I. Biological properties of nickel
Nickel is an essential element for human life and has many beneficial effects on human health. After nickel absorbed through the digestive and respiratory tracts enters the blood, it exists mainly in the form of combined with serum proteins, amino acids and macroglobulins, and is then transported to various metabolic organs through the blood. Nickel has the function of stimulating blood production and promotes the regeneration of red blood cells. Nickel is an essential element for insulin synthesis and can help lower blood lipids. Nickel deficiency can cause diabetes, anemia, cirrhosis, uremia, renal failure and abnormalities in hepatic lipid and phospholipid metabolism.
Nickel is a variety of mainly supplied by vegetables, cereals and kelp. The human body absorbs nickel through oral ingestion, respiratory inhalation and epidermal absorption. A large number of supplies in modern life contain nickel, such as stainless steel and precious metals. In addition to occupations (such as electroplating, smelting, etc.) exposure to nickel causes poisoning, the combustion of some fuels and cigarettes can also produce nickel compounds (mainly nickel carbonyl).
Second, the history of the use of nickel-chromium alloy
Early oral metal restorations are mainly made of gold alloys and other precious metals, expensive, only people with high income can repair dental defects, missing. With the development of society and the rising price of your company, in order to meet the needs of the majority of consumers, cheap, excellent mechanical properties of nickel-chromium alloy is used in the system of oral prostheses, such as nickel-chromium alloy crowns, bridges, inlays, movable denture brackets. With the emergence of metal porcelain technology, nickel-chromium alloy has become the most widely used non-precious metal class metal porcelain alloy. The world with casting nickel-chromium alloy instead of gold alloy for the production of denture restorations began in 1917. At present in China, the number of metal porcelain restorations with nickel-chromium alloy as the base crown accounts for 50%-80% of all metal porcelain restorations. Nickel-chromium alloy has good mechanical and physical properties, easy to make, cheap, and can meet the needs of the majority of low- and middle-income people dental restoration.
Third, the side effects of nickel-chromium alloy
Nickel-chromium alloy has good biological safety for the majority of patients who use restorations containing nickel-chromium alloy. However, a few patients may experience some side effects due to the use of NiCr-containing restorations. The main cause of side effects is the release of nickel ions from NiCr. The release of nickel ions from nichrome restorations is closely related to their corrosion resistance. Oral saliva is a weakly acidic electrolyte, and nickel-chromium alloys will corrode when exposed to saliva for a long period of time. The nickel in the alloy will be released as ions into the saliva and can react with the electrolytes in the saliva to produce various nickel compounds, soluble or insoluble. If too much nickel is released, it can cause side effects of varying degrees in the tissues adjacent to the restoration and in other body parts far away.
1, factors affecting the release of nickel from nickel-chromium alloy.
(1) the content of chromium elements: nickel-chromium alloy contains up to 80% nickel, but the decision of the amount of nickel release due to corrosion is not the content of nickel, but the chromium content. Nickel-chromium alloy corrosion resistance is related to the content of chromium and molybdenum. The content of chromium obviously affects the corrosion resistance of nickel-chromium alloy in the oral cavity. Nickel-chromium alloy containing more than 20% of chromium and more than 4% of molybdenum has excellent corrosion resistance. When the content of chromium element is below 15%, the alloy has poor corrosion resistance in the oral environment, which can lead to obvious side effects.
(2) The nature of the liquid contact: lower pH of oral saliva can significantly increase the release of nickel.
(3) Toothpaste brushing: toothpaste brushing can significantly increase the release of nickel from oral nickel-containing alloys.
(4) use time: the alloy in the first week to release the fastest rate of metal ions, and then with the extension of time, corrosion products gradually cover the metal surface to form a passivation film, resulting in a slowdown in the rate of release of metal ions, while the total amount of metal ions released or increasing.
2, the biological process of nickel in the human body.
It should be noted that most of the nickel released from intraoral restorations or devices is swallowed into the digestive tract and does not accumulate in the oral cavity, and the amount of nickel released from dental alloys is significantly lower than the amount of nickel ingested in people’s diet. Nevertheless, small amounts of nickel are absorbed by the body, and the amount of absorption is related to the type of restoration. Patients wearing nickel-chromium alloy porcelain crowns within a certain period of time, although the nickel content in blood, saliva, urine will increase, but generally within the safe range, will not be harmful to the human body.
3, nickel allergenic effect.
It is now recognized that nickel has a sensitizing effect on some people, which in turn causes allergic reactions. The human immune system response to nickel is usually a type IV allergic reaction, that is, a delayed allergic reaction. It is caused by T cells, monocytes/macrophages, and has two phases. In the first stage, nickel enters the body and sensitizes the body to nickel; this stage usually shows no reaction. The main sources that sensitize the body to nickel are nickel-containing accessories and foods. Foods that contain high levels of nickel include chocolate, soy, nuts, and oatmeal. Re-exposure of the sensitized human body to traces of nickel stimulates an allergic reaction, which manifests as contact mucositis and dermatitis with some mossiness.
Although nickel is a recognized allergen, studies have shown that mere intraoral exposure to nickel-containing devices and restorations does not sensitize humans to nickel, that oral mucosal reactivity is low compared to skin, and that nickel released from dental alloys may not be present in a biologically active form. It is highly likely that the allergic reactions that occur in humans after the use of nickel-based alloys are sensitized by exposure to nickel through non-oral channels prior to wearing the restorations. On the other hand, small doses of nickel released by dental devices can induce tolerance to nickel allergy in humans.
Cases of allergic reactions to wearing nickel-chromium porcelain crowns are uncommon. Complaints of allergic reactions to nickel-chromium porcelain crowns include itchy gums, dry mouth, burning sensation in the mouth, abnormal reduction or increase in saliva, metallic taste and electric irritation. Among them, gingival edge graying and gingivitis is the most common clinical symptoms, the cause of the restoration system in addition to poor, another important reason is the release of metal ions gathered.
4, nickel-chromium alloy porcelain crowns on the periodontal tissue.
As the metal edge of the nickel-chromium alloy porcelain crown is mainly in contact with the gingival tissue, so it is the most common impact on the gingiva research shows that after 6 months of wearing nickel-chromium alloy porcelain teeth, there is a significant increase in the content of nickel-chromium in the adjacent gingival tissue. Most of the exposed nickel-chromium alloy at the edge of porcelain restorations is located in the subgingival area, where saliva flow rinses poorly and nickel ions enter the gingival sulcus fluid and may remain for a longer period of time, resulting in a higher concentration of nickel ions in the gingival sulcus fluid, causing changes in the local periodontal microecological environment, which mediates the immune response of tissue cells, decreases cell proliferation, and interferes with cellular energy metabolism, slowing down cell growth.
The effects of nichrome porcelain crowns on periodontal tissues are manifested by.
(1) tooth free gingival graying gingival discoloration is due to alloy corrosion, the release of metal ions penetrate into the gingival tissue showing dark streaks.
(2) gingival redness and swelling nickel-chromium alloy porcelain restorations on the local gingival tissue damage mechanism is multifaceted, the mechanical stimulation of the restoration edge metal, allergic reactions, the toxic effect of precipitated ions can cause damage to gingival tissue.
5, distant and systemic reactions.
Nickel-chromium alloy porcelain crown restoration caused by adverse reactions in other parts of the body case reports are rare. As for causing systemic reactions are rare reports. Individual reports of kidney damage after wearing nickel-chromium alloy porcelain crowns, due to the lack of in-depth scientific research, it is difficult to confirm the existence of a causal relationship between nickel-chromium alloy porcelain crowns and kidney damage.
Fourth, why not prohibit the clinical application of nickel-chromium alloy
1, nickel-based alloys all contain chromium, forming an alloy with excellent corrosion resistance.
2, the mechanical properties and fabrication properties of nickel-chromium alloy are excellent, and the restorations made with it have a high success rate.
3. inexpensive, enabling dental restorations to be available to a wide range of low and middle income people.
4. Nickel-based alloys have a longer history of use in removable dentures, and adverse reactions are extremely rare.
V. Summary
In summary, nickel-chromium alloy can bring side effects to a small number of patients wearing nickel-chromium alloy porcelain crowns, but most of them are limited to the oral cavity local, causing systemic reactions are rare, causing damage to important organs of the body is extremely rare. After balancing the advantages and disadvantages of Nichrome alloy, most countries in the world, including the United States and Japan, still allow the use of Nichrome alloy and its porcelain crowns in oral clinical restorations.