Development Of The Nano-TiO₂ Ceramic-coated Orthodontic Brackets And Study On Mechanical And Biological Properties Of The Nano-TiO₂ Ceramic Film On Brackets

Orthodontics is a branch of dentistry, dealing with correction of the dento-facial complex deformation. The orthodontic practice involves the application of corrective appliances to move teeth and coordinate the relationship of teeth, maxilla and crania. Brackets are one of main components of the fixed appliance. Nowadays there are various brackets available to patients. In general, according to their materials brackets can be divided into three categories: stainless steel brackets, ceramic brackets and plastic brackets. Stainless steel brackets are stiff enough to bear various applied orthodontic forces, however their appearance can not meet patients aesthetic needs for their color is incomparable with teeth. Ceramic has been used as an aesthetic alternative material to stainless steel to improve the appearance of brackets, and thus to increase patients acceptance. Ceramic brackets also have some disadvantages that result from their properties of material: brittleness, surface roughness and high sliding resistances. And in clinical practice the application of ceramic brackets satisfies patients aesthetic needs andbrings about anchorage loss as well as improves treatment difficulties. Even though plastic brackets have aesthetic advantage and easy to debond, hardness of conventional plastic brackets is below the standard of orthodontic appliance and their hardness degradation in oral cavity is obvious.In clinical practice, the process of teeth acid may result in teeth demineralization inevitably. Fixed appliances in oral will deteriorate oral bacterial condition and increase oral hygiene difficulty. All these factors may contribute to enamel decay around brackets and periodontal disease. In straight wire appliance (SWA) technology, sliding mechanics was introduced to retract anterior teeth. Resistance to sliding of orthodontic brackets with bumps in the slot floors and walls was greatly affected by brackets materials. Such problems discussed above can only be solved by material study evolution.This study is to develop the nano-TiO₂ ceramic-coated orthodontic brackets, and to do some primary study on the mechanical and biological properties of the nano-TiO₂ ceramic film on brackets. Our study involves four parts: (1) The uniform TiO₂ nano-particle was synthesized by the Gel-Sol method. (2) To deposit the nano-Tio₂ ceramic film on the surface of the orthodontic brackets by electron beam physical vapor deposition (e-beam PVD) technology. And the surface characters of the ceramic film were evaluated by Transmission electron microscopy and the method of X ray powder diffraction. (3) To evaluate the mechanical properties of the nano-TiO₂ ceramic coated orthodontic brackets. (4) And to do some study on the biological properties of the nano-TiO₂ ceramic coated orthodontic brackets which includes vitro cytotoxicity test , short-term systemic toxicity test of nano- TiO₂ ceramic material and estimation of antibacterial activity and efficacy.Results:1. Uniform spherical anatase-type titania (TIO2) particles with completely controlled shape , size and crystal structure were prepared by a novel gel-sol method. Diameter of the uniform spherical titania particles is between 6 ± 2 nm. and titania particles present some conglutination to limit degree.2. The nano- TiO₂ ceramic-coated orthodontic brackets were developed, and the ply of the nano- Tio₂ ceramic film was about 5-8 μm. The uniform Tio₂ particle was distributing equably and presented low surface roughness.3. Adhension of nano- TiO₂ ceramic film with orthodontic brackets is efficient enough. Compared with normal stainless steel orthodontic brackets, the nano-TiO₂ ceramic orthodontic brackets exhibit good surficial characters: low friction coefficient, good wearability.4. Vitro cytotoxicity test , short-term systemic toxicity test of nano- TiO₂ ceramic material show that the nano- TiO₂ ceramic orthodontic brackets have no toxicity to human body and no harm to health. And the nano- TiO₂ ceramic orthodontic brackets present efficient antimicrobial effect on streptococcus. Conclusions:1. Uniform spherical anatase-type titania (TiO₂) particles prepared by a novel gel-sol method can be used as material of the nano- TiO₂ ceramic film and photocatalysts. All these provide much opportunity for subsequent experiments. 2.The ply of the nano- Tio2 ceramic film was about 5-8 μm, and the nano- Tio₂ ceramic film scarcely had any influence on the slot size. And the nano-Tio₂ ceramic film took on good surface properties.3. The nano-TiO₂ ceramic coated orthodontic brackets we have developed show good surficial performance and good mechanical properties. The nano-TiO₂...