Establishment Of An Experimental Pulpitis Model In Rats By Pulp Cavity Exposure

Objective:To study the progress of pulpitis in SD(Sprague Dawley)rats after the exposure of pulp cavity of maxillary first molar at different time points.Methods:108 eight-week-old SD rats molars from bilateral maxillary were chose for this experiment.A cavity was prepared with a 1/4 dental round bur on the occlusal surface of the bilateral upper first molars(class 1 cavity).The upper first molar was drilled(medium speed with cooling system)until the pulp was visible through the transparency of the dentin floor of the cavity.Pulp was subsequently exposed using a DG16 probe.The pulp cavities were exposed for 0 h,6 h,12 h,24 h,3 d,5 d,7 d and 10 d,respectively,to establish an experimental pulpitis model in rats.1、Bilateral maxillary bones were scanned by mirco-ct(micro-computed tomography)to locate the location of the medullary opening,and the diameter and depth of the medullary opening were measured.2、HE(hematoxylin-eosin)staining was used to observe themorphological changes of pulp tissue in rats exposed to the pulp cavity of molars for different periods.3、Real-time PCR(Real-time fluorescence policy polymerase chain reaction)detection of rat molar pulp cavity after different time exposure of IL-6(Interleukin-6,IL-6),IL-1β(Interleukin 1 beta,IL-1 beta),NLRP3(NLR family,Expression of pyrin domain containing 3)and caspase-1(cysteinyl aspartate specific proteinase 1)4、ELISA(Enzyme linked immunosorbent assay)was used to detect the expression of IL-6,IL-1β,NLRP3,and caspase-1 in the pulp of molars of rats exposed to different time periods.5、The expression of NLRP3 in the pulp cavity of rat molars exposed for different time was observed by IHC(Immunohistochemistry)staining.Results:1、Mirco-CT showed in pulp is located in the surfaces of the maxillary first molars of rats fovea,(0.50±0.03)mm diameter,depth of(0.63±0.001)mm,teeth surface fovea in the distance to the bottom of the pulp chamber is 1.00 mm,buccal,lingual tooth neck midpoint tooth tissue thickness and size of 0.45 mm,root crown pulp,pulp volume(0.59±0.008)respectively mm~3,(0.57±0.01)mm~3.2、The pulp cavity of the rats was exposed for 0 h to 24 h.Pulpitis was limited to the crown,and the inflammation was mild.The histological score was 3-11.The medullary cavity of the rats was exposed for 3 to 10days,and the inflammation spread to 1/3 of the root tip,with severe inflammation and histological score of 12-15.3、Real-time PCR showed that IL-6 increased to a peak 6 h before exposure to the pulp cavity of rat molars,and then decreased.NLRP3expression increased at 24 h after pulp cavity exposure,while NLRP3,caspase-1 and IL-1βexpression increased significantly at 3 d after pulp cavity exposure.NLRP3 expression peaked at 5 d after pulp cavity exposure,and then decreased.4、ELISA showed that the expression of NLRP3 increased on day 3 after pulp cavity exposure,and the expression of NLRP3,caspase-1 and IL-1βpeaked on day 5 after pulp cavity exposure,and then decreased.5、IHC staining showed that the positive expression of NLRP3 was confined to the odontoblast cells at 24 h after the exposure of the pulp cavity in rats,while the positive expression of NLRP3 was widely expressed in the odontoblast cells and endodontic cells at 3 d after the exposure of the pulp cavity in rats.Conclusion:1、The model of experimental pulpitis in rats constructed by medullary cavity exposure has good reproducibility.2、Different degrees of rat experimental pulpitis model were successfully constructed by controlling the exposure of the medullary cavity at different times.3、IL-6 could be used as an indicator of early inflammation in the pulp,and NLRP3/CASP1 could be used as an important indicator to detect the reaction progression of pulpitis.