional control. The hypoplastic mandible is not only deficient in ramus height and body length, but the affected ramus may lie in a more medial position, resulting in a decreased bigonial distance. The multiplanar device consists of two distraction rods with gradually sliding clamps connected in the middle by universal multiplanar hinge. 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. Linear distraction is performed first (10 mm is recommended) and must be continued throughout the angulation process to prevent the formation of a hinge point or premature consolidation. It is recommended that the patient or parents perform the linear expansion and that the angulation be performed by the surgeon. As mentioned previously, angulation will reduce the amount of linear expansion previously achieved.
  27. Active elastic and mechanical distraction is followed by an 8-week period of consolidation. In some cases in which an open bite has been closed, intermaxillary elastics may be worn during the period of consolidation for skeletal and dental retention.
  28. The development of intraoral mandibular distraction devices progressed in two directions: further minitiarization of external devices and modification of available internal orthodontic expansion appliances
  29. A 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). A 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 process. In some cases, space will have to be created between the teeth before the osteotomy. After a 3- to 4-day latency period, the device is activated 0.5 mm to 1.0 mm per day in two to four activations. The recommended consolidation period is 5 weeks.