Nichrome porcelain teeth are now the most widely used porcelain teeth in China, and they are commonly used in clinical practice because of their low price. At present, the alloy content of domestic nickel-chromium alloy porcelain teeth accounts for about 70% of nickel elements, chromium accounts for about 30%, and the rest is ruthenium, tin, manganese and other metal elements account for 3%.
There are many studies on the black line of the coronal neck caused by domestic nickel-chromium alloy porcelain. The causes of gingival discoloration have been controversial in the field of prosthodontics: some scholars believe that the nickel, chromium and aluminum porcelain in the basal crown compete to form oxides caused by light refraction, while some scholars believe that the nickel-chromium in the basal crown of metal porcelain restorations separates metal ions into the gingiva under the action of the oral microenvironment, and aggregates and causes gingival discoloration. Some scholars speculate that it may be caused by inflammation caused by irritation or injury to the overhanging process of the neck of the restoration. The appearance of black lines on the gums should be the result of the combination of the above reasons, provided that the crown edge is not closed, the inflammation and irritation of the gums appear, and the gums appear swollen and black red. Under this premise, due to the instability of the metal properties, metal ions are released around the gums, resulting in free black lines of metal.
In the complex oral environment, the metal parts exposed to the oral cavity slowly decompose and release black oxides, resulting in local tissue staining, which is the most important reason why this type of restoration can cause dark lines on the gums. The amount of chromium in the alloy has an absolute effect on the corrosion resistance of the nickel-chromium alloy in the oral cavity. When the content of chromium in the nickel-chromium alloy exceeds 20%, the alloy is relatively stable and has high corrosion resistance. If the nickel metal content is too high, it is very susceptible to corrosion, and nickel ions continue to precipitate, and the gums will become black after human absorption. In addition, the results of human skin contact test show that about 15%~20% of the population is allergic to nickel. At present, domestic dental installation of nickel-chromium alloy porcelain teeth does not test patients for nickel allergy, so many patients may suffer a "second sin" - pulling out and re-installing noble alloy porcelain teeth after installation.
For the carcinogenic effect of nickel-chromium alloy porcelain teeth on the human body, there should be a slight toxic reaction introduced by foreign medical journals, but it is relatively mild, and people do not need to panic about it.
To sum up the above, in addition to the price advantage, nickel-chromium alloy porcelain teeth are inferior to other metal porcelain teeth in other aspects such as the instability of metal properties, the stimulation of metal to the human body and slight toxic reactions, and the aesthetics