3. Grinding and polishing
1)Mechanical grinding: Titanium has high chemical reactivity, low thermal conductivity, high viscosity, low mechanical grinding grinding ratio, and is easy to react with abrasives. Ordinary abrasives are not suitable for titanium grinding and polishing. Good use of super thermal conductivity 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 grains between the grinding head and the surface to be polished and the surface to be polished are 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 abrasive tool is used to apply electrolyte and voltage between the abrasive tool and the grinding surface. Under the combined action of mechanical and electrochemical polishing, the surface roughness is reduced and the surface gloss is improved. 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 abrasives move in relative 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 the precise polishing of the denture.
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 role. 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. However, the use of anhydrous chloride electrolyte at a low voltage has a good polishing effect on titanium. Small specimens can be mirror-polished, but for complex restorations, it still cannot achieve the purpose of complete polishing. Maybe change the shape of the cathode and add a cathode The method can solve this problem, which needs further study.
4. Surface modification of titanium
1)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 external voltage, the titanium anode can form a thick 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 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 aesthetics of titanium dentures and prevent the continued discoloration of titanium dentures under natural conditions, surface nitriding, atmospheric oxidation and anodizing surface coloring treatments can be used to make the surface light yellow or golden yellow to improve the titanium denture Beauty. 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 treatment
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 still required.
