the oral environment is particularly favorable to metal biodegradation due to its 
 chemical , thermal , microbiological and enzymatic conditions .
when in contact with saliva and acid / basic foods at 
 different temperatures , the metal components of orthodontic appliances may undergo 
 corrosion .
in addition , the orthodontic treatment , especially with fixed appliances , causes 
 specific alterations in the oral cavity , including decrease of ph , increase of dental 
 biofilm accumulation and elevation 
 of the salivary microbial levels , which are favorable conditions to the 
 occurrence of corrosion .
corrosion of orthodontic appliances may have serious clinical 
 implications that range from loss of dimension of the appliance 's components , which 
 results in application of lower force to the teeth , up to possible failure of the 
 appliance due to tension corrosion . 
 in the corrosive process
, the released metallic ions may get in contact with cells and 
 tissues in the contiguous environment or pervade throughout the body .
absorption of 
 toxic products released during corrosion of metallic orthodontic components by body 
 tissues is undesirable . in dentistry
, corrosion may manifest as biological , functional and esthetic effects , the 
 biological being the most significant .
corrosion in orthodontic appliances has been extensively investigated by analysis of ion 
 release both in vitro 
  and in vivo 
 . considering that fixed orthodontic appliances may act 
 as retention niches for microorganisms and are susceptible to 
 corrosion ,
the development of in situ studies evaluating corrosion from 
 a clinical standpoint is of paramount importance .
this study evaluated in situ the corrosion of the metallic components 
 of haas expanders by stereomicroscopy , scanning electron microscopy ( sem ) and energy 
 dispersive x - ray spectroscopy ( eds ) .
thirty - four patients of both sexes ( 14 male and 20 female ) aged 6 to 12 years ( mean age 
 = 9 years and 7 months ) from the orthodontic clinic of the ribeiro preto dental school , 
 university of so paulo , brazil , who needed maxillary expansion with a haas expander for 
 correction of posterior crossbite were enrolled in this study .
the children were 
 randomly assigned to two groups of 17 individuals each ( groups i and ii ) .
patients who were using antimicrobial mouthwashes , presented any systemic disease and/or 
 had used antibiotics within the previous 3 months were excluded from the trial .
this 
 research project was approved by the local ethics in research committee ( process number 
 2006.1.391.58.9 ) and written informed consent was obtained from the parents or 
 guardians . for construction of the haas expanders ,
the permanent first molars were banded and the 
 metallic bands were silver welded ( dental morelli , sorocaba , sp , brazil ) to 0.9 mm 
 stainless steel orthodontic wires ( dentaurum , ispringen , germany ) .
the active component 
 was an 11 mm expanding screw ( dental morelli , sorocaba , sp , brazil ) .
the bands were 
 cemented with zinc phosphate cement ( ls cement ; vigodent s / a indstria e comrcio , rio 
 de janeiro , rj , brazil ) and the orthodontic wires were fixed to the primary canines or 
 molars with light - cured composite resin ( tph ; 3m / espe , st .
after correction of the posterior crossbite , which lasted 20 days on average , the 
 orthodontic appliance was maintained for additional 3 months in the mouth as a retention 
 period . during the time of use of the appliances ,
the patients of group i were instructed to brush their 
 teeth with a fluoride dentifrice 3 times a day and not to use any antimicrobial 
 mouthrinse solution . for patients of group
ii , in addition to toothbrushing with a 
 fluoride dentifrice , 1-minute mouthrinses with 10 ml of a 0.12% chlorhexidine gluconate 
 solution ( periogard ; colgate - palmolive company , new york , ny , usa ) were 
 prescribed twice a week ( tuesdays and fridays ) . on tuesdays
, mouthrinsing was performed 
 at the dental school under the researcher 's supervision , while on fridays mouthrinsing 
 was performed at the child 's home under parental supervision .
after removal from the mouth , the fixed appliances of both groups were cut with a 
 sterile pair of pliers ( orthopli 021 ; dentaurum , pforzheim , germany ) on either the right 
 or the left side , according to a table of random numbers , in order to obtain a fragment 
 containing a sample of the wire / silver brazing / band region .
the fragments were placed in 
 a 300-mm desiccator ( vidrolabor , paulnia , sp , brazil ) containing silica gel as an 
 indicator of humidity for further analysis of the corrosive process .
after desiccation , 
 the specimens were examined with an optical stereomicroscope ( leica l2 ; wetzlar , 
 germany ) coupled to a digital camera ( sony cyber shot 3.3 mega pixels dsc-575 , tokyo , 
 japan ) at x40 magnification to obtain images of the soldering point areas ( silver 
 brazing / band , silver brazing / wire and wire / silver brazing / band ) , as suggested by 
 wichelhaus , et al .
the 
 images were analyzed with respect to the presence of areas with color change due to 
 oxidation , suggestive of corrosion .
this type of qualitative analysis has been described 
 in several studies and allowed 
 delimiting the areas to be examined by sem and eds .
data referring to the presence ( + ) 
 or absence ( - ) of color change suggestive of in situ corrosion in both 
 groups were compared by fisher 's test using the sas ( statistical analysis system , 
 institute inc . ,
the analysis was 
 undertaken with a scanning electron microscope ( evo 50 ep ; carl zeiss smt ag , germany ) 
 operating at 20 kv coupled to an energy dispersive x - ray spectrometer ( ixrf systems 
 inc .
, houston , tx , usa ) , which allows analyzing the predetermined area at x60 to 194 
 magnification with four - quadrant electron - backscatter detectors ( qbsd ) using a 
 pre - determined depth of penetration of the electron beam . this analysis was performed to 
 identify the peaks of the following chemical elements : nickel ( ni ) , iron ( fe ) , chromium 
 ( cr ) , oxygen ( o ) , carbon ( c ) and phosphorus ( p ) in the region delimited in the fragments 
 of the appliances of groups i and ii
. graphs of the peaks of these chemical elements 
 were obtained using the edx/2004 software .
the analysis of the images obtained under optical stereomicroscopy revealed areas of 
 color change suggestive of corrosion in the soldering point areas ( wire / silver 
 brazing / band region ) in all specimens of both groups ( figure 1a and b ) , with no statistically 
 significant difference ( p=1 ) .
a : stereomicroscopic analysis of a representative group i specimen showing color 
 change in the band / silver brazing / wire joint . 20 magnification .
b : close - up view 
 of a showing color change suggestive of corrosion at the band/ silver brazing / wire 
 joint . 40 magnification .
c : scanning electron microscopy ( sem ) micrograph showing 
 the band / silver brazing / wire joint to be analyzed by energy dispersive x - ray 
 spectroscopy ( eds ) .
d : areas of ag solder ( a ) , 
 material - to - material interface ( b ) and orthodontic wire ( c ) analyzed by eds with 
 four - quadrant electron backscatter detectors qbsd detectors the regions suggestive of corrosion were submitted to sem examination ( figure 1c ) with eds analysis ( figure 1d ) .
graphs representative of the qualitative readings of the 
 specimens of groups i and ii are presented in figures 
 2 and 3 .
quantitative energy dispersive x - ray spectroscopy ( eds ) reading representative of 
 areas of color change suggestive of corrosion in the soldered region in contact 
 with the band and the wire in a group i specimen ( control ) quantitative energy dispersive x - ray spectroscopy ( eds ) reading representative of 
 areas of color change suggestive of corrosion in the soldered region in contact 
 with the band and the wire in a group ii specimen ( periogard mouthrinse ) in both groups , the soldered areas in contact with the band and the wire presented fe , 
 cr , o , c and p peaks .
figure 4 illustrates the reading obtained in a 
 non - assayed region of an orthodontic wire of a haas expander .
no area of corrosion was 
 visible under optical stereomicroscopy , demonstrating how the peaks of chemical elements 
 behave in this situation .
several studies have currently evaluate the resistance to corrosion of orthodontic wires 
 and brackets in an attempt to find materials with greater compatibility with the oral 
 environment .
however , most 
 studies are in vitro experiments that are performed with artificial 
 saliva and methodologies that simulate the oral conditions , reaching results that can not 
 be extrapolated to the clinical situation .
the present investigation was designed as a 
 randomized clinical trial because it is the " golden standard " of studies that evaluate 
 the clinical efficacy of materials and treatment techniques .
soldering is still the prevailing joining technique in the dental laboratory , although 
 problems arise from the susceptibility to corrosion and the low strength of soldered 
 joints . in the flame soldering technique , the wire elements are heated directly , so that 
 the temperature of the wire mostly rises to levels exceeding the fusing temperature of 
 the solder . under these conditions ,
intergranular corrosion occurs due to the change in 
 the composition of grain contours deriving from phase precipitations , concentration of 
 impurities or elementary cr depletion close to the areas of grain contours .
the results of the present study showed the occurrence of failure in the flame - soldered 
 joints between the stainless steel wires occurred during the construction of the haas 
 expanders .
( 2002 ) who evaluated in 
 vitro different soldering techniques produced by various dental technicians 
 and observed incomplete filling of the soldering gap , porosities resulting from the 
 production process , local structural changes due to overheating and deficient alloying 
 at the solder margin .
the eds analysis qualifies chemically the composition of a certain material , being a 
 complementary method to evaluate the presence of corrosion . under ideal conditions , fe and cr peaks in the soldered joint 

graphs with high fe peaks and medium cr peaks and presence 
 of o suggest the occurrence of corrosion due to formation of fe2o3 
 or hydrated ferric oxide ( fe2o3 x h2o ) , indicating rust .
the presence of p with high fe peaks and medium cr peaks suggests the 
 occurrence of a process corrosive by formation of iron phosphate 
 ( fepo4 ) . in the 
 present study
, peaks of these elements were observed in the soldered joints in all 
 specimens of both groups .
the deterioration of orthodontic appliances has been a matter of concern in orthodontic 
 research due to the potential adverse biological reactions associated mainly to ni 
 release . in the present in situ study
, the eds 
 analysis did not reveal ni peaks in the soldered joints of any of the haas expanders 
 worn for approximately 4 months .
although no increase in the ni levels were observed , 
 which would indicate a corrosive process , the presence of corrosion was detected on 
 examination of the images under optical microscopy .
this situation is 
 further aggravated if one considers two other conditions that may contribute to 
 potentialize corrosion : the mouth is an aggressive oral environment to the various types 
 of sensitized alloys and crevice corrosion is intensified where gaps and/or cracks 
 develop .
in addition to intergranular and crevice corrosion , the stainless steel becomes 
 susceptible to the corrosive process , since the alloy has its structure altered and the 
 passivation film can not be reestablished .
this permits the occurrence of different types 
 of corrosion : fatigue corrosion , which occurs frequently in orthodontic wires submitted 
 to long intraoral periods under load ; 
 microbiological corrosion , which causes color change in the presence of microorganisms 
 due to action of sulfur or reduction of sulfates to hydrogen sulfide and formation of 
 insoluble dark sulfites , in addition to pitting ( corrosive attack that occurs in points 
 or small areas ) and deposits that may occur in the presence of microorganisms ; and galvanic corrosion , which is the 
 deterioration of an alloy by transference of electrons due to difference of potential 
 between two materials in the presence of a common electrolyte .
the c peaks observed in the eds analysis were greater in group i , possibly due to the 
 greater accumulation of bacterial biofilm .
the p peaks were very expressive in all 
 specimens , possibly originating from the saliva and/or the zinc phosphate cement used 
 for cementation of the orthodontic bands .
the presence of ag peaks in the graphs of 
 soldered joints distant from material - to - material interface only suggests the presence 
 of the metal used as a soldering material . although the methodology of the present study does not allow determining accurately 
 which factors caused corrosion , alterations occurred in the wire / silver brazing / band 
 joints , since a dark line suggestive of corrosion was observed on the alloy by optical 
 microscopy and sem , though without significant difference between the groups .
under the conditions evaluated in this randomized clinical study , it may be concluded 
 that there were color change and peaks of chemical elements suggestive of corrosion in 
 all specimens of both groups in the soldering point areas between the wire , silver 
 brazing and bands of the haas expanders , with no difference between the groups .
these 
 results suggest that the use of chlorhexidine mouthrinses did not influence the 
 occurrence of corrosion in situ .
 objectivesthe purpose of this study was to evaluate in situ the occurrence 
 of corrosion in the soldering point areas between the wire , silver brazing and 
 band in haas expanders . 
 material and methodsthirty - four 7 - 12-year - old patients who needed maxillary expansion with a haas 
 expander were randomly assigned to two groups of 17 individuals each , according to 
 the oral hygiene protocol adopted during the orthodontic treatment : group i 
 ( control ) , toothbrushing with a fluoride dentifrice and group ii ( experimental ) , 
 toothbrushing with the same dentifrice plus 0.12% chlorhexidine gluconate 
 ( periogard ) mouthrinses twice a week . 
 the appliances were removed 
 after approximately 4 months . 
 fragments of the appliances containing a metallic 
 band with a soldered wire were sectioned at random for examination by 
 stereomicroscopy , scanning electron microscopy ( sem ) and energy dispersive x - ray 
 spectroscopy ( eds ) . 
 data were analyzed statistically by fisher 's test at 5% 
 significance level . 
 resultsthe analysis by optical microscopy revealed areas with color change suggestive of 
 corrosion in the soldering point areas joining the band and the wire in all 
 specimens of both groups , with no statistically significant difference between the 
 groups ( p=1 ) . 
 the peaks of chemical elements ( ni , fe , cr , o , c and p ) revealed by 
 eds were also similar in both groups . conclusion : color changes and peaks of chemical elements suggestive of corrosion were observed 
 in the soldering point areas between the wire , silver brazing and band in both 
 control and experimental groups , which indicate that the 0.12% chlorhexidine 
 gluconate mouthrinses did not influence the occurrence of corrosion in 
 situ . 