DISTRACTION OSTEOGENESIS : THE LATEST CLINICAL APPROACH FOR RIDGE AUGMENTATION

INTRODUCTION

The vertically reduced alveolar process presents a challenge to dental surgeon. The success of prosthetic procedure depends on adequate height and width of the implantation bed and quality of bone. The dilemma is faced by clinician as to decision making in situation for alveolar ridge augmentation of quantatively compromised proposed site. Modalities such as autogenousbone graft, GBR, onlay osteoplasty, interpositional osteoplasty are in use but often present problems with donor site morbidity or soft tissue dehiscence.

More recently, Distraction osteogenesis is an alternative technique to alloplastic and autogenous bone grafts to regenerate vertical dimension of alveolar process prior to prosthodontic rehabilitation.

What is Distraction Osteogenesis?

Distraction osteogenesis is a biologic procedure in which slow and controlled distraction of bone segments with preservation of periosteum and medullary blood supply results in elongation of bone.

Historical Background of Distraction Osteogenesis

In the early 1900s, Codivilla first reported distraction osteogenesis for lengthening long bones of lower extremity. Since 1969the Russian surgeon Gavril Illizarov revisited the concept and developed much of the armamentarium used with current DO technique. Craniofacial distraction osteogenesis applications first reported in the late 1980s. In 1996, Chin and Toth reported the first clinical application of vertical mandibular alveolar distraction osteogenesis.

Application of Distraction Osteogenesis This technique is applied in several areas and can be categorized into

1. Cranial distraction

2. Maxillary and Midface distraction

3. Mandibular lengthening and widening

4. Alveolar ridge distraction

Alveolar ridge distraction

Alveolar ridge distraction can be divided into 2 categories -Vertical distraction and Horizontal distraction .If both vertical and horizontal augmentations are indicated, the alveolar bone can be widen horizontally prior to vertical augmentation. This process can be done for atrophic alveolar process resulting from periodontal disease, trauma, congenital deformity, marginal bone resection of a tumor, extraction and traumatic avulsion of teeth. This process should be avoided for patients with severe osteoporosis, extremely advanced age and patients with space limitations for device placement

Approach to apply distraction osteogenesis for bone augmentation osteotomy

Under local anesthesia a horizontal vestibular incision is used to expose the bone at the level of the planned horizontal osteotomy. During exposure, the soft tissue on crestal and lingual aspect should remain intact to maintain viability of the osteotomy segment. A microsaggital saw is used to create a segmental osteotomy to mobilize the deficient alveolar ridge and sound underlying bone. The osteotomy consists of two vertical components which parallel the roots of the adjacent teeth. The horizontal osteotomy must be positioned to allow as large a transport segment as possible without compromising the structural integrity of the remaining bone. A periosteal elevator or osteotome is used with gentle tapping and levering to mobilize the bone segment. it is critical to ensure that the segment is completely released otherwise the subsequent distraction procedure will be compromised.

Device placement

1. A vertical pilot hole is drilled transmucosally through the top of osteotomy segment

2. Next, the threaded distraction rod is rotated through the pilot hole through the mucosa and the bone segment by combination of pushing and turning until the tip is seen within the horizontal osteotomy

3. The threaded transport plate is engaged by continuing rotation of the rod, which engages the large prethreaded plate hole. When in the proper position, the flat surface of the transport plate should always be facing towards the crest of the ridge

4. The unthreaded base plate fits under the threaded transport plate such that the reduced tip of the threaded distraction rod fits into its end after passing through the threaded transport plate.

5. The superior threads and larger diameter prevent the threaded distraction rod from passing completely through the unthreaded base plate.

6. The axis of distraction can be altered by moving the base plate buccally, lingually or laterally. When satisfactory position is determined , then 1.0-mm pilot holes are drilled and plates are fixed using 1.2-mm square fit screw.

7. Finally, the response of the unthreaded baseplate to the distraction forces should be observed and wound site is closed using standard suturing techniques.

8. The device is activated with a ratchet wrench and adapter to ensure proper function. The threaded transport plate should travel along with it, resulting in a vertical movement of bone segment. The osteotomized segment is then returned to normal position.

Latency period

The period from bone division to the onset of traction , which represents the time required for reparative callus formation between the osteotomized bone segments. Latency period is typically 5 to7 days long.Factors that may affect the duration of latency period include age of the patient, the extent of tissue trauma created during surgery and healing rate

Distraction period
Two major parameters are of critical importance during this period-the rate of distraction and the rhythm of distraction . The pitch on the threaded distraction rod is 0.5 mm, so one complete turn equals this vertical distances. Typically patients are distracted one or two turns (0.5 to 1.00 mm.) on a daily basis until the desired amount of vertical distraction has been achieved

Consolidation period

This period allows mineralization and corticalization of newly formed bone tissue prior to distraction deviceand removal.A 12- week consolidation phase follows the distraction phase . Then, the clinician surgically removes the distractor and simultaneously inserts implant to apply subsequent prosthetic steps.

Advantages of Distraction Osteogenesis

1.Bone lengthening amount unlimited and better controlled

2.No requirement of donor site

3.Soft tissue manipulation easier

4. Less bone resorption

5.Possible earlier implant placement than bone graft.

Complication

1.Infection – most common

2.An undesirable shape of alveolar ridge

3.Some resorption of transport segment

4.Delayed consolidation potentially development of nonunion.

Conclusion

Since free bone graft has a high total morbidity, researchers looked for alternatives. Distraction is an effective therapy for augmentation of the edentulous ridge and alternative to conventional procedures. Distraction is a promising and relatively new augmentation procedure within the discipline of the implant dentistry. Additional results from clinical studies are pending.