the concept ins in restorative dentistry have been continually changing over the last decades and adhesive dentistry has steadily gained in importance .
the concept of adhesive restoration has been essentially the most noteworthy development n this ever progressing science .
there are two different ways by which current adhesive systems obtain acceptable micromechanical retention between resin and dentin .
the first method is based on complete removal of the smear layer and demineralization of subsurface intact dentin using acid - etching with mineral or organic acids , leaving a collagen rich , moist surface into which resin must diffuse to form a hybrid layer , called the  etch and rinse approach  [ 2 , 3 ] .
the second method uses slightly acidic monomers , which partially demineralize the smear layer and underlying intact dentin , incorporating the demineralized smear layer remnants and using them as bonding substrate , called the  self etch approach  [ 3 , 4 ] .
there has been a trend to move from the original type of multicomponent bonding systems toward simplified , consolidated adhesive systems that are more user - friendly . in an effort to search for an effective dentinal bonding agent ,
a large number of bonding systems have been developed that provide a high clinical retention rate of the restorative materials .
the bonding efficacy of adhesive systems has been shown to be different for primary and permanent dentition .
studies have shown bond strength and sealing ability in primary teeth to be less than in permanent teeth [ 7.8 ] .
lower bond strength in primary teeth may be attributed to chemical , physiological and micromorphological differences of primary teeth such as decreased mineralization , small tooth size and less number of dentinal tubules with decreased permeability or more reactivity to acidic conditioner [ 9 , 10 , 11 ] . moreover
, several studies showed that the peritubular dentin was dematerilzed rapidly during acid treatment in primary teeth and the hybrid layer was thicker for primary than permanent dentin ; thus , decreasing the available bonding .
this study was done to evaluate the interfacial morphology and bond strength produced by the three - step , two - step and single - step bonding systems when applied to dentin of primary teeth .
seventy - two caries - free , unrestored , extracted , primary molars were collected for the study . the teeth were stored in distilled water .
the dentin of occlusal surfaces of all teeth was exposed using a hand piece and straight diamond fissure burs ( shofu inc , kyoto , japan ) with water and air spray and then abraded using 600 grit abrasive papers . the bonding agents included in the study were : 
 group i : scotchbond multipurpose ( 3 m , espe , st .
paul , usa)group ii : adh se ( vivadent ) , ontario , canada)group iii : futurabond ( voco , cuxhaven , germany)group iv : optibond all - in - one ( kerr , schweiz , germany ) group i : scotchbond multipurpose ( 3 m , espe , st .
paul , usa ) group ii : adh se ( vivadent ) , ontario , canada ) group iii : futurabond ( voco , cuxhaven , germany ) group iv : optibond all - in - one ( kerr , schweiz , germany ) all the bonding agents were applied as per instructions given by the manufacturer ; following which the teeth were divided into two groups : thirty - two caries - free primary teeth were acquired and the occlusal surface of each tooth was ground to expose the dentin , following which bonding agents were applied ; then blocks of composite resin ( esthet x hd , dentsply ) were built using custom - made hollow split molds .
the sectioned halves were then embedded into self - cure resin , keeping the resin - dentin interface exposed ( for examination ) .
the samples were sequentially polished with 600 and 1200 grit abrasive papers and sof - lex finishing and polishing systems .
all the samples were immersed in 4% naocl ( for deproteination ) for 20 min , and then in 20% hydrochloric acid ( for demineralization ) for 30sec .
all the samples were then sequentially dehydrated in ascending grades of ethanol i.e. 60%,70% , 80% and 90% alcohol for 20 min each and in 100% alcohol for 1 hr . all samples were dried and mounted on aluminum stubs that were then placed in a vacuum chamber , sputter - coated with gold layer and observed under a sem ( leo 430 , philips , england ) .
( leo 430 , philips , england ) at a magnification of 1000x and a series of photographs were taken .
forty caries - free primary teeth were acquired and mounted into self - curing acrylic resin .
the prepared samples were then randomly divided into four subgroups , according to the bonding system to be applied ; specimens of each group were stored separately to prevent mixing between the groups .
a custom made hollow split mold with an internal diameter of 2 mm and height of 5 mm was held on adhesive treated surface of the specimens and then composite resin ( esthet x hd , dentsply , new york , usa ) was placed inside the mold , condensed and light - cured ( gnatus , brazil ) for 40 sec . following curing , the metal mold was split and removed .
all the specimens were immersed in water for 24 hours . then tensile bond strength was measured using an instron universal testing machine ( instron 5566 , usa ) at a crosshead speed of 0.5 mm / min .
all data were subjected to statistical analysis using spss ( statistical package for social sciences ) version 15.0 statistical analysis software and the kruskal - wallis test and dunn s test .
thirty - two caries - free primary teeth were acquired and the occlusal surface of each tooth was ground to expose the dentin , following which bonding agents were applied ; then blocks of composite resin ( esthet x hd , dentsply ) were built using custom - made hollow split molds .
the sectioned halves were then embedded into self - cure resin , keeping the resin - dentin interface exposed ( for examination ) .
the samples were sequentially polished with 600 and 1200 grit abrasive papers and sof - lex finishing and polishing systems .
all the samples were immersed in 4% naocl ( for deproteination ) for 20 min , and then in 20% hydrochloric acid ( for demineralization ) for 30sec .
all the samples were then sequentially dehydrated in ascending grades of ethanol i.e. 60%,70% , 80% and 90% alcohol for 20 min each and in 100% alcohol for 1 hr .
all samples were dried and mounted on aluminum stubs that were then placed in a vacuum chamber , sputter - coated with gold layer and observed under a sem ( leo 430 , philips , england ) .
( leo 430 , philips , england ) at a magnification of 1000x and a series of photographs were taken .
forty caries - free primary teeth were acquired and mounted into self - curing acrylic resin .
the prepared samples were then randomly divided into four subgroups , according to the bonding system to be applied ; specimens of each group were stored separately to prevent mixing between the groups .
a custom made hollow split mold with an internal diameter of 2 mm and height of 5 mm was held on adhesive treated surface of the specimens and then composite resin ( esthet x hd , dentsply , new york , usa ) was placed inside the mold , condensed and light - cured ( gnatus , brazil ) for 40 sec . following curing ,
all the specimens were immersed in water for 24 hours . then tensile bond strength was measured using an instron universal testing machine ( instron 5566 , usa ) at a crosshead speed of 0.5 mm / min .
all data were subjected to statistical analysis using spss ( statistical package for social sciences ) version 15.0 statistical analysis software and the kruskal - wallis test and dunn s test .
the measurements were done on the photographs by means of a standard vernier caliper ( tresna , china ) using the measurement scale given on the photograph and the following findings were revealed : 
 group i ( scotchbond multipurpose ) had a thick hybridized complex and very long tags ( 12.20 to 89.10 m ) ; few small side branches were also seen in a large number of specimens.there was good contact between the resin tags and the hybrid layer and the resin tags were conical .
conical shapes of the upper part of the tags ensured a good seal as the hybrid layer extended into the walls of the dentinal tubules , leading to hybridization of the walls ( fig 1).group ii ( adh se ) had an irregular hybridized complex and thin numerous tubules were empty .
length of the tags varied between 0 to 23.30m ( fig 2).group iii ( optibond all - in - one ) showed a thin irregular hybridized complex and at some points of the interface the complex was absent .
the tags lengths varied between 0 to 22.50m , broken in some places with numerous empty tubules ( fig 3).group iv ( futurabond nr ) showed a thin but continuous hybridized complex with tag lengths that varied between 0 to 35.80m ( fig 4 ) .
evaluations were also done on two photo - micrographs by randomly assessing the tag - length at five different locations .
group i ( scotchbond multipurpose ) had a thick hybridized complex and very long tags ( 12.20 to 89.10 m ) ; few small side branches were also seen in a large number of specimens .
there was good contact between the resin tags and the hybrid layer and the resin tags were conical .
conical shapes of the upper part of the tags ensured a good seal as the hybrid layer extended into the walls of the dentinal tubules , leading to hybridization of the walls ( fig 1 ) .
group ii ( adh se ) had an irregular hybridized complex and thin numerous tubules were empty .
group iii ( optibond all - in - one ) showed a thin irregular hybridized complex and at some points of the interface the complex was absent .
the tags lengths varied between 0 to 22.50m , broken in some places with numerous empty tubules ( fig 3 ) .
group iv ( futurabond nr ) showed a thin but continuous hybridized complex with tag lengths that varied between 0 to 35.80m ( fig 4 ) .
evaluations were also done on two photo - micrographs by randomly assessing the tag - length at five different locations .
observations of tag length in different adhesives revealed that scotchbond had the most widely spread values with a range from 12.20 to 89.10m while optibond aio had the most narrow range ( 0 to 22.50 , table 1 ) ; the intergroup differences were found to be statistically significant ( p<0.001 ) .
table 2 shows that scotchbond had significantly better results as compared to other three groups .
the measurements were done on the photographs by means of a standard vernier caliper ( tresna , china ) using the measurement scale given on the photograph and the following findings were revealed : 
 group i ( scotchbond multipurpose ) had a thick hybridized complex and very long tags ( 12.20 to 89.10 m ) ; few small side branches were also seen in a large number of specimens.there was good contact between the resin tags and the hybrid layer and the resin tags were conical .
conical shapes of the upper part of the tags ensured a good seal as the hybrid layer extended into the walls of the dentinal tubules , leading to hybridization of the walls ( fig 1).group ii ( adh se ) had an irregular hybridized complex and thin numerous tubules were empty .
length of the tags varied between 0 to 23.30m ( fig 2).group iii ( optibond all - in - one ) showed a thin irregular hybridized complex and at some points of the interface the complex was absent .
the tags lengths varied between 0 to 22.50m , broken in some places with numerous empty tubules ( fig 3).group iv ( futurabond nr ) showed a thin but continuous hybridized complex with tag lengths that varied between 0 to 35.80m ( fig 4 ) .
evaluations were also done on two photo - micrographs by randomly assessing the tag - length at five different locations .
group i ( scotchbond multipurpose ) had a thick hybridized complex and very long tags ( 12.20 to 89.10 m ) ; few small side branches were also seen in a large number of specimens .
there was good contact between the resin tags and the hybrid layer and the resin tags were conical .
conical shapes of the upper part of the tags ensured a good seal as the hybrid layer extended into the walls of the dentinal tubules , leading to hybridization of the walls ( fig 1 ) .
group ii ( adh se ) had an irregular hybridized complex and thin numerous tubules were empty .
group iii ( optibond all - in - one ) showed a thin irregular hybridized complex and at some points of the interface the complex was absent .
the tags lengths varied between 0 to 22.50m , broken in some places with numerous empty tubules ( fig 3 ) .
group iv ( futurabond nr ) showed a thin but continuous hybridized complex with tag lengths that varied between 0 to 35.80m ( fig 4 ) .
evaluations were also done on two photo - micrographs by randomly assessing the tag - length at five different locations .
observations of tag length in different adhesives revealed that scotchbond had the most widely spread values with a range from 12.20 to 89.10m while optibond aio had the most narrow range ( 0 to 22.50 , table 1 ) ; the intergroup differences were found to be statistically significant ( p<0.001 ) .
table 2 shows that scotchbond had significantly better results as compared to other three groups .
the clinical success of a restorative material such as composite resins depends on effective sealing of margins of the restoration , enhancing retention and preventing postoperative sensitivity and microleakage .
sound teeth were included in our study as in carious teeth the dentin is decayed and destructed because of the disease process which might influence the results [ 16 , 17 ] .
the preparations were performed on occlusal surfaces , following the methodology described by van meerbeek et al ,   and perdigao et al .
an important characteristic associated with occlusal surfaces used as a substrate for bonding is that a flat cut exposes dentin in different depths in relation to the pulp chamber and this method also allows standardization for the direction of the dentin tubules .
the evaluation of the resin tags in this study showed a great variance between the groups .
three - step bonding agents showed increased number and density of the resin tags along with greater depth of penetration .
bond strength of scotchbond multipurpose was significantly higher ( p<0.001 ) compared to futurabond nr , adh se and optibond - all - in - one .
sbs ( shear bond strength ) is influenced by the length and density of resin tags ; which is a depiction of greater penetration .
courson also supported the above - mentioned finding ; he found that the bond strength of scotchbond multipurpose was greater than the self - etch primers and one - step adhesives but the difference was not significant in primary teeth . while , when the same bonding agents were used on permanent teeth the difference was statistically significant .
confirmation to these results were shown by bolanos - carmona in 2008 who stated that the values of sbs were higher when a total - etch system was compared to other bonding agents .
the sbs of xeno iii increased after pre - etching was included as an additional step .
the bond strength of three - step bonding agents is higher than the self - etching bonding agents or the total - etch bonding agents .
agostini et al . evaluated the bond strength of three self - etching primers ( prompt l - pop - espe , clearfil se bond - kuraray , etch and prime - degussa ) and one adhesive with total etch technique ( prime and bond nt - dentsply ) to deciduous teeth . when observations were done on enamel surface it was seen that prime and bond nt demonstrated significantly higher bond strengths . while clearfil se bond showed the best results with dentin of primary teeth .
clearfil se belongs to the family of self - etching primers and contains 10-methacryloxydecyl dihydrogen phosphate ( 10-mdp ) as functional monomer ; which is dissolved in water .
the excellent performance may be attributed to the additional chemical interaction of hydroxyapatite with the functional monomer 10-mdp .
apart from the total removal of smear layer , another factor which may be responsible for the better penetration of the resin monomers in the three - step bonding agents is that after phosphoric acid application on dentin for a brief etching period , due to the buffering action of the mineral phase of dentin a lower diffusion flux of hydrogen ions has been observed [ 2325 ] .
this phenomenon may contribute to better penetration of adhesives in the demineralized dentin , increasing the bonding efficacy .
courson et al . stated that water occupying the interfibrillar spaces is lost by evaporation during air - drying after etching and rinsing , resulting in a collapse of the proteic network .
puppin - rontani have confirmed the above results in deciduous teeth by testing scotch - bond multipurpose and prime and bond which contains a similar concentration of phosphoric acid .
the testing was done for varying time intervals and the results showed that higher values of sbs were reported at 7 and 15 sec of application as compared to a 20 sec application period . improved bond strength after application of three - step bonding agents may be a result of more dense and long resin tags produced at the bonding interface ; which was also shown in our study .
complete removal of smear layer occurs by means of etching which leads to better penetration of the adhesive ; but at the same time the step of etching also leads to removal of water from in - between the collagen fibrils .
, more research is required to develop newer bonding agents with incorporation of properties of both total - etching systems and self - etching systems .
the longest resin tags were seen in scotch - bond multipurpose ( 12.20 to 89.10 m ) , which was significantly greater than the other three groups .
the bond strength of scotchbond multipurpose was significantly higher ( p<0.05 ) compared to futurabond nr , adh se , and opti - bond all - in - one .
 objective : to evaluate the interfacial morphology and the bond strength produced by the three - step , two - step and single - step bonding systems in primary teeth.materials and methods : occlusal surfaces of 72 extracted human deciduous teeth were ground to expose the dentin . 
 the teeth were divided into four groups : ( a ) scotchbond multipurpose ( 3 m , espe ) , ( b ) adh se ( vivadent ) , ( d ) optibond all - in - one ( kerr ) and ( e)futurabond nr ( voco , cuxhaven , germany ) . the adhesives were applied to each group following the manufacturer s instructions . 
 then , teeth from each group were divided into two groups : ( a ) for viewing interfacial morphology ( 32 teeth ) , with 8 teeth in each group , and ( b ) for measurement of bond strength ( 40 teeth ) , with 10 teeth in each group . 
 all the samples were prepared for viewing under sem . 
 the statistical analysis was done using spss version 15.0 software.results:observational measurement of tag length in different adhesives revealed that scotchbond had the most widely spread values with a range from 12.20 to 89.10m while optibond aio had the narrowest range ( 0 to 22.50 ) . 
 the bond strength of scotchbond multipurpose was significantly higher ( 7.47441.88763 ) ( p<0.001 ) as compared to futurabond nr ( 3.80701.61345 ) , adhe se ( 4.4478  1.3820 ) and optibond - all - in - one ( 4.48561.07925).conclusion : the three - step bonding system showed better results as compared to simplified studied bonding systems 
INTRODUCTION
MATERIALS AND METHODS
Interfacial morphology assessment group:
Preparation of samples:
Sample preparation for scanning electron microscope (SEM) viewing:
Shear bond strength group:
RESULTS
Interfacial morphology
DISCUSSION
CONCLUSION