Mandibular Distraction with MD-DOS Device

Distraction osteogenesis may be defined as the regeneration of bone between vascularized bone surfaces that are separated by gradual distraction.1 The bone is separated by an osteotomy or corticotomy and stabilized by external fixation. Distraction osteogenesis, which was first described by Codvilla2 in 1905, became popular through the work of Illizarov who used the technique to reconstruct long bone fractures without using bone or soft tissue grafts after World War II.3 

Distraction osteogenesis has become widely accepted as a treatment modality in orthopedics4,5 and recently has been broadly applied for the treatment of skeletal deformities and severe bony defects in the craniofacial complex.6–11 The application of distraction osteogenesis in the craniofacial region was first introduced by mandibular lengthening in dogs,10 and a clinical report of distraction osteogenesis of mandible was first published in 1992 and presented 10 years of experience.11 

In this case report, we present the treatment of an adult patient who had skeletal Class II malocclusion because of mandibular retrusion. The patient's chief complaint was his convex profile, and improvement was achieved through the application of an intraoral bone-born distraction device and orthodontic treatment procedures.

A 20-year-old male who had a Class II division I malocclusion was referred to the Department of Orthodontics for treatment. His main concern was his deep bite and unaesthetic profile. Cephalometric and panoramic radiographs, extraoral and intraoral photographs, and study models were obtained according to the usual protocol for orthodontic patients.

His facial profile was convex with a receding chin, a fairly deep mentolabial sulcus, and hypertonic lip musculature (Figure 1A,B). An intraoral examination revealed a Class II division I malocclusion with a deep curve of Spee, excessive overjet, and a severe deep bite. The mandibular incisors were in contact with the palatal mucosa. Diastemata were present between the maxillary anterior teeth, and a mild crowding was present in the lower anterior region. The upper left first premolar was out of occlusion (Figure 2).

Cephalometric analysis indicated an SNA of 86° and an SNB of 80°. A moderate skeletal Class II discrepancy was confirmed by an ANB of 6°. Point A and point B were one and nine mm behind the NV, respectively. The length of the effective mandible (Co-Gn = 119) was short according to the effective maxilla (Co-A = 101), and the corpus length (Go-Gn) was 73 mm, whereas the SN plane was 80 mm. Soft tissue profile analysis revealed that the tip of the upper lip was three mm and the tip of lower lip was five mm behind the esthetic line (E-line). All these norms supported each other and revealed that the patient had a skeletal Class II discrepancy.

The ramus length (Co-Go) was 56 mm, the MP angle was 18°, and the gonial angle was 118°. These values emphasized the anterior rotation of the mandible and skeletal deep bite. The anterior facial height was 120 mm, posterior facial height was 97 mm, and the ratio of these values was 80%, revealing that the patient had a hypodivergent skeletal pattern. Overjet and overbite were measured as 16 and six mm, respectively. The cephalometric landmarks used in this report are shown in Figure 3.

Clinical, radiographic, and study model examination revealed that the patient had skeletal Class II discrepancy, and surgical procedures were deemed required for the correction of the convex profile. The patient was a student at Gulhane Military Medical Academy, and he preferred distraction osteogenesis of the mandible instead of sagittal split osteotomy. Application of an intraoral distractor was planned after the orthodontic treatment.

Preadjusted appliances were placed in the maxillary and mandibular arch for leveling and alignment. Diastemata between the upper incisors were closed, and the deep curve of Spee was corrected. After the leveling phase, the distraction device was applied bilaterally for the lengthening of the mandible. The patient received Class II elastic traction during the distraction period.

The Mandibular Distraction with a Dynamic Osteosynthesis System (MD-DOS) device, produced by Normed Medizin Technik (Tuttlingen, Germany), was used as the mandibular distractor. This device is made of commercial titanium, and it comprises four components: a posterior fixation unit (PFU), a spacer, a distraction unit (DU), and an anterior fixation unit (AFU).

Surgery was carried out under general anesthesia. An intraoral vestibular incision and mucoperiosteal flap were performed in the lower third molar area up to the anterior border of the mandibular rami. Initially, a notch was cut in the anterior aspect of the cortex with a 27 round bur and deepened with the pilot drill at low speed (220 rpm). A 17-mm PFU and five-mm spacer combination were chosen for both mandibular rami. The PFU was placed near the external oblique ridge, lateral to the middle of the retromolar triangle, and as low as possible in the vestibule. The DU was connected with the PFU by a vertical hinge, allowing mediolateral rotation of the DU for comfortable positioning. Finally, the DU was connected to the AFU, which was adapted to the mandibular corpus with five-mm monocortical screws.

Once the device was fixed, a partial osteotomy was performed. The superior, inferior, and buccal cortical borders were completely transected followed by cutting the superior recess region of the lingual cortex while taking care not to damage the lingual nerve. Bone segmentation was performed with a one-cm-wide osteotome. At this point, the lingual cortex was greenstick fractured so that continuity of the cancellous bone was maintained (Figure 4A through D). The wound was closed in the usual manner. An oral antibiotic, analgesic, and mouth rinse were prescribed for daily use postoperatively during the following five-day period. A soft diet was advised during the distraction period.

After a latency period of seven days, the device was activated at a rate of 0.99 mm/day performed in three increments for 14 days. The patient rotated the DU until a different color dot was visible. Intermaxillary elastics were used to control the movement of the mandible. The patient attended the clinic every day so as to assess the progress of distraction.

After the desired position of the mandible was achieved, distraction was continued for three more days for overtreatment so that at the end of the distraction period the patient had a negative overjet with a posterior open bite. Panaromic (Figure 5A) and cephalometric radiographs were taken at the end of the distraction period to observe the distracted bone.

After the consolidation period of 10 weeks, bone formation was seen in the distraction gap on the panoramic radiograph and the distraction device was removed under local anesthesia (Figure 5B). After two months, the negative overjet of the patient had returned to normal and the patient had Class I occlusion with a posterior open bite, and box elastics were used for approximately three months before debonding. Although the transpalatal width of the patient was not narrow, forward positioning of the mandible created a relative crossbite of the upper left molar at the end of the treatment. We could not correct this crossbite because the patient did not want to use elastics any more for social reasons and wanted to end the treatment.

Posttreatment photographs (Figures 6A,B and 7A through C) and cephalograms were taken, and removable Hawley retainers were constructed. The patient was recalled at three-month intervals. A cephalometric radiograph and tomography were taken after a year, and a complete healing was present in the distraction gap on the tomograph (Figure 8).

The analyses of linear and angular changes (Table 1) were undertaken by superimposing on the cranial base. Evaluation of pretreatment and posttreatment cephalograms revealed that the overjet of 16 mm and the overbite of six mm were reduced to four and two mm, respectively. After distraction, the mandible was advanced three mm horizontally, the gonial angle increased from 118° to 126°, and the Y-axis increased from 59° to 63°. The mandible was advanced vertically eight mm, and anterior facial height, which was 120 mm before treatment, was 128 mm at the end of the distraction. Dental norms revealed that upper incisor teeth were retruded and lower incisors were protruded during the treatment (Figure 9). The superimposition of the cephalometric radiographs, taken at the end of the treatment and one year later, revealed three mm more anterior translation of the mandible (Figure 10).

Mandibular retrusion is the most common characteristic of the skeletal Class II malocclusion,12 and functional appliances are frequently used to treat the skeletal disharmony of children during the growth period. Extraction of the upper first premolars to eliminate the excessive overjet may be the treatment approach for the adults, but this method provides only dental compensation and does not address the skeletal problem. Sagittal split osteotomies are the conventional surgical techniques that are preferred for the correction of the profile and the skeletal deficiency of the adults. An alternative to the extraction of upper premolars or a sagittal split osteotomy is the lengthening of the mandible by distraction osteogenesis.

In this case, the chief complaint of this adult patient was his convex profile. Extraction of the first premolars was not preferred because it provides only dental compensation and does not solve the skeletal disharmonies. Mandibular advancement surgery was indicated to improve the facial esthetics. In the previous13,17 reports, it has been suggested that large advancements, greater than six mm, with sagittal split osteotomies increase the relapse risk because the surrounding muscles and connective tissue stretch; this relapse risk exists until adaptation to the new position occurs. The patient had an overjet of 16 mm, and mandibular advancement of over 10 mm was needed; so distraction osteogenesis was preferred to avoid the risk of relapse, although the cost of the distraction device was rather expensive. High quality of the bone regeneration and simultaneous soft tissue elongation that accompanies the distraction process has been reported to enhance stability of the advanced bone segments in the previous studies.3,11,14–18 

One of the most critical components of distraction osteogenesis is the surgical separation of the bony fragments. Although Illizarov14,15 preferred minimal disruption of the central medullary bone using a low-energy corticotomy that divides only the bone cortex, today many clinicians currently prefer a complete osteotomy of bone segments in the craniofacial skeleton for good resultant bone formation. Besides, osteotomy allows better movement of the segments and control of the planned vector of elongation. Additionally, the intraoral devices are not rigid enough to move the segment in the planned direction without an osteotomy. Therefore, an osteotomy was performed for this patient.

The operative time of the distraction osteogenesis was not longer than that of the sagittal split osteotomy. We observed less edema and pain when compared with the conventional orthognathic surgeries, and the two-day hospitalization period was also shorter. Some previous studies reported neurosensory deficiency in the region innervated by the inferior alveolar nerve and reduction in the taste function on the tongue after sagittal split osteotomy.19–21 Another complication that may develop after sagittal split osteotomy has been reported is the worsening of preexisting temporomandibular joint (TMJ) dysfunction.22,23 This patient did not develop sensory disturbances of the inferior alveolar nerve, and he was not subjected to pain at either the distraction site or the TMJs. Thus, the distraction period was not an uncomfortable experience, and he easily got used to the distraction screws.

The mandible is a three-dimensional V-shaped structure that articulates with the skull at two locations. Alteration of one side automatically affects the other side, so determination and control of the distraction vector is an important phase of the treatment. Class II elastics were given to the patient to increase the stability and to direct the movement of the distal segment during distraction. It was more comfortable for the patient to have elastic traction because it minimized the movement of the mobile segments. Position of the midline was observed continually during the advancement, and sometimes the vector of the elastics was changed to correct the deviation of the midline. Patients, who are treated with conventional orthognathic surgery, should also wear continuous elastics in a triangular or box formation. The patient visited the clinic every day so as to control the progress of distraction, but frequent visits were not difficult because he was the student in our academy. In our opinion, five-day intervals are enough during the distraction period.

After the consolidation period of 10 weeks, the distraction device was removed under local anesthesia. The necessity of two operations is a disadvantage of this technique. Another disadvantage may be the difficulty of cleaning the distraction devices but we did not face such a problem in this patient.

Distraction achieved the desired result in this case as assessed clinically and on cephalograms. Pretreatment and posttreatment cephalometric superimposition revealed adequate correction of overbite and overjet. Additionally, a relatively short facial height and reduced gonial angle approached normal values after the elongation and posterior rotation of the mandible. At the end of the one-year follow-up period, it was observed that anterior translation of the mandible continued as a result of remodeling. No relapse was determined.

• Lengthening the mandible with distraction osteogenesis or sagittal split osteotomy for assisting orthodontic procedures may be the treatment alternatives for adults with such deformities.

• Sagittal split osteotomy has relapse risk if mandibular elongation is greater than six mm. In this case report, we preferred distraction osteogenesis to enhance the stability of the treatment.

• The distraction period was not an uncomfortable experience for the patient. No major discomfort was noted either at the distraction site or at the TMJs.

• The disadvantages of distraction osteogenesis seem to be the necessity of two operations, frequent visits to the clinic and the cost of the distraction device.

• Adults with mandibular hypoplasia with deep bite and low facial height can be treated effectively by means of MD-DOS, and this technique may provide a treatment alternative to sagittal split osteotomy.