The Animal Experiment Study Of The Magnetic Treatment System Combined With Miniscrews

Objective:To design the Magnetic Treatment System Combined with Miniscrews(MTSCM),and compare the effects on tooth movement and formation of new bone between MTSCM and mechanical force combined with miniscrews through animal experiment.Method:1.Design and assembling the Magnetic Treatment System Combined with Miniscrews(MTSCM).A new Magnetic Treatment System Combined with Miniscrews was designed based on the attractive forces of N52Nd2Fe14 B magnets combined with a reactivation system.The force/distance(F/D)for the system was determined by using an INSTRON universal dynamometer repeatedly and separately.2.Animal experimentThe experimental sample consisted of 12 mature male beagle dogs aged 12 months,which were assigned randomly to two groups,with 6 dogs in the Magnetic Treatment System Combined with Miniscrews(MTSCM)group receiving the new-designed magnetic system(M group),6 dogs in the mechanical system group receiving the force of nickel titanium tension spring(G1 group)and the other side of the mechanical system group as control group without receiving any force applying device(G2 group).Extracted the dogs' mandibular first and second premolars and truncated the corresponding maxillary canine teeth in the three groups,and planted Dentos miniscrews in the distal side of mandibular canine teeth in the M group and G1 group,immediately;After 2 weeks,M group and G1 group received force to move mandibular third premolars by activating the force applying device.And the duration of loading was 4 weeks.CBCT images were taken at T0(before tooth movement)and T1(after finishing tooth movement).All data of CBCT was processed with the InVivo(ver.5.1.10)software,and linear and angular changes of teeth were studied.The statistical significance of the differences between T0 and T1 was determined by using Paired t-tests.A one-way analysis of variance(ANOVA)was used to assess statistical significance of differences in all measurements among the M group,G1 group and G2 group,respectively(=0.01).All dogs were injected intramuscularly with tetracycline before and after force loading.The specimens contained the target teeth and hard tissue of distal side,which were made to be two blocks.Half of the blocks was decalcified with 10% ethylenediaminetetraacetic acid at 48 ? for 30 days and dehydrated in ethyl alcohol of gradually increasing concentrations from 70% to 100%.After paraffin embedding,the samples were sectioned sagittally to a thickness of 10 um.They were stained with hematoxylin and eosin stain and examined under a light microscope for evaluation of alveolar bone surrounding the moved tooth.The other half of the blocks was prepared as undecalcified tetracycline labeled bone sections which were observed under fluorescence microscope and calculated the width of the mineralization apposition rate by image analysis software(IPP6.0).The SPSS software(ver.22.0)was used to perform all statistical analyses in this experiment.Result:1.The F/D curve of the re-activable magnetic systemThe F/D curve after three force loadings at the distances of 0.5 mm were similar,The distance between the magnets was 0.5 mm and the force range was 60-160 g.2.The measurement of CBCTThe distance between mandibular third premolar and canine showed significant decrease after force loading in the treated groups,and the inclination of mandibular third premolar showed increase.In G2 group,there were also decrease in the distance between mandibular third premolar and canine and increase in the inclination of mandibular third premolar.The changes(T1-T0)of all parameters in M group and G1 group were significantly greater than G2 group,but there was no significant difference between M group and G1 group.3.The measurement of tetracycline labelingThe mandibular third premolar were successfully moved in M group and G1 group,and evident and broad fluorescence bands were detected under fluorescence microscope.G2 group showed narrower and dark green fluorescence bands.After tooth movement,the mineralization apposition rate of both treated groups were significantly greater than that of G2 group,but there was no visible difference between M group and G1 group.4.The measurement of HE stainingThe periodontal membrane fibers in the tension side of target teeth tend to be dense in M group and G1 group,while the large number of angiogenesis and distributed the periodontal membrane near the new bone surface,and even existed trabecular bone formation in good condition,among which there were vascular distribution;While G2 group showed the regular distribution of periodontal membrane fibers,and new bone appeared funicular;Which showed M group and G1 group were more active for vascularization reaction and osteogenetic activity than G2 group.Conclusion:1.The MTSCM could successfully move teeth in this experiment.2.Both of the tooth and skeletal effects of the MTSCM were similar to the mechanical system after movement.