however , controversy exists regarding the role of collagen fibrils on resin adhesion and sealing efficiency of dbas .
nanoleakage , a microscopic leakage inside the thickness of ridl , was first described by sano et al .
, collagen matrix degradation occurs either by the breakdown of the polymer phase or collagen fibrils in the hybrid layer .
also , exposure of collagen matrix of dentin by acid etching may activate matrix metalloproteinase ( mmp ) . in order to prevent this biodegradation ,
various techniques have been employed such as the demineralized collagen removal and the use of mmps inhibitors .
the use of sodium hypochlorite ( naocl ) to deproteinize acid - etched dentin has several disadvantages .
it forms a fragility zone and is cytotoxic with a bad taste and odor . as the dentinal depth increases , the negative impact of naocl increases .
newer techniques for removing collagen network include deproteinizing enzymes such as collagenase or bromelain enzyme .
bromelain is a proteolytic enzyme ( proteases ) which belongs to a group of protein - digesting enzymes obtained commercially from the fruit or stem of pineapple .
the function of proteases is to catalyze the hydrolysis of proteins to give amino acids .
bromelain enzyme can reduce nanoleakage after collagen removal as compared to naocl but there has not been a study to see its effectiveness in improving the bond strength .
therefore , the aim of this study was to assess the deproteinizing effect of bromelain enzyme and compare it with 5% naocl on shear bond strength before application of the adhesive system .
thirty extracted human premolar teeth were taken and stored in 0.1% thymol solution until they were subjected to use .
samples were wet ground on the occlusal surface using a series of silicon carbide discs to prepare flat superficial dentin .
group 1 : teeth were etched with 37% phosphoric acid ( scotchbond multi - purpose etchant , 3 m ) for 15 s and then rinsed with water and blot dried .
group 2 : teeth were etched with 37% phosphoric acid for 15 s , rinsed with water , blot dried and deproteinized with bromelain enzyme ( bangalore sales corporation ) for 1 min .
group 3 : teeth were etched with 37% phosphoric acid for 15 s , rinsed with water , blot dried and deproteinized with 5% naocl ( nice chemicals pvt . ltd . ) for 1 min .
fifth generation dba , adper single bond 2 ( 3 m espe ) , was applied according to manufacturer 's instructions . upon completion of the adhesive procedures ,
the resin composite filtek z-250 ( 3 m espe ) was inserted into the plastic tube and light - polymerized .
all specimens were stored at 37c in water for 24 h before testing , to simulate the oral environment .
after storage , the specimens were transferred to the universal testing machine individually and then subjected to shear bond strength analysis at a crosshead speed of 1.0 mm / min .
data were statistically analyzed using one - way analysis of variance for mean comparison among groups and unpaired t - test for mean comparison of shear bond strength between groups at a significance level of 0.05 .
the statistical analysis was performed using spss version 12.0.1 for windows ( spss inc . ,
data were statistically analyzed using one - way analysis of variance for mean comparison among groups and unpaired t - test for mean comparison of shear bond strength between groups at a significance level of 0.05 .
the statistical analysis was performed using spss version 12.0.1 for windows ( spss inc . ,
the bond strength results were significantly influenced by the application of bromelain enzyme ( p < 0.05 ) as shown in table 1 .
statistically significant differences were not demonstrated in control group and naocl treated group as shown in table 2 .
mean value of shear bond strength in mpa of all three tested groups ( n = 30 ) mean comparison of shear bond strength ( mpa ) between groups
adhesion to tooth structure depends on various factors including the type of the adhesive system , tooth structure , load cycling , and surface contaminations .
inadequate adhesion of composite resin restorations to dentin results in reduced retention , microleakage , and finally recurrent caries .
progressive loss of bond strength of etch - and - rinse adhesives has been demonstrated in some studies .
one of the factors that is responsible for this degradation is incomplete infiltration of resin monomers into unsupported collagen networks after acid etching with strong acids which produces a zone of collagen without any support of either minerals or resins in the base of the hybrid layer .
questions have been raised whether bond strength tests can predict the clinical behavior of adhesively bonded composite resin restorations since they do not represent the complex clinical failure mechanism . in micro tensile tests ,
the fracture does not start at the weakest part of the bond , but always at the insertion point of the load .
the preference for the conventional shear test instead of micro shear test is justified because they are easy to perform , requiring minimal equipment , and specimen preparation .
also , a comparative bond strength study involving three adhesive systems has shown similarities between  macro  and  micro  counterparts regarding material ranking .
numerous studies have evaluated the effects of naocl on adhesion process , and different results have been achieved .
this decrease in bond strength can be attributed to the generation of oxygen after the disintegration of naocl into nacl and o2 .
these reactive residual free radicals in naocl - treated dentin compete with the propagation of vinyl - free radicals generated during light activation of the adhesive system , resulting in premature chain termination and incomplete polymerization .
however , naocl may exert different effects on bond strength depending on the chemical structure of the adhesive system and the type of the initiator in the adhesive system used . in this present study ,
bromelain enzyme performed better which could be because of reduced nanoleakage as shown by the previous study .
it has better effectiveness in removing unsupported collagen matrix as compared to naocl , and lower nanoleakage is seen
. this could be because of the depletion of collagen from the surface of acid - etched dentin resulting in increased permeability of dentin substrate due to the enlargement of dentinal tubules near the outer dentin surface .
the surface energy of the dentin is improved , because the hydroxyapatite has a high surface energy substrate while collagen has a low energy surface , and this leads to enhanced diffusion of adhesive monomers through dentin .
also , the dentin is very porous and rough with many lateral branches of tubules which are detectable in main tubules , which may contribute to the increase in the spreading of adhesive monomers through dentin .
within the limitations of the present study , it was concluded that removal of unsupported collagen fibers with bromelain enzyme after acid etching results in improved bond strength .
 aims : to assess the deproteinizing effect of bromelain enzyme and compare it with 5% sodium hypochlorite ( naocl ) on shear bond strength before application of the adhesive system.materials and methods : a total of 30 extracted human premolars were divided into three groups , each one consisted of 10 teeth . 
 the occlusal surface was wet ground to expose superficial dentin . in group 1 , teeth were etched ; in group 2 , teeth were etched and deproteinized with bromelain enzyme ; in group 3 , teeth were etched and deproteinized with 5% naocl . upon completion of the adhesive procedures , 
 resin composite was inserted into the plastic tube and light - polymerized . 
 all specimens were stored at 37c in water for 24 h , and the specimens were transferred to the universal testing machine , and then subjected to shear bond strength analysis at a crosshead speed of 1.0 mm / min.statistical analysis used : data were statistically analyzed using one - way analysis of variance and unpaired t - test at a significance level of 0.05 . 
 the statistical analysis was performed using spss version 12.0.1 for windows ( spss inc . 
 , chicago , il , usa).results : the bond strength results were significantly influenced by the application of bromelain enzyme . 
 statistically significant differences were not demonstrated in control group and naocl - treated group . 
 the highest bond strength was seen in bromelain enzyme - treated group.conclusions:within the limitations of the present study , it was concluded that removal of unsupported collagen fiber with bromelain enzyme after acid etching results in improved bond strength . 
INTRODUCTION
MATERIALS AND METHODS
Statistical analysis
RESULTS
DISCUSSION
CONCLUSION
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Conflicts of interest