Effect Of Rapid Tooth Movement By Periodontal Ligament Distraction On Collagen Ⅰ And Ⅲ Metabolism In Dog Periodontal Ligament

Objectives:To set up the experimental animal model of distraction of the periodontal ligament (DPDL) after reducing interseptal bone resistance, compared the speeds of tooth movement between methods of DPDL and roution orthodontic tooth movement, and to observe the difference of content changes of collagen I and III between the two methods.Methods:Nine male purebred Beagle dogs were randomly divided into 5 groups as 6W group, 4W group, 2W group, 1 W group (each group has two dogs) and the normal control group(one dog). The second mandibular premolars were extracted on both sides of the nine dogs. We selected one side for DPDL and the other side for roution orthodontic tooth movement.We defined the first mandibular premolars as the movement teeth and the third mandibular premolars as anchorage teeth. The second premolars were extracted and the interseptal bones were undermined then a tooth-borne, custom-made distractor was bonded on DPDL side;While a NiTi spring was bonded on the other side after the second premolar extracted. The distractor was activated 0.35mm/d, twice a day for 2 weeks and followed by retention period. The NiTi spring was activated about 150g force for 2 weeks and followed by retention period. The distance of tooth movement was measured, and periodic X-rays were taken for observation of bone formation.Sacrificed the dogs followed by the above individual group time frame and fixed,decalcified,paraffin-embedded ,sliced. The periodontal ligament tension side changes of the moved tooth were harvested for HE staining and observed under light microscope. The content changes of collagen tape I and III on tension side were observed under a polarizing light microscope with Picrosirius Red Staining (PRS). The statistical analyses were performed using the SPSS11.5 statistical program.Results:After one week, the first mandibular premolars were distalized an average of 1.14mm on the DPDL side compared with 0.37mm on the roution control side. Significant difference was observed between the two methods(P<0.001). By the time of two weeks, the first mandibular premolars were distalized an average of 3.76mm on the DPDL side compared with 0.37mm on the roution control side. Significant difference was observed between the two methods(P<0.001). New alveolar bone was generated and remodeled rapidly in the tension side of PDL during and after the distraction from X-ray views.No obvious bone formation was observed on the roution control side.In the histological study, After one week, periodontal ligament was significantly wider in DPDL side than in roution control side.The proliferation of fibroblasts and osteoblasts in the tension side of experimental side was more than the roution control side.The roution control side showed new bone less homogeneous. The periodontal ligament width in 4W group returned to normal.The periodontal ligament of the 6W group under the two methods had been no significant difference.Through the method of Picrosirius Red Staining, the increment of Collagen Type I in the tension side of DPDL group was less than the routine control group both on the end of one week and two weeks. The peak value of Collagen Type I in the DPDL side appeared at the end of two weeks(75.23%) compared with that in the roution control side(76.27%) at the end of two weeks.Significant difference was observed between the two methods(P<0.01). Under both methods the content increment of Collagen Type I was significantly different compared with the normal control side (P<0.01).The peak value of Collagen Type III in the DPDL side appeared at the end of one week(20.16%) compared with that in the roution control side(20.14%) at the end of two weeks.Significant difference was observed between the two methods(P<0.01).The changes of Collagen Type I and III in both DPDL side and roution control side were time dependent.Conclusions: 1.The animal model of DPDL after reducing interseptal bone resistance of beagle dog was feasible.2. The DPDL method could accelerate the tooth movement through reducing interseptal bone resistance.3. The metabolism of collagen of rapid tooth movement through distraction of the periodontal ligament was similar to the roution orthodontic tooth movement, but it was more quickly. So this method could accelerate the renovation of Periodontal Ligament.Moreover, the long-term effects of this method were unknown and further research was needed.