treatment of nonvital immature permanent teeth with calcium hydroxide ( ca(oh)2 ) is associated with some difficulties such as weakened tooth fracture , root canal reinfection and long treatment time .
mineral trioxide aggregate ( mta ) has overcome all the disadvantages of ca(oh)2 and has addressed the need for an apical seal by inducing hard tissue barriers .
however , mta is difficult to use because of its longer setting time and poor handling properties , necessitating a second appointment for the completion of the procedures such as apexification . to overcome this problem ,
various accelerators such as ( 2% , 5% , 10% ) calcium chloride , ( 1 - 10% ) calcium nitrate , ( 25 - 50% ) calcium nitrite , ( 20% ) calcium formate , low - dose citric acid and lactic acid have been added to mta .
various studies showed that the addition of cacl2 to mta decreased the setting time and improved its sealing ability .
recently , disodium hydrogen orthophosphate and calcium lactate gluconate have been added to mta to reduce its setting time to a significant extent .
there have been no studies reported till date to evaluate and compare the effect of 10% cacl2 , 15% na2hpo4 and 23.1 wt% calcium lactate gluconate ( clg ) on the sealing ability of mta when used as an apical plug .
thus , the purpose of this study was to evaluate and compare the effect of these accelerants on the immediate and delayed sealing ability of mta when used as an apical plug .
15% disodium hydrogen phosphate ( na2hpo4 ) was prepared by taking 1.5 g of powder and mixing with 10 ml of deionized water . for the 10% calcium chloride ( cacl2 )
preparation , 1 g of powder was mixed with 10 ml of deionized water . to prepare 23.1 wt% clg , 27.0 g of lactic acid ( molecular weight of 90.1 g / mol ) , 35.6 g of glucono delta lactone ( molecular weight of 178.0 g / mol ) and 14 g of calcium oxide ( molecular weight of 56.0 g / mol ) were mixed with 100 ml of deionized water .
the respective volumetric flasks were then kept in a sonicator for 500 s for the complete mixing of the powders with the deionized water .
eighty , single - rooted human mandibular premolars , extracted for orthodontic reasons , were included in the study .
access to the root canal was gained and the apical patency was established with a size of 10 k  file .
the specimens were then sequentially prepared by k - files ( dentsply maillefer , ballaigues , switzerland ) to an iso size file # 80 , which could be visualized 1 mm beyond the apex .
final irrigation was performed with 1 ml of 17% edta for 5 min followed by 5 ml of 5.25% naocl .
the canals were then instrumented with a peeso reamer ( dentsply - maillefer ) up to # 4 , with each passing 1 mm beyond the apex .
this was followed by drying of the canals and final flushing with 1 ml of sterile water .
the samples were then randomly assigned into four experimental groups consisting of 16 samples each ( n = 64 ) and two control groups with eight samples each ( n = 16 ) . in the negative control group , proroot white mta ( wmta ) ( dentsply tulsa dental , tulsa , ok , usa )
was mixed in deionized water and in the positive control group , no apical plug was fabricated .
group 1 : proroot wmta mixed with15% na2hpo4 in deionized water group 2 : proroot wmta mixed with 10% cacl2 in deionized water group 3 : proroot wmta mixed with 23.1 wt% clg in deionized water group 4 : proroot wmta mixed in deionized water alone . in group 1 , wmta powder was mixed with 15% na2hpo4 in deionized water in a 3:1 powder  liquid ratio and was placed using a micro apical placement ( map ) system .
wmta was then condensed with a hand condenser and plugger to achieve a 4-mm - thick apical plug .
radiographs were taken to ensure the proper placement of the material and a moistened cotton pellet was placed into the canal just above the apical plug material for 3 h to allow the material to set .
after 48 h , the root canals were obturated using obtura ii ( obtura spartan , fenton , mo , usa ) and ah plus sealer ( dentsply tulsa dental ) . in groups 2 , 3 and 4 ,
the apical plug was fabricated in a manner similar to that described above . to simulate a periapical environment ,
a cotton pellet was fitted into the apical portion to prevent the foam from penetrating into the root canal .
eight samples from each experimental group and four samples from each control group were randomly stored for 72 h and the remaining samples were stored for 2 months in an incubator at 37c and 100% humidity . after this
, the root surfaces of all the samples of the experimental groups were coated with two coats of nail varnish , leaving 1 mm of the root surface around the tooth and an apical plug material interface at the apex .
the apical and coronal openings of the positive control group samples were devoid of any impermeable coating .
the entire root surface of the specimens of the negative control group was coated with two coats of nail varnish .
the samples were then immersed in 0.2% rhodamine b solution at a ph of 7 for 72 h at 37c and 100% humidity in an incubator .
the teeth were then kept in running water , dried and sectioned longitudinally in a buccolingual direction using a safe - sided diamond cutting disc at low speed .
leakage was determined from the most apical part to the most cervical portion of the apical plug , which was evaluated under a 30x stereomicroscope ( olympus , spectro analytical laboratory , delhi , india ) and calibrated with the help of the measurement and image analysis software .
if the leakage was greater than the full length of the mta apical plug , the measurement was stopped at the coronal most point of the plug .
one - way analysis of variance ( anova ) with tukey 's hsd was applied to determine the significance ( p < 0.001 ) among all groups . paired 
test was applied to determine the significant comparison of change in microleakage between the two time intervals ( p < 0.05 ) .
15% disodium hydrogen phosphate ( na2hpo4 ) was prepared by taking 1.5 g of powder and mixing with 10 ml of deionized water . for the 10% calcium chloride ( cacl2 )
preparation , 1 g of powder was mixed with 10 ml of deionized water . to prepare 23.1 wt% clg , 27.0 g of lactic acid ( molecular weight of 90.1 g / mol ) , 35.6 g of glucono delta lactone ( molecular weight of 178.0 g / mol ) and 14 g of calcium oxide ( molecular weight of 56.0 g / mol ) were mixed with 100 ml of deionized water .
the respective volumetric flasks were then kept in a sonicator for 500 s for the complete mixing of the powders with the deionized water .
eighty , single - rooted human mandibular premolars , extracted for orthodontic reasons , were included in the study .
access to the root canal was gained and the apical patency was established with a size of 10 k  file .
the specimens were then sequentially prepared by k - files ( dentsply maillefer , ballaigues , switzerland ) to an iso size file # 80 , which could be visualized 1 mm beyond the apex .
final irrigation was performed with 1 ml of 17% edta for 5 min followed by 5 ml of 5.25% naocl .
the canals were then instrumented with a peeso reamer ( dentsply - maillefer ) up to # 4 , with each passing 1 mm beyond the apex .
this was followed by drying of the canals and final flushing with 1 ml of sterile water .
the samples were then randomly assigned into four experimental groups consisting of 16 samples each ( n = 64 ) and two control groups with eight samples each ( n = 16 ) . in the negative control group , proroot white mta ( wmta ) ( dentsply tulsa dental , tulsa , ok , usa )
was mixed in deionized water and in the positive control group , no apical plug was fabricated .
group 1 : proroot wmta mixed with15% na2hpo4 in deionized water group 2 : proroot wmta mixed with 10% cacl2 in deionized water group 3 : proroot wmta mixed with 23.1 wt% clg in deionized water group 4 : proroot wmta mixed in deionized water alone . in group 1 , wmta powder was mixed with 15% na2hpo4 in deionized water in a 3:1 powder  liquid ratio and was placed using a micro apical placement ( map ) system .
wmta was then condensed with a hand condenser and plugger to achieve a 4-mm - thick apical plug .
radiographs were taken to ensure the proper placement of the material and a moistened cotton pellet was placed into the canal just above the apical plug material for 3 h to allow the material to set .
after 48 h , the root canals were obturated using obtura ii ( obtura spartan , fenton , mo , usa ) and ah plus sealer ( dentsply tulsa dental ) . in groups 2 , 3 and 4 ,
the apical plug was fabricated in a manner similar to that described above . to simulate a periapical environment ,
a cotton pellet was fitted into the apical portion to prevent the foam from penetrating into the root canal .
eight samples from each experimental group and four samples from each control group were randomly stored for 72 h and the remaining samples were stored for 2 months in an incubator at 37c and 100% humidity . after this
, the root surfaces of all the samples of the experimental groups were coated with two coats of nail varnish , leaving 1 mm of the root surface around the tooth and an apical plug material interface at the apex .
the apical and coronal openings of the positive control group samples were devoid of any impermeable coating .
the entire root surface of the specimens of the negative control group was coated with two coats of nail varnish .
the samples were then immersed in 0.2% rhodamine b solution at a ph of 7 for 72 h at 37c and 100% humidity in an incubator .
the teeth were then kept in running water , dried and sectioned longitudinally in a buccolingual direction using a safe - sided diamond cutting disc at low speed .
leakage was determined from the most apical part to the most cervical portion of the apical plug , which was evaluated under a 30x stereomicroscope ( olympus , spectro analytical laboratory , delhi , india ) and calibrated with the help of the measurement and image analysis software .
if the leakage was greater than the full length of the mta apical plug , the measurement was stopped at the coronal most point of the plug .
one - way analysis of variance ( anova ) with tukey 's hsd was applied to determine the significance ( p < 0.001 ) among all groups . paired 
test was applied to determine the significant comparison of change in microleakage between the two time intervals ( p < 0.05 ) .
all the positive control group samples showed complete dye penetration and the negative control group samples did not show any leakage at both the time intervals .
the mean microleakage values of all experimental groups revealed that wmta + 23.1 wt% clg showed the least leakage , followed by wmta + 15% na2hpo4 and wmta + 10% cacl2 , with wmta + deionized water showing the maximum leakage at both the time intervals .
a statistically significant difference existed between all the groups ( p < 0.001 ) and at both the time intervals ( p < 0.05 ) .
the mean dye penetration and its standard deviation along with intergroup comparison are given in table 1 .
intergroup comparison of microleakage at both the intervals , i.e. , after 72 h and after 2 months
in the present study , the sealing ability of wmta mixed with hydration accelerators was significantly better than that of wmta mixed with deionized water at both the time intervals .
the superior sealing ability of wmta with 23.1 wt% clg than the deionized water group as seen in our study might be attributed to the calcium ions released from it during its hydration .
further , the shortening of the setting time of wmta with the addition of 23.1 wt% clg might be responsible for its antiwashout resistance .
many studies have proven that na2hpo4 solution could be used as a cement liquid to accelerate the setting of the cement prepared from -tricalcium phosphate as a cement powder .
the presence of hpo4 ions embedded in 15% na2hpo4 accelerator might lead to the more apatite crystal formation .
this could be one of the reasons for mta with 15% na2hpo4 to show a better sealing ability when compared with deionized water alone in our study .
this is supported by the studies showing a less bacterial penetration in mta when placed in phosphate - buffered solution .
reports have also shown that mta alone was also able to form hydroxyapatite deposits on its surface when it was in contact with hpo4 ions .
the rate of hydroxyapatite formation over a period of time has been suggested as an indicator of the setting reaction . in one study , it was found that the setting time of mta was 151 min , which reduced to 26 min with the addition of 15% na2hpo4 , increasing the washout resistance of mta over a period of time . with the addition of 10% cacl2
, an improved sealing ability of mta was seen in the study as compared with the deionized water group .
a possible explanation for the results observed is the penetration of cacl2 in the pores of cements , which strongly accelerates the hydration of silicates , leading to their faster crystallization and shorter setting time .
the continuous release of ca ions by cacl2 might have a role to play in shortening of the setting time . in a previous study , 10% and 15%
this in turn might accelerate the onset and final setting of the cement , reduce the incorporation of water and allow the cement to resist hydrostatic pressure at early stages , avoiding its leaching out . at both the time intervals ,
the 23.1 wt% clg group showed a significantly better sealing ability than 10% cacl2 . both 23.1 wt% clg and
10% cacl2 solution supplied adequate calcium ions to accelerate the initial setting of the cement , but the crystalline nature of calcium chloride tends to precipitate out as sand - like particles and offers less enhancement of cement cohesiveness .
this might have resulted in the inferior sealing ability of cacl2 when compared with clg .
the results demonstrated that less dye penetration was seen with 23.1 wt% clg when compared with 15% na2hpo4 solution . on the other hand ,
these findings could not be compared with any other study as no study comparing the above two groups has been performed till date . regarding the two variables analyzed ( both time intervals ) , significantly lesser ( p < 0.01 ) leakage
was observed in all samples stored for 2 months , showing that the leakage decreased with time .
slight expansion of the material upon setting could be one of the reasons for the improved sealing ability of mta , without any accelerator , after 2 months of storage
. another explanation could be the formation of apatite - like materials , filling the mta  dentin interfacial space , accompanied with tag - like structures that extend into the dentinal tubules .
it has also been established that the proroot white mta and the mta angelus released calcium and maintained an elevated ph even after 126 h. in case of 15% na2hpo4 , the formation of apatite crystals after the contact of hpo4 ions , embedded in the mta - na2hpo4 cement system , with the moisture over a period of time , might be responsible for the statistically decreased microleakage after 2 months .
an increase in sample weight after 30 days , which might be due to the formation of apatite , has also been shown .
the improved sealing ability of 10% cacl2 after 2 months might be due to the release of more ca ions leading to biomineralization over a period of time .
it has been shown that mtas sealing ability could be improved over a period of time by the addition of cacl2 .
also , a study showed that the addition of cacl2 provided a reduction in the setting time of mta , which might lead to its antiwashout resistance .
this study also showed that wmta with cacl2 exhibited a weight gain , which might be due to the apatite precipitation over a period of time .
the increased precipitation of amorphous 23.1 wt% clg with time could be the reason for it to show a better sealing ability at 2 months .
however , we can not compare these results with those of others in the literature as no study has been done yet .
within the parameters of this study , it could be concluded that the sealing ability of wmta mixed with hydration accelerators was superior to wmta with deionized water alone at both the time intervals .
the sealing ability of all the experimental groups was significantly superior after 2 months as compared with that after 72 h.
 aim : to evaluate and compare the influence of various accelerators , 15% disodium hydrogen phosphate ( na2hpo4 ) , 10% calcium chloride ( cacl2 ) and 23.1 wt% calcium lactate gluconate ( clg ) , on the immediate ( after 72 h ) and delayed ( after 2 months ) sealing ability of white proroot mineral trioxide aggregate ( wmta ) when it is used as an apical plug.materials and methods : eighty , single - rooted mandibular premolars were instrumented and standardized artificial open apices were created . 
 the samples were then randomly assigned into four experimental groups and two control groups . 
 wmta was mixed with the respective accelerators and an apical plug of 4-mm thickness was fabricated . 
 the remaining canal spaces were then backfilled . 
 the samples were stored for the stipulated time periods and then immersed in 0.2% rhodamine b solution for 72 h. dye leakage was analyzed using a stereomicroscope.results:mean microleakage values of all experimental groups revealed that mta + 23.1 wt% clg showed the least leakage , followed by mta + 15% na2hpo4 and mta + 10% cacl2 with mta + deionized water showing the maximum leakage at both the time intervals ( p < 0.001 ) . all the samples stored for a period of 2 months showed less leakage as compared with the samples stored for 72 h ( p < 0.05).conclusions : it was found that all three accelerators significantly accelerated the set of wmta , of which 23.1 wt% clg showed the best results , followed by 15% na2hpo4 and 10% cacl2 . 
 the sealing ability of all the experimental groups was significantly superior after 2 months as compared with that after 72 h. 
INTRODUCTION
MATERIALS AND METHODS
Preparation of accelerants
Statistical analysis
RESULTS
DISCUSSION
CONCLUSION