reality always seems to fall short of conceptualization , a variety of researchers in dentistry , brought a longstanding dream to fruition by providing adhesives that could effectively bond composites to dentin as well as enamel .
however , it is difficult to achieve , as the bonding process to dentin is very different from that for enamel .
dentin is more humid and more organic than enamel , which makes bonding a difficult task , unlike enamel , which is mostly inorganic in nature . in an increasing attempt to simplify clinical procedures in adhesive dentistry ,
the most common approach was to shorten the adhesive system 's application time and reduce the number of steps .
the three - step etch - and - rinse systems have proved to be a gold standard .
self - etching systems were introduced and purported important advantages compared to the etch - and - rinse systems .
the intensity of the interaction of self - etching adhesive systems with dentin was mostly dependant on the acidity and aggressiveness of the primer used .
the total - etch technique simultaneously removes the smear layer from both the enamel and dentin surface , followed by the application of one bottle agent that combines the primer and adhesive in one solution .
the self - etch adhesives use acidic adhesive comonomers that simultaneously demineralize and infiltrate into the dentin ; adhesive stability is related to the effective coupling of the comonomers that simultaneously demineralize and infiltrate into the dentin .
self - etching systems are less sensitive to technique as compared to systems requiring separate acid conditioning and rinsing steps . despite the presence of short resin tags ,
the present day , all - in - one single bottle of self - etching adhesive systems are highly hydrophilic polymers , which are permeable to water movement and are said to be using the most promising adhesive approach .
hence , the purpose of this study is to evaluate the morphology of the resin - dentin interface of the new total- and self - etching systems and to assess the quality of the hybrid layer formed .
the present study was conducted at the department of conservative dentistry and endodontics , a.b .
forty , freshly extracted caries - free human molars were collected and stored in saline at room temperature .
protocols in cross - infection control as per occupational safety and health administration regulations in storing , surfacing , and utilization were observed .
the 40 extracted teeth stored in saline were retrieved and class v cavities ( 2 mm  1.5 mm  1.5 mm ) were prepared in selected teeth using a no .
245 tungsten carbide bur ; the length of the cutting end of the bur was approximately 3 mm .
after preparation of class v cavities in the 40 teeth , they were randomly divided into four groups of 10 specimens each . in group
i , the prepared dentinal surfaces of the teeth were etched with etchant , 35% phosphoric acid , for 30 sec , and washed .
the surface was slightly blotted with gauze to produce a visible moist dentin surface to produce moist dentin .
the resultant moist surfaces were treated with a total etching bonding agent ( xp bond , dentsply ) and cured as per manufacturer 's instructions . in group ii , the prepared dentinal surfaces of the teeth were etched with etchant , 35% phosphoric acid , for 30 sec , and washed .
the surface was slightly blotted with gauze to produce a visible moist dentin surface to produce moist dentin .
the resultant moist surfaces were treated with total etching bonding agent ( adper single bond 2 , 3 m espe ) and cured as per manufacturer 's instructions . in group iii ,
the resultant moist dentin surfaces were treated with one - step self - etching bonding agent ( adper easy one , 3 m espe ) , by applying a uniform layer , avoiding pooling , gently agitating with a microbrush for 20 sec , and allowing them to dry in a mild air stream for 10 sec .
a second layer was applied with a microbrush , avoiding any pooling , and it was allowed to dry in a mild air stream for 10 sec . the bonding agent was light cured for 20 sec . in group iv , all the prepared dentinal surfaces of the teeth were cleaned and blotted with gauze to produce visible moist dentin .
the resultant moist dentin surfaces were treated with a one - step self - etching bonding agent ( xeno v , dentsply ) by applying a uniform layer , avoiding pooling , and allowing them to dry in a mild air stream for 10 sec .
the class v preparations were then restored with hybrid composite in an incremental technique of 1 mm each , curing each layer for 40 sec .
the restored specimens were then subjected to thermocycling ( 500 cycles , 5 to 55 c , 30 sec dwell time ) .
following thermocycling , the teeth were sectioned longitudinally through the restoration in a buccolingual plane .
two sections were made per tooth , producing two specimens , which were polished with an increased grit of silicon carbide paper , under running water .
the specimens were demineralized using 6n hcl for 30 sec and deproteinized with 2.5% naocl ( sodium hypochlorite ) for 10 min , to enable examination of the interface and left to dry for 24 h. the specimens were gold sputtered and morphological evaluation of the resin - dentin interface was conducted using scanning electron microscopy under various magnifications .
group i  scanning electron microscopic evaluation showed a clearly recognizable hybrid layer , which was thick , defined , and continuous . the thickness of the hybrid layer ranged between 3 - 8 m .
however , few areas showing cohesive failure were seen within the resin and the resin - composite interface . the length of the resin tags ranged between 10 - 25 m .
group i  sem image of xp bond with dentin group ii  a scanning electron microscopic evaluation of the specimens showed a clearly recognizable thin hybrid layer .
the hybrid was clearly defined and the thickness ranged between 3 - 6 m . however , there were areas where there was a visible region of separated layers showing adhesive failure between the dentin and resin interface .
there were few areas of separation between the composite and resin interface indicating a cohesive failure .
few voids were seen on the resin tags and they showed few lateral tags [ figure 2 ] .
group ii  sem image of adper single bond 2 with dentin group iii  a scanning electron microscopic evaluation of specimens showed a thin hybrid layer that was not clearly distinct and no discontinuity was noticed .
few resin tags were observed with a range of 1 - 2 m . there were no voids observed and
group iii  sem image of adper easy one with dentin group iv  a scanning electron microscopic evaluation showed no evidence of a hybrid layer .
the junction between the resin - dentin appeared to be tight , thin , and continuous with no adhesive or cohesive failure .
minimal formation of microtags was noticed under higher magnification with a range of 0.6 - 1.5 m . there were no evident lateral tags .
some of the dentinal tubules appeared to be obstructed by smear plugs [ figure 4 ] .
group i  scanning electron microscopic evaluation showed a clearly recognizable hybrid layer , which was thick , defined , and continuous . the thickness of the hybrid layer ranged between 3 - 8 m .
however , few areas showing cohesive failure were seen within the resin and the resin - composite interface . the length of the resin tags ranged between 10 - 25 m .
group i  sem image of xp bond with dentin group ii  a scanning electron microscopic evaluation of the specimens showed a clearly recognizable thin hybrid layer .
the hybrid was clearly defined and the thickness ranged between 3 - 6 m . however , there were areas where there was a visible region of separated layers showing adhesive failure between the dentin and resin interface .
there were few areas of separation between the composite and resin interface indicating a cohesive failure .
few voids were seen on the resin tags and they showed few lateral tags [ figure 2 ] .
group ii  sem image of adper single bond 2 with dentin group iii  a scanning electron microscopic evaluation of specimens showed a thin hybrid layer that was not clearly distinct and no discontinuity was noticed .
few resin tags were observed with a range of 1 - 2 m . there were no voids observed and
group iii  sem image of adper easy one with dentin group iv  a scanning electron microscopic evaluation showed no evidence of a hybrid layer .
the junction between the resin - dentin appeared to be tight , thin , and continuous with no adhesive or cohesive failure .
minimal formation of microtags was noticed under higher magnification with a range of 0.6 - 1.5 m . there were no evident lateral tags .
some of the dentinal tubules appeared to be obstructed by smear plugs [ figure 4 ] .
hybridization of dental hard tissues provides a new frontier in modern adhesive dentistry because : it creates a new , advanced , multifunctional dental material that can be prepared in the subsurface of teeth .
the hybrid layer refers to the structure formed in the dental hard tissues by demineralization of the surface and sub - surface , followed by infiltration of monomers and subsequent polymerization .
dentin is the fundamental substrate of restorative dentistry , and its properties and characteristics are key determinants of nearly all restorative , preventive , and disease processes of the teeth .
dentin is a complex hydrated composite of dentinal tubules , mineralized matrix , collagen , and dentinal fluid .
dentinal tubules are not smooth , and have many lateral branches and microchannels that connect to adjacent tubules and permit fluid movement .
thus , variations in permeability arise from regional differences , tubular irregularities , mineral deposits , organic components of odontoblastic processes , collagen , and dentinal fluid . from the bonding perspective , the hydrated structure and variability of the dentin in its characteristics of permeability , cause substantial difficulties . unless the bonding agent can displace or is miscible in the fluid
, it will be difficult to achieve a stable , long - lasting bond . as bonding is created by impregnation of dentin substrate by blends of resin monomers ,
the stability of the bonded interface relies on the creation of a compact and homogenous hybrid layer . in etch and rinse strategy , bonding monomers impregnate the porous etched substrate ; and stable bonds can be achieved if the etched substrate is fully infiltrated by the monomers .
conversely , the self - etch approach uses acidic adhesive comonomers that simultaneously demineralize and infiltrate into the dentin .
adhesive stability is related to the effective coupling of the comonomers with an infiltrated substrate .
self - etching systems are generally less technique sensitive compared to systems that utilize separate acid conditioning and rinsing steps .
collapse of the air - dried , demineralized collagen is prevented as the smear layer - retained dentin is simultaneously demineralized and polymerized in situ . despite the presence of short resin tags ,
the specimen preparation in the present study involved the preparation of class v cavities for three reasons : first , because it involves three dental hard structures , that is , enamel , dentin , and cementum .
second , a class v cavity simulates a clinical situation of higher stress due to a higher c - factor , and third , due to exposure to varied fluids in the cervical region of the tooth .
radovic i , vulicevic zr , and godoy gf chose class v cavities , because samples prepared in this manner involved the difficulties in achieving the suggestive width of the adhesive layer with a higher c - factor and higher stress contraction stress .
the number of cycles used in the present study was 500 ( 5 to 55 c with 30 sec dwell time ) .
radovic i , vulicevic zr , and godoy gf also used 500 cycles , as it was based on the current iso standard . in the present study , 6n hydrochloric acid was used for demineralization and 2.5% sodium hypochlorite for deproteinization .
this ensured optimal exposure of the resin tags and hybrid layer and enabled viewing under the scanning electron microscope .
nakabayashi and pashley also stated that the study of the usual procedure for specimen preparation under sem involved preparation of polished cross - sections of the bonded interface followed by an acid challenge with 5n hydrochloric acid for 30 sec to demineralized , followed by 1% sodium hypochlorite for 10 min .
this procedure exposed the resin tags to their full length and demarcated the bottom of the hybrid layer .
the present study is in accordance with the study done by radovic , vulicevic , and garcia godoy , who also used 6n hydrochloric acid and 2.5% sodium hypochlorite for demineralization and deproteinization .
scanning electron microscopy is one of the first and most widely used tools to study the interfacial characteristics and process of bonding .
scanning electron microscopy , although very useful , induces shrinkage artifacts in the specimens during processing and in the high vacuum of the microscope , unless the specimens in the resin are perfectly infiltrated with resin .
the usual procedure involves the preparation of polished cross - sections of the bonded interface followed by an acid challenge with 6n hydrochloric acid for 30 sec to demineralize , followed by 2.5% sodium hypochlorite for 10 min .
this procedure exposes the resin tags to their full length and demarcates the bottom of the hybrid layer . in the present study
it was observed that , there was shrinkage artifacts created , which was attributed to the fact that the specimen preparation procedures in scanning electron microscopy induced artifacts .
perdigao and carvalho had investigated and found that specimens prepared for scanning electron microscopy underwent air drying , hexamethyldisilazane , or peldri ii drying .
it was concluded that specimens prepared by air drying showed shrinkage that occurred during specimen preparation and this influenced the exact dimensions of the morphology .
voids seen in the resin tags of the specimens in group i and group ii represent remnants of water , in the form of droplets , which were trapped in the adhesive before polymerization . air drying over a long time reduces the number of water droplets , but total drying is difficult to achieve . during the desiccation procedure , for gold sputtering the specimens , water droplets might have evaporated , leaving voids .
van landuyt et al , in their investigation , found that the number of water droplets was significantly reduced after strong air drying , although they did not completely disappear . in the present study
there is a highly significant difference in the thickness of the hybrid layer and the length of the resin tags formed between the total - etch adhesives ( group i and group ii ) and self - etch adhesives ( group iii and group iv ) . the total - etch adhesives use the etch - and - rinse strategy , thus removing the smear layer and subsequent infiltration of monomers and polymerization .
the primary bonding mechanism is a diffusion - based process leading to the production of a hybrid resin - dentin interdiffusion zone .
in group i , xp bond has been used , which contains t- butanol ; and in group ii , adper single bond 2 ethanol is used , which requires the  wet bonding technique and thus there are lesser regions of adhesive failure seen .
this explains that although the adhesive ( xp bond and adper single bond 2 ) produces resin tags that are long , with thicker hybrid layers , adhesive failure and cohesive failure are seen due to the technique sensitivity of the bonding mechanism .
gentle postconditioning drying of the etched dentin still guarantees effective bonding for ethanol - based adhesives .
however , true chemical bonding is unlikely , because the functional monomers have a weak affinity to the hydroxyapatite - depleted collagen .
group iii and group iv , self - etch adhesives showed thin hybrid layers , with fewer microtags .
however , there is no evidence of adhesive or cohesive failures observed with self - etch adhesives .
the self - etch approach had an important advantage in that the infiltration of the resin occurred simultaneously with the self - etching process resulting in a uniform interdiffusion zone .
de munck et al , in their study concluded that the thickness of the hybrid layer was , however , much smaller than that produced by the strong self - etch adhesive or the etch - and - rinse total - etch approach .
it was proven to be minor in importance with regard to the actual bonding effectiveness .
however , the drawback of the all - in - one adhesive is its behavior as a semi - permeable membrane allowing movement of water across bonded interfaces , which may in the long term lead to potential hydrolytic degradation
. the limitations of conventional scanning electron microscopy compared to more sophisticated methods of examining tooth restoration interfaces have been recognized .
however , regardless of the method used ( sem / tem ) , no correlation between the hybrid layer width and bond strength of the adhesive systems could be determined .
within the limitations of the present study , however , the scanning electron microscopy method can provide basic information , which points to the possible specific features of the interface , which need to be examined closely . in vitro studies depend on variable parameters , such as , sample collection , surfacing , aging , thermocycling , and hurdles in specimen preparation , for scanning electron microscopy .
there being a clinical correlation with long - term studies on the effects of aging , thermal effects on the bonding process need to be examined closely .
from the present study it is concluded that : xp bond , among the total - etch bonding agents , showed good penetration of resin into the dentin by the presence of long resin tags and a thick hybrid layer .
xeno v , among the self - etch bonding agents , did not show a clear hybrid layer with few resin tags , but showed a continuous adaptation along the dentin surface .
the adaptation of self - etch adhesives to the resin- dentin interface was good without voids or separation of phases ; showing a thin , continuous hybrid layer .
it was concluded that such an adaptation of resin with dentin tissue , as in the case of self - etch adhesives , was required for better treatment outcome to reduce postoperative sensitivity .
 aim : the purpose of this study is to evaluate the resin - dentin interface , quality of the hybrid layer of total - etching and self - etching adhesive systems under scanning electron microscopy ( sem).materials and methods : class v cavities were prepared in 40 extracted human molars . in group 
 i xp bond ( dentsply ) , in group ii adper single bond ii ( 3 m espe ) , in group iii adper easy one ( 3 m espe ) , and in group iv xeno v ( dentsply ) were applied . 
 teeth were restored with resin composite , subjected to thermocycling , and sectioned in buccolingual plane . 
 the samples were demineralized using 6n hcl , for 30 sec , and deproteinized with 2.5% naocl for 10 min , gold sputtered , and viewed using a scanning electron microscope.results:among the total - etch systems used , the xp bond showed a clear , thick hybrid layer , with long resin tags and few voids . among the self - etch adhesive systems , 
 the xeno v did not show a clearly recognizable hybrid layer , but there were no voids and continuous adaptation was seen with the dentin.conclusion:the adaptation of self - etch adhesives to the resin - dentin interface was good without voids or separation of phases ; showing a thin , continuous hybrid layer . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
Qualitative evaluation of the resin-dentin interface (SEM images)
DISCUSSION
CONCLUSION