| Modern root canal treatment concept requires thorough disinfection and tight root canal filling.Compared with cold lateral condensation,warm vertical condensation of gutta-percha can provide a high-density filling and better sealing at all portals of entry between the root canal and the periodontium.This technique allows the placement of a homogeneous mass of GP into the canal system with the carrier as a means of compaction and solves the cold lateral condensation gutta-percha some inherent disadvantages [1,2].However,because of the thermal filling,the temperature of the root surface is increased during the filling process.The problem that it may cause damage to periodontal tissue can't be ignored.Notably,evaluation the safe of a root canal filling technology is to see whether the surface temperature rise more than 10?.It is believed that a temperature rise of 10°C is the critical level at which irreversible periodontal injures may occur [3].Many scholars[4,5] have conducted relevant studies in vitro,the results showed that they can cause the root surface temperature rise 6.5-22.1? when used root canal filling with common root filling equipment and temperature settings.It can be presumed that the elevated temperature is likely to cause damage to periodontal tissues.The periodontal ligament is a dense connective tissue that connects between the cementum and the alveolar bone.The temperature of the root surface will be transmitted directly to the periodontal membrane.At the cytological level,little research about the effect of elevated temperature on the biological characteristics of normal periodontal ligament cells and inflammatory periodontal ligament cells,as well as the mechanism of regulation of cell pathways under heat stimulation during filling process.We speculate that the periodontal tissue may cause damage during the process of rising temperature.However,whether the behavior of cytology is consistent? Whether it will exacerbate the development of periodontal disease?Whether it is a transient or irreversible? How is the mechanism of regulation of the inflammatory system in the intracellular immune system?These questions are worthy of our further study.We expect to provide guidance for the clinical thermoplastic gutta-percha filling system selection and temperature control from the cytological level.The experiment consists of three parts: Experiment 1: Study on the temperature variation of root surface caused by B&L system heat source during the root canal filling.Sixty single-rooted teeth that met the inclusion criteria were selected for this study.Teeth were held by a forceps around the crown during preparation and temperature recording.Cut off the crown at the level of CEJ,root canals were prepared and the roots were evenly wrapped with alginate impression material.Then,create a diameter of about 1mm hole connected with the outside at the position of the coronal part of the root canal,the mid-root and 4mm to the apical,which thermocouples were placed directly contact with the root surface.The filling temperatures were set at 230?,200? and 180?,respectively.The study showed that the surface temperature of the three measurement sites increased after the completion of the root filling.The average increase in surface temperature at three measurement sites by 230? were: 12.84??9.68??7.28?.There were 10.37??8.76??6.67? by 200?,and 9.42??8.63??6.61? when using 180? filling temperature.There were significant differences in the temperature rises between the root surface and the filling temperatures(P <0.05).There were significant differences in the temperature rises between the three measurement sites on the root surface of the same filling temperature(P <0.05).It can be concluded that the average temperature rise of the root surface at the coronal part of the root canal increased by more than 10 °C when filled with 230? and 200? temperatures.So it's should be caution with higher filling temperature.Experiment 2: Differences in root surface temperature changes of different root dentin thickness.Cut off the root at three measurement sites after root canal filling is completed.Measure the thickness of the root canal wall,and all teeth were divided into three groups according to the remaining dentin thickness as follows: group 1.0 mm(0.8~1.2mm),group 1.5mm(1.3~1.7mm),group 2.0mm(1.8~2.3mm).Then the temperature changes of different filling temperatures,different measurement sites and different dentin thickness were analyzed.The results showed that the average root surface temperature rises of the groups was 13.74??12.25??10.23? at 230?,10.77??9.98??8.73? at 200?,and 9.86??9.08??8.57? at 180?.There were significant differences between the root surface temperature rise of the dentin thickness group 1.0mm and the group 2.0mm(P < 0.05)at the coronal part.As the root canal wall thickens,the temperature rise reduced.It was exceeded more than 10°C at the coronal part of group 1.0 mm when the filling temperature were 200?and 230?.It is recommended that it should be appropriate to reduce the filling temperature for the thinner dentin teeth,in which to avoid irreversible damage to periodontal tissue.Experiment 3: A preliminary study on the effect of thermal stimulation on the biological characteristics of normal and inflammatory periodontal ligament cellsIn this study,LPS and ATP were used to stimulate the periodontal ligament cells(PDLCs)to simulate the inflammatory environment.Cells at the 3~5th passage were seeded into two 6-well plates,cells were divided into eight groups: Control group,ATP-primed group,LPS-primed group,ATP+LPS stimulation group,thermal stimulation group,ATP+ thermal stimulation group,LPS+ thermal stimulation group,ATP+LPS+ thermal stimulation group.5 mmol/L ATP pre-stimulated for 2 hours,the final concentration of 10 ?g/ml LPS was stimulated for 6 hours,and then incubated at 45?for 2 hours.After thermal stimulation,Cell viability was measured using CCK8 kit.The results indicated that the cell viability was significantly reduced after 2 h of heat exposure.Therefore,the effect of heat on HPDL cells' behavior was studied at up to 2 h of heat exposure in the rest of the experiments.The mRNA expression of NLRP3?caspase-1?IL-1??IL-18 was analyzed by RT-PCR.After ATP and LPS co-stimulated,the mRNA expression of four factors were upregulated.After thermal stimulation 2 hours,HSR-1 and HSF-1 mRNA expression were upregulated,while the expressions of four inflammatory factors were downregulated.This result could suggest that the NLRP3 / Caspase-1 inflammasome may present in the periodontal ligament cells,and it can be activated by ATP+LPS stimulation,thermal stimulation can prevent the activation by the NLRP3 inflammasome and may affect a component necessary for the induction of multiple inflammasome complexes. |
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