| Part Ⅰ: Effects of different concentrations of hydrogen peroxide bleaching solution on human dental pulp cellsObjective: In the process of tooth bleaching,different levels of hydrogen peroxid e reach the pulp cavity through the tooth tissue.In this study,human dental pulp cells(h DPCs)were cultured in vitro to study the effects of different concentrations of hydro gen peroxide bleaching solution on the proliferation of human dental pulp cells and th eir differentiation into odontogenesis/osteogenesis.Methods: Human dental pulp cells were isolated and identified by tissue block m ethod,and the 4th-6th generation cells were selected for the experiment.The study w as divided into control group and experimental group.The control group was cultured with DMEM complete culture medium,and the experimental group was cultured with DMEM complete culture medium containing gradient hydrogen peroxide concentratio n.The gradient concentration is set as 1 μg/m L,5 μg/m L,10 μg/m L,15 μg/m L,20 μg/m L,25 μg/m L,and 30 μg/m L.Firstly,the effect of hydrogen peroxide co-culture with dental pulp cells for 24 h on the proliferation of dental pulp cells was studied by CCK-8 method,and according to cytotoxicity,the concentrations of 1 μg/m L,5 μg/m L,10μg/m L with low cytotoxicity and tolerance to mineralization were selected,and the co ntrol group was co-cultured with pulp cells for 24 h for the study of odontogenic/osteo genic differentiation.ALP activity was detected by alkaline phosphatase(ALP)assay kit.Alizarin red staining was used to detect the formation of mineralized nodules in ea ch group.The expressions of dentin matrix protein 1(DMP-1),dentin sialophosphorin(DSPP),osteocalcin(OCN)and alkaline phosphatase(ALP)were detected by RT-PCR after bone formation induction.Results: CCK-8 method showed that after 24 h co-culture of hydrogen peroxide with dental pulp cells,10 μg/m L,15 μg/m L,20 μg/m L,25 μg/m L,30 μg/m L groups h ad inhibitory effects on the proliferation of h DPCs,while 1 μg/m L and 5 μg/m L group s showed no significant difference in the proliferation of h DPCs.Alkaline phosphatase activity assay,alizarin red staining assay and RT-PCR assay showed that there was no significant difference between the 1 μg/m L group and the control group in the mineral ization induction after 24 h co-culture of hydrogen peroxide and pulp cells.Compared with the control group,5 μg/m L and 10 μg/m L hydrogen peroxide groups could incre ase the activity of ALP and promote the formation of mineralized nodules after 7 days of mineralization induction.After 14 days of mineralization induction,5μg/m L could promote the formation of mineralized nodules and up-regulate the expression of h DPC s DMP-1,DSPP,OCN and ALP genes,but the formation of mineralized nodules was r educed in 10μg/m L group,and the expression of h DPCs DMP-1,DSPP,OCN and AL P genes was down-regulated.Conclusion: After 24 h co-culture of hydrogen peroxide with dental pulp cells,th e proliferation of human dental pulp cells was inhibited by 10 μg/m L or higher concen tration of hydrogen peroxide bleaching solution.After 24 h of hydrogen peroxide co-c ulture with dental pulp cells,the dental pulp cells in 5 μg/m L and 10 μg/m L groups co uld overcome the damage and promote the dentin/osteoblastic mineralization compare d with the control group.After 14 days of mineralization induction,the pulp cells in th e 5 μg/m L group could overcome the damage and promote the dentin/osteoblastic min eralization and up-regulate the related odontogenic/osteoblastic genes,while the result s in the 10 μg/m L group were opposite.Part Ⅱ: Clinical cases of tooth bleaching in young patientsResearch purpose: The cases of In-Office tooth bleaching of young patients were presented to evaluate the bleaching effect,sensitivity and satisfaction after bleaching.Research methods: A total of 5 patients,aged 18-30 years old,were selected from January 2021 to January 2023 in the Department of Prosthetics,Affiliated Hospital of Hangzhou Normal University.Contraindications were excluded and informed consent was signed.All patients were required to undergo full-mouth ultrasonic supracingival cleaning,and undergo In-Office tooth bleaching 2 weeks after surgery,as well as oral health education.Oral colorimetric images were collected before and after tooth bleaching.Satisfaction scores were performed immediately after tooth bleaching,and sensitivity scores were collected within 24 h,48 h and one week,respectively.The patients were revisited and followed up 6 months after surgery.Results: Of the 5 patients in this case,two were male and the remaining three were female.After the surgery,3 patients felt the sensitivity of teeth,and the sensitivity was mild or moderate.All patients could complete the treatment.One patient continued to feel sensitivities 48 hours after surgery,but disappeared after a week.The rest of the patients had no dental sensitivities.The satisfaction scores for the procedure and effect of whitening surgery were all satisfactory,but one patient(case 2)had a low satisfaction score due to her mild dental fluorosis and uneven postoperative color.For the effect of teeth whitening,the postoperative effect was obvious,but after 6 months of follow-up,the tooth color had rebounded.Conclusion: In-Office tooth bleaching is a very fast,effective and safe technology.Tooth bleaching effect of young patients is obvious,sensitivity is easy to accept,and the satisfaction is high.However,the tooth color will rebound after a few months. |
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