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 .