Summer 2000 Presentation Summary:

Distraction osteogenesis is a surgical procedure designed to increase bone dimensions. Its origins are traced to a Russian orthopedist named Ilizarov who used the technique to increase the length of human limbs. Dr. Guerrero has pioneered modifications of Ilizarov's original concepts for use in the m axilla and mandible.

The biological basis for the technique is based on Wolf's Law, which states that bone will change shape when subjected to mechanical forces. Distraction applies tension-stress to bone through the use of traction devices. These devices s timulate the formation of new bone in the areas under stress and allow for the elongation of bones without the use of bone grafts.

Innovative Use of Technique

Dr. Guerrero presented an innovative use of the technique to expand arch length in the anterior portion of the mandible. The ability to increase intercanine width in the mandible with predictability and stability on the order of 7-8mm could revolutionize orthodontic treatment planning. No longer is the intercanine width "inviolate." Extractions of premolars or incisors solely on the basis of anterior segment crowding and avoidance of dental expansion are now unnecessary if patients are willing to undergo the distraction procedure.

Surgical Procedure/Expansion

The surgical procedure is performed on an ambulatory basis with IV sedation and local anesthesia. The expansion appliance is the traditional Hyrax screw, which can be anchored either on the mandibular molars and premolars, or directly attached to the bone of the symphysis. A vertical osteotomy is made through the symphysis and between the roots of the mandibular incisors. (Root separation can be achieved orthodontically in the presurgical preparation.) The initial cuts are made with a #701 fissure bur and completed with a fine chisel. At this point the Hyrax screw is activated 6-8 turns to be certain the bone has been separated completely. Blanching or tearing of the gingival tissue must be avoided. An advancement genioplasty is often done at this time if indicated for cosmetic reasons. A latency period of seven days must follow before distraction can begin.

The Hyrax screw is activated 1 mm per day until the proper width is achieved. Acrylic is placed over the screw to prevent rewinding and a plastic pontic tooth is tied to the archwire in the distraction site for esthetics and stability. Orthodontic movement of the adjacent incisors must wait for 60 days. This is the time required for bone to regenerate in the newly opened site. Radiographs are taken at two-week intervals to assess the radiopacity of the newly formed bone. Light forces are applied to the in cisors and the pontic tooth is reduced to allow incisor alignment.

Traditional orthodontic finishing and retention are then completed. Conventional Hawley, Essix or fixed lingual retainers are recommended.

Advantages

This technique allows nonextraction treatment of a crowded mandibular arch along with dramatically shortened treatment time. These advantages may outweigh the increased cost and morbidity of the distraction surgery for many patients. Presenting this approach as a treatment alternative to our patients will require additional training for the orthodontic/surgical team but the beautifully treated cases presented by Dr. Guerrero should serve as an incentive to move in this direction. An excellent reference for this technique complete with illustrations can be found in The British Journal of Oral and Maxillofacial Surgery {(1997) 35:383-392.

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