mineral trioxide aggregate ( mta ) is a biocompatible material with high sealing ability which has been used for various purposes in endodontics , including root end filling , sealing of perforations , treatment of teeth with open apices , and as a pulp capping agent [ 13 ] . the color of original mta ( grey mta or gmta ) was grey and it had a potential of tooth discoloration . because of this disadvantage , white mta ( wmta ) introduced in order to this problem be solved . asgary et al .   showed that the major differences in chemical component between wmta and gmta are concentrations of al2o3 , mgo , and feo . found that there were no significant differences in pulp responses to both types of mta when used as a pulp capping agent in dog 's teeth . holland et al .   also found that the mechanisms of action of wmta and gmta are similar . however , matt et al .   found that gmta has significantly less leakage than wmta when used as an apical barrier . although wmta was developed to solve the problem of tooth discoloration produced by gmta , several studies have reported tooth discoloration after using both kinds of mta [ 915 ] . this effect limits mta application in treatment of perforations , pulp capping , pulpotomy , and as an apical barrier in aesthetically sensitive areas . bonding to dentin is one of the most significant advances in the past fifty years . the success of this kind of bonding has depended more on creative chemistry than etching with some materials such as phosphoric acid . many generations of dentin bonding agents ( dbas ) have been produced . with new advances in new material 's technology , bonding to dentin has been reported to be favorable . the purpose of this study was to evaluate the effect of the application of dba before usage of mta to prevent tooth discoloration . fifty freshly extracted single - rooted human maxillary central and lateral incisors were used in this study . the teeth were clinically and radiographically examined to be free of caries , cracks , restoration , and calcification . external surfaces of the teeth were cleaned with curettes and stored in a physiologic saline solution until usage . the pulp tissue was removed by using barbed broaches ( dentsply maillefer , tulsa , okla , usa ) . working length was determined visually with stainless steel hand files ( dentsply maillefer , tulsa , okla , usa ) trough the canal until the tip was seen at apical foramen and working length calculated by subtracting 1  mm from this length . each canal was prepared by using k - files ( dentsply maillefer , tulsa , okla , usa ) and gates - glidden drills ( dentsply maillefer , tulsa , okla , usa ) in a step back manner . irrigation was carried out by using 2.5% naocl . after drying root canal with paper points , master gutta - percha was placed at canal and confirmed radiographically , and teeth were obturated using gutta - percha ( arya dent , tehran , iran ) and ah - plus sealer ( dentsply , konstanz , germany ) by lateral condensation technique . then the extruded cones were cut off 3  mm below the orifice and compacted vertically . teeth were randomly divided into five groups . in groups wmta and gmta , 3  mm of white and grey mta ( mta angelus , londrina , pr , brazil ) plug was placed in root canal below the orifice , respectively . in groups dba + wmta and dba + gmta , two layers of dba ( clearfil se bond , kurary , okayama , japan ) was applied in access cavity and light cured for 40 seconds and then 3  mm of wmta and gmta was placed in root canal below the orifice , respectively . after complete cleaning of the access cavity , a moistened cotton pellet was placed in access cavity and coronal access was sealed with coltozol ( coltene , altstatten , switzerland ) for 24 hours . after that , temporary filling was removed and the teeth were restored with resin composite ( z100 , 3 m , usa ) . the last 10 teeth served as control , with no dba and mta and restored with resin composite .   at the baseline , color measurement of all teeth was recorded with a colorimeter ( minolta cr-300 ; minolta , osaka , japan ) . measurements were repeated 3 times for each specimen , and the mean values of data were calculated . the teeth were kept in artificial saliva for 6 months , whereas artificial saliva was replenished each two weeks . at this point , color readings were made using the colorimeter in the manner described for baseline readings . the calculation of the color variation e * between the 2 color measurements is as follows : 
						 ( 1)e=[(l)2+(a)2+(b)2]1/2.l refers to the lightness coordinate with value ranging from zero ( black ) to 100 ( white ) . the values a and b are chromaticity coordinates in the red - green axis and the yellow - blue axis , respectively . preliminary analysis with kolmogorof - smirnov test was used to confirm the normal distribution of the data . the results were analyzed by t - test , with the significance level defined as  = 0.05 . all teeth showed discoloration after 6 months . the mean discoloration after 6 months is shown in figure 1 . the mean tooth discoloration in wmta group was significantly more than dba + wmta and control groups . there was no significant difference between dba + wmta group and control group in mean discoloration . the teeth in gmta group also showed significantly more discoloration than dba + gmta and control groups . there was no significant difference between gmta group and wmta group in mean tooth discoloration , as well as for dba + gmta and dba + wmta groups . mta has been recognized as a bioactive material   that is hard tissue conductive , hard tissue inductive , and biocompatible , so the applications of this material have been rapidly expanding in dentistry . despite such good characteristic , mta has some drawbacks including discoloration potential , difficult handling properties , long setting time , high cost , and absence of a known solvent .   our study revealed that when gmta was placed below the root canal orifice , the crown of teeth , especially in the cervical area , showed significant tooth discoloration after 6 months . this result was coinciding with other studies that showed tooth discoloration after using gmta [ 9 , 10 , 13 ] . due to the potential discoloration of teeth treated with gmta , the manufacturer introduced a new formula of mta with an off - white color . however , this study showed that the application of wmta may also cause tooth discoloration . this can be attributed to the fact that although the concentration of carborundum ( al2o3 ) , periclase ( mgo ) , and feo has been lowered in wmta compared to gmta , these metal oxides are still present in wmta and can cause tooth discoloration . jacobovitz and de lima   used wmta for the treatment of inflammatory internal root resorption . they observed grey discoloration of teeth after 20 months . boutsioukis et al .   which examined the efficiency of two techniques for removal of wmta from root canals also reported dark discoloration of most mta fillings . application of two layers of dba before using mta may prevent tooth discoloration produced by both wmta and gmta . this can be related to the sealing ability of dba that seals dentinal tubules in access cavity and below the orifice before mta application . this process makes a surface that prevents any contamination and remaining mta powder in the access cavity during insertion . remaining powder has a potential to degrade and make colorant material such as feo .   according to the results of this study , it can be recommended to seal dentinal tubules by dba before using both mtas to prevent further tooth discoloration . since dba may interfere with proper sealing ability of mta or have a possible interference with the release of calcium via dentin tubules , it is advisable to conduct other studies to evaluate the effect of dba on these properties of mta .