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ALVEOLAR DISTRACTION
OSTEOGENESIS
Introduction
Distraction osteogenesis
is a surgical process for reconstruction of skeletal deformities. It involves
gradual, controlled displacement of surgically created fractures which results
in simultaneous expansion of soft and
hard tissues with increase in bone volume. It is the ability to
reconstruct combined deficiencies in bone and soft tissue that makes this
process unique and invaluable to all types of reconstructive surgeons. Gavriel
Ilizarov, a Russian orthopedic surgeon, is credited with developing the
armamentarium and describing the biologic basis of this process for the
management of orthopedic limb deformities. The concepts described by Ilizarov
have been adapted and modified for use in maxillofacial surgery. Although the
majority of surgical experience with distraction technology has been in
orthopedics, early results indicate the process to be equally effective in
facial skeletal reconstruction. It is now possible to apply distraction
technology to deformities of the jaws and dentoalveolar process, Fig 1. Development of
miniature, internal distraction devices have made this clinically feasible and
practical.
Fig 1. Missing
Anterior Teeth and Supporting Hard and Soft Tissue
The Process of Alveolar Distraction
Osteogenesis
The process of alveolar distraction
osteogenesis involves mobilization, transport, and fixation of a healthy segment
of bone adjacent the deficient site. A mechanical device, the alveolar
distraction device, is used to provide gradual, controlled transport of a
mobilized alveolar segment, Fig 2. When the desired repositioning of the bone segment
is achieved, the distraction device is left in a static mode to act as a
fixation device. Displacement of the osseous segment results in positioning of a
healthy portion of bone into a previously deficient site. Because the soft
tissue is left attached to the transport segment, the movement of the bone also
results in expansion of the soft tissue adjacent the bone segment. At the
original location of the segment is left a regeneration chamber which has a
natural capacity to heal by filling with bone. This propensity of the
regeneration chamber to heal by filling with bone instead of fibrous tissue is a
function of the surrounding, healthy cancellous bone walls and location within
the skeletal functional matrix. As a result of the gradual distraction, the
alveolar housing, including the osseous and soft tissue components are enlarged
in a single, simultaneous process Fig 2 & Fig 3.
 
Fig 2. Alveolar distraction device in place Fig 3. Alveolar distraction device in place
Alveolar Distraction Device
Development of miniature, internal
distraction devices has made transport of alveolar segments possible. The
alveolar distraction device has been developed for reconstruction of alveolar
process deformities using the distraction osteogenesis process. The implantable
components of the alveolar distraction device consists components that allow for
expansion after being secured to the bone . (fig 3).
When placed into a properly formed
segmental osteotomy, the distraction device allows for controlled elevation of
the segment resulting in coronal displacement of the alveolar crest. The
transport slowly displaces the overlying soft tissue producing expansion. A
regeneration chamber is established in the portion of the osteotomy that is
perpendicular to the transport axis. The portion of the osteotomy that is
parallel to the transport acts to maintain alignment of the segment. After the
desired amount of transport has been achieved, the lead screw is left in place
until bone healing occurs across the sliding component of the osteotomy. The
regeneration chamber fills with bone of several weeks. As a result of the
distraction process the volume of both bone and soft tissue has been increased.
The reconstructed site is them suitable for further rehabilitation with
osseointegrated implants, prosthetic pontic placement, or movement of a tooth
with orthodontics.
 
Fig
4. Alveolar distraction completed
Indications:
Primary indications.
Improve deficiencies in bone and soft tissue.
Secondary indications.
Create site for dental implant placement
Improve ridge esthetics
for pontic
Expand alveolus for
orthodontic tooth movement
Limitations
Must have a minimum quantity of bone
Transport and anchorage segment must have adequate strength to withstand forces
of mobilization
Expansion occurs only in the direction of transport.
Patient must cooperate with activation process
Complications
Fracture of transport segment
Fracture of anchorage segment
Premature consolidation
Undesirable transport vector
Compromised wound healing environment.
Objectives of Distraction
Process
Expansion of bone and soft tissue volume
Displacement of bone into deficient site
Combining Distraction with
other techniques
The distraction process may not produce
the anatomical objective in a single step. Maxillofacial skeletal deformities
are most often complex and three dimensional in nature. Alveolar deformities are
not an exception. It is rare that the distraction process alone would result in
an alveolar ridge of ideal shape and size. Usually additional osteoplasty is
indicated. The distraction process results in the substrate, increased bone
volume and expanded soft tissue, which makes creation of an appropriate alveolar
morphology possible. Knife edge bony alveolar ridges are usually removed and
discarded. If the ridge crest is slightly palatal to the ideal position, the
labial cortex may require labial displacement. The distraction process has
raised the medullary component of the alveolus allowing the labial plate to be
displaced. The resultant increase in alveolar volume is accommodated by the
expanded gingiva so that a nontension soft tissue closure is possible.
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