The Effect Of Mini-implants With Horizontal Force On The Normal Mandibular Growth In Growing Dogs

Objective: An experiment was carried out to study whether mini-implants with horizontal force have effects on normal mandibular growth in growing dogs.Methods:For this purpose 6 growing dogs were choosed .One side of mandible was randomly selected as experiment group. The other side was the control group .On the first week ,lower P3 were extracted from each of 6 dogs .On the sixth week ,mini-implants were placed on the reign of buccal side of P4 M1 M2 and lingual side of M1 M2 ,about 6 mm under the gum margin .On the eighth week , mini-implants located in the buccal of P4 was as anchorage to pull P2 distal ,applying a force 80 g with the power chain . Two mini-implants at the buccal side of M1 M2 were dred each other ,applying a force 80 g . The same to the lingual ones . The power chain was changed one time for three week .The opposite mandibular bone without implants served as a control grorp .Total 30 mini-implants were placed in 6 dogs .On the twentieth week ,6 anesthetized animals were fixed by intracardiac perfusion and taken the X-ray .The segments with mini-implants were dissected for evaluations by histological slice (calcified slice and decalcified slice )and bone morphometry (calcified slice ). The rate of osseointegration was measured by Image-Pro. Plus 4.5 on the longitudinal calcified sections.Result:1. Gross and X-ray studies: In 30mini-implants 86.67% are stable, 13.33% are failed. Few of them have some infection around the neck of the mini-implant and soft tissues hyperplasia. The surface of the compressed root of P2 was not found obviously root resorption .2. The result of measurement was dealt with Windows SPSS 10.0 by Paired-Sample homogeneity of variance test . The F of length between test group and control group is 2.26(P>0.05).The F of width between test group and control group is 1.33 (P>0.05).The F of highth between test group and control group is 1.86 (P>0.05). All of them have no significant difference .3.The teeth P2 are drew distal evidently4.For a few mini-implants there are some inflamed cells around the neck of them. The surface of the compressed root of P2 has found some resorption ,but only restricted at cement .Calcified slice and decalcified slice are shown peri-implant partially touched the mini-implant surface. The rate of osseointegration between the bone and the titanium surface is 18.24±1.13%.5. We can easily pull out the mini-implants with the screws after being used.Conclusion:1. Mini-implants with horizontal force have no significant effect on the normal madibular growth in growing dogs .2. Mini-implant as anchorage in growing period can draw theeth distal effectively .3. As for peri-implant bone, there was only a slight osseointegration between the growing bone and the titanium surface.4. Mini-implant is easy to placing and pulling out with the screws.5. The placing area should better avoid the labial and lingual frenula. After surgical placing, it is very important to keeping intraoral hygiene and stability of the mini-implant.