- Email: [email protected]
Salivary nickel and chromium in subjects with different types of fixed orthodontic appliances
Salivary nickel and chromium in subjects with different types of fixed orthodontic appliances Heidi Kerosuo, Dr. Odont., ~ Grete M o e , b and Arne Hensten-Pettersen, Dr. Odont. ~
Haslum, Norway The aim was to investigate nickel and chromium concentrations in saliva of patients with different types of fixed appliances. Saliva samples were collected from 47 orthodontic patients, ages 8 to 30 years. Four samples from each subject were collected: (1) before insertion of the appliance, (2) 1 to 2 days after, (3) 1 week after, and (4) 1 month after insertion of the appliance. A considerable variation in the concentrations of both nickel and chromium was observed. No significant differences were found between the no-appliance samples and the samples obtained after insertion of the appliances. The results suggest that nickel and chromium concentrations of saliva are not significantly affected by fixed orthodontic appliances during the first month of treatment. (Am J Orthod Dentofac Orthop 1997;111:595-8.)
S t a i n l e s s steel alloys, containing 8% to 12% nickel and 17% to 22% chromium, 1 are generally used for the metallic parts of orthodontic appliances. The amounts of nickel and chromium released from fixed orthodontic appliances in vitro vary, depending on the manipulation of the appliances and different physical and chemical test conditions? -5 Less information exists on corrosion of orthodontic appliances in the oral cavity during treatment. Discoloration on the underlying tooth surface during orthodontic treatment has also been regarded as the consequence of crevice corrosion of the bracket bases. 6,v Kratzenstein et al. 8 observed signs of corrosion on many orthodontic appliances after treatment for 6 months and on all appliances after 10 months. Nickel concentration in saliva has, however, shown no consistent increase in patients with fixed o.rthodontic appliances, but rather an overall large variation. 9,1° Corrosion of alloys in the oral environment may decrease the strength of metallic appliances. There has also been concern about adverse biologic effects of the corrosion products on the patient, such as sensitizing patients to nickel. On the other hand, the prevalence of nickel sensitivity has been reported to be lower in subjects who have received orthodontic treatment at a young age, possibly because of the induction of immunological tolerance. ~-1,12 These aVisiting scientist, NIOM, Scandinavian Institute of Dental Materials. bChemical engineer, Department of Dental Materials, University of Bergen. ~Senior scientist, NIOM, Scandinavian Institute of Dental Materials. Reprint requests to: Dr. Odo~t. Heidi Kerosuo, Vaiveronkatu 58, 05900 HyvinkNi, Finland. Copyright © 1997 by the American Association of Orthodontists. 0889-5406/97/$5.00 + 0 8/1/71896
studies do not, however, include analysis of actua! amounts or concentrations of nickel involved. The aim of this study was to investigate the nickel and chromium concentration of saliva in patients with different fixed orthodontic appliances. MATERIAL AND METHODS
•
The study used saliva samples collected from new patients starting orthodontic treatment at the Municipal Dental Health Center in Hyvinkfifi, Finland, at the Dental Faculty of the University of Oslo and at five private orthodontists in Oslo, Norway. A total of 47 patients, 19 males and 28 females, with different types of metallic appliances participated the study. The mean age of the subjects was 12.4 years (range 8 to 30 years). The appliances used were headgear, quad helix, and fixed appliance with a minimum of two bands and four brackets and the arch wire. The distribution of the patients according to age-group and the appliance used is shown in Table L Sampling of Saliva
Four samples of stimulated saliva were collected from each patient: (1) before insertion of the fixed appliance, (2) 1 to 2 days after, (3) approximately 1 week after, and (4) approximately 1 month after insertion of the fixed appliance. In two cases, sample no. 2 was taken 4 days after insertion of the appliances. Saliva was collected as follows: First, the patient rinsed the mouth thoroughly with a mouthful of deionized and distilled water. After mouth rinsing, using a piece of paraffin as a chewing gum for stimulation of the salivary secretion, the patient collected approximately 10 ml of saliva into an acid-washed plastic test tube (Nunc universal container No. 363282). The samples were stored at -20°C before they were processed° All samples of the Finnish subjects were collected at the dental offÉce.The 595
596
Kerosuo, Moe, a n d Hensten-Pettersen
American Journal of Orthodontics and Dentofacial Orthopedics June 1997
Table h D i s t r i b u t i o n of the subjects a c c o r d i n g to age a n d
Table IIh M e a n c o n c e n t r a t i o n s of nickel a n d c h r o m i u m for
orthodontic appliance
subjects w i t h different o r t h o d o n t i c a p p l i a n c e s
Age/year
Headgear
Quad helix
Fixed appliance
Quad helix
(N= 10) 8-9 10-11 12-15 16-30 Total
-
6 8 14 -
-
5 2 3 10
3 6 10 4 23
-
_
Sample ~ype
_
Table II. P o o l e d m e d i a n v a l u e s a n d r a n g e of n i c k e l a n d c h r o m i u m c o n c e n t r a t i o n s in the saliva s a m p l e s t a k e n at different intervals b e f o r e a n d after i n s e r t i o n of the o r t h o d o n t i c appliances. T h e r e w e r e n o significant differences b e t w e e n saliva s a m p l e s f r o m subjects w i t h different types of a p p l i a n c e s
Nickel (ng/ml)
No appliances 1 to 2 days after insertion of appliances 1 week after insertion of appliances 1 month after insertion of appliances
Chromium (ng/ml)
Median
Range
Median
Range
55 60
0/440 0/205
61 68
0/240 0/285
65
0/190
86
0/300
50
0/240
76
0/320
Nickel I Nickel II Nickel III Nickel IV Chromium Chromium Chromium Chromium
I II III IV
Head gear ( N = 14)
Fixed appliance (N=23)
× (ng/ml)
SD
× (rig~toO
SD
× (rig~toO
SD
65 52 64 60 88 48 76 78
56 6O 61 61 62 58 79 76
52 64 85 58 49 85 108 81
51 57 67 38 49 83 86 57
68 74 55 65 68 90 69 80
95 54 49 60 70 67 61 76
I = Before insertion of the appliance, H = 1 to 2 days after, III = 1 week after,/V = 1 month after the insertion of the appliance.
perature program consisted of drying at 150°C for 30 seconds, ashing at 1200° C for 20 seconds, and atomization at 2700 ° C for 8 seconds. Eleven blanks with deionized distilled water instead of saliva were processed with the samples. Nine of the blanks also included a piece of paraffin. Analysis of Data and Statistics
Norwegian subjects collected samples no. 2 and 3 at home according to written instructions. Preparation and Analysis of the Samples The preparation of the saliva samples was performed according to the procedure previously described by Gjerdet et al. 1° For the processing, 0.5 ml of saliva was transferred to smaller plastic test tubes (Nunc cryo tubes no. 366524), which were pretested for not releasing nickel. For digestion of the organic matter in the saliva, 0.15 ml of concentrated hydrochloric acid (HC1) (Suprapur) was added to each sample. The tubes were closed and kept at 80° C for 8 hours. Analysis of Nickel and Chromium The saliva samples were centrifuged at 3000× g for 2 minutes to settle particulate matter. The chemical analyses were done by electrothermal atomic absorption spectrophotometry (model 372, Perkin Elmer Corp., HGA 76B graphite furnace, Perkin Elmer & Co.). Nickel and chromium standard solutions of between 0.01 ixg/ml and 0.5 ixg/ml were used, with 50 Ixg of the sample injected directly into the graphite tube (Perkin Elmer B00810871, uncoated). The insoluble precipitate was not included in the analysis because of the problem of particles causing variation of the results. After measurement of the peak height, the concentration was calculated from the standard curve. The analytical lines used were 357.9 nm for chromium and 232.0 nm for nickel. Unspecific absorption was corrected by a deuterium background corrector. The graphite tube tern-
The Wilcoxon matched-pairs signed-ranks test was used to test differences between samples before and after insertion of orthodontic appliances. Chi-square test was used to test differences in nickel and chromium concentrations between the variables: age, sex, type of appliance, and place of sampling. RESULTS A large variation in the concentrations of both nickel and chromium in saliva was observed. The range of nickel concentrations was mainly from 0 to 205 ng/ml, with one exception of 440 ng/ml for a 14-year-old girl before appliances. Highest chrom i u m concentrations (200 to 300 ng/ml) were found in six samples. Individual patients with the highest values of nickel or chromium were of both genders and under 15 years of age and of all appliance groups. Before insertion of the orthodontic appliances median concentration for nickel in saliva was 55 ng/ml and for chromium 61 ng/ml (Table II). No significant differences were found between the noappliance samples and the samples taken 1 to 2 days, 7 days, and 1 month after insertion of appliances tested by the Wilcoxon test. The differences between the m e a n concentrations of nickel and chromium in different appliance groups were not statistically significant (p = 0.268) (Table III). No significant differences in nickel and chromium values related to age, sex, or the place of sampling were found.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 111, No. 6
Eight of the 11 blanks showed a nickel and chromium concentration of 0 ng/ml (range 0 to 65 ng/ml for nickel; 0 to 115 ng/ml for chromium). The median nickel and chromium value for blanks was 0 ng/ml, which was used as the indicator of background level. DISCUSSION
The method of sampling shows the momentary, total concentration of soluble nickel and chromium in saliva and a differentiation between nickel and chromium secreted or biodegraded from the appliances cannot be made from this study regimen. The saliva concentrations for nickel and chromium in this study showed a large variation. However, despite the scatter of the values, the metal concentrations detected were altogether very low, generally less than 0.2 ppm. Large variations have also been constantly found in previous reports concerning analysis of metal concentrations in saliva. 9-1°'13 The composition of saliva may be affected by many physiologic variables such as diet, health conditions, and time of the day, ~4 the most important regulating factor being salivary flow rate. Is Stimulated saliva was used to assess also the effect of masticatory function and abrasion on the release of metals from orthodontic appliances. The procedure of sampling, preparation, and analysis of saliva samples on low level concentrations of metals involves a risk of contamination during the procedure. Certain variation for duplicate analyses has to be accepted on these low concentrations. Caution should be exercised if exact concentration values and not levels are discussed. No signif~cant increase or trend of increased nickel or chromium concentration in saliva could be seen in the patients of this study after insertion of different fixed appliances. This is in accordance with the study by Gjerdet et al., a° who also did not find any differences in nickel amounts in saliva before and 3 weeks after insertion of fixed appliances. The continuous flow of saliva in the mouth and the short sampling period may not give time enough for a detectable dissolution of metals from the appliances. Gjerdet et al? ° found, however, a significantly increased nickel concentration in saliva samples taken immediately after placement of the appliances in a group of six cases. In the current study, the first saliva samples with appliances were collected the day after placement of appliances. Conceivably, the difference between these two studies may be related to this time factor. Median concentrations of salivary nickel and
Kerosuo, Moe, and Hensten-Pettersen
597
chromium, with and without appliances, were somewhat higher in this study compared with earlier reports of these metals in saliva. 9-1°,I6 Some of them had a similar study design, but used unstimulated saliva. The range of variation in this study is, however, in good accordance with the earlier studies that indicate low salivary nickel levels, regardless of the presence of orthodontic appliances. Significantly higher saliva concentrations of chromium and cobalt have been detected, by the same methods, from patients with chromium-cobalt dentures. 13 It seems that the great variations in nickel and chromium concentrations between patients and also between samples from the same patient are likely to mask the small amounts of metals released from orthodontic appliances. Only when the amount of metals released in the mouth, or the activity of the corrosion process is considerably higher, the metal concentrations in saliva may reach a level that significantly overrules the natural variation of nickel and chromium in saliva. The actual amounts of nickel and chromium released from fixed appliances in vitro have been distinct but low, 1'3'5'17 and far below the normal daily intake of nickel in diet58,19 Solubilized nickel has been found in the corrosion studies in vitro at higher concentrations than chromium, which has also been found in the corrosion precipitate. 3,s In this study, both nickel and chromium concentrations were approximately at equal levels in saliva. Analysis of corresponding amounts of metals in vivo from saliva, where concentrations are more diluted and affected by the salivary flow rate and diet, seems to be insufficient in differentiating appliance related, apparently small, changes from the overall high normal variation of nickel in saliva. In contrast to the in vitro study,s no statistically significant differences in the saliva concentration of nickel and chromium between patients with different appliances could be seen. Neither did the silver soldering of the quad hetLx constructions have any detectable corrosion increasing effect in this study.2 CONCLUSION
Although the orthodontic appliances did not have any effect on the general level of nickel concentration of saliva, it cannot be excluded that minor amounts of nickel dissolved from appliances could be of importance in cases of hypersensitivity to nickel.2°,21 Local concentrations of nickel on the oral mucosa might be sufficient to elicit allergic reactions,22,23 though it cannot be detected as increased nickel concentration in saliva. Also, over a longer time period, there exists a possibilityfor induction
598 Kerosuo, Moe, and Hensten-Pettersen
of immunological tolerance to nickel through presence of orthodontic appliances in the mouth, n,12 Animal experiments have shown that oral administration of nickel and chromium by the way of a fixed cast occlusal splint or by adding metallic powder in diet can induce partial tolerance to both metals, z4,25The amounts or concentrations of nickel needed in the tissues to induce tolerance in human beings are not known. In conclusion, fixed orthodontic appliances do not seem to affect significantly the nickel and chromium concentration of saliva during the first month of treatment. We express our gratitude to Nils R. Gjerdet, Dr Odont., professor, Department of Dental Materials, University of Bergen, for his advice and for providing the facilities for the analyses. We also thank Dr. Tamer B~iyiikyilmaz, Dr. Kari Kolstad Thrane, Dr. Torstein Tryti, Dr. Espen Dahl, Dr. Oysten Torget, and Sirkka Mononen, dental nurse, for kindly providing the patients and collecting the saliva samples for this study. REFERENCES
1. Grimsdottir MR, Gjerdet NR, Hensten-Pettersen A. Coarposition and in vitro corrosion of orthodontic appliances. Am J Orthod Dentofac Orthop 1992;101:525-32. 2. Berge M, Gjerdet NR, Erichsen ES. Corrosion of silver soldered orthodontic wires. Acta Odontol Scand 1982;40:75-9. 3. Park HY, Shearer TR. In vitro release of" nickel and chromium from simulated orthodontic appliances. Am J Orthod 1983;84:156-9. 4. Gjerdet NR, Hem H. Metal release from heat-treated orthodontic wires. Acta Odontol Scand 1987;45:409-14. 5. Kerosuo H, Moe G, Kleven E. In vitro release of nickel and chromium from different types of simulated orthodontic appliances. Angle Ortbod 1995;65:111-6. 6. Maijer R, Smith DC. Corrosion of orthodontic bracket bases. Am J Orthod 1982;81:43-8. 7. Gwinnett AJ. Corrosion of resin-bonded orthodontic brackets. Am J Orthod 1982;82:441-6.
American Journal of Orthodontics and Dentofacial Orthopedics June 1997 8. Kratzensteiu B, Weber H, Geis-Gersdorfer J, Koppenburg P. In-vivo-Korrosioosuntersuchungen an kieferorthopfidischen Apparaten. Dtsch Zahn~irztl Z 1985;40: / i46-50. 9. Koppenburg P, Bacher M, Geis-Gerstorfer J, Sauer K-H, Kratzenstein B, Weber H. Die kieferorthop/idische Apparatur-ein Schritt zur Sensibilisierung gegen Metalle? Fortschr Kieferorthop 1988;49:62-9. 10. Gjerdet NR, Erichsen ES, Remlo HE, Evjen G. Nickel and iron in saliva of patients with fixed orthodontic appliances. Acta OdontoI Scand 1991;49:73-8. 11. van der Burg CKH, Bruynzeel DP, Vreeburg KJJ, yon Blomberg BME, Scheper RJ. Hand eczema in hairdressers and nurses: a prospective study. Contact Dermatitis 1986;14:275-9. 12. van Hoogstraten IMW, Andersen KE, yon Blomberg BME, Boden D, Bruynzeel DP, Burrows D, et al. Reduced frequeucy of nickel allergy upon oral nickel contact at an early age, Clin Exp Immuuol 1991;85:441-5. 13. de Melo JF, Gjerdet NR, Erichsen ES. Metal release from cobalt-chromium partial dentures in the mouth. Acta Odom Stand 1983;41:71-4. 14. Ferguson DB. Current diagnostic uses of saliva. J Dent Res 1987;66:420-4. 15. Dawes C. The effects of flow rate and duration of stimulation on the concentrations of protein and the main electrolytes in human submandibular saliva. Arch Oral Biol 1974;19:887-95. 16. Catalanatto FA, Sunderman FW, Maclntosh TR. Nickel concentrations in human parotid saliva. Ann Clin Lab Sci 1977;7:146-51. 17. Barrett RD, Bishara SE, Quinn JK. Biodegradation of orthodontic appliances, part I: biodegradation of nickel and chromium in vitro. Am J Orthod Dentofac Orthop 1993;103:8-14. 18. Veien NK, Andersen MR. Nickel in Danish food. Acta Derm Venereol 1986;66: 502-9. 19. Basketter DA, Briadco-Vangosa G, Kaestner W, Lally C, Bontinck WJ. Nickel, cobalt and chromium in consumer products: a role in allergic contact dermatitis? Contact Dermatitis 1993;28:15-25. 20. Bishara SE. Oral lesions caused by an orthodontic retainer: a case report. Am J Orthod Dentofac Orthop 1995;108:115-7. 21. Kerosuo H. Kullaa A, Kerosuo E, Kanerva L, Hensten-Pettersen A. Nickel allergy in adolescents in relation to orthodontic treatment and piercing of ears. Arn J Orthod Dentofac Orthop 1996;109:148-54. 22. Hensten-Pettersen A, Gjerdet NR, Kvam E, Lyberg T. Nikkelallargi og kjeveortopedisk behandling. Nor Tannlegefor Tid 1984;94:567-72. 23. Greppi AL, Smith DC, Woodside DG. Nickel hypersensitivity reactions in orthodontic patients: a literature review. Univ Tor Dent J 1989;3:11-4. 24. Vreeburg KJJ, Groot K, yon Blomberg M, Scheper RJ. Induction of immunological tolerance by oral administration of nickel and chromium. J Dent Res 1984;63: 124-8. 25. yon Hoogstraaten IMW. Oral induction of immune tolerance for nickel and chromium: prevention of allergic contact hypersensitiviW. [Thesis.] Amsterdam: The Vrije Universiteit, 1992.
AAO MEETING CALENDAR 1998 - - Dallas, Texas, May 16 to 20, Dallas Convention Center 1999 - - San Diego, Calif., May 15 to 19, San Diego Convention Center 2000 - - Chicago, Ill., April 29 to May 3, McCormick Place Convention Center (5th IOC and 2nd Meeting of WFO) 2001 - - Toronto, Ontario, Canada, May 5 to 9, Toronto Convention Center 2002 ~ Baltimore, Md., April 20 to 24, Baltimore Convention Center 2003 - - Hawaiian Islands, May 2 to 9, Hawaii Convention Center 2004 ~ Orlando, Fla., May 1 to 5, Orlando Convention Center
Haslum, Norway The aim was to investigate nickel and chromium concentrations in saliva of patients with different types of fixed appliances. Saliva samples were collected from 47 orthodontic patients, ages 8 to 30 years. Four samples from each subject were collected: (1) before insertion of the appliance, (2) 1 to 2 days after, (3) 1 week after, and (4) 1 month after insertion of the appliance. A considerable variation in the concentrations of both nickel and chromium was observed. No significant differences were found between the no-appliance samples and the samples obtained after insertion of the appliances. The results suggest that nickel and chromium concentrations of saliva are not significantly affected by fixed orthodontic appliances during the first month of treatment. (Am J Orthod Dentofac Orthop 1997;111:595-8.)
S t a i n l e s s steel alloys, containing 8% to 12% nickel and 17% to 22% chromium, 1 are generally used for the metallic parts of orthodontic appliances. The amounts of nickel and chromium released from fixed orthodontic appliances in vitro vary, depending on the manipulation of the appliances and different physical and chemical test conditions? -5 Less information exists on corrosion of orthodontic appliances in the oral cavity during treatment. Discoloration on the underlying tooth surface during orthodontic treatment has also been regarded as the consequence of crevice corrosion of the bracket bases. 6,v Kratzenstein et al. 8 observed signs of corrosion on many orthodontic appliances after treatment for 6 months and on all appliances after 10 months. Nickel concentration in saliva has, however, shown no consistent increase in patients with fixed o.rthodontic appliances, but rather an overall large variation. 9,1° Corrosion of alloys in the oral environment may decrease the strength of metallic appliances. There has also been concern about adverse biologic effects of the corrosion products on the patient, such as sensitizing patients to nickel. On the other hand, the prevalence of nickel sensitivity has been reported to be lower in subjects who have received orthodontic treatment at a young age, possibly because of the induction of immunological tolerance. ~-1,12 These aVisiting scientist, NIOM, Scandinavian Institute of Dental Materials. bChemical engineer, Department of Dental Materials, University of Bergen. ~Senior scientist, NIOM, Scandinavian Institute of Dental Materials. Reprint requests to: Dr. Odo~t. Heidi Kerosuo, Vaiveronkatu 58, 05900 HyvinkNi, Finland. Copyright © 1997 by the American Association of Orthodontists. 0889-5406/97/$5.00 + 0 8/1/71896
studies do not, however, include analysis of actua! amounts or concentrations of nickel involved. The aim of this study was to investigate the nickel and chromium concentration of saliva in patients with different fixed orthodontic appliances. MATERIAL AND METHODS
•
The study used saliva samples collected from new patients starting orthodontic treatment at the Municipal Dental Health Center in Hyvinkfifi, Finland, at the Dental Faculty of the University of Oslo and at five private orthodontists in Oslo, Norway. A total of 47 patients, 19 males and 28 females, with different types of metallic appliances participated the study. The mean age of the subjects was 12.4 years (range 8 to 30 years). The appliances used were headgear, quad helix, and fixed appliance with a minimum of two bands and four brackets and the arch wire. The distribution of the patients according to age-group and the appliance used is shown in Table L Sampling of Saliva
Four samples of stimulated saliva were collected from each patient: (1) before insertion of the fixed appliance, (2) 1 to 2 days after, (3) approximately 1 week after, and (4) approximately 1 month after insertion of the fixed appliance. In two cases, sample no. 2 was taken 4 days after insertion of the appliances. Saliva was collected as follows: First, the patient rinsed the mouth thoroughly with a mouthful of deionized and distilled water. After mouth rinsing, using a piece of paraffin as a chewing gum for stimulation of the salivary secretion, the patient collected approximately 10 ml of saliva into an acid-washed plastic test tube (Nunc universal container No. 363282). The samples were stored at -20°C before they were processed° All samples of the Finnish subjects were collected at the dental offÉce.The 595
596
Kerosuo, Moe, a n d Hensten-Pettersen
American Journal of Orthodontics and Dentofacial Orthopedics June 1997
Table h D i s t r i b u t i o n of the subjects a c c o r d i n g to age a n d
Table IIh M e a n c o n c e n t r a t i o n s of nickel a n d c h r o m i u m for
orthodontic appliance
subjects w i t h different o r t h o d o n t i c a p p l i a n c e s
Age/year
Headgear
Quad helix
Fixed appliance
Quad helix
(N= 10) 8-9 10-11 12-15 16-30 Total
-
6 8 14 -
-
5 2 3 10
3 6 10 4 23
-
_
Sample ~ype
_
Table II. P o o l e d m e d i a n v a l u e s a n d r a n g e of n i c k e l a n d c h r o m i u m c o n c e n t r a t i o n s in the saliva s a m p l e s t a k e n at different intervals b e f o r e a n d after i n s e r t i o n of the o r t h o d o n t i c appliances. T h e r e w e r e n o significant differences b e t w e e n saliva s a m p l e s f r o m subjects w i t h different types of a p p l i a n c e s
Nickel (ng/ml)
No appliances 1 to 2 days after insertion of appliances 1 week after insertion of appliances 1 month after insertion of appliances
Chromium (ng/ml)
Median
Range
Median
Range
55 60
0/440 0/205
61 68
0/240 0/285
65
0/190
86
0/300
50
0/240
76
0/320
Nickel I Nickel II Nickel III Nickel IV Chromium Chromium Chromium Chromium
I II III IV
Head gear ( N = 14)
Fixed appliance (N=23)
× (ng/ml)
SD
× (rig~toO
SD
× (rig~toO
SD
65 52 64 60 88 48 76 78
56 6O 61 61 62 58 79 76
52 64 85 58 49 85 108 81
51 57 67 38 49 83 86 57
68 74 55 65 68 90 69 80
95 54 49 60 70 67 61 76
I = Before insertion of the appliance, H = 1 to 2 days after, III = 1 week after,/V = 1 month after the insertion of the appliance.
perature program consisted of drying at 150°C for 30 seconds, ashing at 1200° C for 20 seconds, and atomization at 2700 ° C for 8 seconds. Eleven blanks with deionized distilled water instead of saliva were processed with the samples. Nine of the blanks also included a piece of paraffin. Analysis of Data and Statistics
Norwegian subjects collected samples no. 2 and 3 at home according to written instructions. Preparation and Analysis of the Samples The preparation of the saliva samples was performed according to the procedure previously described by Gjerdet et al. 1° For the processing, 0.5 ml of saliva was transferred to smaller plastic test tubes (Nunc cryo tubes no. 366524), which were pretested for not releasing nickel. For digestion of the organic matter in the saliva, 0.15 ml of concentrated hydrochloric acid (HC1) (Suprapur) was added to each sample. The tubes were closed and kept at 80° C for 8 hours. Analysis of Nickel and Chromium The saliva samples were centrifuged at 3000× g for 2 minutes to settle particulate matter. The chemical analyses were done by electrothermal atomic absorption spectrophotometry (model 372, Perkin Elmer Corp., HGA 76B graphite furnace, Perkin Elmer & Co.). Nickel and chromium standard solutions of between 0.01 ixg/ml and 0.5 ixg/ml were used, with 50 Ixg of the sample injected directly into the graphite tube (Perkin Elmer B00810871, uncoated). The insoluble precipitate was not included in the analysis because of the problem of particles causing variation of the results. After measurement of the peak height, the concentration was calculated from the standard curve. The analytical lines used were 357.9 nm for chromium and 232.0 nm for nickel. Unspecific absorption was corrected by a deuterium background corrector. The graphite tube tern-
The Wilcoxon matched-pairs signed-ranks test was used to test differences between samples before and after insertion of orthodontic appliances. Chi-square test was used to test differences in nickel and chromium concentrations between the variables: age, sex, type of appliance, and place of sampling. RESULTS A large variation in the concentrations of both nickel and chromium in saliva was observed. The range of nickel concentrations was mainly from 0 to 205 ng/ml, with one exception of 440 ng/ml for a 14-year-old girl before appliances. Highest chrom i u m concentrations (200 to 300 ng/ml) were found in six samples. Individual patients with the highest values of nickel or chromium were of both genders and under 15 years of age and of all appliance groups. Before insertion of the orthodontic appliances median concentration for nickel in saliva was 55 ng/ml and for chromium 61 ng/ml (Table II). No significant differences were found between the noappliance samples and the samples taken 1 to 2 days, 7 days, and 1 month after insertion of appliances tested by the Wilcoxon test. The differences between the m e a n concentrations of nickel and chromium in different appliance groups were not statistically significant (p = 0.268) (Table III). No significant differences in nickel and chromium values related to age, sex, or the place of sampling were found.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 111, No. 6
Eight of the 11 blanks showed a nickel and chromium concentration of 0 ng/ml (range 0 to 65 ng/ml for nickel; 0 to 115 ng/ml for chromium). The median nickel and chromium value for blanks was 0 ng/ml, which was used as the indicator of background level. DISCUSSION
The method of sampling shows the momentary, total concentration of soluble nickel and chromium in saliva and a differentiation between nickel and chromium secreted or biodegraded from the appliances cannot be made from this study regimen. The saliva concentrations for nickel and chromium in this study showed a large variation. However, despite the scatter of the values, the metal concentrations detected were altogether very low, generally less than 0.2 ppm. Large variations have also been constantly found in previous reports concerning analysis of metal concentrations in saliva. 9-1°'13 The composition of saliva may be affected by many physiologic variables such as diet, health conditions, and time of the day, ~4 the most important regulating factor being salivary flow rate. Is Stimulated saliva was used to assess also the effect of masticatory function and abrasion on the release of metals from orthodontic appliances. The procedure of sampling, preparation, and analysis of saliva samples on low level concentrations of metals involves a risk of contamination during the procedure. Certain variation for duplicate analyses has to be accepted on these low concentrations. Caution should be exercised if exact concentration values and not levels are discussed. No signif~cant increase or trend of increased nickel or chromium concentration in saliva could be seen in the patients of this study after insertion of different fixed appliances. This is in accordance with the study by Gjerdet et al., a° who also did not find any differences in nickel amounts in saliva before and 3 weeks after insertion of fixed appliances. The continuous flow of saliva in the mouth and the short sampling period may not give time enough for a detectable dissolution of metals from the appliances. Gjerdet et al? ° found, however, a significantly increased nickel concentration in saliva samples taken immediately after placement of the appliances in a group of six cases. In the current study, the first saliva samples with appliances were collected the day after placement of appliances. Conceivably, the difference between these two studies may be related to this time factor. Median concentrations of salivary nickel and
Kerosuo, Moe, and Hensten-Pettersen
597
chromium, with and without appliances, were somewhat higher in this study compared with earlier reports of these metals in saliva. 9-1°,I6 Some of them had a similar study design, but used unstimulated saliva. The range of variation in this study is, however, in good accordance with the earlier studies that indicate low salivary nickel levels, regardless of the presence of orthodontic appliances. Significantly higher saliva concentrations of chromium and cobalt have been detected, by the same methods, from patients with chromium-cobalt dentures. 13 It seems that the great variations in nickel and chromium concentrations between patients and also between samples from the same patient are likely to mask the small amounts of metals released from orthodontic appliances. Only when the amount of metals released in the mouth, or the activity of the corrosion process is considerably higher, the metal concentrations in saliva may reach a level that significantly overrules the natural variation of nickel and chromium in saliva. The actual amounts of nickel and chromium released from fixed appliances in vitro have been distinct but low, 1'3'5'17 and far below the normal daily intake of nickel in diet58,19 Solubilized nickel has been found in the corrosion studies in vitro at higher concentrations than chromium, which has also been found in the corrosion precipitate. 3,s In this study, both nickel and chromium concentrations were approximately at equal levels in saliva. Analysis of corresponding amounts of metals in vivo from saliva, where concentrations are more diluted and affected by the salivary flow rate and diet, seems to be insufficient in differentiating appliance related, apparently small, changes from the overall high normal variation of nickel in saliva. In contrast to the in vitro study,s no statistically significant differences in the saliva concentration of nickel and chromium between patients with different appliances could be seen. Neither did the silver soldering of the quad hetLx constructions have any detectable corrosion increasing effect in this study.2 CONCLUSION
Although the orthodontic appliances did not have any effect on the general level of nickel concentration of saliva, it cannot be excluded that minor amounts of nickel dissolved from appliances could be of importance in cases of hypersensitivity to nickel.2°,21 Local concentrations of nickel on the oral mucosa might be sufficient to elicit allergic reactions,22,23 though it cannot be detected as increased nickel concentration in saliva. Also, over a longer time period, there exists a possibilityfor induction
598 Kerosuo, Moe, and Hensten-Pettersen
of immunological tolerance to nickel through presence of orthodontic appliances in the mouth, n,12 Animal experiments have shown that oral administration of nickel and chromium by the way of a fixed cast occlusal splint or by adding metallic powder in diet can induce partial tolerance to both metals, z4,25The amounts or concentrations of nickel needed in the tissues to induce tolerance in human beings are not known. In conclusion, fixed orthodontic appliances do not seem to affect significantly the nickel and chromium concentration of saliva during the first month of treatment. We express our gratitude to Nils R. Gjerdet, Dr Odont., professor, Department of Dental Materials, University of Bergen, for his advice and for providing the facilities for the analyses. We also thank Dr. Tamer B~iyiikyilmaz, Dr. Kari Kolstad Thrane, Dr. Torstein Tryti, Dr. Espen Dahl, Dr. Oysten Torget, and Sirkka Mononen, dental nurse, for kindly providing the patients and collecting the saliva samples for this study. REFERENCES
1. Grimsdottir MR, Gjerdet NR, Hensten-Pettersen A. Coarposition and in vitro corrosion of orthodontic appliances. Am J Orthod Dentofac Orthop 1992;101:525-32. 2. Berge M, Gjerdet NR, Erichsen ES. Corrosion of silver soldered orthodontic wires. Acta Odontol Scand 1982;40:75-9. 3. Park HY, Shearer TR. In vitro release of" nickel and chromium from simulated orthodontic appliances. Am J Orthod 1983;84:156-9. 4. Gjerdet NR, Hem H. Metal release from heat-treated orthodontic wires. Acta Odontol Scand 1987;45:409-14. 5. Kerosuo H, Moe G, Kleven E. In vitro release of nickel and chromium from different types of simulated orthodontic appliances. Angle Ortbod 1995;65:111-6. 6. Maijer R, Smith DC. Corrosion of orthodontic bracket bases. Am J Orthod 1982;81:43-8. 7. Gwinnett AJ. Corrosion of resin-bonded orthodontic brackets. Am J Orthod 1982;82:441-6.
American Journal of Orthodontics and Dentofacial Orthopedics June 1997 8. Kratzensteiu B, Weber H, Geis-Gersdorfer J, Koppenburg P. In-vivo-Korrosioosuntersuchungen an kieferorthopfidischen Apparaten. Dtsch Zahn~irztl Z 1985;40: / i46-50. 9. Koppenburg P, Bacher M, Geis-Gerstorfer J, Sauer K-H, Kratzenstein B, Weber H. Die kieferorthop/idische Apparatur-ein Schritt zur Sensibilisierung gegen Metalle? Fortschr Kieferorthop 1988;49:62-9. 10. Gjerdet NR, Erichsen ES, Remlo HE, Evjen G. Nickel and iron in saliva of patients with fixed orthodontic appliances. Acta OdontoI Scand 1991;49:73-8. 11. van der Burg CKH, Bruynzeel DP, Vreeburg KJJ, yon Blomberg BME, Scheper RJ. Hand eczema in hairdressers and nurses: a prospective study. Contact Dermatitis 1986;14:275-9. 12. van Hoogstraten IMW, Andersen KE, yon Blomberg BME, Boden D, Bruynzeel DP, Burrows D, et al. Reduced frequeucy of nickel allergy upon oral nickel contact at an early age, Clin Exp Immuuol 1991;85:441-5. 13. de Melo JF, Gjerdet NR, Erichsen ES. Metal release from cobalt-chromium partial dentures in the mouth. Acta Odom Stand 1983;41:71-4. 14. Ferguson DB. Current diagnostic uses of saliva. J Dent Res 1987;66:420-4. 15. Dawes C. The effects of flow rate and duration of stimulation on the concentrations of protein and the main electrolytes in human submandibular saliva. Arch Oral Biol 1974;19:887-95. 16. Catalanatto FA, Sunderman FW, Maclntosh TR. Nickel concentrations in human parotid saliva. Ann Clin Lab Sci 1977;7:146-51. 17. Barrett RD, Bishara SE, Quinn JK. Biodegradation of orthodontic appliances, part I: biodegradation of nickel and chromium in vitro. Am J Orthod Dentofac Orthop 1993;103:8-14. 18. Veien NK, Andersen MR. Nickel in Danish food. Acta Derm Venereol 1986;66: 502-9. 19. Basketter DA, Briadco-Vangosa G, Kaestner W, Lally C, Bontinck WJ. Nickel, cobalt and chromium in consumer products: a role in allergic contact dermatitis? Contact Dermatitis 1993;28:15-25. 20. Bishara SE. Oral lesions caused by an orthodontic retainer: a case report. Am J Orthod Dentofac Orthop 1995;108:115-7. 21. Kerosuo H. Kullaa A, Kerosuo E, Kanerva L, Hensten-Pettersen A. Nickel allergy in adolescents in relation to orthodontic treatment and piercing of ears. Arn J Orthod Dentofac Orthop 1996;109:148-54. 22. Hensten-Pettersen A, Gjerdet NR, Kvam E, Lyberg T. Nikkelallargi og kjeveortopedisk behandling. Nor Tannlegefor Tid 1984;94:567-72. 23. Greppi AL, Smith DC, Woodside DG. Nickel hypersensitivity reactions in orthodontic patients: a literature review. Univ Tor Dent J 1989;3:11-4. 24. Vreeburg KJJ, Groot K, yon Blomberg M, Scheper RJ. Induction of immunological tolerance by oral administration of nickel and chromium. J Dent Res 1984;63: 124-8. 25. yon Hoogstraaten IMW. Oral induction of immune tolerance for nickel and chromium: prevention of allergic contact hypersensitiviW. [Thesis.] Amsterdam: The Vrije Universiteit, 1992.
AAO MEETING CALENDAR 1998 - - Dallas, Texas, May 16 to 20, Dallas Convention Center 1999 - - San Diego, Calif., May 15 to 19, San Diego Convention Center 2000 - - Chicago, Ill., April 29 to May 3, McCormick Place Convention Center (5th IOC and 2nd Meeting of WFO) 2001 - - Toronto, Ontario, Canada, May 5 to 9, Toronto Convention Center 2002 ~ Baltimore, Md., April 20 to 24, Baltimore Convention Center 2003 - - Hawaiian Islands, May 2 to 9, Hawaii Convention Center 2004 ~ Orlando, Fla., May 1 to 5, Orlando Convention Center