Year : 2010 | Volume
: 28 | Issue : 1 | Page : 6--12
Biodegradation of nickel and chromium from space maintainers: An in vitro study
V Bhaskar1, VV Subba Reddy2,
1 Department of Pedodontics and Preventive Dentistry, Ahmedabad Dental College, Bhadaj, Rancodpura Road, Kalol, Ahmedabad, Gujrat, India
2 Department of Pedodontics and Preventive Dentistry, College of Dental Sciences, Pavilion Road, Davangere - 577 004, Karnataka, India
Department of Pedodontics and Preventive Dentistry, Ahmedabad Dental College, Bhadaj, Rancodpura Road, Kalol, Ahmedabad, Gujrat
Band materials are often used in the practice of pediatric dentistry. Nickel and Chromium are the main ingredients of these materials. The potential health hazards of nickel and chromium and their compounds have been the focus of attention for more than 100 years. It has established that these metals could cause hypersensitivity. The study was undertaken to analyze in vitro biodegradation of space maintainers made out of stainless steel band materials from manufacturers Dentaurum and Unitek. The leaching effect simulating the use of one, two, three, and four space maintainers in clinical practice was studied by keeping the respective number of space maintainers in the artificial saliva incubating at 37°C and analyzing for nickel and chromium release after 1,7,14,21 and 28 days using atomic absorption spectrophotometer. Results showed that there was measurable release of both nickel and chromium which reached maximum level at the end of 7 days which was statistically significant (P <0.05) and was very much below the dietary average intake even for four bands used and was not capable of causing any toxicity.
|How to cite this article:|
Bhaskar V, Subba Reddy V V. Biodegradation of nickel and chromium from space maintainers: An in vitro study.J Indian Soc Pedod Prev Dent 2010;28:6-12
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Bhaskar V, Subba Reddy V V. Biodegradation of nickel and chromium from space maintainers: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2010 [cited 2021 Nov 26 ];28:6-12
Available from: https://www.jisppd.com/text.asp?2010/28/1/6/60484
In recent years, there has been a dramatic increase in the use of metals and non-precious alloys in clinical dentistry. Austenitic steel alloys containing nickel and chromium are used for making crowns, bands, wires, denture bases, space maintainers, brackets etc.
Nickel and chromium are two metals often used in the construction of various parts of most pedodontics appliances. Chromium is known to be an essential element for human beings and animals and it plays a role in glucose metabolism. Advantage of this nickel and chromium alloys viz; high strength corrosion resistance and relative low cost have lead to their common use. This has raised questions concerning their biological safety. The potential health effects from exposure to nickel and chromium and their compound have been scrutinized for more than 100 years, and it was established that these metals could cause hypersensitivity, , allergic dermatitis, , asthma,  and ulcers of the mucous membrane .
The nickel one of the most common allergens and the most potent sensitizer of all metals has been described as "ubiquitous contact allergens".  It has been shown those patients who are allergic to nickel will react to certain nickel chromium dental alloys. ,
However, it has been shown that the intraoral exposure to nickel-containing dental alloys did not result in an increased incidence of nickel sensitivity.  In addition, significant carcinogenic and mutagenic potentials have been demonstrated for compound containing nickel and chromium metals. , In pedodontics, the stainless steel crowns and space maintainers are widely used. These are made of base alloy metal alloys mainly containing nickel and chromium as the main constituents. Since the oral environment is particularly ideal for the biodegradation of metals because of its ionic, thermal, micrbiologic, and enzymatic properties, some level of patient exposure to the corrosion products of these alloys could be assumed, if not assured.
Therefore, the objective of the present study was to evaluate in vitro biodegradation of space maintainers made of two different company bands (Dantaurum, Unitek) using atomic adsorption spectrophotometer.
Materials and Methods
A total number of 20 space maintainer were studied, out of which 10 were fabricated using Dantaurum and 10 using unitek band materials. Each group of 10 space maintainers was divided into four subgroups
The test materials in each subgroups of space maintainers were placed in separate glass beakers containing 100 ml of artificial saliva at 37 o C in an incubator for 4 weeks. The required amount of salivary sample were drown out from each beaker and analyzed separately on days 1, 7, 14, 21, and 28 by using atomic adsorption spectrophotometer.
The materials used in the study were:
Dantaurum band material--- Dantaurum Ltd., GermanyUnitek band material--- 3 M Company, USAStainless steel wire (1 mm)--- Dantaurum Ltd., GermanySolder and flux (Unitek --- 3 M companies, USA) Preparation of space maintainers
Two different types of bands (Dentaurum and Unitek) were chosen for making space maintainers as they were commonly used in dentistry. Each type of space maintainers made on first permanent molar using similar casts. In all the space maintainers, Dentaurum stainless steel wire was used for making loops and Unitek solder for soldering. Later, they were trimmed and polished by using a polishing kit.
Preparation of medium
The simulated saliva medium consisted of:
0.8 g of NaC1 (Sodium chloride)2.4 g of KC1 (Potassium chloride)1.5 g NaH 2 PO 4 2H 2 0 (Disodium anhydrous phosphate)0.1 g Na 2 S, 9H 2 0 (Sodium sulphide)2 g (CO(NH 2 ) 2 ) (Urea)2000 ml of distilled deionized waterAlbumin (albumin bovine fraction V) was selected as the protein component because of its presence in saliva and ready availability.
The pH of artificial saliva was adjusted to 6.75 ± 0.15 by adding an increment of 50 µl of 10 N sodium hydroxide. The pH was measured by using Emerk pH indicator papers with a high degree of sensitivity (0.2 units sensitivity).
The analysis was initially performed with atomic absorption spectrophotometer 1800 Hitachi Model; atomic absorption is a technique based on the unique spectrum of each element. For every element analyzed, characteristic wavelengths are generated in a discharge lamp (hallow cathode lamp), which in turn are absorbed by a cloud or vapor of that element. The amount of absorption is proportional to the concentration of the element that is vaporized into the light beam. As the sensitiveness of the equipment that was restricted to analyze the element up to 1 ppm was known after doing a pilot study for one sample by the direct method. An alternative indirect method called "standard addition method" was used to detect the metal.
A 20 ml of known concentration and nickel (6 ppm) is taken. It is analyzed by using atomic absorption spectrophotometer. A standard graph is plotted. A 10 ml of known concentration of nickel is added to 10 ml of a saliva test sample. The values are recorded for the released metal. The values dropped down drastically indicating the very presence of deionized water that made the solution to dilute. To analyze the exact amount of metal released, a standard solution of 10 ml of known concentration of nickel is added to 10 ml of deionized water. Again, the analysis was performed; the ppm was below the salivary sample level. It indicated that the standard solution was diluted because of deionized water showing a lesser ppm level. Finally, the difference between the two (standard solution with saliva - standard solution with deionised water) revealed the exact amount of nickel released.
For each sample, analysis was done three times and an average was taken to obtain the accurate results. Same procedure was carried out for chromium release by using standard solution (5 ppm).
The results were statistically analyzed by using variance Snedecor's F-test. The critical value for statistical significance was set at P = 0.05. The release of nickel in Group I space maintainers in artificial saliva at 1,7,14,21 and 28 days were 2.10, 2.46, 1.23, 0.58 and 0.37 ppm for Dentaurum and 1.10, 1.54, 1.28, 0.73 and 0.30 ppm for Unitek.
The total release of nickel was 6.74 ppm for Dentaurum and 4.95 ppm for Unitek and per day release was 4.80 µg for Dentaurum and 3.60 µg for unitek. The statistical analysis showed that there was no statistically significant difference between the material and between the days [Table 1].
The release of nickel in Group II space maintainers in artificial saliva at 1, 7, 14, 21, and 28 days was 1.87, 2.41, 1.31, 0.68, and 0.41 ppm, respectively, for Dentaurum, and 1.37, 1.74, 1.34, 0.81 and 0.50 ppm, respectively, for Unitek. The total release of nickel was 6.68 ppm for Dentaurum and 5.76 ppm for linitek and per day release was 4.80 µg for Dentaurum and 4.20 µg for Unitek. The statistical analysis showed that there was no statistically significant difference between the materials, whereas there was statistically significant difference between days maximum on 7th day with P P P  reported that in the oral environment biodegradation of metals occurs usually by electrochemical breakdown. Bacteria and their waste products and selective interactions with gases like oxygen and carbon dioxide may also contribute to the breakdown of dental materials placed in the mouth. Yet little attention has been devoted to this aspect of biomaterials in dentistry.
Nickel dermatitis was first reported as early as 1889. Goldman  reported a specific skin disease characterized by sensitivity to nickel compounds. Twenty years later sensitivity was observed to be common in women. Fisher  stated that nickel is one of the most common causes of allergic contact dermatitis especially in women. Darwin and Tarsitano  first reported the sensitivity to chrome cobalt appliances. Svein  studied corrosion base metal alloys by placing in artificial saliva for 2 months and same findings were reported by other investigators.
De Micheli and Riesgo  stated that current nickel alloy composition is such that the amount of nickel and other metals released due to electrochemical corrosion could never reach the toxic dose of 10 mg/kg body weight.
Hensten-Pettersen  and Jacobsen and Sunderman  showed that amount of nickel in human saliva ranges from 0.8 to 4.5 µg/l and demonstrated that concentration of nickel as small as 2.5 mg/ml were toxic to human gingival cells in tissue culture. Robert  stated that the average dietary intake of nickel is 200-300 g/day, but Vreebrug  reported that the lethal oral dose for nickel in humans probably lies between 50 and 500 mg/kg body weight.
The chromate salts which cause skin sensitivity and dermatitis, results from the corrosion of base metal alloys. Chromium allergy related to contact in mouth is rarely reported. The incidence of chromium allergy was reported 10% in males and 3% in females by investigator s,
Chromium is an essential nutrient of man in amounts of 50-200 mg/day in glucose metabolism, and the average dietary intake of chromium is 280 µg/day and the estimated lethal dose for chromium in human is about 50-70 mg/kg body weight.
Keeping in view the above findings, this study was carried out to analyze the biodegradation of base metal alloys in the artificial salivary medium for nickel and chromium.
Space maintainers made of Dentaurum and Unitek stainless steel bands (18-8 steel) were selected, because of their wide usage in routine practice and easy availability.
Maximum of four space maintainers were selected because, usually, in a patient a maximum of four space maintainers can be given.
Artificial saliva was used as medium in the study to simulate the natural saliva, and albumin was selected as the protein component because of its presence in natural saliva and ready availability. All the samples were kept in an incubator at 37°C to simulate the oral temperature. Atomic absorption spectrophotometer was used to analyze nickel and chromium release because other analysis like calirometric analysis and ultraviolet spectrophotometry were not as accurate as atomic absorption spectrophotometer to measure the nickel and chromium levels below 1 ppm.
So for the accuracy and convenience, we measured the levels on 1, 7, 14, 21, and 28 days by keeping each group in 100 ml of freshly prepared artificial saliva.
In all the four groups space maintainers made with two company bands, i.e. Dentaurum and Unitek, the maximum release of nickel and chromium was seen within seventh day, and thereafter the release of nickel and chromium was progressively decreased. The possible explanation would be if nickel and chromium present on the surface of the space maintainers may quickly corrode during the first 7 days of the experiment, then the rate of release drops off as the surface nickel and chromium is depleted.
The release of nickel and chromium was directly proportional to the number of space maintainers in the artificial saliva. This may be because with the increase in the number of space maintainers its available content of nickel was increased for corrosion. All these values were much below than the average dietary intake of 200-300 µg/day.
There was no significant difference between the space maintainers made with different company bands.
WHO (1988)  and WHO (1991 ) stated that 0.2 mg/kg body weight of nickel and 50 mg/kg body weight of chromium can cause systemic manifestations. However, in this study all the released nickel and chromium values were very much less than the values to cause any toxicity.
It has been observed that there is increased sensitivity of nickel in females because of costume jewellery, , used by them containing nickel has been found to be responsible for a significant number of nickel hypersensitivity. In case of history of nickel and chromium sensitivity, an alternate alloy should be recommended. A patch test could be performed before selecting nickel- and chromium-containing alloys.
Base metal alloys used in the pediatric dentistry, i.e. Band and loop space maintainers, release measurable amount of the nickel ranging from 4.95 to 7.78 ppm and chromium 1.70 to 4.54 ppm in an artificial salivary medium.
Both nickel and chromium release reaches a peak level on 7 th day, then the rate of release diminishes with time.
The release of nickel and chromium very much below when compared with the average dietary intake of nickel (200-300 µg/day) and chromium (280 µg/day) which were not capable of causing any toxic effects.
There was no significant difference of release between the space maintainers made with different band materials.
In case of history of nickel and chromium sensitivity an alternate alloy should be recommended and a patch test could be performed before selecting nickel- and chromium-containing alloys.
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