|Year : 2018 | Volume
| Issue : 1 | Page : 58-64
Evaluation of nickel releasing from stainless steel crowns regarding to “trimming”: An in vitro study
Leila Basir1, Maryam Shamsaei2, Sayed Ali Ziaei3
1 Department of Pediatric Dentistry, School of Dentistry, Ahvaz Jundishapur, University of Medical Sciences, Ahvaz, Iran
2 Department of Pedodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran
3 Department of Prosthodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran
|Date of Web Publication||28-Mar-2018|
Dr. Maryam Shamsaei
Department of Pedodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Daneshjoo Boulevard, 1983969411, Tehran
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Context: Stainless steel crowns (SSCs) are the most durable and effective restorations for the primary teeth. Allergy to nickel as major components is common. Aims: The purpose of this study is to evaluate the effect of pH, time, oral temperature, and SSCs trimming on the nickel releasing. Settings and Design: This in vitro study was done on 18 same size crowns. Subjects and Methods: Group A (without trim 0 and Group B (with trim) were immersed in 5 ml artificial saliva. The amount of nickel releasing in each 18 subgroup composed from 3 pH (3.5, 5, and 6.75) and 3 temperatures (27°C, 37°C, and 47°C) in 3 times (1, 7, and 21 days), was measured by Atomic Absorption Spectrophotometer. Statistical Analysis: Data were analyzed by SPSS software (SPSS 20, IBM, Armonk, NY, USA) and use of t-test, Duncan, and Tukey's test for analysis of variances. Results were reported with 95% confidence. Results: The amount of nickel releasing reduced with crown trimming, significantly (P = 0.0001). A significant difference was observed in the amount of released nickel in temperature 47°C in comparison with 37°C (P = 0.0001); this measurement was not significant between 47°C and 27°C (P = 0.442). There was no significant difference between concentration of released nickel in 3 pH conditions and also in 3-time situations. The concentration of nickel was lower in trimmed group in comparison to intact group (P = 0.0001). Conclusions: The concentration of released nickel decreased with trimming of margins and increased when temperature increased. Time and pH had no significant effect on released nickel.
Keywords: Atomic absorption spectrophotometer, nickel hypersensitivity, nickel releasing, stainless steel crown, trimming
|How to cite this article:|
Basir L, Shamsaei M, Ziaei SA. Evaluation of nickel releasing from stainless steel crowns regarding to “trimming”: An in vitro study. J Indian Soc Pedod Prev Dent 2018;36:58-64
|How to cite this URL:|
Basir L, Shamsaei M, Ziaei SA. Evaluation of nickel releasing from stainless steel crowns regarding to “trimming”: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2018 [cited 2020 Apr 6];36:58-64. Available from: http://www.jisppd.com/text.asp?2018/36/1/58/228747
| Introduction|| |
Despite communities' hygiene improvement, dental caries is the problem of all the world, especially in poor populations. Caries treatment in children varies depending on the size of lesion, the child behavior, and parent's cooperation, and it can be performed by very conservative methods, such as indirect pulp capping and restorations with various materials to more extensive treatments, prefabricated crowns, and ultimately tooth extraction and use of space maintainer.
Studies and evidences support “more biologic” and “more conservative” methods for controlling and treatment of primary dentition., Among the numerous restorative materials that are used in pediatric dentistry, the preformed metal crowns have a special position, undoubtedly.
Stainless steel crowns (SSCs) are the most effective and most durable restorations for restoring the primary molars in all of the world. Some retrospective studies evaluated the durability and survival of SSCs in comparison with amalgam. All of them indicate the superiority of SSCs to multisurfaces amalgam.,,
SSCs and orthodontic appliances are the common nickel containing appliances, used in pediatric dentistry. The content of these crowns includes iron (65%–70%), chromium (17%–20%), nickel (8%–13%), and <2% of manganese, silicone, and carbon.,
The main components used in orthodontic appliances, brackets, space maintaining bands, and SSCs – that all are stainless steel – are nickel and chromium. Up to 100 years, harming potential of nickel and chromium and their compositions is noted.,
Several studies indicated that orthodontic appliances release metal ions in saliva through electrogalvanic current and saliva action as a mediator.,,,,, Electrogalvanic reactions are called “Corrosion” that destroy the metal surface and release the metal ions. Intrinsic factors of corrosion are determined by composition and structure of that metal, and extrinsic factors depend on the environment (the composition of mediator, pH, temperature, and strain).
Nickel, as the main element used in these crowns, was entitled “contact allergen of year” in 2008 by the American Association of Contact Dermatitis. Allergy to this element is too common.
Actually, the allergy begins in 2–5 years and come to maximum level in 10–15 years. Nickel is the most common allergen known in the world. The prevalence of allergy to the nickel is explanted 30% in girls and 3% in boys  and elsewhere 10% in females and 1% in males. Actually, total allergy is 4–10 times more common in the females than males. It is interesting to know that the cause of this matter is the females' use of jewels in their childhood.,,
Many evidences indicate that nickel, chromium, and combination of them can lead to allergy, dermatitis, and asthma. Contact dermatitis has the ability to limit an individual's life. Because of the vast application of nickel in dentistry, allergy to it may be harmful for health. Actually, the main problem that results from the use of nickel-containing appliances is allergy and hypersensitivity.
The oral manifestations of allergy to nickel in dentistry include lichen plan, stomatitis, severe inflammatory hyperplasia around nickel containing crowns, alveolar bone recession, edema of throat, palate, and gingiva. Many of oral allergies associated with nickel-containing alloys, are type 4 hypersensitivity reaction, that are mediated by T-lymphocytes. The hypersentisized patients may suffer constant dermatitis even if they prevent dermal contact with nickel.
The biologic effects such as cytotoxicity, genotoxicity, renal dysfunction, and carcinogenicity properties are attributed to this element.,,
Based on the evidences, orthodontic appliances and SSCs release the measurable amounts of nickel and chromium into the saliva and serum in below the toxic level but not up to daily regimen intakes. Current investigations indicated 600–2500 and 300–500 micrograms for critical concentration and daily intake of nickel, respectively.
Since the prefabricated crowns in the market do not have full adaptation to the undertreatment tooth, occasionally, the height of margins may interfere with crown sitting or blanch the gingiva. The dentist should “TRIM” the crown in these situations that means shortening the margins. Trimmed area is polished and smoothened by heatless stone or rubber wheel.,
Our hypothesis was that the crown shearing (trimming) can affect the amount of nickel releasing and probably reach it to the critical level, because of integrity disturbance. According to vast usage of SSCs in pediatric dentistry and since similar studies on SSCs and potential adverse effects of released metals are rare, and also that there was no investigation about trimming effect on nickel releasing to this date, we decided to evaluate The effect of pH, time, oral temperature, and SSCs trimming on the nickel releasing.
| Subjects and Methods|| |
This in vitro study was performed on 18 same size (E #3) SSCs (3M/ESPE. St. Paul MN, USA). The samples were divided into 2 main Groups A and B. Group A included intact crowns and Group B included trimmed crowns. Then, they were divided into 9 subgroups A (1A to 9A) and B (1B to 9B), that each of them had had own special temperature (27°C, 37°C, or 47°C) and pH (3.5, 5, or 6.75) that will explain later.
For trimming the B-grouped samples, first, a line was drawn on 1-mm distance from the crown margin with a narrow marker. To equally shortening all crowns, an index was made from the thin wire and was adhered and fixed on 1-mm distance from the margin [Figure 1], [Figure 2], [Figure 3]. For trimming the 9 crowns in this group, the cutting of each 3 crowns was made by the special crown scissors (MIB/IdeBartar Co. France). Then, cut margins was polished and smoothed by pink mullet (Corundum731/ Meisinger/ Germany) and green polish rubber (universal polisher 9511H/Meisinger/ Germany). The surface of selected crowns was cleaned ultrasonically in a solution of 50% v/v acetone and 50% v/v ethanol and filled with glass ionomer cement (Fuji; Tokyo, Japan). Then, each of the prepared samples was floated in 5 ml artificial saliva in numbered polyethylene containers (Axigen, Union City, CA, USA).
The applied artificial saliva in this study was made in the formulation of 0.8 g NaCl, 2.4 g KCl, 1.5 g NaH2 PO4, 0.1 g Na2S, and 2 g CO (NH2) 2 and with 3 pHs consisting 6.75, 7, and 3.5. A1, A2, A3 and B1, B2, B3 were incubated in 37 degree of centigrade (Memet; NB500, E60529-IP20/Schutzart, Germany). After 1 day, the concentration of released nickel in artificial saliva was measured by atomic absorption spectrophotometer (Furnace Atomic Absorption Spectrophotometer Analytic Jena, AAS5EA, Germany), analyzed, and recorded [Figure 4].
Since there was the possibility of change in the primary composition of artificial saliva for any reason, the fresh saliva with preceding characteristic was used for continuing the investigation. After 7 days, all of the samples were measured, analyzed, and recorded. The same protocol was performed for the third time in day 21 with replacement of new saliva, placement of crowns in incubator, and measurement of nickel releasing.
Same protocol was made for A4, A5, A6 and B4, B5, B6 subgroups in 47 degree of centigrade and for A7, A8, A9 and B7, B8, B9 in 27 degree of centigrade incubator. As the same, the results of these samples were recorded in days 1, 7, and 21.
Collectively, all of 18 crowns were tested 3 times that led to 54 assessments. Data were analyzed by SPSS software and use of t-test, Duncan, and Tukey's test for analysis of variances. Results were reported with 95% confidence.
| Results|| |
Based on the descriptive analysis, the mean released nickel was 0.1996 for day 1, 0.0771 for day 7, 0.0562 for day 21, and 0.1067 ppm for total time and associated standard deviation was 0.1438, 0.0312, 0.0934, and 0.1121, respectively. Total release of nickel for untrimmed and trimmed crowns are collected in [Table 1]. According to t-test, the amount of nickel releasing was reduced with crown trimming, significantly (P = 0.0001); as the samples of Group B had less released nickel average than Group A [Table 2].
|Table 2: Comparison of the effect of temperature on nickel releasing from stainless steel crowns|
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Just as shown in [Table 3] using Tukey's test, a significant difference was observed in amount of released nickel in temperature 37°C in comparison to both 47°C (P = 0.0001) and 27°C (P = 0.011); however, this measurement was not significant between 47°C and 27°C (P = 0.442).
|Table 3: Comparison of the effect of temperature on nickel releasing from stainless steel crowns|
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There was no significant difference between concentration of released nickel in 3 pH conditions and also in 3-time situations. In other words, increased acidity and time did not have significant effect on nickel releasing [Table 4].
|Table 4: The average concentration of nickel releasing from stainless steel crowns|
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| Discussion|| |
Nowadays, great advancements are created in composition and quality of alloys used to construct intraoral appliances, and their bioavailability and durability in the oral environment have improved. Nevertheless, the cases of hypersensitivity and toxic reactions related to these appliances have been reported. However, it is difficult to differentiate between the symptoms of contact dermatitis and mechanical damage to the mucosa arising from orthodontic appliance or the crown.
In spite of the possibility that the amount of nickel releasing from the crown in laboratory or oral environment does not reach to critical level, but if assume that the high number of SSCs are applied in one child in one general anesthesia appointment, or if it may be that the child has orthodontic appliance and space maintainer simultaneously, this problem can become important. Yilmaz et al. have reported the symptoms of delayed hypersensitivity in a child that were resulted from only one crown on permanent molar.
The amount of nickel releasing in our assessment was below the critical level (toxic dose: 2.5 mg/ml), [Table 1], so it seems that its systemic toxic effects are so improbable, but such this low amount has the ability to inducing allergic reactions too, because orthodontic appliances (and crowns) remain in the mouth for a long time by scissors or burs.
The ability of nickel to induce allergic reaction has been contributed to high haptenic capacity of released metal. Haptens are small molecules that cannot activate immune system solely but can do it if forms the protein-hapten conjugates. Actually, this composition converts to antigen and results in creation of anti-hapten antibody. Such antibodies may be developed against metallic ions such as nickel; the element that is found in some dental material. These findings indicate that dental staff should have enough knowledge about allergy-inducing ability of nickel and its compositions.
The atomic absorption apparatus detected some amount of nickel in saliva sample in 1 day after beginning the present experiment. The nickel releasing from orthodontic appliances are indicated in several studies.,,,, Some studies have reported the nickel releasing from the SSCs that are parallel to our study.,,, However, the results of Setcos et al. indicated that orthodontic appliances did not only have significant relationship with hypersensitivity, but this low exposure can lead to toleration against allergen.
According to the results, maximum concentration of nickel releasing occurred in day 1 (=0.522 ppm) and then reduced in day 7 and day 21. Although it is not significant but can contribute to the element behavior that following the initial release of ions from the surface, the stable oxide layer may be formed and protect the remaining surface against corrosion.,
The cause of increasing in metallic ion concentration in artificial saliva can be contributed to “corrosion.” Actually, saliva may be considered as a mediator for electrochemical battery and resultant corrosion of metallic crown surfaces. The past investigations have indicated that metal releasing from orthodontic appliances depends on wire composition and not metal content. Studies have shown that the releasing of metallic components from the SSCs has no effect on their concentration in the crown. It can conclude from these evidences that the crowns release the low amount of their nickel in the oral environment; however, it does not change the primary composition of the crowns and strength and other advantages associated to composed elements.
Nevertheless, studies have indicated that the released nickel from dental alloys may aggregates in cells over the period of time and results in several adverse effects on them  that include leukocyte chemotaxis suppression and changing in DNA synthesis and enzymes activity.,
A few studies have evaluated the nickel releasing from SSCs and our findings on nickel releasing ability are parallel to them.,,, However, in spite of numerous cases of necessity to correct and “trim” the crowns in pediatric dentistry, there is no study that assessed its effect until our examination.
In this study, the mean released nickel was different significantly in two trim status (with trimming and without trimming). Our hypothesis was that we would encounter with more ion releasing because of alloy integrity disturbance due to shearing the crown margins. The results showed that trimming and polishing do not lead to increase in nickel releasing but oppositely, decrease it significantly (P = 0.0001). Based on these observations, it can be concluded that the amount of released nickel is more affected by the crown surface “area-land” rather than its margins and modifying them. In reality, the larger crown surface has more metal ions subsequently, that probably can release the larger amount of them.
Several studies have evaluated the nickel releasing from orthodontic appliances that more of them have accomplished in different pH and times without temperature changing.,,
The current study demonstrated that both increasing and decreasing in temperature from the normal (37°C) can increase the amount of released nickel from the crowns. In other hand, if the normal temperature of the mouth increases or decreases in amount of 10 degree of centigrade after eating or drinking the hot and cold foods and drinks, can cause the significant higher nickel releasing from nickel-containing alloys. Considering that the children rarely tend to eat the hot or very cold foods and drinks, it seems that this factor does not have critical effect in nickel releasing, clinically. It is attractive that the differentiation between the lowest and highest used temperatures was not significant [Table 3] and [Table 4].
Based on available evidences, changing in acidity has strong effect on metal ions release. Actually, it is expected that ion releasing increse as a result of solubility of alloy after decrease the pH value. Some available studies have shown that the more acidic environment can lead to higher nickel releasing but the findings of the present study were differ.,, In Merritt study, pH changing had no effect on corrosion in saline solution but was effective in albumin solution. In the present study, the effect of pH on nickel releasing was not significant, that was parallel to Merritt study here on; although the mediator solutions are different in two mentioned studies.
In the oral cavity, it is possible that the metals are released in saliva as a mediator. It can be affected with high chloride content or eating foods and drinks with low pH. Furthermore, saliva characteristics are different according to individual health and vary times in day.,
Clinically, considering that the consumption of sport and energy drinks in children that have low acidity (some of them have pH = 3–4), is becoming to increase, it seems that corrosion of nickel-containing oral appliances such as SSCs due to pH drop does not a critical concern, although other adverse effects are persisting.
In this study and other available data, nickel ions releasing from stainless steel appliances was demonstrated. In spite of that findings of all studies indicated that the amount of released nickel is below the critical level for allergy-inducing, but it may be better to ask the patients – especially the girls – about the probable allergy to the nickel, in primary appointment and patient examination form because of existing case reports of allergy to SSCs and transpalatal arch.,In vitro studies cannot reconstruct in vivo conditions completely, such as biofilms that form on tooth or dental material surface in oral cavity. Future studies can perform in higher number of crowns and closer conditions to actual conditions of oral cavity. Furthermore, it is better that the dimensions of crown surface are measured before and after trimming in the future studies so that the role of crown dimensions in width, height, and area land can be known and also “real same size” crowns can be compared together instead of “numerical same size crowns.”
| Conclusions|| |
The concentration of released nickel decreased with trimming of margins and increased when temperature increased. Time and pH had no significant effect on released nickel.
The authors of the current study wish to thank the Research Deputy of the Jundishapur University of Medical Sciences for kind support and assistance.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Petersen PE, Lennon MA. Effective use of fluorides for the prevention of dental caries in the 21st
century: The WHO approach. Community Dent Oral Epidemiol 2004;32:319-21.
Ripa LW. Nursing caries: A comprehensive review. Pediatr Dent 1988;10:268-82.
Innes NP, Evans DJ. Modern approaches to caries management of the primary dentition. Br Dent J 2013;214:559-66.
Kidd E. Should deciduous teeth be restored? Reflections of a cariologist. Dent Update 2012;39:159-62, 165-6.
Kilpatrick NM. Durability of restorations in primary molars. J Dent 1993;21:67-73.
Kindelan SA, Day P, Nichol R, Willmott N, Fayle SA, British Society of Paediatric Dentistry. et al.
UK National Clinical Guidelines in Paediatric Dentistry: Stainless steel preformed crowns for primary molars. Int J Paediatr Dent 2008;18 Suppl 1:20-8.
Randall RC. Preformed metal crowns for primary and permanent molar teeth: Review of the literature. Pediatr Dent 2002;24:489-500.
Dean JA. McDonald and Avery's Dentistry for the Child and Adolescent. St. Louis: Elsevier Health Sciences; 2015. p.197.
Casamassimo PS, Fields HW Jr., McTigue DJ, Nowak A. Pediatric Dentistry: Infancy Through Adolescence. St. Louis: Elsevier Health Sciences; 2013. p. 292, 318-23, 589.
Keinan D, Mass E, Zilberman U. Absorption of nickel, chromium, and iron by the root surface of primary molars covered with stainless steel crowns. Int J Dent 2010;2010:326124.
Bhaskar V, Subba Reddy VV. Biodegradation of nickel and chromium from space maintainers: An in vitro
study. J Indian Soc Pedod Prev Dent 2010;28:6-12.
] [Full text]
Amini F, Borzabadi Farahani A, Jafari A, Rabbani M.In vivo
study of metal content of oral mucosa cells in patients with and without fixed orthodontic appliances. Orthod Craniofac Res 2008;11:51-6.
Amini F, Jafari A, Amini P, Sepasi S. Metal ion release from fixed orthodontic appliances – An in vivo
study. Eur J Orthod 2012;34:126-30.
Fors R, Persson M. Nickel in dental plaque and saliva in patients with and without orthodontic appliances. Eur J Orthod 2006;28:292-7.
Matos de Souza R, Macedo de Menezes L. Nickel, chromium and iron levels in the saliva of patients with simulated fixed orthodontic appliances. Angle Orthod 2008;78:345-50.
Khaneh Masjedi M, Haghighat Jahromi N, Niknam O, Hormozi E, Rakhshan V. Effects of fixed orthodontic treatment using conventional (two-piece) versus metal injection moulding brackets on hair nickel and chromium levels: A double-blind randomized clinical trial. Eur J Orthod 2017;39:17-24.
Khaneh Masjedi M, Niknam O, Haghighat Jahromi N, Javidi P, Rakhshan V. Effects of fixed orthodontic treatment using conventional, copper-included, and epoxy-coated nickel-titanium archwires on salivary nickel levels: A Double-blind randomized clinical trial. Biol Trace Elem Res 2016;174:27-31.
Kuhta M, Pavlin D, Slaj M, Varga S, Lapter-Varga M, Slaj M, et al.
Type of archwire and level of acidity: Effects on the release of metal ions from orthodontic appliances. Angle Orthod 2009;79:102-10.
Patriarca M, Lyon TD, Fell GS. Nickel metabolism in humans investigated with an oral stable isotope. Am J Clin Nutr 1997;66:616-21.
Clayton TH, Wilkinson SM, Rawcliffe C, Pollock B, Clark SM. Allergic contact dermatitis in children: Should pattern of dermatitis determine referral? A retrospective study of 500 children tested between 1995 and 2004 in one U.K. Centre. Br J Dermatol 2006;154:114-7.
Van Hoogstraten IM, Andersen KE, Von Blomberg BM, Boden D, Bruynzeel DP, Burrows D, et al.
Reduced frequency of nickel allergy upon oral nickel contact at an early age. Clin Exp Immunol 1991;85:441-5.
Bourauel C, Fries T, Drescher D, Plietsch R. Surface roughness of orthodontic wires via atomic force microscopy, laser specular reflectance, and profilometry. Eur J Orthod 1998;20:79-92.
Barrett RD, Bishara SE, Quinn JK. Biodegradation of orthodontic appliances. Part I. Biodegradation of nickel and chromium in vitro
. Am J Orthod Dentofacial Orthop 1993;103:8-14.
Saglam AM, Baysal V, Ceylan AM. Nickel and cobalt hypersensitivity reaction before and after orthodontic therapy in children. J Contemp Dent Pract 2004;5:79-90.
Todd DJ, Burrows D. Nickel allergy in relationship to previous oral and cutaneous nickel contact. Ulster Med J 1989;58:168-71.
Menek N, Başaran S, Karaman Y, Ceylan G, Tunc ES. Investigation of nickel ion release from stainless steel crowns by square wave voltammetry. Int J Electrochem Sci 2012;7:6465-71.
Setcos JC, Babaei-Mahani A, Silvio LD, Mjör IA, Wilson NH. The safety of nickel containing dental alloys. Dent Mater 2006;22:1163-8.
Veien NK, Hattel T, Laurberg G. Low nickel diet: An open, prospective trial. J Am Acad Dermatol 1993;29:1002-7.
Chen B, Xia G, Cao XM, Wang J, Xu BY, Huang P, et al.
Urinary levels of nickel and chromium associated with dental restoration by nickel-chromium based alloys. Int J Oral Sci 2013;5:44-8.
Park HY, Shearer TR.In vitro
release of nickel and chromium from simulated orthodontic appliances. Am J Orthod 1983;84:156-9.
Yilmaz A, Ozdemir CE, Yilmaz Y. A delayed hypersensitivity reaction to a stainless steel crown: A case report. J Clin Pediatr Dent 2012;36:235-8.
Ramazani N, Ahmadi R, Darijani M. Assessment of nickel release from stainless steel crowns. J Dent (Tehran) 2014;11:328-34.
Aǧaoǧlu G, Arun T, Izgi B, Yarat A. Nickel and chromium levels in the saliva and serum of patients with fixed orthodontic appliances. Angle Orthod 2001;71:375-9.
Jamilian A, Moghaddas O, Toopchi S, Perillo L. Comparison of nickel and chromium ions released from stainless steel and NiTi wires after immersion in oral B®, orthokin® and artificial saliva. J Contemp Dent Pract 2014;15:403-6.
Mikulewicz M, Chojnacka K, Woźniak B, Downarowicz P. Release of metal ions from orthodontic appliances: An in vitro
study. Biol Trace Elem Res 2012;146:272-80.
Ousehal L, Lazrak L. Change in nickel levels in the saliva of patients with fixed orthodontic appliances. Int Orthod 2012;10:190-7.
Kodaira H, Ohno K, Fukase N, Kuroda M, Adachi S, Kikuchi M, et al.
Release and systemic accumulation of heavy metals from preformed crowns used in restoration of primary teeth. J Oral Sci 2013;55:161-5.
Jones SB, Taylor RL, Colligon JS, Johnson D. Effect of element concentration on nickel release from dental alloys using a novel ion beam method. Dent Mater 2010;26:249-56.
Hamano H. Fundamental studies on biological effects of dental metals – Nickel dissolution, toxicity and distribution in cultured cells. Kokubyo Gakkai Zasshi 1992;59:456-78.
Eliades T, Zinelis S, Eliades G, Athanasiou AE. Nickel content of as-received, retrieved, and recycled stainless steel brackets. Am J Orthod Dentofacial Orthop 2002;122:217-20.
Eliades T, Zinelis S, Papadopoulos MA, Eliades G, Athanasiou AE. Nickel content of as-received and retrieved NiTi and stainless steel archwires: Assessing the nickel release hypothesis. Angle Orthod 2004;74:151-4.
Huang HH, Chiu YH, Lee TH, Wu SC, Yang HW, Su KH, et al.
Ion release from niTi orthodontic wires in artificial saliva with various acidities. Biomaterials 2003;24:3585-92.
Karnam SK, Reddy AN, Manjith CM. Comparison of metal ion release from different bracket archwire combinations: An in vitro
study. J Contemp Dent Pract 2012;13:376-81.
Sfondrini MF, Cacciafesta V, Maffia E, Scribante A, Alberti G, Biesuz R, et al.
Nickel release from new conventional stainless steel, recycled, and nickel-free orthodontic brackets: An in vitro
study. Am J Orthod Dentofacial Orthop 2010;137:809-15.
Milheiro A, Kleverlaan C, Muris J, Feilzer A, Pallav P. Nickel release from orthodontic retention wires-the action of mechanical loading and pH. Dent Mater 2012;28:548-53.
Merritt K, Brown SA. Effect of proteins and pH on fretting corrosion and metal ion release. J Biomed Mater Res 1988;22:111-20.
Danaei SM, Safavi A, Roeinpeikar SM, Oshagh M, Iranpour S, Omidkhoda M, et al.
Ion release from orthodontic brackets in 3 mouthwashes: An in-vitro
study. Am J Orthod Dentofacial Orthop 2011;139:730-4.
Clarke M, Locker D, Berall G, Pencharz P, Kenny DJ, Judd P, et al.
Malnourishment in a population of young children with severe early childhood caries. Pediatr Dent 2006;28:254-9.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4]