The Animal Research On The Effect Of The Re-activable Magnetic Expansion Device With Diamond Like Carbon (DLC) Coating

Objective：The purpose of this study was to assess the effect of the re-activable magneticexpander vs the expanding screw expander by animal experiment, with the aid ofcone beam computed tomography(CBCT) and histological observation, to providereference for the future basic research and clinical application.Method：1.Tested the mechanical properties of the re-activable magnetic expanderIn this study, high-energy N52Nd2Fe14B magnets were chosen to be made up ofthe re-activable magnetic expander, the size of magnets were11.5mm×2.73mm×2.3mm. The curve of force-distance of the re-activable magnetic expander wasmeasured by INSTRON universal dynamometer separately after twice force loadingin the distance of3mm.2.Animal experiment18beagle dogs of six months old and about8kg were randomly assigned to3groups, with6dogs in the magnetic expansion group,6dogs in the screwedexpansion group and6dogs in the control group. Two pairs of link pins(left and right)were placed in each dog: one pair on the line connected by the upper first premolars（PM1）and about3mm away from the palatal suture; and another pair on the lineconnected by the upper forth premolars（PM4）and about3mm away from thepalatal suture. Then we made the maxillary impression and expander for dogs. Themagnetic expansion group received the re-activable magnetic expander; the screwedexpansion group received the expanding screw expander; the expanders were placedon the intersection of the lines which linked by contralateral upper canines and upperfirst molars(M1). The control group did not receive any expander. The screwedexpansion group loaded force2times a week,3/4circle a time.The magneticexpansion group loaded force1time two weeks,all dogs were sacrificed after fourweeks of expansion.CBCT images were taken at baseline(T1) and immediately afterexpansion(T2). We measured the distances between upper canines, PM4, M1; the inclination of PM4and M1; the distances between the pins at PM1area and PM4area.The SPSS statistical software was applied to analysis the liner and angular data. Thedogs were sacrificed after four weeks of expansion, the tissues pieces of palatal sutureat the PM1area, expander area and M1area were collected and HE staining wereperformed. Then the histological changes of palatal suture were observed under themicroscope.Result：1.The mechanical properties of the re-activable magnetic expanderIt showed nearly the same curve after twice force loading. The force with thedistance between magnets range from0to3mm varied from8.18N to1.6N.2.The result of animal experiment2.1.The measurement of CBCTThe maxillary transverse dimensions of all parameters displayed significantincreases after expansion in the two experimental groups. In the control group, it alsoshowed a significant increases in all parameters except the inclination of PM4fromT1to T2. The comparison of absolute transverse changes (T2-T1) among the groupsshowed that the two experimental groups were significantly differed from the controlgroup in all parameters; the absolute change of the distance between cannies inmagnetic expansion group was significantly greater than in screwed expansion group;the absolute change of the distance between PM1pins in screwed expansion groupwas significantly greater than in magnetic expansion group; the absolute change ofthe distance between PM4pins in screwed expansion group was also significantlygreater than in magnetic expansion group.2.2.The histological changes of midpalatal sutureThe midpalatal suture were expanded significantly in the experimental groups. Agreat amount of fibroblasts and osteoblasts which presented in exuberant excretivestate were observed in the midpalatal sutures. New bone was deposited around thesuture especially in the magnetic expander area where a great amount of osteoblasts,osteoclasts and vascular section were found, the level of tissue remodeling andreconstruction was higher than screwed expansion group.Conclusion： 1.A significant increase in all measured transversal dimensions were producedby the re-activable magnetic expander in this research.2.The bone effect of the re-activable magnetic expander after expansion wassmaller than the expanding screw expander, but the tooth effect of the re-activablemagnetic expander was greater than the expanding screw expander.3.Both the re-activable magnetic expander and expanding screw expander couldstimulate the reconstruction of palatal suture during the expansion.4.The level of tissue remodeling and reconstruction in the expander area of there-activable magnetic expander was higher,it suggestes the static magnetic field maypromote the remodeling of bone.