The density of titanium is small, so the inertia of the titanium liquid is small, and the flowability of molten titanium is poor, resulting in a low casting flow rate. The difference between the casting temperature and the mold temperature (300°C) is large, and the cooling is fast. The casting is carried out in a protective atmosphere. Defects such as pores are unavoidable on the surface and inside of the titanium casting, which greatly affects the quality of the casting. Therefore, the surface treatment of titanium castings is more important than other dental alloys. Due to the unique physical and chemical properties of titanium, such as small thermal conductivity, low surface hardness, low elastic modulus, high viscosity, low electrical conductivity, and easy oxidation Etc., which brings great difficulty to the surface treatment of titanium, and it is difficult to achieve the desired effect using conventional surface treatment methods. Special processing methods and operating methods must be used. The later surface treatment of the casting is not only to obtain a smooth and shiny surface, to reduce the accumulation and adhesion of food and plaque, etc., to maintain the patient's normal oral microecological balance, but also to increase the beauty of the denture; more importantly, it is through These surface treatment and modification processes improve the surface properties and suitability of castings, and improve the physical and chemical characteristics of dentures such as wear resistance, corrosion resistance and stress fatigue resistance. 1. Removal of the surface reaction layer The surface reaction layer is the main factor affecting the physical and chemical properties of titanium castings. Before grinding and polishing the titanium castings, the surface contamination layer must be completely removed to achieve a satisfactory polishing effect. The surface reaction layer of titanium can be completely removed by pickling after sandblasting. 1. Sand blasting: The sand blasting treatment of titanium castings is generally better to use white corundum for rough blasting. The pressure of sand blasting is smaller than that of non-precious metals, generally controlled below 0.45Mpa. Because, when the injection pressure is too large, the sand particles hit the titanium surface to generate a fierce spark, and the temperature increase can react with the titanium surface, forming secondary pollution, which affects the surface quality. The time is 15~30 seconds. Only the sticky sand, sintered layer and part of the surface of the casting and the oxide layer can be removed. The remaining surface reaction layer structure should be quickly removed by chemical pickling. 2. Pickling: Pickling can quickly and completely remove the surface reaction layer, and the surface will not be polluted by other elements. Both HF-HCl series and HF-HNO3 series pickling solutions can be used for titanium pickling, but HF-HCl series pickling solution has a large hydrogen absorption capacity, while HF-HNO3 series pickling solution has a small hydrogen absorption capacity to control HNO3. The concentration of hydrogen is reduced, and the surface can be treated brightly. The general concentration of HF is about 3%~5%, and the concentration of HNO3 is about 15%~30%. Second, the treatment of casting defects Internal pores and shrinkage internal defects: can be removed by hot isostatic pressing (hot isostatic pressing), but it will affect the accuracy of dentures. It is best to use X-ray inspection to remove the exposed pores on the surface. Use laser repair welding. Surface pore defects can be repaired directly by laser local welding. 3. Grinding and polishing Mechanical grinding: Titanium has high chemical reactivity, low thermal conductivity, high viscosity, low mechanical grinding and grinding ratio, and is easy to react with abrasives. Ordinary abrasives should not be used for titanium grinding and polishing. Hard abrasives, such as diamond, cubic boron nitride, etc., the polishing linear speed is generally 900~1800m/min., otherwise, the titanium surface is prone to grinding burns and micro cracks. 2. Ultrasonic grinding: Through the action of ultrasonic vibration, the abrasive particles between the grinding head and the surface to be polished and the surface to be polished can be moved relative to each other to achieve the purpose of grinding and polishing. The advantage is that the grooves, sockets and narrow parts that cannot be ground by conventional rotary tools become easier, but the grinding effect of larger castings is still not satisfactory. 3. Electrolytic mechanical compound grinding: A conductive grinding tool is used to apply electrolyte and voltage between the grinding tool and the grinding surface. Under the combined action of mechanical and electrochemical polishing, the surface roughness is reduced to improve the surface gloss. The electrolyte is 0.9NaCl, the voltage is 5v, and the speed is 3000rpm/min. This method can only grind the plane, and the grinding of complex denture brackets is still in the research stage. 4. Barrel grinding: the centrifugal force generated by the revolution and rotation of the grinding barrel is used to make the dentures in the barrel and the abrasive material relatively move in friction to reduce the surface roughness. The grinding is automated and efficient, but it can only reduce the surface roughness and not improve the surface gloss. The grinding accuracy is poor, and it can be used for deburring and rough grinding before denture polishing. 5. Chemical polishing: Chemical polishing is to achieve the purpose of leveling and polishing through the redox reaction of metals in chemical media. The advantage is that chemical polishing has nothing to do with the hardness of the metal, the polishing area and the shape of the structure. All parts in contact with the polishing liquid are polished without special complicated equipment, and the operation is simple. It is more suitable for the polishing of titanium denture brackets with complex structures. However, the technical parameters of chemical polishing are difficult to control, and it is required to have a good polishing effect on the denture without affecting the accuracy of the denture. The better titanium chemical polishing liquid is HF and HNO3 prepared according to a certain proportion. HF is a reducing agent, which can dissolve titanium metal and play a leveling effect. The concentration is <10%. HNO3 acts as an oxidant to prevent excessive dissolution of titanium and hydrogen absorption , At the same time can produce a bright effect. Titanium polishing solution requires high concentration, low temperature, and short polishing time (1~2min.). 6. Electrolytic polishing: also known as electrochemical polishing or anode dissolution polishing, due to the low conductivity of titanium and extremely strong oxidation performance, the use of aqueous acidic electrolytes such as HF-H3PO4 and HF-H2SO series electrolytes can hardly polish titanium. After the external voltage is applied, the titanium anode oxidizes immediately, and the anode dissolution cannot proceed. But the use of anhydrous chloride electrolyte at low voltage has a good polishing effect on titanium, small specimens can be mirror polished, but for complex restorations still can not achieve the purpose of complete polishing, maybe change the shape of the cathode and additional cathode The method of solving this problem needs to be further studied. 4. Surface modification of titanium Nitriding: The use of chemical heat treatment techniques such as plasma nitriding, multi-arc ion plating, ion implantation and laser nitriding to form a golden yellow TiN coating on the surface of titanium dentures, thereby improving the wear resistance, corrosion resistance and resistance of titanium Fatigue. However, the technology is complicated and the equipment is expensive. It is difficult to achieve clinical practicality for the surface modification of titanium dentures. 2. Anodizing: Titanium's anodizing technology is relatively easy. In some oxidizing media, under the effect of applied voltage, the titanium anode can form a thicker oxide film, thereby improving its corrosion resistance, wear resistance and weather resistance. The anodized electrolyte generally uses H2SO4, H3PO4 and organic acid aqueous solution. 3. Atmospheric oxidation: Titanium can form a thick and strong anhydrous oxide film in a high-temperature atmosphere, which is effective for comprehensive corrosion and gap corrosion of titanium, and the method is relatively simple. 5. Coloring In order to increase the beauty of titanium dentures and prevent the discoloration of titanium dentures under natural conditions, surface nitriding, atmospheric oxidation and anodizing can be used to make the surface light yellow or golden yellow. The beauty of titanium dentures. The anodizing method utilizes the interference effect of the titanium oxide film on the light to naturally develop color, and can form a colorful color on the surface of the titanium by changing the bath voltage. 6. Other surface treatments 1: Surface roughening: In order to improve the bonding performance of titanium and facing resin, the titanium surface must be roughened to increase its bonding area. Sandblasting is commonly used in clinical practice, but sandblasting will cause aluminum oxide pollution on the titanium surface. We use oxalic acid etching to obtain a good roughening effect. The surface roughness (Ra) can reach 1.50 after etching for 1h ±0.30μm, etching for 2h Ra is 2.99±0.57μm, which is more than double that of sandblasting Ra (1.42±0.14μm), and its bonding strength is increased by 30%. 2: High temperature oxidation-resistant surface treatment: In order to prevent the rapid oxidation of titanium at high temperatures, titanium silicon compounds and titanium aluminum compounds are formed on the titanium surface, which can prevent the oxidation of titanium at temperatures above 700°C. This surface treatment is very effective for the high-temperature oxidation of titanium. Perhaps the titanium surface is coated with such compounds, which is beneficial to the combination of titanium and porcelain, and further research is needed.