Property Evaluation Of Phase-Transited Lysozyme/Casein Phosphopeptide-Amorphous Calcium Phosphate Coating Of Clear Aligner

PurposeClear aligners has both beauty and comfort,while it would cover the large-area of teeth surface for a long term,which hinders the self-cleaning effect of saliva on the teeth surface to remineralize the enamel.When patients have poor oral hygiene,a large number of plaque accumulates in the relatively closed space formed by the clear aligner and the teeth surface,forming a microenvironment like a "bacterial storage pool",which increases the risk of gingivitis and enamel demineralization.Therefore,this study used the strategy of surface modification to prepare the phase-transited of lysozyme/casein phosphopeptide-amorphous calcium phosphate coating(PTL/CPP-ACP)on the surface of clear aligner without affecting the inherent mechanical properties.Such a coating can not only improve the antibacterial ability of the clear aligner to avoid tooth demineralization,but also promote the remineralization of the demineralized tooth surface to prevent dental caries and demineralization.Methods1.In-situ transferring method was used to prepare PTL/CPP-ACP coating on the thermoplastic polyurethane,a kind of clear aligner material.Using technologies like scanning electron microscope(SEM),atomic force microscope to characterize and the surface morphology and microstructure of the coating.2.The antibacterial performance of PTL/CPP-ACP coating was evaluated by colony forming unit counting,live/dead bacteria staining test and other methods.3.Simulate the oral environment in vitro to carry out the remineralization experiment.After PTL/CPP-ACP coating is applied to the demineralized enamel,the morphological changes of the demineralized enamel are observed by SEM;the structure of the remineralized layer is detected by X-ray diffraction;and the hardness of the enamel are detected by microhardness tester.4.The biocompatibility of PTL/CPP-ACP coating was tested by CCK-8 method and cytoskeleton staining.The stability of PTL/CPP-ACP coating was tested by tape tear test,and the water absorption of PTL/CPP-ACP coating was tested by saliva immersion test.Results1.Preparation and characterization of the PTL/CPP-ACP coating:the results showed that the PTL/CPP-ACP coating is uniformly adhered to the TPU surface,and the characterization results of element composition and microstructure showed that all functional components in the coaitng are successfully fixed on the TPU surface.2.Antibacterial activity:taking blank TPU as the control group.CFU results showed that there were a large number of bacteria colonies on the surface of the control group,which was decreased by more than 90%on the surface of PTL/CPP-ACP coating compared with the control group.The results of live/dead bacteria staining test showed that PTL/CPP-ACP coating significantly reduced the amount of adhered bacteria.The SEM results showed that the bacteria on the surface of the control group proliferated vigorously,while the number of bacteria on the surface of PTL/CPP-ACP coating decreased,and the cell membrane of bacteria shrunk or even cracked.3.Remineralization assay:using the demineralized enamel treated by blank TPU as the control group.The SEM results showed that PTL/CPP-ACP coating can effectively promote enamel remineralization.The X-Ray diffraction results showed that the remineralization layer formed by PTL/CPP-ACP coating is hydroxyapatite.The microhardness results showed that PTL/CPP-ACP coating can significantly improve the hardness of demineralized enamel compared with the control group.4.Biocompatibility evaluation and mechanical property test:using the blank TPU as the control group.The PTL/CPP-ACP coating did not affect the proliferation of L-929 cells and the adhesion and extension of human gingival fibroblast cells,indicating its good biocompatibility.The results of the tape tearing test demonstrated that the PTL/CPP-ACP coating can adhere to the TPU surface stably.In the saliva immersion test,PTL/CPP-ACP coating did not significantly affect the water absorption of TPU.ConclusionsPTL/CPP-ACP coating was successfully prepared on the surface of TPU by in-situ transferring method.PTL/CPP-ACP coating not only has good antibacterial properties,but also can effectively promote remineralization of demineralized enamel.In addition,PTL/CPP-ACP coating has good biocompatibility,and can stably adhere to the surface of TPU without affecting the water absorption of TPU.This study will provide new ideas for the development and clinical promotion of the new type of anti-caries clear aligner.