# Intermodular Mandibular Distraction Osteogenesis--A Preliminary Report
## 2 Materials and Methods
### Treatment Sequence  
1. Pre-operative orthodontic treatment  
If possible, a small gap was created orthodontically between the distal root of the first mandibular molar and the mesial root of the second molar. This is where the transverse interpolar osteotomy is performed (Figure 2). The class II/2 relation in the upper jaw was decompensated as much as possible by orthodontic treatment.  
Figure 1: Cephalometric analysis before Intermolar mandibular distraction osteogenesis (IMDO) treatment. (**a**) Class II/1 occlusion. (**b**) Desired mandibular advancement distal to the first mandibular molar.  
Figure 2: Distractor placement in the molar region of the lower jaw. Osteotomy between first and second molar. © Copyright Kei Koyama 2020. All rights reserved.  
Surgical procedure  
All patients were treated under general anesthesia via nasal intubation. Peri- and postoperatively, patients were shielded with antibiotics for one week. After incision of the mucosa from the second premolar to the retromolar region in the deepest point of the vestibular crease the mental foramen was identified. After subperiosteal preparation a fine fissure drill was used to mark the vertical osteotomy line between the first and second molars. The distractors used were the Zurich Pediatric Ramus Distractors(r) and the Zurich II Distractors(r) from KLS Martin (Tuttlingen, Germany) with a distraction length of 20 mm. The distractor was adapted and temporarily fixed before osteotomy. Since DOG is unidirectional, care must be taken to ensure that the distraction vector is aligned as parallel as possible to the occlusal plane. Only in cases of an extreme deep bite, the vector must be directed slightly caudally. After removal of the distractor, the buccal cortical osteotomy was completed with a fine Lindemann drill and deepened between the roots with the micro saw and a fine straight 5 mm chisel. The osteotomy in the mandibular canal and lingual cortical region was performed with utmost care. The osteotomized jaw segments were mobilized and the distractor was definitely fixed. An identical procedure was performed on the opposite side. The distractors were then activated to check function and vector direction. Hemostasis and wound irrigation with saline before wound closure with Vicryl(r) 4x0 (Ethicon, Somerville, NJ, USA) were performed. Care was taken to ensure a comfortable position of the activation rods, which were mostly located in the fold of the envelope behind the lower lip.  
Active distraction  
One week postoperatively patients were advised to start with distractor activation once a day by 0.5 mm. If there was no midline deviation, symmetrical activation on both sides was advised. Duration of the active treatment phase depended on the growth deficit of the mandible. Once a week patients were seen by the orthodontist or surgeon. The activation was stopped when cusps and molars were in class I relation or a slight overcorrection was reached.  
After active distraction, a consolidation period of approximately 8 to 12 weeks followed. To make this period more convenient the activation rods were detached. All patients had reached a class I occlusion at the end of the combined orthodontic-orthognathic procedure. After active distraction and a consolidation interval of 3-5 months the distractors were removed.  
Distractor removal  
General anesthesia was again required for distractor removal.  
Orthodontic treatment was continued after distractor removal until a perfect class I occlusion had been reached.  
For this study we have measured the length of advancement of the mandible. All measurements were conducted from the panoramic X-rays one day postoperatively and just preoperatively to distractor device removal. The difference in length of the distractor on each side was measured on these X-rays. Since the actual length of the distractor device is known, the scale from image to reality could be calculated. Finally the measured number could be converted to the actual distance of advancement.