Regenerating Fluorapatite To Obturate Root Canalsvia Amineralizing Strategy

Objectves:Root canal therapy（RCT）is one of the most effective method to treat pulpitis and periapical periodontitis.Root canals are obturated after being cleaned,shaped and sterilized in sequence.The most common materials applied presently is gutta percha as core materials combined with root canal sealer.Although the aim of the method is to obdurate the space of root canal and stop the growth of microorganism,microorganism can survive in dentine tubules even if the dentine has been treated by hydrogen peroxide（H₂O₂）and sodium hypochlorite（NaClO）.Besides,microleakge and gap exist at the interface between materials and root canal or between core materials and sealer.Tissue fluid from periapical tissue or saliva may reach the bacterials and act as their nutriment via microleakge or gap.Finally,the proliferation of these bacterials and their product may lead to the breakdown of material-dentin interface and reinfection of periapical tissue.The purpose of this study was developing a novel strategy for sealing and obturating dental root canals and dentine tubules by tooth-like tissue regeneration.Methods:63fresh molars were collected from clinic,dentin slices were obtained by sawing the molars vertically to root-coronal direction.Then the dentin slices were treated by 17%ethylene diamine tetraacetic acid disodium salt（EDTA）solutionfor 1minute in the presence of ultrasound after being polished by 2000-grit silicon carbide paper.After being rinsed by deionised water,the dentin slices were treated by 5.25%sodium hypochlorite（NaClO）solution for 5minutes in the presence of ultrasound and were rinsed by deionised water.According to the differences in treatment after being rinsed,all the dentin slices are divided into two groups randomly.There were43 dentin slices and 20dentin slices in experimental group（mineralization group）and control group respectively.Samples in the experimental groupweredivided into 5subgroups and then immersed in stirred mineralization solution,the solution was refreshed every12 hours.After mineralization,1 dentin slice in the first subgroup was characterized by scanning electron microscope（SEM）;the mineral precipitates on 1 dentin slice surface in the second subgroup was characterized by transmission electron microscope（TEM）;the mineral precipitates on the dentin slice surface in the third subgroup was characterized by X-ray diffaraction（XRD）;cells were seeded on the surface of 20samples in the fourth subgroup after the dentin slices were sterilized;and in the fifth subgroup,the mineral precipitates on the 20 dentin slices surface were used to obtain leach solution after being scraped,pulverized and sterilized.And the leach solution was used to evaluate the effect of mineral precipitates on cell proliferation by CCK-8.And the same with the fourth subgroup,cells were also seeded on the surfaces of the 20 dentine slices in the control group.14 fresh premolar were collected from clinic,roots were obtained by sawing the premolar at enamel-dentinal junction vertically to root-coronal direction.Radicular pulp tissue was then removed and the canals were treated mechanically.After that,the root canals weretreated by 17%ethylene diamine tetraacetic acid disodium salt（EDTA）solution for 1 minute in the presence of ultrasound.Next to that,the root canals were rinsed by deionised water and treated by 5.25%sodium hypochlorite（NaClO）solution for 5minutes in the presence of ultrasound.Finally,they were rinsed with deionised water.According to the differences in treatment after being rinsed,all the root canalswere divided into two groups randomly.There were13root canals and 1root canal in experimental group（mineralization group）and control group respectively.In the experimental group,samples were immersed in stirred mineralization solution,the solution was refreshed every 12 hours.After the mineralization,all the samples including the one in the control group were split up or sawed in the crown-root direction and characterized by SEM.All the samples in the experimental group were divided into 4 subgroups,in the first subgroup,obturation of dentinal tubule was characterizedin 1 root canal after1 day mineralization;in the second subgroup,interface between dentin and mineral precipitates was evaluated by SEM in 1 root canal after 3 day mineralization;in the third subgroup,in order to observe the stereoscopical structure around the interface,1 root canal was etched before being characterized;in the fourth subgroup,10root canals were characterized by SEM to evaluate the process of obturating apical foramen.Results:The precipitates were mainly composed of fluoridated hydroxyapatite（FHA）with a hexagonal prism morphology and gained a higher resistance to acid etching than the dentine.FHA initially nucleated and grew from the root canal dentine surface to the root canal centre,the regenerated FHA densely packed together with a c-axis extension and finally obturate root canals.In the root canal,.The FHA precipitate and root canal dentine intergraded together such that the interface became hardly distinguishable and showed a tight junction.Besides,the precipitates grow into and obturate the dentinal tubules.The mineral precipitates is beneficial for the growth of cells,there is no significant difference between experimental group and control group in cell proliferation.Conclusion:Biomimetic mineralization can promote the growth of fluorapatite on the surface of root canal dentin,which finally lead to the obturation of root canal space.It’s a novel strategy for sealing root canal system via mineralization.