Jason B. Cope

Biomechanical considerations of mandibular lengthening and widening by gradual distraction using a computer model

PURPOSE Experience using distraction osteogenesis for limb lengthening has shown the importance of appliance orientation. Although successful results of mandibular lengthening using osteodistraction have been reported, optimal orientation of the distractors relative to the mandible has not been determined. The purpose of this study was to evaluate the biomechanical effects of linear distractors placed parallel to the body of the mandible or parallel to the axis of distraction. MATERIALS AND METHODS A two-dimensional model of the human mandible was generated for computer simulation of mandibular osteodistraction. Linear distractors were then analyzed based on their orientation, either parallel to the body of the mandible or parallel to the axis of distraction. In addition, two types of distraction osteogenesis procedures for mandibular reconstruction were analyzed: 1) bilateral mandibular lengthening, and 2) bilateral mandibular lengthening in combination with midline mandibular widening. RESULTS Distractors oriented parallel to the body of the mandible caused a lateral displacement of the posterior components of the distraction devices and a reduction of the midline distraction gap during mandibular lengthening. These effects were eliminated when the device was oriented parallel to the axis of distraction. Midline symphyseal widening created axial rotation of the mandibular condyles regardless of the orientation of the distractors. CONCLUSIONS Distraction appliances must be oriented parallel to the axis of distraction to prevent adverse biomechanical effects during bilateral mandibular lengthening. Additional ramus osteotomies, using hinged devices for angular correction, may be necessary to compensate for rotational movements of the mandibular condyles secondary to midline osteodistraction.

Mandibular distraction osteogenesis: A historic perspective and future directions

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.

Quantitative evaluation of craniofacial changes with Jasper Jumper therapy.

Although the Jasper Jumper is becoming a widely accepted orthodontic appliance, no quantitative guidelines exist for therapy. The purpose of this investigation was to describe the orthopedic and orthodontic changes associated with Jasper Jumper therapy. A sample of 31 consecutively treated Class II patients was collected from three orthodontic practitioners who were using the same procedures and methods. Lateral cephalograms were taken immediately before appliance placement and immediately after appliance removal (mean interval of 0.4 years). The sample was case matched to untreated controls based on age, sex, and mandibular plane angle. The cephalograms were superimposed using anterior cranial base, maxillary, and mandibular reference structures to distinguish between growth/displacement and tooth movement. The results show that the majority of Class II correction was due to dental, rather than skeletal change. The maxilla underwent significant posterior displacement. The maxillary incisors retroclined and the maxillary molars tipped distally. Clockwise or backwards rotation was evident for the mandible. The mandibular incisors proclined significantly and the mandibular molars translated and tipped mesially. Jasper Jumper therapy is a valuable procedure for the correction of Class II dental malocclusions. Like all other treatment modalities, there are both indications and contraindications for its use.

Regenerate Bone Formation and Remodeling During Mandibular Osteodistraction

The purpose of this study was to evaluate the newly formed bone during the consolidation period of mandibular osteodistraction using quantitative histology. Seventeen skeletally mature conditioned male beagle dogs underwent 10 mm of bilateral mandibular lengthening. After distraction, the regenerates were allowed to consolidate for 0, 2, 4, 6, or 8 weeks, at which time the animals were sacrificed and tissues harvested for standard histologic and histomorphometric analyses. Mineralization began at the host bone margins by the end of the distraction period, followed by a progressive increase in trabecular bone, with a concomitant decrease in the amount of fibrous tissue. Between 4 to 6 weeks of consolidation, 3 types of relatively mature distraction regenerates were evident. The mineral apposition rate gradually increased from the end of distraction to the fourth week of consolidation, at which time it remained constant until sometime before the eighth week, when it tapered off slightly as remodeling increased.

Evaluation of inferior alveolar nerve function during distraction osteogenesis in the dog

PURPOSE A series of electrophysiologic studies were performed in a canine model to evaluate inferior alveolar nerve (IAN) function during distraction osteogenesis of the mandible. MATERIALS AND METHODS Fourteen dogs, including two controls, were used in the study. Twelve dogs underwent a 10-mm bilateral mandibular lengthening with an intraoral bone-borne appliance and midbody osteotomy. By using sensory nerve action potentials, IAN function was assessed before and immediately after surgery, before and at the completion of distraction, and before necropsy after 4, 6, or 8 weeks of fixation. RESULTS Twelve of the 24 nerves showed a complete loss of evoked potential after surgery without recovery at any point throughout the study. Acute nerve injury caused by either the osteotomy or screw encroachment was identified at necropsy. The other 12 nerves showed reproducible responses after surgery. Eight of these nerves had significant amplitude attenuation of the evoked potentials, which was identified at necropsy as a result of acute injury. The remaining four nerves did not show significant evoked potential abnormalities and appeared to be grossly normal at necropsy. During distraction, the amplitude of evoked potentials in all 12 nerves remained at the postoperative level, whereas latency showed a significant delay. In 7 of these 12 nerves, various degrees of evoked potential recovery were identified at the completion of the study. CONCLUSIONS The high incidence of acute IAN injury in the current study was primarily related to device construction and osteotomy technique. If acute nerve injury is avoided at surgery, distraction osteogenesis with 10 mm mandibular lengthening appears to produce minimal deleterious effect on IAN function.

Evaluation of the consolidation period during osteodistraction using computed tomography.

The use of distraction osteogenesis offers an alternative approach to the correction of craniofacial deformities. However, little is known with respect to the appropriate length of the consolidation period for the newly formed bone. The objective of this study was to evaluate, by quantitative computed tomography, the regenerate bone produced during osteodistraction of the dog mandible at three different consolidation times. Twelve skeletally mature male beagle dogs were equally separated into three experimental groups. Each dog underwent 10 mm of bilateral distraction osteogenesis to lengthen the mandible. After the distraction period, the bone was allowed to consolidate for 4, 6, or 8 weeks, at which time the animals were sacrificed and the mandibles harvested for computed tomographic imaging. The results demonstrate a significantly lower mean bone density of the regenerate in the 4 week group when compared with either the 6 or 8 week groups (P < .01). There was no significant difference, however, in mean bone density between the 6 and 8 week groups.

Distalization of the mandibular dentition with mini-implants to correct a Class III malocclusion with a midline deviation

This article describes the orthodontic treatment for a young woman, aged 23 years 5 months, with a Class III malocclusion and a deviated midline. Two orthodontic mini-implants (C-implants, CIMPLANT Company, Seoul, Korea) were placed in the interdental spaces between the mandibular second premolars and first molars. The treatment plan consisted of distalizing the mandibular dentition asymmetrically and creating space for en-masse retraction of the mandibular anterior teeth. C-implants were placed to provide anchorage for Class I intra-arch elastics. The head design of the C-implant minimizes gingival irritation during orthodontic treatment. Sliding jigs were applied buccally for distalization of the mandibular posterior teeth. The active treatment period was 18 months. Normal overbite and overjet were obtained, and facial balance was improved.

Biomechanics of mandibular distractor orientation: An animal model analysis

PURPOSE Previous reports suggest that device orientation may be one of the most important parameters affecting the successful application of osteodistraction. However, only computer models or cadaver mandibles have been used to investigate the biomechanical effects of device orientation during mandibular distraction osteogenesis. Therefore, the purpose of this study was to compare two different device orientations during bilateral mandibular osteodistraction in an animal model. MATERIALS AND METHODS Fifteen skeletally mature beagle dogs underwent 10 mm of bilateral mandibular lengthening by intraoral distraction osteogenesis. The dogs were divided into two groups based on the orientation of the distraction device relative to the mandible when viewed occlusally: either parallel to the body of the mandible (group I) or parallel to the axis of distraction (group II). The effects of device orientation during osteodistraction were then analyzed clinically, radiographically, and by dental cast measurements. RESULTS Distractors oriented parallel to the body of the mandible caused an increase in the anterior width of the proximal mandibular segments. This lateral displacement of the proximal segments led to several clinical complications, including screw fixation failure and bone resorption under the fixation plates. These effects were minimized when the device was oriented parallel to the axis of distraction. CONCLUSIONS Device orientation plays an important role when applying distraction osteogenesis in a clinical setting. Although other intrinsic and extrinsic factors affect the success of osteodistraction, the devices should be oriented parallel to the axis of distraction to minimize adverse biomechanical effects during bilateral mandibular lengthening.

The Effect of Sagittal Orientation of the Distractor on the Biomechanics of Mandibular Lengthening

PURPOSE It has been previously demonstrated that distractors placed parallel to the mandible in the transverse plane, without regard to the vector of distraction create lateral displacement tendencies at the appliance-bone interface, leading to potential clinical problems and complications. The purpose of this study was to evaluate the biomechanical effects of linear distractor orientation in the sagittal plane relative to the anatomic axis of the mandible (mandibular plane) and the maxillary occlusal plane. MATERIALS AND METHODS A 2-dimensional model of the human mandible was generated for computer simulation of osteodistraction. Positional changes of the distal mandibular segment were then analyzed during 10 mm of incremental lengthening based on distractor orientation relative to the maxillary occlusal plane. RESULTS Distractors placed parallel to the inferior border of the mandible without regard to the maxillary occlusal plane created a vertical translation of the distal bone segment resulting in an anterior open bite. The magnitude of the anterior open bite was proportional to the angle between the vector of distraction and the maxillary occlusal plane, and to the amount of distraction. Placement of the distractors parallel to the maxillary occlusal plane eliminated the tendency for an anterior open bite. CONCLUSIONS The orientation of the distractors relative to the maxillary occlusal plane is one of the important biomechanical parameters that must be included in preoperative planning for mandibular osteodistraction.

Experimental tooth movement through regenerate alveolar bone: A pilot study.

The purpose of this pilot study was to experimentally evaluate tooth movement through regenerate bone at an early time point during the consolidation phase after bilateral mandibular osteodistraction. Two beagle dogs underwent 10 mm of bilateral mandibular lengthening via intraoral distraction osteogenesis between the fourth premolars and first molars. After 1 week of consolidation, retraction of the fourth premolars was initiated. Immediately after completing premolar retraction, the dogs were sacrificed and the mandibles were analyzed radiographically, histologically, and by dental cast measurements. Initially, all 4 fourth premolars moved distally, with 2 of the 4 touching the first molars at the time of sacrifice. Based on the current data, it is possible to move teeth through regenerate bone, and it appears that tooth movement can begin within weeks of starting the consolidation period.