| Dental caries is one of the most common chronic diseases in children’s oral cavity,and untreated dental caries has adverse effects on children’s growth and development,psychological health and other aspects.Stainless steel crown(SSC)is currently the main material for restoring large areas of dental caries in milk molars and young permanent molars,which has the advantages of less preparation,simple operation method and better restoration of tooth shape and function.However,compared with personalized restorations,SSC has poor marginal fit and is prone to microleakage,which leads to secondary caries;in addition,the surface free energy of stainless steel material is high,which is prone to adhesion of plaque and stimulation of periodontal tissue inflammation.Therefore,whether to optimize the performance of SSC materials so that they have suitable antibacterial properties and good biocompatibility is a clinical issue of concern to pediatric dentists.Currently,strategies to reduce microbial adhesion on the material surface mainly include chemical and physical methods.Chemical methods kill and decompose bacteria by modifying the surface of the material with different chemical agents or changing the composition of the material,but they cannot prevent bacterial adhesion in the long term and are even potentially toxic to the organism.Physical methods inhibit the formation of bacterial biofilms by physically altering the surface morphology,structure and properties of the material,and have good histocompatibility and biosafety.Recent research has revealed that Ultrafast laser technology can produce Microtopographic surfaces on the surface of materials,which is a surface antibacterial strategy to influence microbial adhesion and bioactivity through physical and mechanical forces.In our previous study,we used Femtosecond laser(FS)to prepare a variety of nano-microstructures on the surface of titanium alloy,which significantly inhibited the growth and reproduction of E.coli.Can ultrafast laser surface treatment be applied to stainless steel metal preformed crowns to reduce the occurrence of gingivitis and secondary caries after dental restoration?Based on the results of the previous study,this project firstly used ultrafast laser technology to treat the surface of 304 L stainless steel and prepared two specimens with nanostructures to compare their morphological structure,physicochemical properties,antibacterial effect and biocompatibility,etc.;secondly,the SSC axial surface was treated with nanostructure preparation technology with better comprehensive performance,and then a Beagle dog dental restoration model was established to detect and analyze the crown plaque adhesion,the Finally,the clinical prospective trial of SSC with nanostructure was carried out for the restoration of dental caries in deciduous teeth to evaluate the clinical translation effect of SSC with ultrafast laser surface treatment;in order to reduce the complication rate of SSC for the restoration of dental caries in deciduous teeth and improve the efficacy of SSC for the prevention and treatment of dental caries in children.In order to reduce the complication rate of SSC for the restoration of dental caries,improve the efficacy of SSC for the prevention and treatment of dental caries in children,and provide a theoretical basis and experimental foundation for its clinical translation.Part one: Study of material surface properties of stainless steel treated by ultrafastlaser Objective: To examine and analyse the morphological structure,physicochemical properties,antibacterial effect and biocompatibility of stainless steel specimens with two different nanosurface structures.Methods: Firstly,the surface of 304 L stainless steel specimens were treated with ultrafast laser technology,grouped into nano-ripple +particles group(S1 group),nano-ripple group(S2 group),and 304 L stainless steel untreated group(Control group),and the surface morphology was observed by scanning electron microscopy(SEM);secondly,the surface structure and roughness were examined by atomic force microscopy(AFM),energy dispersive X-ray spectroscopy(EDS)to detect the chemical elemental composition of the surface,and WCA to detect the wettability of the surface;then the inhibition effect on common oral pathogenic bacteria was detected by colony plate counting,live dead bacteria staining and SEM;finally,CCK-8,fluorescence staining and SEM were used to comprehensively evaluate the biocompatibility of different specimens.Results: SEM showed that the S1 group showed an irregular structure composed of nanoscale particles and ripples,the S2 group showed a periodic nano-ripple structure and the control group showed a flat and smooth structure;AFM showed that the surface roughness of the specimens increased;WCA showed that the Control and S1 groups showed hydrophilic and the S2 group hydrophobic;EDS showed that the carbon and oxygen content on the surface of the specimens increased while the metal element content was slightly The EDS showed an increase in carbon and oxygen content and a slight decrease in metal content.The results of colony plate count and live dead bacterial staining showed that the S2 group inhibited the proliferation of Streptococcus pyogenes,while the S1 and S2 groups inhibited the proliferation of Porphyromonas gingivalis and Fusobacterium nucleatum(P < 0.05);SEM showed morphological stretching and disintegration of Porphyromonas gingivalis and Fusobacterium nucleatum in both S1 and S2 groups.The cytotoxicity assay showed better biocompatibility in the S2 group.Conclusion: The nano corrugated surface structured stainless steel prepared by ultrafast laser technology has better material properties,good antibacterial properties and ideal biocompatibility.Part two: Animal studies of ultrafast laser surface modified SSC for dentalrestorations Objective: To investigate the effectiveness and safety of nano-rippled surface structured SSC for restorative dentistry in Beagle dogs.Methods: Firstly,the nano-ripple surface structure(FS-SSC)was prepared below the marginal ridge of the SSC using ultrafast laser technology,and its microscopic surface morphology was observed by SEM.The gingival index(GI),plaque index(PLI)and probe depth(PD)were measured at different time points.Gingival sulcus fluid samples were collected and the enzyme-linked immunosorbent assay(ELISA)was used to detect interleukin 1β(IL-1β)and Tumour Necrosis Factor ɑ(TNF-ɑ);the marginal plaque was collected from the crown and neck of the teeth,and the number of Porphyromonas gingivalis and Fusobacterium nucleatum was determined by real-time quantitative polymerase chain reaction(q PCR);radiographs were taken to observe the dental and periodontal tissues.Finally,histological methods were used to analyse the pathological manifestations of periodontal tissues and SEM to observe the surface morphology of SSC under the influence of the oral environment.Results:SEM showed that the surface of FS-SSC exhibited a periodic nano-ripple structure.The periodontal health indexes showed an increasing trend with time,while all indexes in the FS-SSC group were lower than those in the SSC group(P < 0.05);the number of inflammatory factors and bacterial adhesions also showed the same results.Histological analysis showed that the degree of inflammation in the gingival sulcus was significantly lower in the FS-SSC group than in the SSC group,and the SEM results showed that the surface of FC-SSC retained its nano-ripple pattern.Conclusion: The nano-ripple surface structure of SSC can be used for restorative dentistry in Beagle dogs to reduce plaque adhesion and facilitate the health of periodontal tissues.Part three:Clinical prospective trial of ultrafast-laser-modified SSC for therestoration of deciduous dental caries Objective: To evaluate the translational application of ultrafast laser surface treated SSC for the restoration of dental caries in deciduous teeth.Methods: Nine children who met the inclusion and exclusion criteria were selected for a prospective clinical trial.Bilateral mandibular first milk molars were chosen as subjects and randomly divided into SSC or FS-SSC groups;longitudinal changes in gingival index(GI),plaque index(PLI)and probing depth(PD)were recorded before and after restoration of stainless steel preformed crowns;radiographs were taken to observe the dental and periodontal tissues;crowns were collected The gingival plaque was collected and quantitative real-time polymerase chain reaction(q PCR)was used to detect the change in the number of Streptococcus pyogenes and Clostridium perfringens.Results: At the 6-month follow-up,clinical examination revealed no signs of allergy,oral ulcers,periapical inflammation or pulpitis;X-rays showed no significant differences between the alveolar bone and periapical tissue in the SSC and FS-SSC groups;specialist examination showed that the periodontal health index of the affected teeth decreased after the pre-crown restoration compared with that before the pre-crown restoration,and was slightly lower in the FS-SSC group than in the SSC;laboratory examination revealed that the surface of the FS-SSC The number of Streptococcus mutans and Fusobacterium nucleatum was significantly lower in the FSSSC group than in the SSC group(P < 0.05).Conclusion: Ultra-fast laser surface treatment of stainless steel crown can reduce bacterial adhesion,improve periodontal health and prevent adjacent surface caries,with better treatment results than conventional SSC,suggesting that FS-SSC has good biosafety and ideal clinical application prospects. |
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