The Study Of Repair Dog's Mental Bone Defects With Built-in Arch Distraction Device

Objective:1. To investigate the feasibility of osteogenesis at the mode of linear stretch. To explore the difference of osteogenic mechanism between the mode of linear and leveraged distraction. 2.To observe the feasibility of repair canine mental bone defect with built-in arch distraction device. To study the shape and function of new bones via built-in arch distraction device whether or not to meet the clinical needs. 3.To compare the quality and quantity of new bones via three methods of distraction osteogenesis. 4.To explore the displacement of forming orbit board during the distraction using mandibular built-in arch distraction device.Material and Methods:Ten Chinese pastoral dogs were randomly divided into 4 groups. Two dogs with mental bone defect were distracted intermittently by the rate of 1mm every day. The left mandibular defects of 4 dogs were distracted continuously by the rate of 2mm every day, while the right defects were distracted continuously by the rate of lmm per day. After the mandibular mentums of 2 dogs were excised, the animal model of mandibular mentum bone defect was prepared.Then the distraction device was placed without distraction, as a control. Two cases were picked for the blank control. Mandibular anterior teeth of 8 dogs were removed a month before operate. In accordance with the existing conventional DO requirements, osteotomy was performed to prepare the animal model of mental bone defect and the distraction devicement was placed. Then observed marker was implanted and distraction device shift was checked. After a interim period of one week or so, the 6 dogs which accepted DO experiment entered the distraction period. They were distracted at four time points (6:00,12:00,18:00,24:00) per day, until the stretch finished. Experimental control group, blank control group and other experimental animals were fed in the same conditions until the experiment finished. After a fixed period of 4-8 weeks, distraction Osteogenesis Group completed the whole distraction osteogenesis. In the 4^th and 8^th week after distraction, the animals were killed with tetracycline hydrochloride and calcein via subcutaneous injection as two groups, the relevant parameteres were measured. After mandibular X-ray and CT examination was performed, the productions of hard tissue mill films were made so as to be observed under the fluorescence microscope.At the same time, conventional pathological sections were made to investigate the quality and quantity of new bones.Results:After distraction, the mandiblar contour of the six Chinese pastoral dogs appeared to be similar to the normal, but the mental shapes were broader than those in normal dogs. Backward shift in varying degrees appeard for distraction devices. X-ray and three-dimensional CT showed that the conveyor plate distal end of both sides succeeded in docking at the middle. In the 4^th week after distraction, three-dimensional CT and the experimental observation of histology found that new bone formed in distraction gaps, the bone conveyor plates of both sides connected at the middle of mandible mainly by fiber, secondary by bone. And active osteoblasts and the conversion activity can be seen. In the 8^th week after distraction, new bone within the distraction gap became more sophisticated, the bone conveyor plates of both sides connected at the middle of mandible gradually mainly by bone, secondary by fiber. Tissue samples showed that in the 4^th and 8^th week, there were active fibrous tissues hyperplasia and angiogenesis, osteogenic trend, bone-like matrix, woven bone structure with heteropolarity of various developmental stages, more mature bone tissues, and no cartilage-like structure was found in all specimen. The speed and quality of the left sides were better than these of the right sides in continuous distraction group. The speed and quality of continuous distraction group were better than these of intermittent distraction group. There were more woven bone tissues in left distraction gaps of continuous distraction dogs whose bone tissues were more mature. Fluorescence labeling microspecimen by tetracycline hydrochloride and calcein showed that the new bone, arraying poloidally, had Obvious fluorescence in the 4^th week after distraction; the new bone,still arraying poloidally, had many and intensive fluorescence in the 8^th week after distraction. The fluorescence width of the left side was bigger than that of the right side in the continuous distraction dogs in the 4^th and 8^th week after distraction. But no significant difference of fluorescence width between continuous distraction group and intermittent distraction group was found.Conclusions:1 .Osteogenesis at the mode of linear distraction is certain. 2.The mechanism of osteogenesis at the mode of linear distravtion is intramembranous ossification, which almost like leveraged distraction osteogenesis model . 3.The mandibular built-in arch distraction device can be used to repair mental bone defects. 4.To repair mental bone defects by mandibular built-in arch distraction device can better recover the defects and achieve the perfect combination of shape and function. 5.The quality of new formation bone by continuous distraction at the rate of 2mm per day is better than that by continuous distraction at the rate of 1mm per day. Continuous distraction is better than intermittent distraction. 6.The orbital plate can backward shift in a way when repairing mental bone defects by mandibular built-in arch distraction device.