Introduction
Stainless steel orthodontic brackets can release metal ions into the saliva. Fluoridated mouthwashes are often recommended to orthodontic patients to reduce the risk of white-spot lesions around their brackets. However, little information is available regarding the effect of different mouthwashes in ion release of orthodontic brackets. The purpose of this study was to measure the amount of metal ion release from orthodontic brackets when kept in different mouthwashes.
Methods
One hundred sixty stainless steel brackets (0.022-in, 3M Unitek, Monrovia, Calif) were divided randomly into 4 equal groups and immersed in Oral B (Procter & Gamble, Weybridge, United Kingdom), chlorhexidine (Shahdaru Labratories, Tehran, Iran), and Persica (Poursina Pharmaceutical Laboratories, Tehran, Iran) mouthwashes and distilled deionized water and incubated at 37°C for 45 days. Nickel, chromium, iron, copper, and manganese released from the orthodontic brackets were measured with an inductively coupled plasma spectrometer. For statistical analysis, 1-way analysis of variance (ANOVA) and the Duncan multiple-range tests were used.
Results
The results showed that ion release in deionized water was significantly ( P <0.05) higher than in the 3 mouthwashes. Higher ion release was found with chlorhexidine compared with the other 2 mouthwashes. There was no significant difference ( P >0.05) in nickel, chromium, iron, and copper ion release in the Oral B and Persica mouthwashes. The level of manganese release was significantly different in all 4 groups.
Conclusions
If ion release is a concern, Oral B and Persica mouthwashes might be better options than chlorhexidine for orthodontic patients with stainless steel brackets.
During the last decade, there has been increased interest among dental and biomedical professionals in the side effects associated with the use of biomaterials, especially the metallic materials. Fixed appliances in orthodontics involve brackets and archwires that are metallic. These brackets are exposed to the oral cavity, which is a potentially hostile environment where electrochemical corrosion phenomena can occur. Thus, orthodontic brackets and other auxiliary components should be made of highly corrosion-resistant metals and metal alloys. In recent years, it has been reported that bracket corrosion can occur in the oral environment. In an acidic environment and in the presence of fluoride ions, the corrosion resistance of certain materials, particularly titanium and titanium alloys, can deteriorate. Practitioners can choose from a wide range of wires and brackets made from various alloys such as stainless steel (iron, chromium, and nickel), titanium, and cobalt-chromium alloy. Generally, stainless steel alloys that contain 8% to 12% nickel and 17% to 22% chromium are used for the metallic parts of orthodontic appliances.
The harmful effects of nickel—its carcinogenicity, allergenicity, and mutating substances—have been systematically investigated at the cell, tissue, organ, and organism levels. Approximately 10% of the general population has a hypersensitive reaction to nickel. Peltonen reported that women are 10 times more sensitive to nickel than men. Nickel can cause hypersensitivity, contact dermatitis, asthma, and cytotoxicity. In a study in which cultured human cells were used, nickel was recently reported to be moderately cytotoxic, whereas chromium was considered to have little cytotoxicity. Park and Shearer measured the in-vitro average amounts of nickel and chromium released per day, and Barrett et al studied the corrosion rate of simulated orthodontic appliances. However, the ion release in only a short time was not enough to evaluate the biocompatibility of orthodontic appliances that are in the mouth for 2 to 3 years.
During orthodontic treatment, practitioners recommend that their patients use mouthwashes, especially since most are adolescents who do not always follow a satisfactory oral-hygiene regimen and have a high risk of dental caries. Nowadays, the regular use of fluoride-containing products such as toothpastes and mouthwashes during orthodontic treatment is recommended to reduce the risk of the development of white spots around orthodontic brackets. Although fluoride ions in the prophylactic agents have been reported to cause corrosion and discoloration, little information is available regarding the effect of different mouthwashes in ion release of orthodontic brackets. The purpose of this study was to measure the levels of metal ions released from orthodontic brackets after immersion in several mouthwashes. These results should help practitioners to decide which mouthwash to prescribe for their patients.
Material and methods
One hundred sixty premolar stainless steel brackets (0.022-in, 3M Unitek, Monrovia, Calif) were used for this study. All brackets were used in as-received condition. The brackets were divided randomly into 4 equal groups and immersed in Oral B (Procter & Gamble, Weybridge, United Kingdom), chlorhexidine (Shahdaru Labratories, Tehran, Iran), and Persica (Poursina Pharmaceutical Laboratories, Tehran, Iran) mouthwashes, and distilled deionized water.
These mouthwashes were chosen because of their commercial availability and identical methods of application.
Group 1 used Oral B mouthwash containing water, glycerin, alcohol, aroma, methyl paraben, poloxamer 407, cetyl pyridinum chloride, sodium fluoride, sodium saccharin, and propylparaben. Group 2 used chlorhexidine mouthwash with 0.2% chlorhexidine digluconate and 13.65% ethanol. Group 3 used Persica herbal mouthwash containing extracts of Salvadora persica , mint, and yarrow with the main ingredients of tannin, flavonoid, calcium, fluoride, chloride, and essence. Persica mouthwash was prepared by diluting 15 drops of the original solution into 15 mL of distilled deionized water. In addition to these 3 mouthwashes, distilled deionized water was used in group 4 (control).
Each bracket was incubated in an oven set at a constant temperature of 37°C in individual 20-mL plastic-capped vials containing 15 mL of 1 mouthwash solution or distilled deionized water for 45 days.
After incubation for 45 days, the immersion solution was tested with an inductively coupled plasma (ICP) spectrometer (ICP-OES, Varian, Vista-Pro model, Mulgrave, Victoria, Australia; 1400W applied power). Unlike other methods such as atomic emission spectrometry, ICP has the advantage of extracting each ion simultaneously and detecting the metals without the interference of other ions.
Standard stock solutions (100 mg mL −1 ) of chromium, copper, iron, manganese, and nickel were prepared by dissolving their appropriate salts in distilled deionized water. More dilute solutions (0.1-10 mg mL −1 ) of each ion were freshly prepared daily by appropriate dilutions of their stock solutions. To minimize the matrix effect in ICP measurements, the stock solution of each ion was diluted with the appropriate mouthwash. Each solution was analyzed for chromium, copper, iron, manganese, and nickel ions. Measurements of pH for each mouthwash and the distilled deionized water were made with a pH meter (model 781, Metrohm AG, Herisau, Switzerland) by using a combined glass electrode.
Statistical analysis
One-way analysis of variance (ANOVA) was used to analyze the differences among mean ion concentrations in the 4 groups. The Duncan multiple range test was applied to show the differences between groups.
Results
Mean levels of the ions released in the groups are shown in the Table. The results of the Kolmogorov-Smirnov test showed that, except for copper and iron ions, all other ions had normal distributions. Therefore, a nonparametric test (Kruskal-Wallis) showed that the release of copper and iron in the 4 mouthwashes was significantly different. ( P = 0.00) Also, the Mann-Whitney test with a significance level of less than 0.008 showed no significant difference in iron release between Oral B and Persica ( P = 0.031) and was significantly lower than what was observed for water. Copper release between chlorhexidine and Persica and also between chlorhexidine and distilled water was not significantly different ( P = 0.384 and P = 0.009, respectively).
The test of homogeneity (Levene statistic) showed that chromium, manganese, and nickel releases were not homogenous; a post-hoc test (Tamhane) was used to compare the groups. Only nickel release between Oral B and Persica was not significantly different ( P = 0.239). Nickel release was similar in Oral B and Persica ( P >0.05) ( Table ), and this was significantly lower than in chlorhexidine and water.
| Solution | Chromium | Copper | Iron | Manganese | Nickel |
|---|---|---|---|---|---|
| Oral B (group 1) (n = 40) | 90.7 ± 8.9 (0.0-300.0) |
0.0 ± 0.0 (0.0-0.0) |
53.5 ± 6.3 (0.0-220.0) |
1064.8 ± 17.4 (700.0-1510.0) |
171.5 ± 18.4 (0.0-540.0) |
| Chlorhexidine (group 2) (n = 40) | 484.8 ± 39.5 (0.0-1380.0) |
19.0 ± 5.8 (0.0-310.0) |
61.1 ± 28.1 (0.0-175.0) |
206.9 ± 8.2 (0.0-320.0) |
1198.3 ± 36.4 (540.0-1950.0) |
| Persica (group 3) (n = 40) | 25.1 ± 2.3 (0.0-80.0) |
4.1 ± 1.0 (0.0-50.0) |
73.1 ± 4.5 (0.0-170.0) |
748.2 ± 35.3 (0.0-137.0) |
109.7 ± 4.4 (4.0-180.0) |
| Deionized water (group 4) (n = 40) | 838.1 ± 32.9 (0.0-1620.0) |
80.4 ± 11.8 (0.0-390.0) |
882.4 ± 114.7 (4.0-230.0) |
1861.1 ± 62.7 (550.0-4160.0) |
2627.4 ± 151.0 (0.0-7040.0) |
Nickel release in other mouthwashes (chlorhexidine and distilled deionized water) and chromium and manganese release in all the mouthwashes were significantly different ( P = 0.00).
Also, the level of chromium in chlorhexidine was significantly lower than in water. The level of manganese release was in the following order: chlorhexidine <Persica <Oral B <water. Except for copper release, which was similar in chlorhexidine and distilled water, the amounts of all ions released in deionized water were significantly higher than the amounts released in the 3 mouthwashes. Compared with the other ions, the level of copper release was the least among all the groups studied.
For further elucidation of the reasons for ion release in the different solutions, the pH values of the 3 mouthwashes and distilled deionized water were measured. The values were 7.5 for distilled deionized water, and 5.5, 5.2, and 5.4 for Oral B, chlorhexidine, and Persica, respectively.
Results
Mean levels of the ions released in the groups are shown in the Table. The results of the Kolmogorov-Smirnov test showed that, except for copper and iron ions, all other ions had normal distributions. Therefore, a nonparametric test (Kruskal-Wallis) showed that the release of copper and iron in the 4 mouthwashes was significantly different. ( P = 0.00) Also, the Mann-Whitney test with a significance level of less than 0.008 showed no significant difference in iron release between Oral B and Persica ( P = 0.031) and was significantly lower than what was observed for water. Copper release between chlorhexidine and Persica and also between chlorhexidine and distilled water was not significantly different ( P = 0.384 and P = 0.009, respectively).
The test of homogeneity (Levene statistic) showed that chromium, manganese, and nickel releases were not homogenous; a post-hoc test (Tamhane) was used to compare the groups. Only nickel release between Oral B and Persica was not significantly different ( P = 0.239). Nickel release was similar in Oral B and Persica ( P >0.05) ( Table ), and this was significantly lower than in chlorhexidine and water.
