| Abstract|| |
Context: Moist environment in the mouth varies and causes variable amounts of corrosion of dental materials. This is of concern particularly when metallic implants, metallic fillings, orthodontic appliances are placed in the hostile electrolytic environment in the human mouth. Components of diet rich in salt and spices are important factors influencing the corrosion of metallic appliances placed in the oral cavity.
Aims: To study in vitro corrosion of orthodontic metallic brackets immersed in solutions of salt and spices in artificial saliva.
Materials and Methods: Orthodontic brackets were used for corrosion studies in artificial saliva, salt, and spices using electrochemical technique and surface analysis. Electrochemical studies using different parameters were done in solutions of artificial saliva containing salt and spices. Photomicrographs from the optical microscope were also obtained.
Results: Results of corrosion studies have clearly demonstrated that certain spices such as turmeric and coriander are effective in reducing corrosion, whereas salt and red chili have been found to enhance it. Surface analysis of small pits present on the surface of the as-received bracket will initiate corrosion which leads to more pitting.
Keywords: Coriander, corrosion, dental alloy, dental materials, orthodontic metallic brackets, pitting corrosion, spices, turmeric
|How to cite this article:|
Chaturvedi T P. Corrosion of orthodontic brackets in different spices:In vitro study
. Indian J Dent Res 2014;25:630-4
Corrosion-related failures are feasible. Different types of corrosion commonly occurring related to dental materials are accessible in dental literatures. , Many of these will occur inside mouth and deteriorate the metallic dental appliances. As most of the available published information is focusing on western life-style, the diet may not be strictly applicable to Indian conditions. Therefore, it would be useful to produce data and technical information under Indian lifestyle to help dentists Diet is an important factor influencing the corrosion of metallic appliances placed in the oral cavity. , A spice is a dried seed, fruit, root, bark, or leaf, that is an important part of Indian diet. For our investigation, we used four most commonly used spices-coriander (Coriandrum sativum), turmeric (Curcuma longa), black pepper (Piper nigrum), and red chili (Capsicum annuum).
The objective of this paper is to study in vitro corrosion of orthodontic brackets in artificial saliva and extract of spices using electrochemical techniques and surface analysis test.
| Materials and methods|| |
Orthodontic Brackets used for the study have composition as mentioned in [Table 1]. Chemicals for preparation of artificial saliva  are potassium dihydrogen orthophosphate, sodium hydrogen orthophosphate, potassium hydrogen carbonate, sodium chloride (NaCl), magnesium chloride hexahydrate, citric acid (3-carboxy-3-hydroxypentanedioic acid, C6H8O7), and calcium chloride used for preparing artificial saliva. Most of the orthodontic brackets [Figure 1] and [Figure 2] available in the market for orthodontic applications are made of stainless steel.
Corrosion studies were conducted using brackets exposed to aqueous media viz aqueous NaCl solution, aqueous extracts of spices. In each case, anodic and cathodic polarization behavior as well as variation of free corrosion potentials (Ecorr) with time was recorded. Corroded specimens were also examined under optical microscope for changes in the surface morphology.
| Spices|| |
In the present investigation, a collection of commonly used spices popular in Indian cuisine was prepared. Extracts of spices used for our investigation, were four most commonly used spices coriander (C. sativum), turmeric (C. longa), black pepper (P. nigrum), and red chili (C. annuum) for orthodontic brackets [Table 2]. Celite (545 mesh) and silica gel (20-120 mesh) were used for the filtration of extracts of spices.
|Table 2: Chemical composition of the spices used in the present investigation |
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Preparation of extracts of spices
The selected spices were crushed and dried in an electric oven to remove the moisture. To prepare extracts, 50 g of spice was weighed on the digital balance and added to 250 ml distilled water in a round-bottomed flask. The mixture was then refluxed for an hour, followed by cooling. After cooling, the contents were filtered using filter paper and thick cotton swab first and then subjected to fine filtration over silica gel (20-120 mesh) and Celite (545 mesh) using a vacuum pump to obtain a clear and transparent extract. 20 ml of this extract was then taken and placed in 100 ml volumetric flask, and artificial saliva was added to make up the volume. Solutions with artificial saliva containing 1% salt were also made in a similar manner.
Apparatus for electrochemical and surface morphology studies
For orthodontic brackets and stainless steel wires, 604C (CH Instruments 604C) corrosion systems were used. The surface morphology of the different alloys before and after corrosion was examined under Zeis Phase Contrast Optical Microscope.
The dental materials used in the experiment were stainless steel brackets. The test samples were prepared by painting lacquer onto the backside of the bracket, and the bracket is then connected to the working electrode part using a stainless steel wire which was painted again with lacquer to avoid its corrosion. After the preparation of the test medium and test sample, the sample is connected to the working electrode using a copper rod. The test medium was taken in the chemical corrosion cell. Then graphite rod, used as a counter electrode, is connected to the probes of electrochemical Analyzer (CH Instruments 604C). The reference electrode, i.e., saturated calomel electrode inserted in the lug in probe unit. Slopes for Tafel plot having Tafel constant for anodic (βa) and cathodic curves (βc) were obtained with microprocessor-based corrosion system. The value of corrosion current density (Icorr), Ecorr and pitting potential (Epit,) were determined. The software of the system calculates the corrosion rates by Tafel analysis and potentiodynamic data.
| Results|| |
The results exhibit an accelerated corrosion process on addition of NaCl to the artificial saliva containing extracts of spices. Artificial saliva and artificial saliva containing 1% NaCl were used as the reference solutions. The Icorr values, calculated using cathodic polarization method, were 0.537 μA/cm 2 for brackets in artificial saliva and 0.993 μA/cm 2 in artificial saliva containing 1% NaCl. The corrosion rate of bracket in artificial saliva containing 1% NaCl was more than that in artificial saliva. This is due to the fact that the presence of NaCl makes the medium more conducting. The passive region at lower potential seems to be similar for both the cases and Ecorr values were obtained in close vicinity. However, the difference lies in the region of higher potential where the polarization curve for bracket material in artificial saliva did not show any breakdown or Epit at all and the bracket material in artificial saliva containing 1% NaCl showed Epit at 0.59 V which signifies beginning and propagation of pitting corrosion on the steel surface at and beyond this potential [Table 3] and [Table 4].
|Table 3: Corrosion parameters of orthodontic brackets in artificial saliva containing extract of spices |
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|Table 4: pH of artificial saliva containing spice extracts measured before and after electrochemical experiments on orthodontic bracket |
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The polarization curves of orthodontic brackets in artificial saliva containing black pepper extract and artificial saliva containing coriander extract, and 1% NaCl along with those of artificial saliva and artificial saliva containing 1% NaCl are displayed in [Figure 3]. It did not show any sign of pitting at all. Some constituents of coriander seem to be preferentially adsorbed on the passive film, thereby preventing Cl− adsorption, which is mainly responsible for pitting. The Ecorr values obtained for both are in close vicinity to that for artificial saliva and artificial saliva containing 1% NaCl and the Icorr values obtained are 0.089 and 0.043 μA/cm 2 which are lower compared with Icorr values obtained in artificial saliva and artificial saliva containing 1% NaCl, respectively. The results suggest a decline in the corrosion process in coriander extract added to artificial saliva and artificial saliva containing 1% NaCl. This spice may be taken as an effective ingredient for arresting pitting mode of corrosion.
|Figure 3: Overlay of polarization curves of the orthodontic bracket in artificial saliva and artificial saliva containing 1% NaCl and in coriander|
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Corrosion potential values of the potentiodynamic polarization curves of bracket in artificial saliva containing turmeric extract and artificial saliva containing turmeric extract and 1% NaCl have curves were obtained at −0.30 and −0.19 V, respectively which is toward more negative potential when compared to the polarization curves in artificial saliva and artificial saliva containing 1% NaCl suggesting an increased tendency of corrosion. The polarization curves for both bracket materials in artificial saliva containing turmeric extract and 1% NaCl exhibited Epit at 0.91, suggesting some effects of turmeric on bracket material.
The polarization curves in artificial saliva containing black pepper extract and artificial saliva containing black pepper extract and 1% NaCl showed Ecorr values at −0.31 and −0.27 V, respectively, which are more negative with respect to the Ecorr values of brackets in artificial saliva and artificial saliva containing 1% NaCl indicating an increased corrosion process in the presence of this spice. The Icorr values for the above said polarization curves were calculated as 0.596 and 0.489 μA/cm 2 , respectively, which also indicate an enhancement of the corrosion process. There is an increased corrosion process in the case of black pepper. The polarization curves in artificial saliva containing black pepper extract did not exhibit Epit, although the polarization curves in artificial saliva containing black pepper and 1% NaCl, showed Epit, at 0.61 V which is similar to that in case of artificial saliva containing 1% NaCl. Thus, black pepper increases the corrosion rate with pitting tendency remaining unaffected.
Corrosion potential values remained more or less unaltered on addition of red chili to the artificial saliva and artificial saliva containing 1% NaCl [Figure 4]. Both the polarization curves show breakdown in the polarization curve indicating that the addition of red chili extract to the artificial saliva solution increases aggressiveness of the oral solution and enhances the probability of pitting of the bracket surface exposed to it. Epit on the polarization curve of the bracket in artificial saliva containing red chili extract and 1% NaCl appeared at 0.37V which was much earlier than the Epit value obtained in artificial saliva containing 1% NaCl only. The Epit value obtained for artificial saliva containing red chili extract was at 1.04V. This breakdown potential is not very sharp and shows the tendency of repassiveness. The pH results were in accordance with the electrochemical results and suggest that red chili extract added to the artificial saliva solution increased the aggressiveness of the later and addition of 1% NaCl further aggravated it. Thus, the presence of red chili in the spices is highly detrimental to the bracket material.
|Figure 4: Overlay of polarization curves of the orthodontic bracket in artificial saliva and artificial saliva containing 1% NaCl and in red chilli|
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Surface analysis of orthodontic brackets
[Figure 5] shows optical microscopy image of a normal bracket as received. [Figure 6] represents the corrosion of bracket in red chili solution, where there is more pitting. [Figure 7] represents the corrosion of the bracket in coriander solution, which reveals that there is less corrosion, as well as pitting. The small pits present on the surface of the as-received bracket will initiate corrosion which leads to more pitting.
|Figure 5: Optical microscopy images of stainless steel brackets as received|
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|Figure 6: Optical microscopy images of stainless steel brackets in red chilli|
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|Figure 7: Optical microscopy images of stainless steel brackets in coriander extract|
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| Discussion|| |
Spice extracts are complex mixtures of various organic substances and minerals. It is very difficult to figure out which component is responsible for the observed corrosion behavior. For orthodontic brackets, according to Icorr values, the aggressiveness of artificial saliva containing extracts of spices can be arranged in the decreasing order as follows:
Black pepper > Artificial saliva > Red chili > Coriander > Turmeric
On adding 1% NaCl to the mixture of artificial saliva containing extract of spices, the order is slightly different and is as follows:
Artificial saliva > Black pepper > Red chili > Turmeric > Coriader
Chloride ion combines with a metal ion to form metal chloride and facilitates dissolution of the latter and propagates in an autocatalytic manner. Depending upon their pitting characteristics, spices can be arranged in the following decreasing order:
Red chili > Black pepper > Artificial saliva > Turmeric > Coriander
The order shows that most of the spices enhance the pitting of the material in the presence of salt. Red chili is rated most aggressive and turmeric as well as coriander as the least aggressive for the orthodontic brackets. Role of turmeric is well-documented in medical and dental literature for its usefulness.  It is further supported by the fact that addition of 1% NaCl also did not increase the aggressiveness of the solution to the extent that pitting might be induced on the bracket surface. Due to the manufacturing defects present and mishandling during transportation, there may be breakage of protective oxide layer present on the surface acting as sites for the corrodent to form pits.
Kim and Johnson  showed that nickel-titanium and stainless steel wires were susceptible to pitting and localized corrosion. Many studies , have shown that components of diet and fluoride ions can destroy the protectiveness of the surface TiO2 passive film on Ti or Ti alloy, leading to attacked corrosion morphology, decreased polarization resistance, and an increased anodic current density or metal ion release. Further, the soluble corrosion products released from metals into the surrounding biological compartment, their biodistribution in the body, may lead to toxic effects in the mouth and body. Particles/ions released from the metallic appliance are finally reside in tissues and affects indirectly its effectiveness. The potential toxicity and biological risks associated with ions and/or particles released due to corrosion of metallic brackets are a health concern for the patients with dental/orthodontic treatments, due to long duration stay of appliances inside the body.  The corrosion products formed, as a result of metal-environment interactions have an effect on the biocompatibility and long-term stability of the appliances. Fouling caused by deposition of dissolved materials on the dental metallic restorations may invite problems such as microbial growth, tarnish, etc. Thus, these results from metallic brackets will enable dentist/orthodontists to recommend to their patients to avoid spicy food and use food with lower salt content to reduce the corrosion of brackets.
| Conclusion|| |
Results of corrosion studies have clearly indicated that certain spices such as turmeric and coriander are effective in reducing corrosion whereas salt, red chilies, and black pepper have been found to enhance it for metallic brackets. Strict compliance to use suggestive additive in diet may be helpful in both the prolonging the life of orthodontic brackets, eliminate their failure during 1-3 year of orthodontic treatment.
| References|| |
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T P Chaturvedi
Department of Orthodontics, Faculty of Dental Sciences, IMS, BHU, Varanasi, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3], [Table 4]