in some clinical situations , such as root canal overinstrumentation , apical resorption and teeth with open apices , there may be extrusion of the filling material , either gutta - percha , root canal sealer or both , due to the difficulty or impossibility to lock the master gutta - percha cone . in these situations ,
fabrication of an apical plug with calcium hydroxide and , more recently , with mineral trioxide aggregate ( mta ) has been suggested2,4,13,21,25,26 .
mta was introduced in the early 1990 's as an experimental material developed by dr .
mahmoud torabinejad at loma linda university , usa . this material was originally indicated as a retrograde filling material for use in endodontic surgery and cases of intraradicular and furcal perforations18 . since then
, it has been used in different clinical situations , such as communicating internal and external resorptions , as capping material in mechanically exposed pulps , as intracoronal barrier during internal bleaching of endodontically treated teeth , and as apical plug in case of difficulty to lock the master gutta - percha cone4 .
these indications of mta are related to the possibility of use in moist environments , as in most aforementioned indications , and mainly to its biocompatibility4,26 .
the sealing ability of mta apical plug and its thickness have been investigated by several authors2,13,16,17,20,21,26 .
four - millimeter - thick plugs have been shown to be the most efficient with respect to root canal sealing ability and resistance to displacement13,20,21,26 .
all of these studies have sought an alternative to mta apical plug as well as its most appropriate thickness .
wucherpfennig and green27 ( 1999 ) have called the attention to the fact that mta and portland cement were similar materials .
other studies were conducted and confirmed this similarity by means of microbiological , chemical , physical and biological behavior tests1,5,8,10,11,15,23 .
the purpose of this study was to evaluate the sealing ability of apical plugs made of white and gray mta - angelus ( angelus solues em odontologia , londrina , pr , brazil ) and white portland cement ( votorantim cimentos , votorantim , so paulo , sp , brazil ) placed via the root canal and having different thicknesses ( 2 , 5 and 7 mm ) .
this study was approved by the institutional review board of the dental school of bauru , university of so paulo , brazil .
ninety extracted human single - rooted teeth with intact roots and completely formed apices were used .
the teeth were obtained from the files of the department of endodontics of the dental school of bauru and were kept in 10 % aqueous formalin solution .
the dental crowns were sectioned at the cementoenamel junction with a low - speed diamond saw ( kg sorensen , so paulo , sp , brazil ) under continuous water spray to obtain access to the root canal .
the root canal length was determined by inserting a size 15 k - file ( dentsply - maillefer instruments sa , ballaigues , switzerland ) into the canal until its tip reached the apical foramen . the working length was established by subtracting 1 mm from this measurement .
the stepback technique was employed and the root canal was flared using a size 60 k - file to the working length .
instrumentation was aided by irrigation with 1 ml of 1% sodium hypochlorite solution ( biodinmica qumica e farmacutica ltda , ibipor , pr , brazil ) alternated with the sequence of instruments , followed by a final flushing with 1 ml of sterile water .
the teeth were assigned to 3 groups ( n=30 ) , according to the material used for fabrication of the apical plugs : group a = placement of gray mta - angelus plugs ; group b = placement of white mta - angelus plugs ; group c = placement of white portland cement plugs .
the groups were further subdivided into groups of 10 teeth each , according to the thickness of the apical plugs , namely 2 , 5 and 7 mm ( table 1 ) . before standardization of the foraminal opening
, the roots were made impermeable by application of a layer of epoxy adhesive ( araldite - ciba - geigy s.a .
, taboo da serra , sp , brazil ) , followed by two coats of nail polish ( cosbra cosmeticos ltda . , so paulo , sp , brazil ) .
the foramen diameter was standardized by inserting the 40 k - file 1 mm beyond the apical foramen , so that only the apical opening would not be impermeable . for fabrication of the apical plugs ,
the tested materials were applied with a size 4 lentulo spiral ( dentsply - maillefer instruments sa , ballaigues , switzerland ) at the apical end of the root , trying to fill it completely .
the material was condensed with the tip of a size 40 k - file involved in cotton for achievement of the plug19 .
next , using a size 40 k - file with a rubber stop positioned 2 , 5 and 7 mm shorter than the root canal length , the excess material was removed for fabrication of 2- , 5- and 7-mm - thick apical plugs , respectively .
finally , the root canal walls were cleaned with the tip of an instrument wrapped in moist cotton .
then , the canal entrances were sealed with epoxy adhesive and nail polish , and the roots were immersed in 0.2 % rhodamine b solution ( labsynth produtos para laboratrios ltda , diadema , sp , brazil ) at ph 7.0 for 72 hours at 37c . after this period , the roots were removed from the dye , washed in running water for 24 hours , had the impermeable coating scraped away and were washed for additional 12 hours .
the roots were then sectioned longitudinally in a buccolingual direction for exposure of the apical plugs , photographed with a digital camera ( canon eos rebel 300 d ) and analyzed by image tool software ( university of texas health science center , san antonio , tx , usa ) .

 table 2 shows the percent marginal leakage for the different materials for each plug thickness .
tables 3 , 4 and 5 show the results of the kruskal - wallis statistical test for comparison among groups a ( mta - angelus gray ) , b ( mta - angelus white ) and c ( white portland cement ) with respect to the plug thicknesses ( 2 , 5 and 7 mm ) . a statistically significant difference ( p<0.05 )
was observed between groups a and b as to the leakage in 2- mm - thick plugs , with better results for group a ( table 3 ) .
materials did not show statistically significant difference ( p>0.05 ) when groups with 5-mm - thick plugs were compared to each other ( table 4 ) . regarding the 7-mm - thick plugs , there was statistically significant difference ( p<0.05 ) between groups a and b and between groups b and c , with worst results for group b in both comparisons ( table 5 )
. in figure 1 shows the graphic presentation of percent marginal leakage ( 0.2% rhodamine b ) in the root canals , regarding the tested materials and plug thicknesses .
it is possible to verify that 2-mm - thick plugs yielded the least satisfactory results in all groups , whereas the 7-mm - thick plugs yielded the best results for groups a and c , yet not for group b , in which the 5-mm - plugs had the best results as to dye leakage .
this study investigated the sealing ability of gray mta , white mta and white portland cement used for fabrication of apical plugs , given that this procedure is often required in the clinical practice12,14,19 , mainly in cases where appropriate adaptation of the master gutta - percha cone is difficult .
torabinejad and chivian25 ( 1999 ) pointed out that the goal of an apical plug is to induce hard tissue formation , in order to prevent filling material extrusion in teeth with open apices .
the use of methylene blue in marginal sealing studies has been questioned , due to its incompatibility with alkaline substances , which may induce discoloration of the dye .
when calcium oxide is mixed with water , it results in the formation of calcium hydroxide , with a subsequent increase in ph , as previously demonstrated by duarte , et al.9 ( 2003 ) .
therefore , rhodamine b dye solution is more appropriate for evaluating the sealing ability of mta22,24 . in the present study , 5- and 7-mm - thick plugs
were more efficient for apical sealing than 2-mm - thick plugs , regardless of the material utilized ( table 1 and figure 1 ) , which is in agreement with the findings of previous2,13,21,26 . in group
b ( white mta ) , the 5-mm - thick plugs had better performance than the 2- and 7-mm - thick plugs , yet without statistically significant difference .
with regard to tested materials , no statistical difference was expected among them because the chemical components of mta and portland cement are the same , except for bismuth oxide , which provides radiopacity to mta8,10,11 .
camilleri , et al.7 ( 2005 ) evaluated the chemical constitution and biocompatibility of white and gray portland cement , white and gray mta , portland cement clinker without calcium sulfate and portland cement clinker without calcium sulfate with addition of bismuth oxide .
they concluded that the chemical composition of the tested materials is similar , primarily containing tricalcium silicate and dicalcium silicate .
the white cements differ from the gray cements by the small quantity of iron oxide ( feo ) , while mta differs from portland cement due to the presence of bismuth oxide .
there was no difference between white and gray mta , and the addition of bismuth oxide did not interfere with the biocompatibility of cements . in the present study , white mta showed poorer results than gray mta and white portland cement for all tested plug thicknesses ( table 1 ) .
asgary , et al.3 ( 2005 ) observed significant differences between gray and white mta , especially in the contents of aluminum trioxide ( al2o3 ) , magnesium oxide ( mgo ) and iron oxide ( feo ) .
however , these differences are not enough to explain the results of the present study , in which gray mta showed better results than white mta as to dye leakage .
matt , et al.21 ( 2004 ) observed similar results in their study , where apical plugs made with gray mta were more efficient than those made with white mta .
as to the fabrication of apical plugs , torabinejad and chivian25 ( 1999 ) recommended carrying the mta with a large amalgam carrier to the root canal and then condensing the material to the apical end of the root with pluggers or paper points .
sometimes , this procedure is difficult due to the root canal diameter and anatomy . in the present study ,
mta and portland cement were carried to the root canal with a size 4 lentulo spiral , according to the technique proposed by bramante , et al.6 ( 2004 ) .
the lentulo spiral is used to carry the mta in paste consistence more easily to the root canal end in a fast and correct manner .
another important factor is material condensation at the end of the root canal because the apical plug should resist the filling material .
this condensation is more effective when performed with a k - file compatible with the root canal diameter and with the tip wrapped in a cotton mesh .
cleaning of the root canal walls and removal of excess material must be performed with the same k - file wrapped in moist cotton in sterile saline , not to interfere with the proper root canal filling .
the findings of the present study showed that gray mta and portland cement had better sealing ability than white mta when used as apical plugs .
dye leakage was smaller for 5- and 7-mm - thick plugs compared to 2-mm - thick plugs .
 this study evaluated the sealing ability of apical plugs made of white and gray mta - angelus and white portland cement placed via the root canal and having different thicknesses ( 2 , 5 and 7 mm ) . 
 ninety extracted human single - rooted teeth were instrumented using a size 40 k - file to standardize the foraminal opening by the stepback technique . 
 the teeth were assigned to 3 groups ( n=30 ) , according to the material used for fabrication of the apical plugs : a = gray mta ; b = white mta ; c = white portland cement . 
 the groups were subdivided into groups of 10 teeth each according to the apical plug thickness ( 2 , 5 and 7 mm ) . 
 marginal apical dye leakage was assessed using 0.2% rhodamine b solution in which the specimens were immersed for 72 hours at 37c . 
 the roots were sectioned longitudinally in a buccolingual direction for apical plug exposure , and digital photographs were taken and analyzed by image tool image - analysis software . 
 data were analyzed statistically by kruskal - wallis and dunn 's tests . 
 significance level was set at 5% . 
 the least percent leakage was observed for 5- and 7-mm - thick plugs ( p<0.05 ) . 
 no significant difference ( p>0.05 ) was found between gray mta and white portland cement . among the three materials analyzed , white mta presented the highest marginal leakage ( p<0.05 ) . 
 the findings of the present study showed that gray mta and portland cement had better sealing ability than white mta when used as apical plugs . 
 dye leakage was smaller for 5- and 7-mm - thick plugs compared to 2-mm - thick plugs . 