| In orthodontic clinic, fixed appliance has been widely used for its efficiency and gained fine therapeutic effect. But the structure of its main composition-brackets is complex, leading to dental plaque increasing and having impact on micro-circumstance in oral cavity, so enamel decalcification, gingivitis and periodontitis were caused. Prevention and control of dental plaque adhesion is the key of dental caries and periodontitis prevention. Improve the material of brackets so to inhibit adhension and growth of pathogenic bacterium in oral cavity is one of the investigative directions in orthodontics sphere. Along with the development of the science of dental materials, the appearance of nanometer antibiosis materials provids new choice for new bracket materials exploitation.Most nanometer antibiosis materials utilize single nanometer antibacterial agent such as nanometer titanium dioxide, nanometer sliver and so on. These materials have defect of their own, so the application are constrainted. Silver-loaded titanium dioxide becomes an important direction of new antibiosis materials investigation. It has specific mechanical property, antibiosis function and biocompatibility, so it has broad prospect of application.There is no report of using nanometer Ag/TiO2materials and technique in orthodontics brackets at home and abroad. This study plans to make nanometer Ag/TiO2coating on ordinary metal brackets so to develop nanometer Ag/TiO2coating on brackets that has fine appearance, high intensity, visible photocatalytic activity and bacteriostasis effect even in dark circumstances. Detect the efficiency of physics, chemistry, antibiosis and biocompatibility of the brackets so as to confirm the specific mechanical and biological properties of the brackets. Our aim is to provide effective method for solving adamantine caries and periodontal inflammation, and to promote the use of nanometer technology in orthodontic materials area. This study consists of three chapters below:Part One Development of nanometer Ag/TiO2coated brackets and physicochemical properties detectionObjectiveTo develop nanometer Ag/TiO2coated bracket and detect its physicochemical properties.MethodsIn this study, we chose ordinary metal brackets widely used in clinic, polish, ultrasonic clean, flush and dry. TiO2gel was produced by sol-gel method. TiO2film was coated on brackets surface, and then soaked in AgNO3solution. Ag/TiO2film was heat treated under120degree, then annealing under120,200,300degree respectively, then nanometer Ag/TiO2coated bracket A,B,C were produced.Scanning electron microscope (SEM) was used to observe the micromorphology of surface of ordinary metal brackets, nanometer TiO2coated bracket and nanometer Ag/TiO2coated bracket. Cross-section topography of nanometer Ag/TiO2coated bracket group A was also observed.The surface roughness of metal bracket, nanometer TiO2coated bracket and nanometer Ag/TiO2coated bracket were measured.The combination intensity between smear layer of nanometer TiO2and nanometer Ag/TiO2with basis material were analyzed by scratch experimentation. The crystal structure and phase of nanometer TiO2coated bracket and nanometer Ag/TiO2coated bracket were analyzed by XRD.The chemical components of nanometer TiO2coated bracket and nanometer Ag/TiO2coated bracket were characterized using XPS.The transmittance of nanometer TiO2coating and nanometer Ag/TiO2coating on quartz glass were mearsured by UV-VIS.ResultsSEM results showed that the surface of ordinary metal bracket was rough and existenced major ravine andpitlike depression. Nanometer TiO2coating film was constructed by many sphericity micro-particles, the diameter of which was10-30nm. Nanometer Ag/TiO2film was also constructed by many sphericity micro-particles, with orderly structure, the diameter of TiO2particles were uniformity, Ag particles were distributed on the film, the diameter of which was50-100nm. Aggregation phenomenon was seen seldomly. The diameter of Ag particles became bigger and distributed more intensively with the annealing temperature arising.The section micromorphology showed that the thickness of nanometer Ag/TiO2film was about120nm, the film was well-distributed and had smooth surface, Ag particles could be seen deposited on the film.There were no statistically differences among the surface roughness of five groups of brackets. The combination intensity of the nanometer TiO2smear layer with basis material was1.18kg, the numerical value of A,B,C groups of nanometer Ag/TiO2were1.16,1.12,1.26kg respectively.XRD showed that there were anatase TiO2diffraction peak in both curves of TiO2and Ag/TiO2films. Ag0diffraction peak appeared in the curve of Ag/TiO2, and the intensity became larger as the temperature arising.XPS showed main components of TiO2and Ag/TiO2were Ti, O,C and Ag,Ti,O,C respectively. The Ti2p level in TiO2was divided into2levels:Ti2p1/2and Ti2p3/2, the central peak were464.6ev and458.9ev, the difference was5.7ev. The peak value of binding energy of Ti2p drifted to high energy after Ag deposoted. The Ag3d level in Ag/TiO2was divided into2levels:Ag3d5/2and Ag3d3/2, the central peak were368.1ev and374.1ev, the difference was6ev.The TiO2transmittancy spectrogram showed ultraviolet light<350nm could be completely absorbted, red shift of the absorption happened and transmittancy decreased after Ag deposited. The transmittancy decreased as the annealing temperature decreasing.Conclusion1. The results confirmed that nanometer Ag/TiO2coated brackets were developed successfully by sol-gel method.2. This nanometer Ag/TiO2coating was well-distributed, the thickness and diameter of particles were all in nanometer scale, so that the characteristics of nanometer materials were guaranteed. It had smooth surface and enough combination intensity with basis material, which could meet the clinical demand of orthodontics.3. TiO2in the film was anatase TiO2. Ag existed by the form of simple substance. Ag particles grew up as the annealing temperature increasing.4. The photochemical catalytic activity of TiO2increased by the deposition of Ag, and made it owned visible light photoresponse.5. The visible light photoresponse increased by the decrease of diameter of Ag.6. The result indicated that choose120degree as annealing temperature is suitable, for the diameter of Ag and TiO2were small, which owned enough combination intensity and strong visible light photoresponse.Part TwoResearch on bactericidal ability of nanometer Ag/TiO2coated bracketsObjectiveTo study the bactericidal ability of nanometer Ag/TiO2coated bracket and investigate the mechanism initially, in order to provide theoretical evidence.MethodsA group nanometer Ag/TiO2bracket was prouduced and TiO2and Ag/TiO2coatings were coated on stainless steel17-4with the same method. S.mutans, S.sangui, A.actinomycetemcomitans, F.nucleatum, P.gingivalis and P.intermedia were anabiosised and cultured into bacteria liquid. Film applicator coating method was used to test the antibacterial efficacy of Ag/TiO2coating.3groups of brackets were soaked in the mixed bacteria liquid. After48h, SEM was used to observe the anti-adhesive efficacy of the coating.Cocultured S.mutans with Ag/TiO2coated bracket for6,18,24,48h, then extracted coarse GTF. The content of reducing sugar in supernatant was tested by Somogyi-Nelson method, and activity of GTF was calculated in order to analyze the influence of Ag/TiO2coating on GTF in different times.The activity of gingpains ecto-cellular and intra-cellular and protein level were measured and specific activity of gingpains was calculated in order to analyze the effect of Ag/TiO2coating on gingpains.ResultsThe result showed more than80.2%of bacteria were killed within20minutes in dark circumstance which confirm fine antibacterial effect of Ag/TiO2coating. The coating could kill all the bacteria after30-60min, while TiO2coating did not exhibit antibacterial effect after240min. There were differences among the time of killing different strains.SEM showed the bacterial number adhered on the surface of nanometer Ag/TiO2coated bracket was obviously fewer than on the surface of metal bracket and nanometer TiO2coated bracket. There were considerable bacteria adhere to the surface of metal bracket, distributed compactly and formed multilayer pellicle. There were also massive bacteria adhere to the surface of nanometer TiO2coated bracket, in grainy structure, no multilayer pellicle was seen. There were obvious slight bacteria adhere to the surface of nanometer Ag/TiO2coated bracket, scattered distributed.In different times, GTF activity of metal bracket group, nanometer TiO2coated bracket group and nanometer Ag/TiO2coated bracket group descended by turns, GTF activity in nanometer Ag/TiO2coated bracket group was obviously lower than3orther groups, GTF activity in nanometer TiO2coated bracket group was lower than blank control group besides at48h, there were statistically differences among these groups. There were no statistically differences between GTF activity of metal bracket group and nanometer TiO2coated bracket group. The sequence of inhibition of nanometer Ag/TiO2coated bracket on GTF activity were:18h>24h>6h>48h. There were statistically differences between the inhibition in different times besides18h and24h.The specific activity of gingpains ecto-cellular and intra-cellular both had downtrend as the time lasting. The specific activity of gingpains intra-cellular was obviously bigger than ecto-cellular within10min, the difference became small after10min. The specific activity of gingpains ecto-cellular did not change much within20min, then assumed slow downtrend. The specific activity of gingpains intra-cellular descented obviously within20min, then steped down downtrend.Conclusion1. The results confirmed the outstanding antibacterial property of nanometer Ag/TiO2coated bracket in dark circumstance.2. Nanometer Ag/TiO2coated bracket had fine adherence resistance to common bacteria in oral cavity.3. The bracket could effectively restrain the activity of GTF so that it has excellent adherence resistance to S.mutans.4. The bracket could lead to gingpains degradation ecto-cellular and intra-cellular while killing P.gingivalis.Part ThreeBiocompatibility evaluation of nanometer Ag/TiO2coated bracketObjectiveBiocompatibility of nanometer Ag/TiO2coated bracket was examined in order to provide experimental evidence for its use in clinic.MethodsTiO2and Ag/TiO2coatings were spreaded on the surface of stainless steel wafer. Add DEME to the wafers, and cocultured with L929cell. The morphous of cell were observed under inverted phase contrast microscope. Relative growth rate was calculated by MTT method and carried out toxity degree grading. The death of cell was observed under fluorescene microscope. Cell cycle was detected by flow cytometry.Leaching liquor was extracted from TiO2and Ag/TiO2coatings and added to fresh anticoagulation cony blood, optical density was measured and hemolysis rate was calculated.Lavaging mouse with leaching liquor extracted from TiO2and Ag/TiO2coatings, observing toxicity physical sign, measuring body weigh change before and after experiment, and then observe pathological change of organs heart, hepar, lien, lung and kidney.Sutured the wafer to the cheek pouch of inaurate hamster, observed the activity of animals and mucous membrane reaction in the contact region, then observe the full-thickness of cheek pouch under microscope, and carry out pathology reaction grading.ResultsThere were no differences among3groups of cells under inverted phase contrast microscope and fluorescene microscope.Toxicity levels of3groups were0-1. There were no abnormality seen in cell cycle.Optical density in test group was obviously lower than positive control group. The hemolysis rate of TiO2group and Ag/TiO2group were0.255%and0.637%. They were both less than5%, which meaned no acute haemolysis was induced.There was no death in all the animals, clinical toxicity physical sign were all asymptomatic, there was no difference between test group and control group in body weigh increasing, the organs were observed under microscope and no pathological change was found.The animals acted and took food normally, no pathological change was observed in the contact mucous membrane of cheek pouch both in macroscopic and microscope observation.Conclusion1. Nanometer Ag/TiO2coated bracket had no toxicity for cell. 2. No acute haemolysis was induced by nanometer Ag/TiO2coated bracket.3. The influence of leaching liquor extracted from Ag/TiO2coating on mouse had no difference with sodium chloride and no short-term systemic toxicity was observed.4. Nanometer Ag/TiO2coated bracket had no stimulation to oral mucosa of hamster, so it had fine biological properties.Above all, nanometer Ag/TiO2coated bracket was developed successfully, which could meet the clinical demand for it has excellent mechanical function, owns outstanding bactericidal ability and adhesion resistance, and possesses fine biocompatibility. But futher study should be carried out before it be used in orthodontic clinic. |
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