Exploration Of An Animal Model Of Root Damage And Repair

Background:Pathological root absorption, as common dental clinical phenomenon, often follows the replantation of evulsed tooth, impacted tooth, oncothlipsis and severe infection. It could be ceased by removal of the pathological factors in some cases, and still advances in other cases. Root resorption is a complex pathological process, involved by odontoclast and various other factors. However, it is still rare known regarding the mechanism and the relationship between root resorption and self-reparation.The relative experiments upon root resorption and repair are necessary for the exploration of the exact mechanism. Because of the irreversibility of the process, root resorption is primarily explored by retrospective clinical studies. Therefore, it is necessary to establish an animal model of root resorption/damage and repair in order to observe exactly the process and the involving factors. In most of previous studies, excessive orthodontic force was used to induce root resorption and the force was ceased until the occurrence of root resorption so as to observe the response of root reparation. However, the process of root resorption and repair is apt to be interferenced by various factors, such as modes of orthodontic force placed, force degradation and some locally non-controllable factors, so the established animal models is unstable and difficult to repeat. Objective:1. Beagle dogs'teeth are subjected to surgery expose and damage at the root surfaces or insert anchorage miniscrew implants and spin out at the root sites for the purpose of generatation of root damage and observation of repair. One of the aims of the study is to explore the better experimental animal model of root damage and repair based on the comparison of both of the above procedures.2. By the relevant measurement of anatomy regarding the Beagle dogs'teeth root, the other aim of the study is to to provide the data for the location of the insertion site of the implant in the experimental animal model of root damage and repair.Methods:Experiment I:Comparison of two experimental animal models of root damage and repair.Four experimental Beagle dogs were selected in this study to made root damage:1. Root surface exposed and damaged:There were three damaged sites in each quadrant. They were the junction of apical 1/3 and middle 1/3 on the distal root surface of canine, the junction of cervical 1/3 and middle 1/3 on the mesial root surface of canine and the middle 1/3 on the mesial root surface of the third incisor. A total of 48 sites, as 12 sites for each dog were included in this study. The mucoperiosteal incision was made near the scheduled damaged sites, the mucoperiosteal flap elevated, the root positioned, the bone removed by the ball drills, and defect made in the sites of root surface with 4.0 mm long,1.2 mm wide and 1.2 mm deep. The operation area was rinsed, and the mucoperiosteal flap was reset and sutured. 2. Root damaged by MIA implanted:There were four damaged sites in each quadrant. The teeth included left and right first, second, third and fourth premolars in maxilla and second, third, fourth premolar and first molar in mandible of each dog. In details, the damaged sites were selected at the distal surface of the mesial roots of upper second and third premolars, and lower second, third, fourth premolar and first molar. The mesial surface of the distal roots of upper fourth premolars and the distal root surface of upper first premolar (as the upper first premolar was of single root) were selected as the damaged sites. A total of 64 sites, as 16 sites for each dog were included in this study. Anchorage miniscrew implants (MIA) with 1.5 mm in diameter were inserted perpendicularly to the long axis of the teeth at the pre-designed sites at about 10 mm deep, and spinned out immediately.The situation of the root damage was evaluated by CT right after operation. Penicillin was injected intramuscularly for 1—3d to prevent infection after operation. Semi-liquid food is given in postoperative day and all soft food after that. The wound healing was observed regularly. Animals were sacrificed by excessive anesthetic 8 weeks later. Specimens of each damage site were harvested and decalcificated by EDTA for 8 to 10 weeks, then proceeded routine section, HE staining and morphological observation. The morphology of periodontal and root damage was observed and the surgical healing and cementum repair by two procedures were compared.Experiment II:The applied anatomical survey of dog's posterior teeth as the guide for MIA implanting in the experiment of root damage and repair:Five well-developed and healthy adult Beagle dogs were selected and sacrificed by excessive anesthetic. The buccal bone of upper and lower second, third, fourth premolar (Pm2, Pm3, Pm4) and lower first molar (M1) was removed to expose their roots. The crowns of the teeth were kept intact carefully during the operation. A total of 70 teeth, as 14 teeth for each dog were included in this study. The anatomy of the each teeth was observed, and the indices such as AB (the greatest mesiodistal diameter of the crown which is perpendicular to the long axis), Dm (the distance from the point D to the mesial root surface), Dd (the distance from the point D to the distal root surface) and Df (the distance from the point D to the root furcation) of each teeth were measured and analyzed statistically.Results:Comparison of two experimental animal model of root damage:1. After 8 weeks, various repair response could be found at the root surface and defect area prepared by both of the damage procedures, the formation of new cementum and periodontal ligament reattached can be seen at the surface of root damage.2. The form of root and periodontal damage:CT showed that the shape of root defects prepared by the method of surface exposed and damaged was irregular, and the damage shadow can be seen in the surrounding tissue. The defects of root and periodontal tissue prepared by MIA implanted were uniformly round, and no significant damage was found at the surrounding tissue.3. Situation of the surgical healing:four dogs kept alive after the operation and their diet and activity is normal. The healing of surgical wound left by the method of surface exposed and damaged was delayed, and the wound was still red or swelling a week postoperatively. However, no overflow pus was found, and the wounds healed 2 weeks later. By contrast, the surgical wound prepared by the method of MIA implanted has not been found infected or pus overflow, and healed well a week postoperatively.4. Repair of cementum:The histological observation showed that the shape of periodontal defects prepared by the method of surface exposed and damaged was irregular. it was rugged on the bottom of the defect of root surface. Twenty one sites were observed repair of root damage successfully, as total 48 sites of root damage of four dogs, accounting for 43.8%. The remaining sites were left not damage at the roots or damage too deep to injure the pulp. No cementum repair was observed at some root damage. The defects of root and periodontal tissue prepared by MIA implanted was uniformly round. It appeared approximate arc on the bottom of the defect of root surface. Forty two sites were observed repair of root damage successfully, as total 64 sites of root damage of four dogs, accounting for 65.6%. A few sites were found damage just limited to alveolar bone, periodontal ligament or the pulp.The applied anatomical survey of dog's posterior teeth that MIA implanted in the experiment of root damage and repair:1. The observation of anatomic form of the posterior teeth of Beagle dogs:the second, third, fourth premolar and first molar of upper and lower jaws had their own characteristics and morphology.2. The value of specific sites Dm, Dd, Df of the teeth on both sides with the same name had no significant difference (t values equal to 0.466,-1.871,1.763 respectively; P values equal to 0.644,0.070,0.087 respectively). The measured values of index of teeth in upper and lower jaws were normally distributing, Dd and Dm values were almost equal, the average of Df value was more than 4.0 mm.3. The interspace between the posterior tooth root of Beagle dogs was small relatively, while the interspace of root furcation area was large. This area between the furcation was relatively satisfactory for implanting MIA, and it was initially recognised that D points can be used as point of reference for MIA implanted here. During positioning MIA implantation, the author suggests that the following formula can be refered to:d=Dm (Dd)-Φ/2.Conclusion: 1. Eight weeks after operation, various repair response appeared at the root surface and defects prepared by both the method of surface exposed and damaged and the method of MIA implanted. The formation of new cementum and periodontal ligament reattached can be seen at the surface of root damage. It seems that the animal model of root damage and repair has been established successfully.2. The method of MIA imlplanted is better for the animal model of root damage and repair than the method of surface exposed and damaged.3. By achieving the quantitative measurement of real specimens of posterior tooth root of Beagle dogs, the reference point that the study selected is ideal. The location method d=Dm (Dd)-Φ/2 that based on this is more simple. It can be a meaningful reference for the establishing of the animal model of root damage and repair.