Ion release from orthodontic appliances.
OBJECTIVE
The microbiological and enzymatic characteristics of the oral cavity would seem to provide a suitable environment for the corrosion of metals. We assayed the release of metal ions from one orthodontic appliance which included two 304 and 316 steel molar bands, ten 316 steel brackets, one nickel-titanium archwire and a brazing alloy to connect the elements of molar bands and brackets.


METHODS
The orthodontic appliance was dipped in both inorganic (pH 3.5-6.5) and organic acid solutions (w/v 1% each of tartaric, citric and ascorbic acid at pH 2.2 or 1.5% each of lactic and acetic acid at pH 2.5). The release of nickel (Ni), chromium (Cr), copper (Cu), silver (Ag) and palladium (Pd) was determined using an atomic absorption spectrophotometer Varian AA 10.


RESULTS
The release of Ni, Cr and Cu was markedly less at pH 6.5 than at pH 3.5 at all time points in acid solution. Daily release/single appliance after the first day decreased. Contrary to expectations, appliances immersed in organic acid solutions at pH 2.2 or 2.5 after 28 days generally released an amount of ions similar to that observed in inorganic acid solution at pH 3.5, with the exception of Cu. Release of silver and palladium, two metals present in the brazing alloy, proved to be very low (approximately 0.2 microgram after 28 days).


CONCLUSIONS
The daily release of Ni, Cu and Cr by an orthodontic appliance in acid pH, particularly favourable to corrosion, was well below that ingested with a normal daily diet. It is therefore concluded that the quantities of metal ions released in our experimental conditions should not be cause for concern in utilising the appliance.
Institute of Clinical Odontology, University of Perugia, Italy.
N
N
Staffolani
F
F
Damiani
C
C
Lilli
M
M
Guerra
N J
NJ
Staffolani
S
S
Belcastro
P
P
Locci
D002857:Chromium / Q000032:analysis; D003300:Copper / Q000032:analysis; D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008422:Materials Testing; D009532:Nickel / Q000032:analysis; D009967:Orthodontic Appliances; D010165:Palladium / Q000032:analysis; D012834:Silver / Q000032:analysis; D013054:Spectrophotometry, Atomic; D013193:Stainless Steel / Q000737:chemistry
D003722:Dental Alloys; D007477:Ions; D002857:Chromium; D013193:Stainless Steel; D012834:Silver; D010165:Palladium; D003300:Copper; D009532:Nickel