the self - etching approach has been proposed in an effort to simplify the dentin / enamel bonding systems .
the elimination of separate etching and rinsing steps simplified the bonding technique and has been responsible for the increased popularity of these systems in daily practice33 .
self - etching adhesive systems differ from etch - and - rinse adhesives in several aspects , such as the initial ph , type of acidic monomer , number of bottles and steps , concentration of water and solvents , and the hydrophilicity of the bonding layer .
they are classified into two- or one - step systems depending on the number of procedures required for bonding , as well as in mild , moderate and acidic systems depending on their initial ph31 .
the clinical application of these systems would be even further promising if their performance were at least similar to that of three - step etch - and - rinse adhesive systems , which are considered clinically favorable on bonding to enamel and dentin23 because both substrates need to be hybridized in most clinical situations . as the ph of self - etching systems is not similar to that of phosphoric acid used in the etch - and - rinse approach , increasing concern about their performance on intact
is slightly ground during a bevel or cut during cavity preparation , which provides a more receptive substrate for bonding13 .
however , there are cases such as bonding of orthodontic brackets or conservative and preventive restorative procedures , where bonding should be made on intact enamel . therefore , it is clinically important to determine the performance of such systems on ground vs. unground enamel substrates .
some studies have demonstrated that self - etching adhesives can provide resin - enamel bond strength values as high as those obtained by phosphoric acid treatment , as long as the bonding is performed on ground enamel13 .
however , other authors have not observed any difference on the performance of self etching systems when applied on ground and unground enamel10 .
one of the differences that might have accounted for the conflicting results of these two studies was the way enamel was prepared . while in the former study13 enamel
was prepared with a high - speed diamond bur , silicon carbide paper was used the latter study10 .
it is likely that the use of high - speed diamond bur may expose deeper enamel surface than the use of silicon carbide paper .
based on that , we hypothesize that the kind of enamel preparation might affect the bond strength of self - etching adhesive systems to enamel .
therefore , the purpose of this study was to evaluate the bond strength and etching pattern of enamel after application of two - step self - etching and etch - and - rinse adhesive systems to unground , bur - prepared and silicon carbide paper - treated enamel .
the null hypothesis tested was that the bonding performance of the self - etching adhesives does not vary for the studied parameters .
this study was approved by the institutional review board of the dental school ( faculty of dentistry , university of so paulo , fousp ) under protocol number 208/03 .
fifty - four extracted third molars were obtained and immersed in 0.5% chloramine at 4c during 7 days5 before the beginning of the laboratorial setting .
the teeth were then sectioned in a mesiodistal direction in order to obtain tooth halves that were randomly distributed to each experimental condition .
the obtained buccal and lingual surfaces were cleaned with a pumice and water and examined under a stereomicroscope to ensure that they were free of surface cracks , decalcification or any sign of previous grinding .
the occlusal third of the buccal and lingual surfaces were usually outside the bonding area due to their inclination .
the tooth halves were then randomly assigned to 3 groups according to the type of enamel surface preparation : group 1 : pumice prophylaxis ( no grinding was done ) ; group 2 : after prophylaxis , a wheel medium - grit diamond bur ( # 4142 , particle size ca 100 mm , kg sorensen , barueri , sp , brazil ) was applied on enamel surface using a high - speed handpiece with water coolant . this procedure created 0.5-mm - deep grooves on the surface , which was then flattened with a tapered round - end fine - grit diamond bur ( # 4138 , particlesize ca 46 mm , kg sorensen ) ; group 3 : after prophylaxis , the enamel was ground with a 60-grit silicon carbide paper14,30 under water cooling for 60 s. each group was further divided into six subgroups according to the adhesive system used .
four two - step self - etching adhesive systems were used : a mild system ( ph = 2.0 ) ( clearfil se bond - cse ; kuraray medical inc , tokyo , japan ) , two intermediate strong systems ( ph = 1.5 ) ( optibond solo plus self - etch primer - op ; kerr co , orange , ca , usa and adhese - ad ; ivoclar vivadent , schaan , liechtenstein ) and an acidic system ( ph<1 ) ( tyrian self priming etchant - ty ; bisco inc , schaumburg , il , usa ) . the ph of each system is provided by their manufacturers and have also been measured in a previous study14 .
two and three - step etch - and - rinse adhesive systems - adper scotchbond multi - purpose plus - sbmp and adper single bond - sb ( 3m / espe , st paul , mn , usa ) , respectively - were used as controls .
all adhesive systems were applied under controlled environmental conditions ( 24c/60% relative humidity ) by a single operator , following the bonding protocols summarized in figure 1 .
special care was taken to ensure that the enamel surfaces were adequately coated by monomer after solvent evaporation . in the event matte enamel
was observed , an additional coat of adhesive was applied to produce shiny surfaces prior to light - curing with a vip unit ( 600 mw / cm , bisco inc , schaumburg , il , usa ) .
next , a 3-mm - high composite resin ( filtek z250 , 3m / espe ) block was incrementally built up on the treated enamel surface and each 1-mm thick increment was light cured individually .
after storage in distilled water at 37c for 24 h , the specimens were sectioned longitudinally in both " x " and " y " directions across the bonded interface with a diamond saw in a labcut 1010 machine ( extec ; enfield , ct , usa ) to obtain approximately 5 - 7 bonded sticks per tooth with a cross - sectional area of about 0.8 mm .
the number of prematurely debonded sticks ( pd ) per tooth during specimen preparation was recorded .
each stick was examined with a stereomicroscope ( x10 ) in order to check the inclination of the bonding interfaces in the four sides of each stick .
the cross - sectional area of each stick was measured with a digital caliper accurate to the nearest 0.01 mm ( absolute , mitutoyo , tokyo , japan ) and recorded for calculation of the bond strength .
each stick was then individually fixed to a custom - made testing jig and tested in microtensile strength to failure in a universal testing machine ( emic , so jos dos pinhais , pr , brazil ) running at a crosshead speed of 0.5 mm / min .
the bond failure modes were evaluated at x400 with light stereomicroscope ( hmv- 2 , shimadzu , tokyo , japan ) and classified as cohesive ( failure exclusively within enamel or composite resin ) and adhesive / mixed ( failure at resin / enamel interface or mixed with cohesive failure of the neighboring substrates ) . a bond strength index ( bsi )
the bs index is a weighted mean assuming the relative contribution of the possible mode of failures , according to the following equation ( values in mpa ) : 
 ba / m mean bond strength of sticks with adhesive / mixed fracture pattern ; 
 % a / m percentage of sticks with adhesive / mixed fracture pattern ; 
 cd cohesive strength of enamel ; % d percentage of sticks that failed cohesively in enamel ; 
 cr cohesive strength of resin ; 
 % r percentage of sticks that failed cohesively in resin ; 
 bds bond strength attributed to sticks that spontaneously debonded during preparation ; % ds percentage of sticks debonded during preparation .
the cohesive strength of the composite resin and the cohesive strength of enamel are considered as the mean value of all the specimens ( from a single tooth ) that failed in that manner .
the mean value attributed to specimens that failed prematurely during preparation is arbitrary , and corresponded to approximately half of the minimum bond strength value that could be measured in this study .
the microtensile bsis were subjected to a two - way repeated measures analysis of variance and tukey 's post - hoc test ( =0.05 ) for pair - wise comparisons .
the effect of conditioning with 35% phosphoric acid and the self - etching primers on ground and unground buccal or lingual enamel surfaces was analyzed .
enamel surfaces that were not treated with the conditioners and bur - cut and silicon carbide paper - treated surfaces were also observed for comparison purposes .
teeth ( n=2/condition ) were bisected longitudinally in a mesiodistal direction to provide two halves .
a deep lingual guiding slit was prepared with a diamond bur to facilitate subsequent fracture of the etched surfaces .
free enamel surfaces were cleaned with pumice / water slurry - prophylaxis ( group 1 ) . after cleaning , the enamel surfaces from group 2 were bur - cut and those from group 3 were ground with wet 60-grit silicon carbide paper for 60 s , as described for the microtensile bond strength testing .
enamel surfaces from groups 1 , 2 and 3 were treated with 35% phosphoric acid and self - etching primers as described in figure 1 .
phosphoric acid - etched enamel was rinsed with water spray for 15 s , while enamel etched with self - etching primers was rinsed with alternate baths of ethanol and acetone ( 20 s each ) in order to remove the monomers6 .
thereafter , the same specimens were gently split with a hammer and scalpel blade along the pre - formed slits to provide a sagittal view of the etched enamel .
specimens were stored in a desiccator containing silica gel for 12 h. following that , they were mounted on aluminum stubs with colloidal silver and gold sputter - coated ( balzers scd 050 sputter coater , bal - tec , germany ) to be observed under a scanning electron microscope ( philips xl30 ; eindhoven , the netherlands ) at 15 kv of accelerating voltage .
both the buccal and lingual etched surfaces as well as the sagittally fractured surfaces of the same tooth were examined .
fifty - four extracted third molars were obtained and immersed in 0.5% chloramine at 4c during 7 days5 before the beginning of the laboratorial setting .
the teeth were then sectioned in a mesiodistal direction in order to obtain tooth halves that were randomly distributed to each experimental condition .
the obtained buccal and lingual surfaces were cleaned with a pumice and water and examined under a stereomicroscope to ensure that they were free of surface cracks , decalcification or any sign of previous grinding .
the occlusal third of the buccal and lingual surfaces were usually outside the bonding area due to their inclination .
the tooth halves were then randomly assigned to 3 groups according to the type of enamel surface preparation : group 1 : pumice prophylaxis ( no grinding was done ) ; group 2 : after prophylaxis , a wheel medium - grit diamond bur ( # 4142 , particle size ca 100 mm , kg sorensen , barueri , sp , brazil ) was applied on enamel surface using a high - speed handpiece with water coolant .
this procedure created 0.5-mm - deep grooves on the surface , which was then flattened with a tapered round - end fine - grit diamond bur ( # 4138 , particlesize ca 46 mm , kg sorensen ) ; group 3 : after prophylaxis , the enamel was ground with a 60-grit silicon carbide paper14,30 under water cooling for 60 s. each group was further divided into six subgroups according to the adhesive system used .
four two - step self - etching adhesive systems were used : a mild system ( ph = 2.0 ) ( clearfil se bond - cse ; kuraray medical inc , tokyo , japan ) , two intermediate strong systems ( ph = 1.5 ) ( optibond solo plus self - etch primer - op ; kerr co , orange , ca , usa and adhese - ad ; ivoclar vivadent , schaan , liechtenstein ) and an acidic system ( ph<1 ) ( tyrian self priming etchant - ty ; bisco inc , schaumburg , il , usa ) . the ph of each system is provided by their manufacturers and have also been measured in a previous study14 .
two and three - step etch - and - rinse adhesive systems - adper scotchbond multi - purpose plus - sbmp and adper single bond - sb ( 3m / espe , st paul , mn , usa ) , respectively - were used as controls .
all adhesive systems were applied under controlled environmental conditions ( 24c/60% relative humidity ) by a single operator , following the bonding protocols summarized in figure 1 .
special care was taken to ensure that the enamel surfaces were adequately coated by monomer after solvent evaporation . in the event matte enamel
was observed , an additional coat of adhesive was applied to produce shiny surfaces prior to light - curing with a vip unit ( 600 mw / cm , bisco inc , schaumburg , il , usa ) .
next , a 3-mm - high composite resin ( filtek z250 , 3m / espe ) block was incrementally built up on the treated enamel surface and each 1-mm thick increment was light cured individually .
after storage in distilled water at 37c for 24 h , the specimens were sectioned longitudinally in both " x " and " y " directions across the bonded interface with a diamond saw in a labcut 1010 machine ( extec ; enfield , ct , usa ) to obtain approximately 5 - 7 bonded sticks per tooth with a cross - sectional area of about 0.8 mm .
the number of prematurely debonded sticks ( pd ) per tooth during specimen preparation was recorded .
each stick was examined with a stereomicroscope ( x10 ) in order to check the inclination of the bonding interfaces in the four sides of each stick .
the cross - sectional area of each stick was measured with a digital caliper accurate to the nearest 0.01 mm ( absolute , mitutoyo , tokyo , japan ) and recorded for calculation of the bond strength .
each stick was then individually fixed to a custom - made testing jig and tested in microtensile strength to failure in a universal testing machine ( emic , so jos dos pinhais , pr , brazil ) running at a crosshead speed of 0.5 mm / min .
the bond failure modes were evaluated at x400 with light stereomicroscope ( hmv- 2 , shimadzu , tokyo , japan ) and classified as cohesive ( failure exclusively within enamel or composite resin ) and adhesive / mixed ( failure at resin / enamel interface or mixed with cohesive failure of the neighboring substrates ) . a bond strength index ( bsi )
the bs index is a weighted mean assuming the relative contribution of the possible mode of failures , according to the following equation ( values in mpa ) : 
 ba / m mean bond strength of sticks with adhesive / mixed fracture pattern ; 
 % a / m percentage of sticks with adhesive / mixed fracture pattern ; 
 cd cohesive strength of enamel ; % d percentage of sticks that failed cohesively in enamel ; 
 cr cohesive strength of resin ; 
 % r percentage of sticks that failed cohesively in resin ; 
 bds bond strength attributed to sticks that spontaneously debonded during preparation ; % ds percentage of sticks debonded during preparation .
the cohesive strength of the composite resin and the cohesive strength of enamel are considered as the mean value of all the specimens ( from a single tooth ) that failed in that manner . the mean value attributed to specimens that failed prematurely during preparation is arbitrary , and corresponded to approximately half of the minimum bond strength value that could be measured in this study .
the microtensile bsis were subjected to a two - way repeated measures analysis of variance and tukey 's post - hoc test ( =0.05 ) for pair - wise comparisons .
the effect of conditioning with 35% phosphoric acid and the self - etching primers on ground and unground buccal or lingual enamel surfaces was analyzed .
enamel surfaces that were not treated with the conditioners and bur - cut and silicon carbide paper - treated surfaces were also observed for comparison purposes . teeth ( n=2/condition ) were bisected longitudinally in a mesiodistal direction to provide two halves .
a deep lingual guiding slit was prepared with a diamond bur to facilitate subsequent fracture of the etched surfaces .
free enamel surfaces were cleaned with pumice / water slurry - prophylaxis ( group 1 ) . after cleaning , the enamel surfaces from group 2 were bur - cut and those from group 3 were ground with wet 60-grit silicon carbide paper for 60 s , as described for the microtensile bond strength testing .
enamel surfaces from groups 1 , 2 and 3 were treated with 35% phosphoric acid and self - etching primers as described in figure 1 .
phosphoric acid - etched enamel was rinsed with water spray for 15 s , while enamel etched with self - etching primers was rinsed with alternate baths of ethanol and acetone ( 20 s each ) in order to remove the monomers6 .
thereafter , the same specimens were gently split with a hammer and scalpel blade along the pre - formed slits to provide a sagittal view of the etched enamel .
specimens were stored in a desiccator containing silica gel for 12 h. following that , they were mounted on aluminum stubs with colloidal silver and gold sputter - coated ( balzers scd 050 sputter coater , bal - tec , germany ) to be observed under a scanning electron microscope ( philips xl30 ; eindhoven , the netherlands ) at 15 kv of accelerating voltage .
both the buccal and lingual etched surfaces as well as the sagittally fractured surfaces of the same tooth were examined .
the mean cross - sectional area ranged from 0.73  0.2 mm and no difference was detected among the treatment groups ( p>0.05 ) .
the mean bsis ( mpa ) and standard deviations , as well as the number of tested sticks and the number of prematurely debonded specimens are shown in table 1 .
neither the main factor surface treatment ( p=0.48 ) nor the interaction adhesive x surface treatment were statistically significant ( p=0.06 ) .
the highest resin - enamel mean bond strength value was observed for the two etch - and - rinse adhesive systems ( sbmp and sb ) .
op , ad and ty showed the lowest resin - enamel mean bond strength values , which were statistically different from all others adhesives .
cse showed the highest mean bond strength value among the self - etching adhesive systems ( table 2 ) .
the bond failures modes were predominantly of the mixed type . scanning electron microscopy ( sem ) micrographs of ground and unground enamel surfaces treated with phosphoric acid and the self - etching primers are shown in figures 3 to 7 . the effect of prophylaxis , diamond bur or sic paper treatments was also analyzed ( figure 2 ) .
enamel surface after prophylaxis was very smooth , with small and shallow grooves and few exposed enamel rods .
an apparently rougher surface than that created by prophylaxis with more grooves could be seen after enamel grinding with 60-grit sic paper .
diamond bur - prepared enamel showed larger and deeper grooves than those created by the other methods of preparation as well as an apparently rougher smear layer .
regardless of the surface treatment , only the diamond bur removed the prismless enamel ( figure 2 ) .
sem micrographs of the enamel surfaces etched with 35% phosphoric acid revealed little difference among the methods of preparation ( figure 3 ) . in all specimens ,
the smear layer was totally removed by phosphoric acid and enamel rods were exposed and etched .
the selective etching of prism cores ( type 1 pattern ) and prism peripheries ( type 2 pattern ) along with areas without selective demineralization could be observed in the same specimen .
the enamel surfaces following treatment with cse showed a predominant smooth surface with shallow depressions along the enamel surface ( figure 4 ) . when mild self - etching primer was used on prepared surfaces
the etching pattern created by the cse primer was more evident on the intact enamel surface .
the etching appearance of ad and op presented similar morphological features ( figures 5 and 6 respectively ) .
the ph of these moderate self - etching primers allowed them to remove the smear layer created by the sic paper and by the diamond bur in a more effective way than the mild cse primer .
areas of un - etched and smooth surfaces were intercalated with some deep and large grooves on enamel .
the demineralization pattern of these systems was more pronounced when they were applied on the diamond bur - prepared surface , i.e. , prismatic enamel surface . unlike the enamel microporosities produced by 35% phosphoric acid , the porosities produced by the most acidic self - etching primer , ty , were less numerous , deeper and larger ( figure 7 ) .
it was also evident the presence of fine surface roughening on the enamel surface with an uneven conditioning pattern .
regardless of the preparation method and the ph of the primer , none of the evaluated self - etching primers was able to expose the enamel rods as did the 35% phosphoric acid .
the mean cross - sectional area ranged from 0.73  0.2 mm and no difference was detected among the treatment groups ( p>0.05 ) .
the mean bsis ( mpa ) and standard deviations , as well as the number of tested sticks and the number of prematurely debonded specimens are shown in table 1 .
neither the main factor surface treatment ( p=0.48 ) nor the interaction adhesive x surface treatment were statistically significant ( p=0.06 ) .
the highest resin - enamel mean bond strength value was observed for the two etch - and - rinse adhesive systems ( sbmp and sb ) .
op , ad and ty showed the lowest resin - enamel mean bond strength values , which were statistically different from all others adhesives .
cse showed the highest mean bond strength value among the self - etching adhesive systems ( table 2 ) .
scanning electron microscopy ( sem ) micrographs of ground and unground enamel surfaces treated with phosphoric acid and the self - etching primers are shown in figures 3 to 7 .
the effect of prophylaxis , diamond bur or sic paper treatments was also analyzed ( figure 2 ) .
enamel surface after prophylaxis was very smooth , with small and shallow grooves and few exposed enamel rods .
an apparently rougher surface than that created by prophylaxis with more grooves could be seen after enamel grinding with 60-grit sic paper .
diamond bur - prepared enamel showed larger and deeper grooves than those created by the other methods of preparation as well as an apparently rougher smear layer .
regardless of the surface treatment , only the diamond bur removed the prismless enamel ( figure 2 ) .
sem micrographs of the enamel surfaces etched with 35% phosphoric acid revealed little difference among the methods of preparation ( figure 3 ) . in all specimens , the smear layer was totally removed by phosphoric acid and enamel rods were exposed and etched .
the selective etching of prism cores ( type 1 pattern ) and prism peripheries ( type 2 pattern ) along with areas without selective demineralization could be observed in the same specimen .
the enamel surfaces following treatment with cse showed a predominant smooth surface with shallow depressions along the enamel surface ( figure 4 ) . when mild self - etching primer was used on prepared surfaces
the etching pattern created by the cse primer was more evident on the intact enamel surface .
the etching appearance of ad and op presented similar morphological features ( figures 5 and 6 respectively ) .
the ph of these moderate self - etching primers allowed them to remove the smear layer created by the sic paper and by the diamond bur in a more effective way than the mild cse primer .
areas of un - etched and smooth surfaces were intercalated with some deep and large grooves on enamel .
the demineralization pattern of these systems was more pronounced when they were applied on the diamond bur - prepared surface , i.e. , prismatic enamel surface . unlike the enamel microporosities produced by 35% phosphoric acid , the porosities produced by the most acidic self - etching primer , ty , were less numerous , deeper and larger ( figure 7 ) .
it was also evident the presence of fine surface roughening on the enamel surface with an uneven conditioning pattern .
regardless of the preparation method and the ph of the primer , none of the evaluated self - etching primers was able to expose the enamel rods as did the 35% phosphoric acid .
the null hypothesis was not totally accepted because the bond strength and the morphology of surface enamel varied depending on the adhesive system .
the morphological structure of the intact peripheral enamel surface is different from that of the middle and inner enamel layer .
it has been widely reported that the superficial layer of enamel is less reactive to acids than the middle layer . as the acidity of the self - etching adhesive systems
are relatively lower than that of phosphoric acid treatment , the presence of this superficial enamel layer has been partially blamed for the lower performance of the self - etching systems in this substrate3,11,13,15,16 .
this study demonstrated that the 0.5-mm - deep grinding produced by the diamond bur was the only treatment able to homogeneously remove the prismless enamel .
pumice prophylaxis and sic paper abrasion did not remove this layer . despite these morphological results ,
it was impossible to distinguish under sem differences in the surface micromorphology of ground ( sic paper and diamond bur ) and unground enamel after conditioning with phosphoric acid , since all treatments depicted the presence of enamel rods
. this may be one of the reasons why differences between enamel surface preparations were not found in the phosphoric acid group .
this finding is in accordance with other studies that evaluated the performance of etch - and- rinse adhesives on ground and unground enamel10,13,22,27 . when the morphological findings of the same adhesive system were compared on ground and unground enamel some differences in the etching pattern
the two moderate ( op and ad ) and the most acidic ( ty ) self - etching systems demineralized the ground enamel surface more effectively than the intact enamel . despite these variations ,
some studies have demonstrated that enamel abrasion with diamond burs can improve the bond strength of self - etching systems to enamel13,27 .
other studies , in agreement with the present findings , have observed that the bond strength to unground or ground enamel does not differ7,10 or it is dependent on the adhesive system evaluated22 .
this apparent controversy means that the lower performance of self - etching adhesive systems on enamel3,11,13,15,16 can not be solely attributed to the presence of the prismless enamel .
variation in adhesive viscosity , surface tension , acidity of the self - etch system , chemical interaction of acidic monomers with enamel34 , water concentration9 , cohesive strength of the adhesives24,28 are important features to be considered .
this is somewhat true that although a more retentive etching pattern was observed for the moderate ( op and ad ) and particularly for the most acidic ( ty ) adhesives in comparison to the mild cse , higher bond strength values were not observed for ty .
the ty adhesive applied on diamond bur - prepared enamel produced an etching pattern that resembled that of 35% phosphoric acid etching , although the delineation of enamel rods was not as evident as that created by phosphoric acid .
contrary to these findings , other studies have demonstrated that more acidic self - etching systems were able to produce an extremely defined pattern of enamel etching , similar to phosphoric acid conditioning1,8 even when applied on intact enamel surface21 .
it is likely that differences in the composition of adhesive systems employed in these studies could have played a role on this apparent controversy .
in addition to the concentration and the type of acidic monomers that directly alter the acidity of self - etching adhesive systems18 , differences in the water concentration among in the systems can also contribute to partial or total dissociation of the acid functionalities18 .
it has been demonstrated that increasing water concentration from 10 to 20 vol% resulted in an increase in the degree of ionization of an acidic monomer , lowering the ph of the self - etching primer solution and further increasing their depth of demineralization9 .
sem examination of the surface morphology of enamel has shown that cse produced a very mild etching effect8 , with the bulk of the surface remaining unetched .
this means that among the adhesive systems tested in the present study , cse has only superficial interaction with enamel and a reduced potential for micromechanical interlocking . despite these morphological findings , cse achieved the highest bond strength values among the self - etching adhesive systems .
indeed , this finding is in accordance with previous studies , which demonstrated that mild self - etching adhesive systems perform well when compared to more acidic systems either in intact enamel or dentin4,11,12,15 .
it is clear from the micromorphological findings of this study that the use of a stronger acid resulted in a more dramatic dissolution and a more defined etching pattern , as previously reported21 .
low bond strength values are usually reported for more acidic self - etching adhesive systems when they are compared under microtensile bond strength approach4,11,31 .
the absence of relationship between the depth of demineralization and the strength of bonds produced by the more aggressive self - etching and etch - and - rinse adhesive systems on enamel shown in the present investigation is consistent with previous works10,21,29 .
as already reported , this means that other factors , apart from the etching pattern , may have a more important role on the bond strength values .
for instance , cse is a self - etching primer that contains 10- methacryloxydecyl dihydrogen phosphate ( 10-mdp ) as functional monomer dissolved in water to result in a ph of around 2 .
the excellent performance of this system in vitro 
 4,12,15 and in vivo investigations32 may be partially attributed to the additional chemical interaction of hydroxyapatite with the functional monomer 10-mdp34 .
this can theoretically contribute to the actual adhesive potential to enamel that consists of nearly only mineral substance , with which 10-mdp can chemically react .
20 , using a modeling approach , demonstrated that the theoretical strength of the resin - dentin bond strength should be proportional to the strength of the adhesive used to infiltrate demineralized dentin .
this was also confirmed in some laboratorial studies24,28 . when bonding to dentin , a strong relationship between the resin- dentin bond strengths and the mechanical properties of cured resin was observed for the self - etching adhesive systems24 .
the high initial ph of more acidic systems appear to dramatically weaken the bonding performance , either via chemical interacting with the adhesive layer placed next26 or via the presence of solvents within the polymer , which render the adhesive layer thinner and may weaken the polymer formed2 , thus compromising their bond strength to enamel .
as the acidity of self - etching adhesives is increased with the incorporation of higher concentration of hydrophilic and acidic monomers , the problems that are associated with acid - base incompatibility and water permeability become even more accentuated .
the acidic components of these adhesives may also adversely interact with the composite 's photoinitiator and so weaken the bonding complex2,6 .
another point to be considered is the reported low hydrolytic stability of methacrylates in acidic solutions17,19 . according to some authors17,19 , the ester portion of functional methacrylate , such as hema , used for a self - etching primer can become hydrolyzed in aqueous solutions when the ph values were below 2 .
they also suggested that the hydrolysis rate of the ester portion of methacrylates is also dependent on the storage temperature , which means that the self - etching primer should be kept refrigerated when not in use .
although phosphorus - containing monomers , such as mdp , are said to be more stable in acid environment , they should also be kept refrigerated when not in use .
in summary , it may be concluded that preparation of enamel surface ( prophylaxis , diamond bur or sic - paper ) did not influence the bonding performance of the self - etching adhesive systems evaluated in this study .
the highest bond strength values were observed for the etch - and - rinse adhesive systems .
 objectives : to assess the bond strength and the morphology of enamel after application of self - etching adhesive systems with different acidities . 
 the tested hypothesis was that the performance of the self - etching adhesive systems does not vary for the studied parameters.material and methods : composite resin ( filtek z250 ) buildups were bonded to untreated ( prophylaxis ) and treated ( burcut or sic - paper ) enamel surfaces of third molars after application of four self - etching and two etch - and - rinse adhesive systems ( n=6/condition ) : clearfil se bond ( cse ) ; optibond solo plus self - etch ( op ) ; adhese ( ad ) ; tyrian self priming etching ( ty ) , adper scotchbond multi - purpose plus ( sbmp ) and adper single bond ( sb ) . 
 after storage in water ( 24 h/37c ) , the bonded specimens were sectioned into sticks with 0.8 mm2 cross - sectional area and the microtensile bond strength was tested at a crosshead speed of 0.5 mm / min . 
 the mean bond strength values ( mpa ) were subjected to two - way anova and tukey 's test ( =0.05 ) . 
 the etching patterns of the adhesive systems were also observed with a scanning electron microscope.results:the main factor adhesive system was statistically significant ( p<0.05 ) . 
 the mean bond strength values ( mpa ) and standard deviations were : cse ( 20.53.5 ) , op ( 11.32.3 ) , ad ( 11.22.8 ) , ty ( 11.13.0 ) , sbmp ( 21.94.0 ) and sb ( 24.93.0 ) . 
 different etching patterns were observed for the self - etching primers depending on the enamel treatment and the ph of the adhesive system.conclusion:although there is a tendency towards using adhesive systems with simplified application procedures , this may compromise the bonding performance of some systems to enamel , even when the prismless enamel is removed . 
INTRODUCTION
MATERIAL AND METHODS
Microtensile Bond Strength
Enamel Etching Pattern
RESULTS
Microtensile Bond Strength
Enamel Etching Pattern
DISCUSSION
CONCLUSION