stainless steel alloys have remained the material of choice despite the emergence of the more recent titanium , composite and polycarbonate orthodontic brackets .
stainless steel alloy contains 8%-12% nickel , 17%-22% chromium and other elements such as copper , iron molybdenum , manganese , silicon and sulfur[3 - 5 ] in the oral environment , orthodontic brackets are subjected to mechanical and chemical damaging which results in susceptibility to corrosion .
corrosion leads to loss of substance from the material , change in its structural characteristics , or loss of structural integrity . due to the electrolytic capabilities of saliva
various types of brackets are commercially available and each demonstrates a unique pattern of corrosion . in soldered brackets ,
this corrosion is due to the presence of dissimilar metals ( i.e. the silver solder and the stainless steel ) , a phenomenon termed galvanic corrosion .
metal injection molding ( mim ) brackets are manufactured as a single unit and therefore do not demonstrate galvanic corrosion .
corrosion can have detrimental effects on the surface of stainless steel brackets due to the continuous loss of metal ions .
corrosion can increase the surface roughness of the bracket which leads to elevated friction forces between the bracket and the archwire .
this increase in friction results in unfavorable distribution of forces and reduces the effectiveness of archwire guided orthodontic tooth movement.[7 - 8 ] moreover , by means of increased stress , the friction would further accelerate the corrosion process .
the release of metal ions following the corrosion of brackets has concerned clinicians and has instigated research in this field . among these metal ions ,
furthermore , direct and prolonged contact of orthodontic appliances and the resulting corrosion products have been shown to cause local pain and swelling in the adjacent tissues .
edema , gingivitis , gingival hyperplasia , perioral stomatitis , dna instability and altered cellular metabolism are among other reported side effects .
corrosion also has detrimental effects on the teeth , and permanent staining around the bracket base has been reported .
due to the wide diversity of options regarding bracket selection , orthodontists look for brackets which possess satisfactory biomechanical properties while presenting with a reasonable price .
it was mentioned that corrosion has a detrimental effect on the physical properties of brackets and causes unwanted biological side effects ; therefore , brackets with minimal corrosion tendencies are more desirable . the present study aimed to investigate five different brands of stainless steel brackets and compare their tendency towards corrosion by measuring ion release in an in - vitro setting . 

five different brackets ( dentaurum , 3 m , ortho organizer , cobas and o.r.g ) were selected based on their popularity among faculty members of the orthodontic department .
( table 1 ) ten central incisor brackets were selected from each brand . in order to simulate conventional orthodontic treatment , 8 mm of 0.016  stainless steel archwire ( dentaurum , germany )
was tied in each bracket using 10 mm of 0.25 mm ligature wire ( dentaurum , germany ) .
once the brackets were prepared , they were placed in poly - ethylene capped vials containing 10 ml of artificial saliva at a ph of 7.2 .
the vials were incubated at 37c for 6 weeks and then they were subjected to thermocycling with 500 temperature cycles from 5c to 55c to simulate the effect of temperature changes in the oral cavity .
the brackets were immersed in each bath for 30 seconds with 2 seconds at air temperature in - between the immersions . 
 
the details of the brackets selected for the study 
  after thermal - cycling the solutions from the vials were analyzed to determine the amount of nickel , chromium , manganese , and iron using an inductively coupled plasma ( icp ) spectrometer ( icp - oes ; varian , vista - pro model , mulgrave , victoria , australia ; 1400w applied power ) . for the purpose of analysis , the icp device had to be calibrated for each of the metal ions .
calibration was performed using standard stock solutions ( 100 mg / ml ) prepared by dissolving nitrate salts of the aforementioned ions in distilled deionized water .
the standard stock solutions were then diluted to render the concentrations necessary ( 0.1- 10 mg / ml ) . once the icp device was calibrated and a standard calibration curve obtained , the samples were analyzed and the readings were recorded . before each reading a drop of 65% nitric acid
the addition of nitric acid facilitates the stabilization of the released ions by producing nitrate salts .
a vial containing only the artificial saliva was used as the device blank so that the ions present in the saliva itself do not compromise the readings . 
 
statistical analyses were performed using spss software for windows ( version 11 ; spss inc , chicago , iii ) .
the kruskal - wallis test was used to analyze the differences among mean ion concentrations in the 5 groups .
the median levels of ion release were measured for chromium , iron , manganese and nickel using an icp device ( figure 1 ) .
the overall amount of ion release was greatest in the cobas bracket , while ortho organizer and org brackets demonstrated minimal corrosion . 
 
ion release from brackets made by 5 different manufacturers measured in milligram per liters ( mg / l ) 
  the level of chromium release was highest in the cobas bracket followed by 3 m , dentaurum , org and ortho organizer .
it should be noted that the difference between cobas and 3 m was statistically insignificant ( p > 0.05 ) as was the difference between org and ortho organizer ( p > 0.05 ) .
iron release presented the same order that was observed for chromium ; however , the levels were generally higher for iron especially in the cobas bracket . 
  considering manganese , it can be observed that the levels are higher in 3 m followed by cobas , dentaurum , org and ortho organizer .
the differences between all brackets except dentaurum and org were statistically significant ( p < 0.05 ) .
nickel release however was more pronounced in cobas followed by 3 m , org , ortho organizer and dentaurum . 
 
only the cobas bracket demonstrated statistically significant differences with the other brackets ( p > 0.05 ) . from the ions that were analyzed ,
iron was released the most , followed by nickel , manganese and chromium ( figure 2 ) .   a : total iron release , rendered by adding the median values for the analyzed brackets .
b : percentage of total ion release attributed to each bracket if we consider looking at the brackets separately , iron release was found to be greater than the other ions in every bracket .
due to the importance of the biocompatibility of orthodontic armamentaria , in the present study we chose five popular brackets among orthodontists and determined their susceptibility to corrosion by measuring ion release in anin - vitro environment .
the brackets and wires in this study were all manufactured from 18 - 8 stainless steel ( 18% chromium , 8% nickel ) . based on the results of this study , we found that except for manganese , the cobas bracket had the highest level of ion release .
furthermore , we observed that among the studied brackets , iron was released more than the other ions .
and in contrast with the findings of huang et al . in which nickel release was more profound .
moreover the amount of ion release in our samples was higher compared to similar studies.[3,16 - 17 ] this difference in ion release may be due to the fact that we chose to tie a segment of archwire to the bracket to better simulate conventional orthodontic treatment .
first , by increasing the amount of alloy available to be subjected to corrosion and second , the potential for galvanic corrosion increases since the alloy for the archwire is different from the alloy used in the bracket .
another reason for greater levels of ion release may be due to the technique used for detection of ions .
the values obtained in the present study closely match the values presented by kuhta et al . who elected to use an icp device for ion detection . 
 
the results of the present study indicated that soldered brackets do not necessarily demonstrate less resistance to corrosion when compared to brackets made by metal injection molding ( mim ) .
when the org ( soldered ) and the dentaurum ( mim ) bracket are compared we observed that , except for iron which was released more by the dentaurum bracket , the other ions were not significantly different . while it has been argued that soldered brackets present a tendency towards galvanic corrosion , mim brackets have increased porosity rendering them susceptible to another kind of chemical breakdown , termed pitting corrosion .
this may be the reason why similar studies also found no measurable advantage regarding the utilization of mim brackets .
the presence of an archwire may be a confounding factor which may induce galvanic corrosion to mim brackets that cancels out any possible differences . 
 
the results of the present study indicated that iron was released more than the other ions , followed by nickel .
while this was the overall pattern , in the 3 m bracket , it was observed that manganese was released more than nickel .
this finding is in contrast to the findings of karnam et al . who reported that nickel was the major ion released from orthodontic brackets .
the findings of this study also suggest that there were no statistically significant differences between the 3 m and dentaurum brackets in any of the ions studied .
these differences could be due to study design , addition of an archwire element , testing conditions and measurement methods .
it is noteworthy that in the present study , an icp - ms was used to measure the released ions .
icp - ms has shown lower detection limit compared to atomic absorption spectrometry used in similar studies .
another advantage of the icp device over atomic absorption is that it can measure several ions simultaneously without interference from other ions .
this study in agreement with previous findings declares that the values of ions released from orthodontic brackets falls short of the permissible daily doses determined by the world health organization .
the maximum tolerable dose of nickel , iron , manganese and chromium for a 60-kg individual is 1.2 , 15 , 10 and 50 - 200 mg / day , respectively .
however the chronic nature of metallic exposure resulting from orthodontic treatment is a cause for concern .
it has been reported that chronic exposure to metal ions can cause alterations in cell morphology and metabolism leading to inflammation and dna instability.[21 - 26 ] iron ions in particular have been demonstrated to cause mitochondrial dysfunction in cells with active mitochondrial activity .
they have also been linked with lysosome instability which could result in cell death and apoptosis . regarding irreversible damage to oral tissues resulting from orthodontic treatment however ,
hafez et al . concluded that 6 months after the removal of the orthodontic appliance , no difference was observed between the orthodontic patients and the controls . 
 
the findings of this study are based on an in - vitro experimental design , and therefore suffer from the inadequacies related to the simulation of the in - vivo environment .
a bracket in the oral environment is subjected to many kinds of chemico - thermal insults including rapid changes in ph , the intake of hot and cold beverages and mechanical challenges . while in many senses
the in - vitro design is a drawback , in measuring ion release such a setup is rather useful .
not all of the ions released from orthodontic brackets are found in the oral fluids .
some of the ions are absorbed into the oral and gingival tissues , while others are ingested and could disperse into distant organs .
the advantage of the in - vitro design is that it presents the total ions released from the bracket , which could better show the true effect of this phenomenon .
another drawback to this study is that we did not evaluate the effects of different wire - bracket combinations and only used a single wire for all of the brackets .
based on the findings of the present study , regarding ion release levels , the org and ortho organizer brackets were superior while dentaurum and 3 m did not demonstrate any significant differences . 

 statement of the problem : stainless steel brackets release metallic ions following the process of corrosion in the oral environment . 
 these released ions have potential adverse effects on health , friction between wire and bracket , staining , strength of brackets . choosing a bracket with favorable corrosive properties ; therefore , should be a goal of every practitioner . 
 
 purpose : the goal of this study is to compare the amount of corrosion among five different brands of brackets using inductively coupled plasma ( icp ) mass spectrometry . 
 materials and method : five different brands of brackets ( dentaurum , 3 m , ortho organizer , cobas and o.r.g ) were chosen and ten brackets were selected from each brand . 
 a piece of stainless steel wire was ligated to each bracket . 
 the bracket - archwire complex was then immersed in artificial saliva . 
 subsequently , the samples were analyzed using an icp device and the levels of iron , chromium , nickel , and manganese ions were measured . 
 
 results : the findings of this study demonstrated that iron was released the most from the tested brackets , followed by nickel . 
 we also found that the cobas bracket had the most ion release among the tested brackets ( p < 0.05 ) , while ortho organizer and org performed favorably . 
 there was no significant difference between dentaurum and 3 m ( p > 0.05 ) . 
 
 conclusion : based on the results , ortho organizer and org brackets are suggested in terms of resistance to corrosion . 
 