44.) Distraction osteogenesis of the craniofacial skeleton in the patients with dento-facial deformities
Distraction osteogenesis is a clinical therapy which enables new bone and soft tissues to be generated by expanding the bone after a corticotomy, and is now becoming an alternative of surgical treatments for the patients with a severe hypoplasia of the craniofacial skeleton. Ilizarov, a Russian orthopedic surgeon, brought this concept into wide clinical application for the purpose of treating the patients with bone defects ranging from posttraumatic injury to congenitally shortened lower extremities in the mid 20th century.
Application of distraction osteogenesis into craniofacial deformities has rapidly spread worldwide in this decade since McCarthy et al. at New York University reported extensive animal studies and clinical applications of mandibular distraction osteogenesis. To date, many intraoral and extraoral distraction devices have been manufactured for various types of usage in the dento-facial deformity patients.
II. Biological basis of distraction osteogenesis
It is reported that a success of distraction osteogenesis is dependent on the patient variables (age, type of abnormality), devices (intraoral, extraoral), latency period before mechanical activation, and the rate and frequency of the activation.
Consolidation period is also indispensable for stabilizing the newly generated bone. Many experimental studies based on the animal models have illustrated that primitive mesenchymal cells appear at the site of corticotomy, and they form new blood vessels and fibrovascular networks at early phase of the latency period. During the distraction, collagen bundles increase in size and become oriented in parallel with the distraction force.
Osteoid synthesis and the subsequent mineralization take place at the edge of the cut bone surfaces and adjacent to the newly formed blood vessels. Ossification is completed by membranous bone formation, as well as by endochondral bone formation.
III. Treatment of dento-facial deficiencies by distraction osteogenesis
Distraction osteogenesis can be applied to various types of skeletal deficiency in the craniofacial region. Distraction is sometimes performed in small children with micrognathia causing severe airway obstruction. Unless there is airway compromise, distraction may often be postponed until the stage of post puberty. In case of midface deficiency, distraction may be planned in combination with Le Fort I and /or Le Fort III corticotomy using the rigid external device. In this presentation, clinical cases of dento-facial deformities treated by distraction osteogenesis will be presented, and the role of orthodontists in the team approach to those patients will be discussed.
1) Unilateral and bilateral distraction of mandibular hypoplasia
Non-surgical and surgical orthodontic treatments of Class III malocclusion
I. General aspects of Class III malocclusion
Class III malocclusion is one of the relatively common orthodontic problems in the Japanese orthodontic population with an incidence higher than that of the Caucasian or African-American orthodontic populations. Class III is a classification of the molar relationship in which the mesiobuccal cusp of the maxillary first molar occludes distal to the buccal groove of the mandibular first molar.
Those malocclusion patients who have the Class III molar relationship may often associate with various problems in the dento-facial components not only in horizontal, but also in transverse and vertical dimensions. It is also notable that some patients with Class III malocclusion would concern about the functional and psychosocial discomforts caused by such morphological problems.
The etiology of Class III malocclusion is mostly unclear in each individual case, but it is speculated that some genetic or environmental causes may contribute to the excessive growth of the mandible or the underdevelopment of the maxilla in these cases.
II. Diagnosis and treatment planning of Class III malocclusion
It is no doubt that the careful examination and diagnosis of the dento-facial structure and function in consideration of the growth stage of the patients are the keys to success in the treatment of Class III malocclusion.
Class III malocclusion represents various degrees of occlusal disharmonies.
For example, CR-CO shift in growing patients, which creates a cross bite of the incisors, so to speak pseudo Class III, may be a less severe situation in the category of Class III malocclusion.
Elimination of the premature contact of the teeth may sometimes allow the both jaws to grow in a harmonized manner. If a tendency of transition to skeletal Class III malocclusion is noticed, chin cup or reverse-pull headgear therapy may be indicated.
On the contrary, a severe skeletal Class III malocclusion, which is associated with a significant negative overjet even in the presence of dental compensation, might be a case beyond the limitation of the orthodontic approach, and a surgical orthodontic treatment will be performed in such kind of cases.
III. Treatment of Class III Malocclusion
_1) Non-surgical orthodontic treatment
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