CONTINUING EDUCATION ARTICLE Mandibular distraction

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Distraction osteogenesis has become widely accepted as the treatment of choice in. CONTINUING EDUCATION ARTICLE. Mandibular distraction osteogenesis: ...

CONTINUING EDUCATION ARTICLE Mandibular distraction osteogenesis: A historic perspective and future directions Jason B. Cope, DDS,a Mikhail L. Samchukov, MD,b and Alexander M. Cherkashin, MDc Dallas, Texas Although orthognathic surgery has gained a generalized acceptance for maxillomandibular deformity correction, several limitations are associated with acute advancement of osteotomized bone segments. Furthermore, large skeletal discrepancies, such as those seen in syndromic patients, require such extensive bone movements that the surrounding soft tissues will not adapt to their new position, resulting in relapse or compromised function and esthetics. Recently, a number of experimental and clinical investigations have demonstrated that gradual mechanical traction of bone segments at an osteotomy site created in the craniofacial region can generate new bone parallel to the direction of traction. This phenomenon, known as distraction osteogenesis, opens up new possibilities in the correction of craniofacial deformities by orthodontists and maxillofacial surgeons. Hence, the purpose of this article is to review the historic development and biologic foundation of mandibular distraction osteogenesis, critically evaluate the current mandibular distraction devices with their clinical applications, and predict the future evolution of mandibular osteodistraction techniques. (Am J Orthod Dentofacial Orthop 1999;115:448-60)

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axillomandibular hypoplasia, facial asymmetry, and congenital micrognathia are relatively common abnormalities of the craniofacial complex. Traditionally, these skeletal deformities have been addressed in nongrowing patients via osteotomies followed by acute orthopedic movements and skeletal fixation, with or without interpositional bone grafts.1-5 Despite the fact that conventional orthognathic surgery and craniofacial reconstruction have experienced widespread success, several limitations are associated with these treatment modalities.2,5,6 One of these limitations is the inability of the muscles to be acutely stretched without the inherent risk of relapse.4,7-9 Moreover, many of the congenital deformities require such large musculoskeletal movements that the soft tissues simply will not accommodate the change, leading to comproSupported in part by NIDR Grant DE07256, an AAOF Grant, and the Center for Craniofacial Research and Diagnosis at the Texas A&M University System–Baylor College of Dentistry. aClinical Assistant Professor, Department of Orthodontics; PhD Fellow, Center for Craniofacial Research and Diagnosis, Department of Biomedical Sciences, Texas A&M University System-Baylor College of Dentistry. bAssociate Director of Ilizarov Research, Department of Orthopedics, Texas Scottish Rite Hospital for Children; Assistant Professor, Department of Orthopedic Surgery, University of Texas Southwestern Medical Center; Assistant Professor, Department of Orthodontics and Department of Biomedical Sciences, Center for Craniofacial Research and Diagnosis, Texas A&M University System-Baylor College of Dentistry. cResearch Scientist, Department of Research, Texas Scottish Rite Hospital for Children. Reprint requests to: Jason B. Cope, DDS, Baylor College of Dentistry, Department of Orthodontics, PO Box 660677, Dallas TX 75266-0677; E-mail: [email protected] Copyright © 1999 by the American Association of Orthodontists. 0889-5406/99/$8.00 + 0 8/1/91724

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mised function and esthetics unless additional soft tissue procedures are performed.10-12 In addition, modern surgical intervention only permits acute changes in the spatial arrangement of bones with limited possibilities for new bone growth. It does not allow complete bone sculpting, ie, changing the shape and form of the bones to maximize the three-dimensional structural, functional, and esthetic needs of the patient. In light of these limitations, recent approaches have been directed at modulating de novo bone growth through osteoconduction and/or osteoinduction. An alternative approach is the method of callus distraction known as distraction osteogenesis, which is a process of new bone formation between the surfaces of bone segments gradually separated by incremental traction.13-15 Specifically, the process is initiated when incremental traction is applied to the reparative callus that joins the divided bone segments and continues as long as this tissue is stretched. The traction generates tension within the callus and stimulates new bone formation parallel to the vector of distraction. Importantly, distraction forces applied to bone also create tension in the surrounding soft tissues, initiating a sequence of adaptive changes termed distraction histogenesis.16 Under the influence of tensional stresses produced by gradual distraction, active histogenesis occurs in different tissues, including: skin, fascia, blood vessels, nerves, muscle, ligament, cartilage, and periosteum.17-25 These adaptive changes in the soft tissues may allow larger skeletal movements while minimizing the potential relapse seen in acute orthopedic corrections. Distraction osteogenesis has become widely accepted as the treatment of choice in

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Fig 2. Eiselberg’s steplike sliding osteotomy for acute mandibular advancement. (Reprinted with permission from Limberg A. A new method of plastic lengthening of the mandible in unilateral microgenia and asymmetry of the face. J Am Dent Assoc 1928;15:851-71.)

Fig 1. Angle’s palatal expansion device. A, Before placement; B, after placement on the maxillary teeth. (Reprinted with permission from Anglel EH. Treatment of irregularity of the permanent or adult teeth. Dental Cosmos 1860;1:540-4, 599-600.)

orthopedics for correcting limb-length discrepancies, skeletal deformities, and severe bony defects. Recent clinical reports have documented the successful application of gradual osteodistraction in treating skeletal deformities of the oral and maxillofacial region.26-46 The use of slow incremental traction has allowed up to 20 mm of mandibular lengthening with no associated pain. Because these conditions are typically treated by a team approach, a thorough understanding of the evolution and future development of osteodistraction is of paramount importance to the orthodontist. ORIGINS AND EVOLUTION

The evolution of craniofacial distraction osteogenesis was based on the development and improvement of dentofacial traction, craniofacial osteotomies, and skeletal fixation methods. Later, modifications of these techniques were merged into osteodistraction procedures that were finally improved based on experiences with distraction osteogenesis on long bones.47 Dentofacial Traction

From an orthodontic perspective, the application of tensile and compressive forces to bones of the

craniofacial skeleton is not a new concept. Principles of dental traction for the correction of skeletal deficiencies have been practiced in dentistry since the eighteenth century. As early as 1728, Fauchard 48 described the use of the expansion arch. When the ideally shaped metal plate was ligated to the crowded dentition, the teeth were broadened to a normal form. However, this form of traction was limited to tooth movement only and had little effect on the shape of the bone. Wescott49 first reported the placement of mechanical forces on the bones of the maxilla in 1859. He used two double clasps separated by a telescopic bar to correct a crossbite in a 15-year-old girl. However, the entire expansion procedure was slow and tedious and lasted several months. A year later, Angell50 performed a similar procedure with a differentially threaded jackscrew connected to the premolars (Fig 1). Palatal expansion was achieved rapidly in 2 weeks through the separation of the maxillary bones at the midpalatal suture. Goddard,51 in 1893, further standardized the palatal expansion protocol. He activated the device twice a day for 3 weeks followed by a stabilization period to allow the deposition of “osseous material” in the created gap. Craniofacial Osteotomies

Although orthodontic treatment provides a means of correcting maxillomandibular skeletal discrepancies, it is limited to actively growing children. In nongrowing individuals, surgical intervention has been implemented to circumvent this limitation. The first surgical procedure for the correction of a craniofacial

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Fig 5. Ilizarov’s low-energy subperiosteal corticotomy technique. Fig 3. Kazanjian’s “over the face” appliance for gradual advancement of mandible. (Reprinted with permission from Kazanjian VH. The interrelationship of dentistry and surgery in the treatment of deformities of the face and jaws. Am J Orthod Oral Surg 1941;27:10-30.)

Fig 6. Zonal structure of the distraction regenerate. Diagram demonstrating two zones of mineralization (mz) with longitudinally oriented primary osteons, divided by a fibrous interzone (fz) with collagen bundles directed parallel to the vector of distraction. Fig 4. Stader’s external skeletal fixation device for treatment of mandibular fractures. (Reprinted with permission from Waldron CW, Kazanjian VH, Parker DB. Skeletal fixation in the treatment of fractures of the mandible. J Oral Surg 1943;1:59-83.)

deformity was reported in 1848, at which time Hullihen52 successfully performed a partial osteoplastic resection of a prognathic mandible. The subapical osteotomy of the anterior mandible was followed by the removal of a wedge-shaped section of bone from each side of the mandibular body. Surgical treatment of mandibular retrognathia, however, was not reported

until the first decade of the twentieth century, when Blair7 demonstrated the use of a bilateral horizontal ramus osteotomy to advance the mandible. Osteotomy of the mandibular corpus has also been advocated for advancement of the retrognathic mandible.53 According to Limberg,54,55 Brown in 1918 and Bruhn-Linderman in 1921 each performed a vertical osteotomy of the mandibular body followed by acute advancement of the anterior segment. The ensuing defect usually healed by new bone ingrowth. However, the amount of advancement with these osteotomies was limited and often associated with instability of bone segment fixation.

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Fig 7. A, Position of Hoffman Mini Lengthener (Howmedica Co., Rutherford, NJ) during mandibular lengthening; B, McCarthy’s predrilled osteotomy technique. (Reprinted with permission from McCarthy JG, Schreiber J, Karp N, Thorne CH, Grayson BH. Lengthening the human mandible by gradual distraction. Plast Reconstr Surg 1992;89:1-8.)

In an attempt to increase the contact surface area between divided bone segments and provide greater stability of bone fixation, different modifications of mandibular osteotomies were developed. For example, Limberg54 and Cryer55 performed C-shaped and oblique L-shaped osteotomies, respectively, to enhance bone segment contact. Likewise, Eiselberg and Pehr Gadd developed step-like sliding osteotomies for lengthening55,56 or widening56 of the mandible (Fig 2). Although corrective osteotomies were gaining widespread acceptance at that time, it was apparent that several limitations were associated with these procedures, especially when combined with acute mandibular lengthening. Problems included intraoperative nerve damage, marked postoperative displacement of bone segments due to inadequate bony contact and insufficient fixation stability, and partial or total relapse as a result of acute muscle stretching.7,8,57 Initial Mandibular Distraction Techniques

According to Wassmund,58 in 1927 Rosenthal performed the first mandibular osteodistraction procedure by using an intraoral tooth borne appliance that was gradually activated over a period of 1 month. In 1937, Kazanjian59 also performed mandibular osteodistraction by using gradual incremental traction instead of acute advancement. After performing modified L-shaped osteotomies in the corpus, he attached a wire hook to the symphysis, thereby providing direct skeletal fixation to the bone segment to be distracted. Three days postoperatively, an “over the face” appliance was placed and acti-

vated with an elastic band, thereby exerting traction on the chin and gradually pulling the mandibular anterior segment forward (Fig 3). Seventeen days later, the elastic force was removed. Occlusal splints, connected by rigid bars, remained in place for 11 weeks at which time complete consolidation of the jaw had taken place. Crawford,60 in 1948, applied gradual incremental traction to the fracture callus of the mandible. A patient presented 2 weeks after a mandibular symphyseal fracture in which a lower central incisor was lost. Before treatment, the mandibular halves had collapsed medially, obliterating the incisor space and creating an apparent crossbite. By using a jackscrew appliance, the fracture callus was stretched over a 3-day period to reestablish the original jaw position, which remained fixed with a sectional occlusal splint. Even though the first distraction osteogenesis procedures applied gradual traction to the bone segments and surrounding soft tissues, this technique did not gain immediate acceptance. This was primarily because of the lack of control over bone segment manipulation, inadequacy of distraction appliances, and the instability of osseous fixation. Instead, corrective osteotomies remained a principal treatment modality for the management of mandibular deformities, especially after the introduction of sagittal split osteotomies by Trauner and Obwegeser.2 Skeletal Fixation

Although acute orthopedic movements remained the treatment of choice, the adaptation of external

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Table I. Reported

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osteodistraction parameters for mandibular lengthening and widening

Authors (year)

Procedure (No. of patients)

Guerrero46 (1990) McCarthy et al37 (1992) Perrott et al36 (1993)

Mandibular widening (10)

Takota et al33 (1993)

Unilateral mandibular lengthening (4) Unilateral mandibular lengthening (1) Bilateral mandibular lengthening (1) Unilateral and bilateral mandibular lengthening (15)

Habal30 (1994) Havlik and Bartlett26 (1994) McCarthy27 (1994)

Moore et al32 (1994) Guerrero et al38 (1995) Klein and Howaldt35 (1995) Kocabalkan et al42 (1995) Molina and OrtizMonasterio29 (1995) Pensler et al34 (1995)

Unilateral and bilateral mandibular lengthening (4) Mandibular widening (1)

Bilateral mandibular lengthening (1) Bilateral mandibular lengthening or widening (20) Unilateral and bilateral mandibular lengthening (9) Bilateral mandibular lengthening (1) Unilateral and bilateral mandibular lengthening (106)

Klein and Howaldt39 (1996)

Unilateral and bilateral mandibular lengthening (9) Unilateral and bilateral mandibular lengthening (3) Unilateral mandibular lengthening (2) Unilateral and bilateral mandibular lengthening (18)

Corcoran et al43 (1997)

Unilateral mandibular lengthening (28)

Polley and Figueroa44 (1997) Wangerin and Gropp45 (1997) Razdolsky et al41 (1998)

Unilateral mandibular lengthening (2) Unilateral and bilateral mandibular lengthening (15) Unilateral and bilateral mandibular lengthening (43)

Rachmiel et al28 (1995) Guyette et al40 (1996)

Bone division

Device

Latency

Vertical symphyseal osteotomy Oblique angle osteotomy

Intraoral tooth-borne, unidirectional Extraoral, unidirectional

0 days

Periosteal preserving osteotomy Corticotomy

Extraoral, unidirectional

7 days

Extraoral, unidirectional

14 days

Periodsteal preserving subtotal corticotomy Osteotomy thru previous bone graft Osteotomy

Extraoral, unidirectional

7 days

Extraoral, unidirectional

14 days

Extraoral, unidirectional

7 days

Corticotomy

Extraoral, unidirectional

5 days

Vertical symphyseal, ramus, or midbody osteotomy Oblique ramus corticotomy

Intraoral tooth-borne or hybrid, unidirectional Extraoral, unidirectional

10 days

Oblique angle corticotomy

Extraoral, unidirectional

5 days

Oblique angle corticotomy or double level ramus/ corpus osteotomy Oblique ramus or vertical midbody corticotomy Horizontal ramus or oblique angle corticotomy Mandibular osteotomy

Extraoral, unidirectional, and bidirectional

4 days

Extraoral, unidirectional

1 day

Extraoral, unidirectional

7 days

Extraoral, unidirectional

Not reported

Single or double level ramus/corpus osteotomy

Extraoral, bidirectional

4-5 days

Oblique angle osteotomy thru host bone or rib graft Oblique angle osteotomy

Extraoral, unidirectional

7 days

Extraoral, unidirectional

7 days

Horizontal ramus osteotomy

Intraoral bone-borne, unidirectional Extraoral and intraoral tooth-borne, unidirectional

6 days

Midbody osteotomy

skeletal fixation to the mandible and the introduction of distraction osteogenesis protocols for limb lengthening rekindled interest in mandibular osteodistraction. The application of external skeletal fixation for craniofacial fractures was first reported by Haynes61 in 1939. Using a number of pins connected to a rigid bar, he applied this technique to a comminuted, compound fracture of

7 days

5 days

3-5 days

the mandible. In 1941, two other external mandibular fixation devices were developed based on appliances for external skeletal fixation of the lower extremities. The Mowlem appliance62 and the Converse and Waknitz63 appliance were similarly designed and consisted of three main parts: two pairs of fixation pins with locking plates located on either side of the fracture and an inter-

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Rate and rhythm

Distraction

Problems and complications

Consolidation

3 mm acutely, then 0.25 mm 1×/day 0.5 mm 2×/day

4-6.5 mm 4-14 days

12 weeks

None reported

18-24 mm 20 days

8-10 weeks

Pin tract scars, loose and infected pins, relapse

0.33 mm 1×/day

10 mm 30 days

0.36 mm 2×/day

17-22 mm 28-35 days

Infected pins, mild discomfort, disproportional movement of interior and superior cortices Pin tract scar

0.5 mm 2×/day

Not reported

0 weeks-replaced by iliac bone graft and miniplate 10-12 weeks-activator used for additional 6-12 months for retention 4 weeks

0.25-0.5 mm 2×/day 0.5 mm 2×/day

30 mm 46 days

Loose and infected pins, device instability

18-36 mm 18-36 days

0 weeks–replaced by iliac bone graft and miniplate 8 weeks

1 mm 1×/day

20 mm 20 days

6 weeks

Pin tract scars, dentigerous cyst developed 2° to pin placement, ankylosis of coronoid process/zygoma None reported

2 mm acutely, then 1 mm 2×/day 1 mm 1×/day

3-10 mm 3-10 days

12 weeks

None reported

15-25 mm 15-25 days

9 weeks

0.25 mm 4×/day

18 mm 18 days

6 weeks

Pin tract scars, loose fixation pins, facial nerve motor deficit TMJ pain, 2nd distraction procedure required

0.25 mm 4×/day

12-29 mm 12-29 days

6-8 weeks

TMJ pain, occlusal interferences, loose and infected pins

0.25 mm 4×/day

13-23 mm 16-40 days

3-7 weeks

Device interference with mastoid process

1 mm 1×/day

21 mm 21 days

7 weeks

None reported

Not reported

35-45 mm 40-50 days

Not reported

1 mm 1×/day per osteotomy level

7-50 mm 7-50 days

7-9 weeks

0.5 mm 2×/day

9-25 mm 13-56 days

4-7 weeks

1 mm 1×/day

30-35 mm 30-35 days

Not reported

Unilateral openbite and crossbite, velopharyngeal inadequacy Pin tract scars, loose pins, TMJ pain, trismus, premature consolidation, facial nerve motor deficit Pin tract scars and infections, device failure, fibrous pseudoarthrosis, transient neuropraxia Unilateral crossbite

1 mm 1×/day

7-25 mm 7-25 days

6 weeks

Transient loss of mandibular nerve sensation

0.25 mm 4×/day

10-23 mm 10-23 days

3-7 weeks

None reported

vening telescoping fixation bar. Stader,64 in 1942, further modified the mandibular external fixator by adding double-plane-joint elements and a threaded rod to connect both pin fixation clamps (Fig 4). Stader’s fixation appliance was the first mandibular device allowing angular adjustments in two planes as well as anteroposterior incremental compression or distraction.

Pin tract scar

Ilizarov Method

Subsequently, Ilizarov13-15 introduced his distraction osteogenesis technique for limb lengthening. The procedure was initiated by surgical bone division with maximum preservation of periosteum and endosteum—a technique that he called a corticotomy. Specifically, Ilizarov divided two thirds of the bony cortex

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Fig 8. A, Molina’s partial osteotomy technique; B, Molina Bidirectional Mandibular Distractor (Wells Johnson Company, Tuscon, Ariz). (Reprinted with permission from Molina F, Ortiz-Monasterio F. Mandibular elongation and remodeling by distraction: a farewell to major osteotomies. Plast Reconstr Surg 1995;96:825-40.)

for remodeling of the regenerate tissue) began and continued until the newly formed bony tissue in the distraction gap had remodeled. CURRENT TECHNIQUES

Fig 9. Extraoral ACE/Normed Multi-Directional Distractor (NORMED Medizin-Technik GmbH, Germany) developed in cooperation with Bitter and Klein. (Reprinted with permission from NORMED Medizin-Technik.)

with a narrow osteotome followed by the completion of bone separation with rotational osteoclasis (Fig 5). His distraction protocol used a 5 to 7 day latency period (the time frame between bone division and the initiation of traction forces). The bone segments were then gradually separated at a rate of 1 mm per day in four equal increments of 0.22 mm. On the completion of distraction, the consolidation period (the time required

The first report demonstrating the application of Ilizarov’s principles to the mandible appeared in 1973. In order to simulate a mandibular deformity, Snyder et al65 resected a unilateral 15 mm bone segment from a canine mandible, thereby creating a crossbite. Ten weeks later, the shortened mandible was osteotomized and an extra-oral distraction appliance was placed. After a 7 day latency period, the device was activated at a rate of 1 mm per day for 14 days, at which time the occlusion was restored. Reestablishment of the mandibular cortex and medullary canal across the distraction gap was noted after 6 weeks of fixation. Using a similar distraction protocol a few years later, Michieli and Miotti66 demonstrated the feasibility of intraoral mandibular lengthening. Implementing a device cemented to the teeth, they lengthened the mandibles of two dogs—one by 5 mm, the other by 15 mm—after a bilateral reverse-step osteotomy. Histologic examination revealed new bone formation originating from the parallel ordered collagenous fibers, which subsequently remodeled to form lamellar bone. In 1982, Panikarovski et al67 performed the first significant histologic evaluation of mandibular distraction regenerates in 41 dogs. A fibrous interzone was observed in the central region of the distraction gap with collagenous fibers and capillaries oriented parallel to the direction of distraction. Newly created bone, in the form of longitudinally oriented trabeculae, originated

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Fig 10. Multi-Guide Mandibular Distraction Device (Howmedica Leibinger, Inc., Rutherford, NJ) developed by McCarthy. (Reprinted with permission from Howmedica Leibinger, Inc.)

from the residual mandibular segments and progressed toward the fibrous interzone (Fig 6). The results of these studies demonstrated that the mechanism of new bone formation during gradual mandibular distraction was similar to that during limb lengthening. Karp et al68 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 the craniofacial complex. Refer to Table I for recent clinical protocols. Extraoral Mandibular Distraction

In 1989, McCarthy et al37 were the first to clinically apply the technique of extraoral osteodistraction on four children with congenital craniofacial anomalies. They used a Hoffman Mini Lengthener (Howmedica Co., Rutherford, NJ) attached to the osteotomized bone segments with two pairs of pins (Fig 7A). Bone division was initiated by placing a series of drill holes along the osteotomy line, which were then connected with a narrow osteotome (Fig 7B). 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. Molina and Ortiz-Monasterio29 simplified the methods established by McCarthy et al. Their tech-

nique used a corticotomy, which left the medial cortical plate intact (Fig 8A). Only one fixation pin was inserted on either side of the corticotomy and secured to the distraction device, which they termed a semirigid extraoral fixation system. According to Molina and Ortiz-Monasterio, the muscles exert constant forces over the appliance, slightly bending it and reflecting externally the bone remodeling taking place internally. Although these initial reports demonstrated the successful application of osteodistraction to the human craniofacial skeleton, the first extraoral devices were capable of unidirectional mandibular lengthening only, either horizontal or vertical. When treating patients with mandibular deficiencies located either in the ramus or the corpus, this strategy may provide complete correction of linear bone discrepancies. In patients with congenital syndromes involving mandibular microsomia or micrognathia, however, severe deformities often involve the ramus, corpus, and the angle of the mandible. Restoration of the mandible in these cases can be more adequately addressed using independent distraction in two directions. Molina and Ortiz-Monasterio were the first to use bidirectional osteodistraction in the mandible (Fig 8B). They generated two distraction sites via double-level corticotomies (horizontal in the ramus and vertical in the corpus), which enabled them to lengthen both parts of the mandible simultaneously. In addition, later modifications of bidirectional devices provided an adjustment in the angular relationship between the two distraction vectors during lengthening, thereby allowing augmentation of the gonial angle.

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Fig 11. Classification of mandibular distraction osteogenesis devices.

The introduction of extraoral bidirectional distraction appliances significantly improved the adaptability of distraction osteogenesis in cases with mandibular deficiency. Anatomically, however, the mandible consists of two halves that are fused at an acute angle in the midline forming a V-shaped bone structure; each mandibular half consists of a horizontal corpus and a vertical ramus angularly oriented to each other. Therefore, in order to correct severe mandibular deformities in three-dimensional space, independent lengthening of the mandibular corpus and ramus must be combined with gradual angular adjustments. As a result, two multidirectional extraoral distraction appliances were developed (Figs 9 and 10), thereby allowing manipulation of bone segments in multiple planes of space. Despite the advantages of extraoral distraction devices in the hands of clinicians (application for very small children, simplicity of attachment, ease of manipulation, bidirectional and multidirectional distraction), patients are apprehensive about wearing bulky external appliances because of the social inconvenience and the potential of permanent facial scars. Moreover, both currently available extraoral multidirectional devices still have design limitations as well. Although the ACE/Normed device (Normed MedizinTechnik GmbH, Germany) (Fig 9) permits double-level lengthening, multidimensional correction can only be done acutely, after loosening the hinge screws. In contrast, the Multi-Guide Mandibular Distractor (Howmedica Leibinger, Inc, Rutherford, NJ) (Fig 10) provides a gradual and independent three-dimensional rotation of the bone segments but does not allow two distraction sites or bidirectional independent correction. These disadvantages and limitations were the pri-

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Fig 12. Guerrero’s et al intraoral distractor is attached superiorly to teeth by orthodontic bands and inferiorly to bone by bendable forked arms. (Reprinted with permission from Guerrero C, Bell WH, Flores A, Modugno VL, Contasti G, Rodriguez AM, et al. Intraoral mandibular distraction osteogenesis. Odontol Dia 1995;11:116-32.)

mary force driving the evolution of mandibular lengthening and widening toward the development of intraoral devices (Table I). Intraoral Mandibular Distraction

Guerrero,46 in 1990, was the first to report the results of intraoral mandibular widening on 11 patients with transverse deficiencies ranging from 4 to 7 mm. Further development of intraoral mandibular distraction progressed in two directions: (1) miniaturization of external devices,45,69 and (2) modification of available orthodontic expansion appliances.41,70 The intraoral distractors can be classified (Fig 11) as bone-borne (attached to the bone only), tooth-borne (attached to the teeth only) or hybrid (simultaneously attached to the teeth and bone).71 In 1994, McCarthy et al69 developed a miniaturized bone-borne Uniguide Mandibular Distraction Device (Howmedica Leibinger, Inc.) suitable for intraoral placement. Similar to their extraoral appliance, the device consisted of two clamps attached to the bone via pairs of pins connected by a telescopic distraction rod. At the same time, Wangerin45 in Germany designed a similar appliance, the Intraoral Titanium Mandibular Distraction Device (Medicon Instrumente, Tuttlingen, Germany). The device consists of miniplates (for bone fixation) connected by a square-shaped distraction cylinder, which eliminates the tendency toward rotational movement. The introduction of intraoral appliances significantly improved mandibular osteodistraction techniques. The major advantages included the inconspicuous nature of the devices and the absence of facial scars. However, the development of intraoral appliances has design limitations primarily related to the limited size

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of the device and the restricted access of the oral cavity. Because of these limitations, further development of intraoral distraction appliances took alternative approaches. For example, the French surgeons Diner et al72 developed two types of intraoral bone-borne devices for mandibular lengthening based on the anatomic location of distraction—horizontal corpus or ascending ramus. Guerrero et al38 presented different tooth-borne, bone-borne, and hybrid intraoral devices for mandibular lengthening and widening. The appliances can be modified and attached either to orthodontic bands or to pairs of bendable metal arms having fork-shaped ends. The bendable nature of the device allows intraoperative adaptation that minimizes the possibility of mandibular nerve damage as a result of screw placement (Fig 12). In addition, the device can be removed following the consolidation period by cutting the metal arms and pulling the fork ends of the appliance, leaving the fixation screws in the bone. Similarly, Razdolsky et al41 developed a series of tooth-borne and hybrid devices (ROD) (Oral Osteodistraction, LP, Buffalo Grove, Ill) in which the distraction mechanism can be attached to stainless steel crowns or miniplates (Fig 13). In addition, they designed a special laboratory instrument to allow preprogrammed fabrication of the device along a predetermined axis of distraction based on preoperative records. After the appliance is cemented to the teeth or fixed to the bone, the distractor mechanism is removed and the corticotomy is performed using a special saw, followed by replacement of the distractors.

Cope, Samchukov, and Cherkashin 457

Fig 13. Razdolsky’s toothborne ROD Appliance (Oral Osteodistraction, LP, Buffalo Grove, Ill). A, Tooth-borne ROD-1 device for interdental distraction; B, Hybrid ROD2 device for distraction posterior to the molars. (Reprinted with permission from Oral Osteodistraction, LP)

FUTURE DIRECTIONS

The future development of osteodistraction for craniofacial applications will probably establish a more complete understanding of the biology of new bone formation under the influence of gradual traction. Major trends may include: (1) refinement of distraction protocols, (2) modification of osteotomy techniques, (3) further improvement of distraction devices, (4) enhancement of regenerate maturation with pharmacologic agents, such as growth factors and cytokines, and (5) development of new techniques to monitor distraction regenerate formation and remodeling. Distraction Protocol

Further improvements of the distraction protocol should be based on both experimental research and clinical investigations with long-term outcome assessments. Studies will probably concentrate on finding the optimal values for the critical parameters of distraction. These critical parameters, as demonstrated by

the orthopedic literature,13,14 include: (1) osteotomy technique with maximal preservation of blood supply to the osteotomized bone segments, (2) duration of the latency period, (3) rate (total daily amount of lengthening) and rhythm (number of increments into which the total daily lengthening is divided) of distraction, (4) time span of the consolidation period, and (5) loading environment of the regenerate. Because these variables affect the outcome of distraction osteogenesis in bones of endochondral origin, they may also be expected to affect the outcome of distraction osteogenesis in the membranous bones of the craniofacial complex. Yet investigations dedicated to elucidating the critical parameters associated with mechanically mediated bone formation in the craniofacial region are lacking. Therefore, it is important to systematically investigate the influence of each one of these variables on new bone formation during osteodistraction in the craniofacial region.

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lar region affect the eruption and movement of teeth? What is the effect of distraction on the periodontal ligament and associated oral soft tissues? Do undesirable tooth movements occur when an intraoral tooth-borne or hybrid device is used in lieu of a bone-borne (direct skeletal fixation) device? Or does this occur with all devices, if at all? Osteotomy Techniques

Because of the anatomy of the mandible, the osteotomy will remain one of the most critical components of distraction osteogenesis. Improvements in osteotomy techniques should proceed toward a division of bone without disruption of the periosteum, endosteum, and neurovascular bundle. This is particularly important at sites with insufficient host bone at the ends of the osteotomized segments, as is the case with bone cuts between teeth. Recently, Bell et al73 demonstrated that marginal alveolar bone at interdental osteotomy sites had to be maintained in order to maximize bone formation within the regenerate tissue. The osteotomy should also be refined to allow bone deformity correction and lengthening while preserving maximum contact area between bone surfaces. Novel methods of soft tissue closure using light cured adhesives74 can shorten operative procedures while establishing an intact barrier over the operative site to the oral flora. Distraction Devices

Fig 14. Tooth movement initiated through distraction regenerate at 1 week into the consolidation period. A, Before distraction; B, After distraction and before tooth movement; C, After tooth movement (11 week duration).

Future directions in the development of an ideal distraction device should proceed toward a multidirectional intraoral appliance with the capability of simultaneous linear and angular adjustments. The device may be anchored to the mandible with bioresorbable materials,75,76 thereby simplifying insertion and removal of the distraction component of the device while maintaining adequate strength and rigidity of the appliance. Motorized distraction units with remote activation and monitoring can allow precise directional control, as well as calibration of distraction forces. This would simplify the distraction activation procedure for the patient or parents. Finally, the device must be relatively inexpensive in order to be used in an outpatient setting. Enhancement of Regenerate Maturation

In addition, other questions must be addressed before distraction osteogenesis can be broadly applied to deformities of the craniofacial skeletal. How does distraction osteogenesis affect the growing craniofacial skeleton? What is the long-term stability of bone lengthened by osteodistraction? What are the limits of the soft tissues to stretch during distraction osteogenesis? How does osteodistraction in the maxillomandibu-

Although modification of distraction devices and optimization of distraction parameters remain the primary focus of most current research, our ability to regulate regenerate formation during the distraction process will broaden the spectrum of craniofacial distraction osteogenesis applications in the future. In endochondral bones, where the final length of the forming regenerate is usually more than 30 mm and the distrac-

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tion period is longer than 4 weeks, regenerate formation can be controlled by adjusting the rate and rhythm of distraction based on radiographic appearance of the forming bone. When distracting craniofacial bones, in contrast, distraction is often less than 20 mm and regenerate tissue is formed over a shorter period of time (1 to 2 weeks). During this time frame, it is often impossible to visualize the regenerate with current monitoring techniques. Therefore, adjustment of regenerate development by manipulating the rate or rhythm of distraction is not feasible. In these cases, amplification of distraction regenerates, either by the addition of growth factors and cytokines to the milieu of reparative and formative cells in the distraction gap or by adjusting the mechanical forces within the loading environment during the consolidation period, may be a plausible alternative. Recently, the addition of recombinant human Bone Morphogenetic Protein-2 (rhBMP-2)77-79 and other growth factors80,81 to the bone healing environment has demonstrated enhanced bony healing and remodeling of fracture and implant sites. Monitoring of Regenerate Formation and Remodeling

Presently, noninvasive procedures such as plain radiography have been used clinically to determine when the regenerate bone is capable of functional loading. However, the correlation between radiographic density and the biomechanical integrity of newly formed bone is poor.82,83 Therefore, more reliable quantitative and qualitative approaches with mechanical, histologic, and biochemical markers need to be developed in order to determine the optimal duration of the fixation period. The incorporation of new biological advances with the current concepts of distraction osteogenesis will extend the application of osteodistraction to areas other than deformity correction. Osteodistraction provides new horizons to the orthodontist in treating crowded dental arches by increasing arch length or circumference, possibly reducing extraction therapy required in severely crowded cases. Based on our recent experiments with the canine mandible (data unpublished), it appears that tooth movement can begin shortly after the initiation of the consolidation period (Fig 14). As the mean age of the population continues to increase, more patients with tooth loss and alveolar ridge atrophy will demand inexpensive, yet functionally satisfactory approaches to the treatment of partially edentulous jaws. Distraction osteogenesis offers the possibility of regenerating new alveolar bone before implant or fixed partial denture placement in patients with alveolar ridge atrophy. Once placed, osseointe-

grated implants are unable to passively erupt with the remaining dentition. A related problem, although less frequently encountered, is localized ankylosis of permanent teeth. Selectively placed interdental osteotomies, when followed by gradual callus distraction, may provide superior treatment methods in comparison to prosthodontic therapy alone. CONCLUSIONS

The application of osteodistraction offers novel solutions for surgical-orthodontic management of developmental anomalies of the craniofacial skeleton. Similar to distraction osteogenesis in the long bones, craniofacial osteodistraction evolved from skeletal traction, osteotomy techniques, and external fixation methods. Likewise, the underlying biological mechanisms of craniofacial distraction are comparable to that of long bones. Osteodistraction provides a means whereby bone may be molded into different shapes to more adequately address the nature of skeletal deformities and asymmetries. In addition, the phenomenon of distraction histogenesis may allow larger skeletal movements without the inherent risk of relapse. Furthermore, many of the congenital deformities that require extensive musculoskeletal movements may be addressed with fewer procedures eventually achieving the same structural, functional, and esthetic results commonly seen with modern orthognathic procedures. REFERENCES 1. Wolford LM, Wardrop RW, Hartog JM. Coralline porous hydroxylapatite as a bone graft substitute in orthognathic surgery. J Oral Maxillofac Surg 1987;45:1034-42. 2. Trauner R, Obwegeser H. The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty: part I, surgical procedures to correct mandibular prognathism and reshaping of the chin. Oral Surg Oral Med Oral Path 1957;10:677-89. 3. Caldwell JB, Amaral WJ. Mandibular micrognathia corrected by vertical osteotomy in the rami and iliac bone graft. J Oral Surg 1960;18:3-15. 4. Schendel SA, Epker BN. Results after mandibular advancement surgery: an analysis of 87 cases. J Oral Surg 1980;38:265-82. 5. Converse JM, Horowitz SL. The surgical-orthodontic approach to the treatment of dentofacial deformities. Am J Orthod Dentofacial Orthop 1969;55:217-43. 6. Cassidy DW, Herbosa EG, Rotskoff KS, Johnston LE Jr. A comparison of surgery and orthodontics in “borderline” adults with Class II, Division 1 malocclusions. Am J Orthod Dentofacial Orthop 1993;104:455-70. 7. Blair VP. Operations on the jaw-bone and face. Surg Gyn Obstet 1907;4:67-78. 8. Babcock WW. The surgical treatment of certain deformities of the jaw associated with malocclusion of the teeth. J Am Med Assoc 1909;53:833-9. 9. Ellis E, III, Carlson DS. Stability two years after mandibular advancement with and without suprahyoid myotomy: an experimental study. J Oral Maxillofac Surg 1983;41:426-37. 10. Caldwell JB, Hayward JR, Lister RL. Correction of mandibular retrognathia by vertical L osteotomy: a new technic. J Oral Surg 1968;26:259-64. 11. Longaker MT, Siebert JW. Microsurgical correction of facial contour in congenital craniofacial malformations: the marriage of hard and soft tissue. Plast Reconstr Surg 1996;98:942-50. 12. Vargervik K, Ousterhout DK, Farias M. Factors affecting long-term results in hemifacial microsomia. Cleft Palate Craniofac J 1986;23(Suppl 1):53-68. 13. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues: part II, the influence of the rate and frequency of distraction. Clin Orthop Rel Res 1989;239:263-85. 14. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues: part I, the influence of stability of fixation and soft tissue preservation. Clin Orthop Rel Res 1989;238:249-81. 15. Ilizarov GA. Clinical application of the tension-stress effect for limb lengthening. Clin Orthop Rel Res 1990;250:8-26.

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