Effects Of Different Root Canal Preparation And Immune Status On Periapical Biofilm Formation In Rats With Root Canal Infection

Root canal therapy is the preferred treatment of periapical disease,namely the maximum in the treatment of root canal infection,and three-dimensional packing to prevent the infection again.In a few teeth,even if accepted the standard of root canal therapy,periapical periodontitis is still persistent,we usually call this refractory periapical periodontitis.Periapical biofilm is considered to be the important cause leading to the refractory point periarthritis.Periapical biofilm come from infected root canal have reached a consensus in periodontal health of tooth.But the root canal of bacteria spilled the apical foramen to form periapical biofilm due to environmental factors,or by extrusion is still controversial.In order to study the causes of the formation of apical biofilm,our previous experiments were studied in vitro.It was shown that bacteria and apical biofilm were detected at the apical only under the condition of long root canal preparation and super-preparation.But in vitro experiments ignored the body's immune response.The pathological reaction of the periapical periodontitis is inseparable from the immune response of the body,and the periapical biofilm formation may be related to the immune response.In this study,immunosuppressive rat model and root canal infection rat model were established.Different length of root canal intervention was performed in immunized normal group and immunosuppressive group to observe the effects of different root canal intervention and immune status on the formation of periapical biofilm.It is provided theoretical basis for the prevention of refractory periapical periodontitis in clinical work.ObjectiveImmunosuppressive rat model and root canal infection rat model were established to investigate the effects of different immune states and root canal intervention on periapical biofilm formation in rats with root canal infection.Materials and Methods1.Immunosuppressive rat model was established: 54 rats were divided into immunized normal group(n = 27)and immunosuppressive group(n = 27).Immunosuppressive group was injected intraperitoneally with cyclophosphamide 50 mg / kg to establish an immunosuppressive animal model followed by 1 week 1time.2.Establishment of infected root canal rat model:Immunized normal group were randomly divided into control group A(n = 3),experimental group B,C,D,E(n = 6);immunosuppressive group were randomly divided into control group a(n = 3),experimental group b,c,d,e(all n = 6).The bilateral maxillary first molar of the experimental group were pulp exposed.Pulp cavity was exposure to oral environment 4 weeks,to establish animal model of infected root canal.3.Root canal intervention: B and b group after opening the pulp do not do any treatment.Mesial root canal of maxillary first molars in C and C group were prepared to two-thirds on root canal working length,D and d group were prepared to full working length,and E and e group were prepared to over the working length one millimeter.On the 7th day and 21 th day after root canal preparation,3 rats were sacrificed in each group,and the surface of mesial root canal of the left maxillary first molar was examined by PCR.The mesial root canal of right maxillary first molar was used for scanning electron microscopy to observe the formation of periapical biofilm.ResultsThe 16 Sr DNA-specific primer fragment was amplified from the apical area of the full-length group(D,d group)and the over long group(E,e group)on the 7th and 21 th day after root canal preparation.In the control group(A,a group),Open pulp group(B,b group)and two-thirds interference group(C,c group)were not detected.On the 7th day after root canal preparation,the apical area of A and a groups showed a large amount of collagen fibers covering the root surface,and no visible cementum and absorption lacunae were observed.The presence of bacterial biofilm was not observed under scanning electron microscopy in B,C,D,E,b,c,d and e groups,but the cementum of the apical area was exposed and the root surface was almost free of collagen fibers,and visible with bone resorption lacunae.On the 21 st day after root canal preparation,only one sample in group E observed the presence of small-scale bacterial biofilms,mainly composed of bacilli,which surrounded by a small amount of amorphous matrix-like material.The remaining groups were consistent with the 7th day.Conclusions1.An immunosuppressive rat model and a root canal infection rat model were establish.2.Under the immune mechanism,the full length and over length preparation have a positive effect on Bacteria overflow the formation,but there is no evidence to suggest that stimulates the formation of periapical biofilm.