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 .
 
 objective . determination of the effect of dentin bonding agent ( dba ) on the prevention of tooth discoloration produced by mineral trioxide aggregate ( mta ) . methods . 
 50 teeth were endodontically treated and after removal of 3  mm of obturating materials were divided into five groups . in white mta ( wmta ) and 
 grey mta ( gmta ) groups , these materials were placed in root canal below the orifice . in dba + wmta and dba + gmta groups , 
 dbas were applied in the access cavity . 
 then , 3  mm of wmta and gmta was placed . 
 the last 10 teeth served as control . 
 all of teeth were restored and color measurement was recorded for each specimen at this time and 6 months later . results . 
 the mean tooth discoloration in wmta and gmta groups was significantly more than dba + wmta and dba + gmta groups , respectively . 
 there was no significant difference between dba + wmta and dba + gmta groups and control group . 
 conclusion . 
 application of dba before mta may prevent tooth discoloration . 
1. Introduction
2. Materials and Methods
3. Results
4. Discussion