loose or inaccurately placed brackets that require repositioning during treatment are a 
 common complication faced by orthodontists . for a variety of reasons ,
clinical bond 
 failure occurs in 5 to 7% of brackets bonded with light - cured or chemicalcured resin 
 composite . as a result
re - use of a debonded bracket is practical and lowers costs , making rebonding a common 
 procedure in orthodontic treatment .
however , any 
 distortion of the bracket base or change in slot size that occurs during bracket 
 reconditioning may reduce bracket bond strength and the efficacy of orthodontic 
 treatment .
the bond strength of a recycled bracket may also be less than that of a new 
 bracket if the bracket base is not properly treated .
resin composite may 
 be cleaned from debonded brackets by stoning with green stones , burning with a bunsen 
 flame ( 3 s ) , sandblasting , or electropolishing ( 20 s ) .
sandblasting 
 with aluminum oxide particles also creates a slight roughness that increases the surface 
 area , thereby enhancing mechanical and chemical bonding .
however , the use of sandblasting alone may not be 
 enough to obtain reliable bond strength , especially after thermocycling .
advances in silane coupling agents have 
 contributed to high bond strength by promoting a chemical bond between resin composite , 
 ceramic ( silica - based ) and metal ( base metal ) .
tribochemical silica coating provides ultrafine mechanical retention and is used in 
 conjunction with a silane coupling agent . with this technique , 
 metal or ceramic surfaces
are abraded with cojet - sand ( 3 m espe ag , seefeld , germany ) , a 
 30-mgrained aluminum oxide ( al2o3 ) chemically modified with 
 silica , using an intraoral sandblaster .
not only is the surface abraded ; it acquires a silica 
 coating derived from the silica - coated aluminum trioxide particles used in abrasion .
the 
 technique of silica coating has many applications in dentistry and has been shown to 
 increase the bond strength of aluminum and zirconium oxide ceramics to resin composite 
 and of metal and ceramic brackets to enamel . nevertheless , little information is available regarding 
 the effects of silica coating followed by silanization on the bond strength of recycled 
 metal and ceramic brackets .
the aim of this study was to evaluate the effects of tribochemical silica coating and a 
 silane coupling agent on the bond strength of recycled metal and ceramic brackets .
the 
 null hypothesis tested was that tribochemical silica coating and silane agent treatment 
 increase the bond strength of rebonded metal and ceramic brackets .
the study was conducted with 20 freshly extracted human caries - free , restoration - free 
 maxillary premolars .
teeth were cleaned of residual organic material , and the labial and 
 lingual surfaces were polished with flour of pumice using a rubber cup , rinsed with tap 
 water and dried with an air - syringe . 

metal ( n=20 ) ( generus - roth , stainless steel , # b577 ; gac international , 
 bohemia , ny , usa ) and ceramic ( n=20 ) ( allure , 99.9% pure alumina , # 2530013 ; gac 
 international , bohemia , ny , usa ) maxillary premolar brackets were bonded to unetched , 
 damp tooth surfaces using light - polymerized bis - gma resin composite luting cement ( light 
 bond , # 402270 ; reliance orthodontic products , itasca il , usa ) polymerized using a fast 
 halogen light curing unit ( hilux 250 , first medica , greensboro , nc , usa , light intensity 
 of 600 mw/ cm ) .
brackets were manually placed using bracket pliers , and 
 excess resin was removed from the bracket periphery prior to polymerization .
the luting 
 resin was light - polymerized for a total of 30 s - 10 s over the bracket face and 20 s 
 interproximally ( 10 s mesially , 10 s distally ) .
the bonded brackets were then separated 
 from the tooth surfaces using a sharp - edged bracket - removal pliers ( i00579 ; rocky 
 mountain orthodontics , denver , co , usa ) . the debonded metal and ceramic brackets
were randomly assigned to different groups to 
 receive the following surface treatments ( n=10 for each group ) : ( 1 ) sandblasting with 
 50-m aluminum oxide ( sb ) ( control ) ; ( 2 ) airborne particle abrasion with 30 m aluminum 
 trioxide particles modified by silica+silane ( scs ) .
sandblasting was performed with 
 50-m aluminum oxide ( dentsply gac , # 73613 ; ny , usa ) using an intraoral sandblaster 
 ( microetcher ii , danville engineering , san ramon , ca , usa ) at 65 psi for 7 - 12 s until 
 bonding resin was no longer visible to the naked eye .
each sandblasted bracket base was 
 then rinsed with water for 5 s and dried with an air spray .
prior to rebonding , the debonded brackets were visually 
 reinspected , and if any remaining resin was observed on the bracket surfaces , 
 sandblasting , rinsing and air - drying was repeated as described above .
silica coating was 
 performed with 30 m silicon dioxide ( cojet sand,#267044 ; 3 m espe ag , seefeld , germany ) 
 using an intraoral sandblaster ( microetcher ii , danville engineering ) . in accordance 
 with the manufacturer 's instructions
, abrasion was performed vertically to the bracket 
 surfaces at a distance of 10 mm with 0.25 mpa pressure for 15 s. residual coating agents 
 were removed using a stream of dry , oil - free air .
one coat of silane ( espe - sil ag , 
 # 265030 ; seefeld , ) was applied to conditioned specimens using a clean brush and was 
 allowed to air - dry for 5 min in accordance with the manufacturer 's recommendations .
any 
 residual adhesive remaining on labial and lingual surfaces after debonding was removed 
 with a finishing carbide bur ( komet , # 047523 , lemgo , germany ) until the enamel surface 
 regained its gloss .
teeth were then 
 polished with flour of pumice and a rubber cup , rinsed with tap water , and dried with an 
 air - syringe .
labial and lingual surfaces were etched for 15 s with 35% phosphoric acid 
 ( dentsply caulk , # 070910 ) , rinsed for 20 s and air - dried for 5 s with oil - free 
 air .
rebonding was performed by 
 applying a thin layer of a bis - gma bonding agent ( light bond , # 403100 ; reliance 
 orthodontic products ) .
excess resin was removed with an air - syringe , and the bonding 
 agent was cured using a fast halogen light curing unit ( hilux 250 , first medica , 
 greensboro , nc , light intensity of 600mw / cm ) for 20 s , according to the 
 manufacturer 's instructions .
brackets were then rebonded to the enamel surfaces with 
 light - polymerized bis - gma resin composite luting cement ( light bond , # 402270 ; reliance 
 orthodontic products ) .
brackets were manually placed using bracket pliers , and excess 
 resin was removed with an air - syringe from the bracket periphery prior to 
 polymerization .
the luting resin was light - polymerized for a total of 30 s - 10 s over 
 the bracket face and 20 s interproximally ( 10 s mesially , 10 s distally ) . in the bonding 
 and rebonding procedure ,
all brackets were cemented by the same investigator using to as 
 great extent as possible the same pressure , according to the manufacturer 's 
 instructions .
test specimens were stored in distilled water at 37c for 1 week , thermocycled using a 
 custom - made thermocycling device ( ankara university , ankara , turkey ) for 5,000 cycles 
 between 5c and 55c , with a transfer time of 30 s and a dwell time of 30 s. following 
 thermocycling , specimens were embedded in autopolymerizing clear acrylic resin 
 ( meliodent , # 013013 ; heraus , kulzer , dormagen , germany ) and mounted in a universal 
 testing machine ( lloyd lrx ; lloyd instruments ltd , fareham , uk ) . an occlusogingival load 
 was applied to each specimen using a knife - edge blade at a crosshead speed of 0.5 mm / min 
 until failure , with the test assembly adjusted to ensure that the shear force was 
 directed at the bracket - tooth interface , not at the bracket itself .
the surface area of 
 the bracket base was calculated by measuring the length and width of each bracket base 
 with a digital caliper ( model cd-15cpx , mitutoyo , tokyo , japan ) and computing the mean 
 area ( 12.69 mm for both metal and ceramic brackets ) .
bond strength was 
 derived by dividing the failure load ( n ) by the bonding area ( mm ) and was 
 expressed in mpa .
debonded specimens were examined under a stereomicroscope ( leica mz 12 , leica 
 microsystems , bensheim , germany ) at x80 magnification by the same operator to assess the 
 mode of failure , as represented by adhesive remnant index ( ari ) value , according to the 
 following criteria : 0 , no adhesive 
 left on the tooth ; 1 , less than half of the adhesive left on the tooth ; 2 , more than 
 half of the adhesive left on the tooth ; and 3 , all adhesive left on the tooth . following 
 this , 1 specimen from each group was sputter - coated with a gold - palladium alloy ( hummer 
 vii ; anatech ltd , alexandria , va , usa ) and examined under a scanning electron microscope 
 ( sem ) ( jsm-5600 ; jeol ltd , tokyo , japan ) at x100 and x200 magnification to observe the 
 topographic patterns .
statistical analysis was performed using the statistical software 
 package spss 12.0 ( spss inc . ,
mean shear bond strengths of groups was 
 compared using student 's t - test , and differences in ari scores between groups were 
 assessed using the chi - square test ( with scores combined as ari 0 - 1 and ari 2 - 3 ) . 

the mean shear bond strength of the 
 ceramic scs group ( 17.74.4 mpa ) was significantly higher than that of the ceramic sb 
 group ( 2.40.8 mpa ) .
the mean shear bond strength of the metal scs group ( 153.9 mpa ) 
 was also higher than that of the metal sb group ( 13.63.9 mpa ) , but the difference 
 between groups was not statistically significant ( p=0.44 ) .
results of t - test for rebonded metal and ceramic brackets ns indicates not significant ; sd= standard deviation the distribution of failure modes , as expressed by ari scores , is given in table 2 .
rebonded metal brackets exhibited 
 primarily cohesive failure in resin and mixed failure . whereas all sandblasted ceramic 
 specimens failed at the bracket - adhesive interface ( 100% ari-3 ) , none of the 
 silicone - coated specimens failed at the bracket - adhesive interface ( 0% ari-3 ) .
chi square test showed a 
 statistical difference in ari scores between the metal ( chi square value=6.4 , df=1 , 
 p=.01 ) and ceramic ( chi square value=10 , df=1 , p=.002 ) bracket groups .
sem images of 
 metal and ceramic bracket base surfaces are shown in figures 1 and 2 , respectively .
surface 
 patterns of the metal scs ( figure 1a ) , and sb 
 ( figure 1b ) specimens were similar ; however , 
 greater surface irregularity was observed in the ceramic scs specimen when compared to 
 the ceramic sb specimen ( figures 2a , b ) .
failure modes of groups according to ari ab ari indicates adhesive remnant index ari : 0 , no composite left on tooth ; 1 , less than half of composite left on 
 tooth ; 2 , more than half of composite left on tooth ; 3 , all the composite on 
 tooth n : number of groups ( values in the brackets ) a , scanning electron microscope ( sem ) ( original magnification x200 ) of the surface 
 of a metal bracket airborne - particle abraded with 50-m 
 al2o3 ( group sb ) .
b , sem image ( original magnification 
 x200 ) of the surface of a metal bracket subjected to high - speed impaction with 
 30-m al2o3 modified by silica followed by silanization 
 ( group scs ) . note the similar surface textures of a and b a , scanning electron microscope ( sem ) image ( original magnification x100 ) of the 
 surface of a ceramic bracket airborne- particle abraded with 50-m 
 al2o3 ( group sb ) .
b , sem image ( original magnification 
 x100 ) of ceramic bracket surface subjected to high - speed surface impaction with 
 30-m al2o3 modified by silica followed by silanization 
 ( group scs ) . note the greater irregularities on surface texture in b
rebonding of ceramic and metal brackets is often required in orthodontic practice ; 
 however , limited data is available about the bond strength of rebonded brackets treated 
 with different surface treatments .
this study evaluated the effects of tribochemical 
 silica coating and a silane coupling agent on the bond strength of recycled metal and 
 ceramic brackets .
the null hypothesis that tribochemical silica coating and silane 
 treatment increases the bond strength of rebonded metal and ceramic brackets was 
 partially confirmed .
silica coating followed by silanization resulted in higher bond 
 strengths of rebonded ceramic brackets .
although silica coating and silane surface 
 treatment slightly increased the bond strength of recycled metal brackets , a significant 
 difference was not found . in clinical practice , sandblasting of debonded bracket surfaces
is frequently performed 
 prior to rebonding them to enamel . not only does 
 sandblasting remove any residual material from the restoration surface , but also the rough surface produced as 
 a result of sandblasting increases the surface area and wettability of the material , 
 thereby enhancing mechanical and chemical bonding . with silica coating ,
the high - speed surface impact of the silica - modified aluminum 
 particles used in air - abrasion alter the surface of the debonded brackets , permitting 
 micromechanical bonding between bracket and resin luting agent .
in addition , a chemical bond is formed between the 
 silica - coated surface and the resin material . following silica coating ,
a silane agent is applied in a process 
 known as silanization , which promotes adhesion between dissimilar materials .
the 
 trialkoxy silanes used in the process are comprised of the general formula r - y - six3 
 ( where r is a non - hydrolyzable organic group , e.g. , methacrylate ; y , a linker ; and x , 
 the hydrolyzable group ) and are polymerized with the resin composite to form chemical 
 bonds .
we found the bond strength of recycled ceramic brackets treated with a tribochemical 
 silica coating followed by silanization ( 17.74.4 mpa ) to be significantly higher than 
 rebonded brackets treated by sandblasting ( 2.40.8 mpa ) .
this finding is in line with 
 those of previous in vitro studies showing silane and/or silica coating 
 treatment increased the bond strength of ceramic brackets .
( 2002 ) compared the bond strengths of new , rebonded / sandblasted 
 and rebonded / sandblasted / silane - treated ceramic brackets to enamel and found that the 
 new brackets had the highest mean bond strength ( 15.6 mpa ) , followed by the 
 rebonded / sandblasted / silane - treated brackets ( 5.9 mpa ) and the rebonded / sandblasted 
 brackets ( 2.9 mpa ) .
torolu and yaylali ( 2008 ) compared the effects of sandblasting , silica coating and 
 silanization on the bond strengths of rebonded ceramic brackets and found the greatest 
 improvements in bond strengths came from silica coating+silane ( 12.7 mpa ) , followed by 
 sandblasting+silane ( 10.5 mpa ) and sandblasting alone ( 4.5 mpa ) .
in contrast to the findings for ceramic brackets , the present study showed silica 
 coating and silane surface treatment did not significantly improve the bond strength of 
 rebonded metal brackets , with the silica - coated and silane treated group demonstrating 
 only a slightly higher bond strength ( 15 mpa ) than the sandblasted control group ( 13.6 
 mpa ) .
although silica coating followed by silanization has been previously used to treat 
 metal bracket surfaces , a literature 
 review found no references to the effects of silica and silane surface treatment on the 
 bond strength of recycled metal brackets to enamel .
( 2006 ) found sandblasting with 90-m 
 aluminum oxide particles had no statistically significant affect on the bond strength of 
 recycled metal brackets .
( 1998 ) found no significant differences among the mean 
 bond strengths of new metal brackets and new and recycled metal brackets microetched 
 with 50 m aluminum oxide particles to previously bonded teeth . in the present study , 

the bond strength of sandblasted recycled metal brackets was similar to that of metal 
 brackets treated by silica coating , which creates a surface texture similar to that of 
 sandblasting .
clinically , bond strength can be influenced by many environmental factors , 
 including thermal changes .
in general , the minimum bond strength required to withstand 
 normal orthodontic forces is believed to be between 6 - 8 mpa .
this study 
 showed that the mean shear bond strengths to enamel of thermocycled silicone - coated 
 recycled metal and ceramic brackets exceeded these limits , as did thermocycled 
 sandblasted recycled metal brackets ; however , the mean shear bond strength of 
 sandblasted recycled ceramic brackets was below this threshold .
this indicates that the 
 shear bond strengths of silica - coated / silane treated recycled ceramic and metal brackets 
 and sandblasted recycled metal brackets are sufficient for clinical application .
numerous other studies have used shear bond testing to evaluate the bond strength of 
 brackets to enamel .
however , shear tests 
 have been criticized for producing a nonhomogeneous distribution of stress on the bonded 
 interface , resulting in either an underestimation or a misinterpretation of the test 
 results stemming from the fact that failure often begins in one of the substrates rather 
 than in the adhesive zone .
it is possible that the findings of previous research indicating 
 that increased bond strength resulted in failure within the resin was affected by the test 
 geometry .
this limitation 
 should be taken into consideration when interpreting the results of shear tests . in line with previous studies ,
the silicacoated / silane treated ceramic specimens in our study 
 exhibited cohesive failure within the resin and adhesive failure at the enamel - adhesive 
 interface , but no cohesive failure within the enamel .
ari scores for the recycled metal 
 brackets in our study primarily indicated cohesive failure within resin and mixed 
 failure .
sem micrographs of the ceramic brackets revealed greater irregularities on the 
 surface of the ceramic bracket - base of the silica - coated / silane - treated specimen when 
 compared to the sandblasted specimen , whereas no significant differences in the surface 
 texture of silica - coated / silane - treated and sandblasted metal specimens were observed . 

these findings are in line with the finding of differences in bond strength values 
 between the silica - coated / silane - treated and sandblasted ceramic groups , but not between 
 the silica - coated / silane - treated and sandblasted metal groups . an important requirement in bracket
bonding is that there should be no or minimal risk 
 of iatrogenic damage to the enamel surface during debonding .
although ceramic brackets are rigid and unyielding , no 
 enamel fractures were observed during debonding in this study .
further investigations 
 could be performed with the different orthodontic adhesives and tribochemical silica 
 coating and silane surface conditioning .
clinician must consider cost effective and a 
 less time - consuming method when choose rebonding of orthodontic brackets .
moreover , 
 controlled clinical trials are needed before clinical recommendations can be 
 provided .
within the limitations of this study , the following conclusions were drawn : 1- tribochemical silica coating followed by silanization significantly increased the 
 mean bond strength of recycled ceramic brackets .
2- the bond strength of recycled metal brackets treated with tribochemical silica 
 coating followed by silanization was slightly higher than sandblasted recycled metal 
 brackets , but the difference in bond strengths was not statistically significant .
3- the bond strength of recycled metal and ceramic brackets treated with a tribochemical 
 silica coating system was adequate for clinical use .
in addition to being both 
 economical and ecological , the use of recycled metallic and ceramic brackets can reduce 
 chair time .
 objectivethe aim of this study was to evaluate the effects of tribochemical silica coating 
 and silane surface conditioning on the bond strength of rebonded metal and ceramic 
 brackets.material and methodstwenty debonded metal and 20 debonded ceramic brackets were randomly assigned to 
 receive one of the following surface treatments ( n=10 for each group ) : ( 1 ) 
 sandblasting ( control ) ; ( 2 ) tribochemical silica coating combined with silane . 
 
 brackets were rebonded to the enamel surface on the labial and lingual sides of 
 premolars with a light - polymerized resin composite . 
 all specimens were stored in 
 distilled water for 1 week and then thermocycled ( 5,000 cycles ) between 5 - 55c . 
 
 shear bond strength values were measured using a universal testing machine . 
 
 student 's t - test was used to compare the data ( =0.05 ) . 
 failure mode was assessed 
 using a stereomicroscope , and the treated and non - treated bracket surfaces were 
 observed by scanning electron microscopy.resultsrebonded ceramic brackets treated with silica coating followed by silanization had 
 significantly greater bond strength values ( 17.74.4 mpa ) than the sandblasting 
 group ( 2.40.8 mpa , p<0.001 ) . 
 no significant difference was observed between 
 the rebonded metal brackets treated with silica coating with silanization ( 153.9 
 mpa ) and the sandblasted brackets ( 13.63.9 mpa ) . 
 treated rebonded ceramic 
 specimens primarily exhibited cohesive failure in resin and adhesive failure at 
 the enamel - adhesive interface.conclusionsin comparison to sandblasting , silica coating with aluminum trioxide particles 
 followed by silanization resulted in higher bond strengths of rebonded ceramic 
 brackets . 
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS