Titanium easily at a high temperature react with the elements of O, H, N, etc. in the air and the entrapped compound of the elements such as Si, Al, Mg, and the surface contaminated layer is formed in the casting surface, deterioration of their excellent physical and chemical properties, hardnessincreased plasticity, decreased elasticity and increased fragility. The density of titanium, titanium liquid flow is small inertia, the molten titanium liquidity flow difference resulting cast low. Larger, casting temperature, mold temperature difference (300 ℃) cooled fast casting in a protective atmosphere, the surface of the titanium castings and the internal porosity and other defects inevitably occur, a great influence on the quality of the castings. Therefore, processing and other tooth surface for titanium castings compared alloy becomes more important, due to the unique physical and chemical properties of titanium, such as a small thermal conductivity, the surface hardness, and low elastic modulus, viscous, low conductivity, easily oxidized, etc., which brought the surface treatment of titanium very difficult, using the conventional surface treatment method is difficult to achieve the desired results. Must use special methods of processing and operating means. The late casting surface treatment is not only to maintain the patient's normal oral microflora balance in order to get a smooth and shiny surface, reducing food and plaque accumulation and adhesion, also increase the beauty of the denture; important throughsurface treatment and modification process, improve the surface properties of the casting and suitability, the to improve denture wear, corrosion, and resistance to stress, fatigue and other physical and chemical characteristics.

 Removal of the surface reaction

 layer Layer of the surface reaction is the main factors to affect the physical and chemical properties of titanium castings in titanium castings before polishing, must achieve complete removal of surface contamination layer, in order to achieve a satisfactory polishing effect. The surface of the reaction layer of titanium can be completely removed by sandblasting after pickling.

1. Sandblasting: sandblasted titanium castings generally used white fused alumina coarse spray better the sandblasting pressure than smaller, non-precious metal generally control following 0.45Mpa. Because, when the injection pressure is too large, grit generate intense spark impact titanium surface temperature can react with the titanium surface, the formation of secondary pollution, and affect the surface quality. The time is 15 to 30 seconds, to remove only the sticky sand, the surface of the sintered layer and part of the casting surface, and the oxide layer can. The rest of the surface of the reaction layer structure should chemical pickling method rapid removal.

 2. Pickling: pickling can quickly and completely remove the surface reaction layer, and the surface does not produce pollution of the other elements. HF-HCl system and HF-HNO3-based pickling solution can be used for the pickling of titanium, but the HF-HCl-based pickling solution a larger quantity of hydrogen absorption, while the HF-HNO3-based pickling solution a small quantity of hydrogen absorption can be controlled HNO3 reduce the concentration of hydrogen absorption, and bright surface treatment, generally the concentration of HF in the range of 3% to about 5%, the HNO3 concentration is preferably in the range of 15% to about 30%.

 The processing of the casting defects

Internal porosity and shrinkage internal defects: can hot isostatic pressing (hot isostatic pressing) to remove, but will impact the accuracy of the denture, the best X-ray testing, surface grinding addition to exposure stomatal laser repair welding. Surface porosity defects can be directly used laser local welding repair. Grinding and polishing

1．Mechanical polishing: titanium high chemical reactivity, and low coefficient of thermal conductivity, viscosity, mechanical polishing grinding ratio is low, and easy abrasives react, ordinary abrasive should not be used for grinding and polishing of the titanium is preferably used the good thermal conductivity of ultrahard abrasive, such as diamond, cubic boron nitride, polishing line speed is generally 900 ~ 1800m/min. appropriate, otherwise, the titanium surface prone to grinding burn and microcracks.

2．Ultrasonic grinding: by ultrasonic vibrations, so that the abrasive grains with the polishing surface to produce relative movement between the grinding head and the polishing surface to achieve the grinding, the purpose of polishing. The advantage is that the conventional rotary tool grinding not ditch, nest and stenosis easier, but larger castings grinding effect is not satisfactory.

3．Electrochemical Mechanical Polishing: conductive abrasive electrolyte and a voltage is applied between the abrasive and grinding surface, reducing surface roughness by the combined action of mechanical and electrochemical polishing to improve the surface gloss. Electrolyte was 0.9NaCl, and voltage is 5v the speed to 3000rpm/min., This method can only grind the plane is still in the research phase of complex grinding denture frameworks.

4．Barrel grinding: the centrifugal force generated by the use of the revolution and rotation of the mill barrel, the barrel of the dentures and abrasive relative frictional movement and serve to reduce the surface roughness of the grinding purpose. Grinding automation, efficiency is high, but only reduce the surface roughness and can not improve the surface gloss, poor precision grinding, deburring available denture before the finish polishing and coarse grinding.

5．Chemical polishing: chemical polishing is the reduction reaction by the oxidation of the metal in the chemical medium and for leveling the purpose of polishing. The advantage is that the chemical polishing and the hardness of the metal, the polishing area and regardless of the structural shape, where the site of contact with the polishing liquid are polished, do not need special complex equipment, easy to operate, and more suited to the polishing of the titanium complex structure denture stent. However, chemical polishing process parameters are difficult to control and capable of dentures in the case of denture accuracy does not affect the good polishing effect. The titanium preferred chemical polishing solution of HF and HNO3 formulated by a certain percentage, HF is the reducing agent, can dissolve the titanium metal, play a leveling effect, a concentration of <10% of HNO3 from oxidation, to prevent the excessive dissolution of the titanium and hydrogen , simultaneously creating a bright role. Titanium polishing solution requires high concentration, low temperature, the polished short time (1 ~~ 2min.)

6．Electrolytic polishing: also known as electrochemical polishing or anodic dissolution polished, strong oxidation resistance, due to the low conductivity of titanium, the use of the water acidic electrolyte such as HF-H3PO4, HF-H2SO based electrolyte for titanium hardly polished.after the external voltage is applied, the titanium anode immediately oxidation occurs, leaving anodic dissolution can not be performed. But the use of anhydrous chloride electrolyte at a low voltage, and have good polishing effect on the titanium small specimen mirror polishing can be obtained, but for complex prosthesis still can not achieve the purpose of completely polished, perhaps using the change of the cathode shape and the additional cathode the method can solve this problem, and needs further research.

A surface modification of titanium

1．Nitride: plasma nitriding, multi-arc ion plating, ion implantation and laser nitrided chemical heat treatment technology, golden TiN Permeation Layer formation in titanium denture surface, so as to improve the wear resistance of the titanium, corrosion resistance and resistance tofatigue resistance. But the technology is complex and expensive equipment for surface modification of titanium denture difficult to achieve clinical practical.

 2．Anodic oxide: titanium anodic oxidation is relatively easy, in oxidizing medium, the effect of the applied voltage, the titanium anode may be formed on the thick oxide film, thereby improving its resistance to corrosion and abrasion resistance and weathering resistance. The anodizing electrolyte General H2SO4, H3PO4 and organic acid aqueous solution.

3．Atmospheric oxidation: titanium may be formed in a high-temperature atmosphere thicker sturdy anhydrous oxide film, titanium general corrosion, crevice corrosion, the method is relatively simple.

Coloration

 In order to increase the titanium denture aesthetic, to prevent discoloration of titanium denture under natural conditions continue oxidation, surface nitriding treatment, atmospheric oxidation and anodic oxidation surface shading can be used, so that the surface of the formation of pale yellow or golden yellow, improve titanium denturebeauty. Light interference effects of the use of titanium oxide film of the anode oxidation method, the natural hair color, can be formed by varying the cell voltage in the titanium surface colorful colors. Other surface treatment

1: Surface roughening: In order to improve the bonding properties of the titanium and facing resin, must be performed on the titanium surface roughening treatment to improve its bonding area. Blasting roughening treatment is often clinically used, but the blast will cause pollution of the titanium surface of alumina, we used oxalic acid-etching method to obtain good roughening, etching 1H surface roughness (Ra) can reach 1.50 ± 0.30μm, etching the 2h Ra 2.99 ± 0.57μm, than individually sandblasting Ra (1.42 ± 0.14μm) to improve more than doubled, and a 30% increase in its bond strength.

 2: The high temperature oxidation resistance of the surface treatment: In order to prevent rapid oxidation of titanium at a high temperature, the surface of the titanium to form a titanium silicon compound and a titanium-aluminum compound, to prevent oxidation of the titanium in the temperature above 700 ℃. This surface treatment is very effective in the high-temperature oxidation of titanium and titanium surface coating of these compounds may combine favorable titanium porcelain, need further study.