Dynamic changes of inflammation in ligation-induced rat periodontitis model

Objective:To study the dynamic changes of inflammation in rat models of periodontitis induced by ligation.Methods:Twenty-one healthy male SD rats were selected and randomly divided into 7 groups,namely normal control group and ligation group A-F(the ligation group A-F were ligated 1,3,5,7,14 and 21 days respectively,and then sacrificed).In addition to the normal control group,ligature was used to ligate the neck of the right maxillary first molar.The experimental periodontitis model was established in rats.By observing the changes in rat body weight within 21 days,we explored the intervention of ligature wires on inflammation.The impact of the process,through monitoring the debris index simplified(DIS),Sulcus Bleeding Index(SBI),Tooth Mobility(TM),to evaluate the periodontal inflammation of the target tooth within 21 days of ligation.In addition,in order to more accurately assess the dynamic changes of the alveolar bone during the inflammatory phase,we use CBCT Observe the alveolar bone resorption.Results:The body weight of the ligation group decreased during the 3 days after ligation,and compared with the normal control group,there was no statistically significant difference in body weight growth rate in the ligation group from 3 to 21 days(P≥0.05),indicating that due to the intervention of the ligation wire,the rat will have a 3-day adaptability phenomenon.The ligation of silk after day will not affect the growth and development of rats.The DIS on the ligated side was higher than that of the normal control on the first,third,fifth,and seventh days after the ligation.The side increased significantly(P<0.05),and the DIS value increased in the first 3 days,and gradually decreased on the 5th day,until the 21st day after ligation,compared with the normal control group,the difference was not statistically significant(P≥0.05);SDI on the ligation side increased significantly on the 5th day,and gradually decreased after reaching the peak on the 7th day(P<0.05),until there was no statistical difference between the ligation side and the normal control group on the 21st day(P≥0.05);The day began to change and gradually increased until the 21st day,which was statistically significant compared with the normal control group(P<0.05);the CEJ-ABC distance of the ligation group A,B,and C was not statistically significant compared with the normal controlgroup(P>0.05),the CEJ-ABC distance of the ligated group D,E,and F was significantly higher than that of the normal control group(P<0.05),and bone resorption was more significant in group F compared with D and E groups(P<0.01).Conclusion:Three days after the ligation of the ligature,it affects the molar eating in rats,and induces inflammation.Ligation-induced experimental periodontitis is in the acute inflammatory phase during 3-7 days of ligation,and turns to chronic inflammatory phase in 14-21 days.Our study provides a more precise definition of the occurrence and development of ligation-induced periodontitis in rats,which provides a new direction for the subsequent study of periodontitis models and provides a basis for better and more accurate clinical research.

Impact of Grid Topology on Pole-to-ground Fault Current in Bipolar DC Grids:Mechanism and Evaluation

The fault current level analysis is important for bipolar direct current(DC)grids,which determines the operation and protection requirements.The DC grid topology significantly impacts the current path and then the fault current level of the grid,which makes it possible to limit the fault current by optimizing the grid topology.However,the corresponding discussion in the literature is indigent.Aiming at this point,the impact of grid topology,i.e.,the connecting scheme of converters,on the pole-to-ground fault current in bipolar DC grids,is investigated in this paper,and the ground-return-based and metallic-return-based grounding schemes are considered,respectively.Firstly,the decoupled equivalent model in frequency domain for fault current analysis is obtained.Then,the impacts of converters with different distances to the fault point on the fault current can be analyzed according to the high-frequency impedance characteristics.Based on the analysis results,a simplified fault current index(SFCI)is proposed to realize the fast evaluation of impact of grid topology on the fault current level.The SFCI is then applied to evaluate the relative fault current level.Finally,the simulation results validate the model,the analysis method,and the SFCI,which can effectively evaluate the relative fault current level in a direct and fast manner.