the quest for newer materials is never ending in the field of restorative dentistry and endodontics .
ideal  characteristics lead to the introduction of mineral trioxide aggregate ( mta ) by torabinejad et al . , in 1993 .
mta was recommended initially as a root - end filling material ; however , its use has been subsequently expanded to pulp capping , pulpotomy , apexogenesis , apical barrier formation in teeth with open apexes , repair of root perforations , and as root canal filling material .
mta is composed of fine hydrophilic particles ; its main components are tricalcium silicate , tricalcium aluminate , tricalcium oxide , silicate oxide , and other mineral oxides .
the original formulation , grey mta , was introduced first ; however , white mta was developed later as this version improved esthetics .
mta powder sets in presence of water and results in formation of a colloidal gel , which solidifies to a hard structure in approximately 3 - 4h .
mta is a biocompatible material , promotes cementum formation and apical root closure , it is an effective material in preventing leakage , as perforation repair and root - end filling material .
the ph of mta is approximately 12.5 and is similar to that of calcium hydroxide , a material with proven antibacterial activity . despite its favorable properties
a shorter setting time would be beneficial because it would allow less time for contaminants in the oral environment to adversely affect the material , allow safer placement of restorative material over it ( pulp capping ) , and also shorten the period when washout of cement can occur .
it is thus of interest to attempt to use chemicals to accelerate the setting time of mta .
also mta has low compressive strength compared with most other materials , a reason for its limited application in restorative dentistry as this parameter is of major significance for indication of mta as coronal restorative material .
the extended endodontic use and its potential of use in restorative dentistry necessitates the development of new formulation of the material , which optimizes both its strength and its setting time without compromising its ph and biocompatibility .
mta and construction grade portland cement ( pc ) are very similar in chemical and physical characters .
since setting time of pc can be accelerated by addition of certain accelerating admixtures ; addition of these construction grade pc setting accelerators to mta may induce a faster set .
some of the commonly used cement accelerators are calcium chloride ( cacl2 ) , calcium formate ( caf ) , disodium hydrogen orthophosphate ( na2hpo4 ) , and potassium chloride .
however , it is important that these accelerants should not adversely affect the other properties of mta .
therefore , this study was designed to evaluate the effect of 10% cacl2 , 20% caf , and 15% na2hpo4 on the setting time , ph , and compressive strength of white mta .
samples were prepared by mixing 0.8 g of white mta ( pro root mta ; dentsply tulsa dental , ok ) powder with various additives .
each mix was prepared using a stainless steel cement spatula on a glass slab and was then immediately transferred into the molds . before mixing ,
the test materials , molds , pluggers , spatulas , and glass slabs were kept at room temperature for a period of 24 h. the samples were divided into four groups : group 1 ( control ) : 0.8 g of mta mixed with 0.3ml distilled water ( n = 10 ) .
group 2 : 0.8 g mta with 0.08 g of cacl2 ( lab chem . ,
kanpur , india ) mixed with 0.3 ml distilled water ( n = 10 ) .
group 3 : 0.8 g mta with 0.16 g of caf ( otto , mumbai , india ) mixed with 0.3 ml of distilled water ( n = 10 ) .
group 4 : 0.8 g mta mixed with 0.3 ml of 15% na2hpo4 ( fisher scientific , mumbai , india ; n = 10 ) .
samples were prepared by mixing cement and placing them in circular acrylic mold ( 10.0 mm inner diameter and 5.0 mm height ) .
for ph , 10specimens were prepared for each group by filling hydrated samples into a cylindrical teflon mold ( 6.0 mm in diameter and 12.0 mm high ) .
specimens were individually immersed in holders containing 60 ml of deionized distilled water , sealed , and stored for 24 hours at 37c .
each material was mixed and placed in a split stainless steel mold ( 4.0 mm inner diameter and 6.0 mm height ) .
cement was then compacted into each mold using a spatula and further compacted using a dental plugger to ensure dense uniform sample with minimal porosity .
once filled , the excess was scraped off with the edge of a glass microscopic slide to leave a flat uniform surface .
no later than 120 s after mixing , the complete assembly was transferred to a cabinet maintained at 37c for 6 h , after which they were removed from the molds and checked visually for any air voids or chipped edges .
all defective specimens were discarded , and 10 accepted samples were prepared for each time interval .
the specimens were immersed in distilled water for 24 h , 3 days , and 7 days and maintained at 37c .
setting time was determined using a vicat apparatus ( aimil , new delhi , india ) .
the vicat indenter is 400  5 g in weight containing a needle with a flat end and 1.0  0.1 mm in diameter .
ninety seconds after mixing , the indenter needle was lowered vertically onto the surface of the test material .
the process was repeated every 10 s until the needle failed to make a complete circular indentation in the test material .
setting time was defined as the time elapsed between the end of mixing and the time when the needle failed to make a complete circular indentation on the test material .
after 24 h , the immersed solution was mixed by vortexing for 30 s and ph was measured using a phmeter ( si , mainz , germany ) , which was calibrated using standard solutions of ph 4.0 , 7.0 , and 12.0 .
compressive strength was measured by using a universal testing machine ( instron 1195 , norwood , ma , usa ) at a crosshead speed of 1.0 mm / min .
the maximum load needed to fracture each specimen was measured , and the compressive strength ( c ) was calculated in megapascals ( mpa ) according to formula : where p is the maximum load applied in newton and d is the mean diameter of the specimen in millimeters .
comparison of mean values was done using analysis of variance ( anova ) with post - hoc games - howell test .
samples were prepared by mixing cement and placing them in circular acrylic mold ( 10.0 mm inner diameter and 5.0 mm height ) .
the assembly was placed in a cabinet at 37c and relative humidity of 95% . for ph , 10specimens were prepared for each group by filling hydrated samples into a cylindrical teflon mold ( 6.0 mm in diameter and 12.0 mm high ) .
specimens were individually immersed in holders containing 60 ml of deionized distilled water , sealed , and stored for 24 hours at 37c .
each material was mixed and placed in a split stainless steel mold ( 4.0 mm inner diameter and 6.0 mm height ) .
cement was then compacted into each mold using a spatula and further compacted using a dental plugger to ensure dense uniform sample with minimal porosity .
once filled , the excess was scraped off with the edge of a glass microscopic slide to leave a flat uniform surface .
no later than 120 s after mixing , the complete assembly was transferred to a cabinet maintained at 37c for 6 h , after which they were removed from the molds and checked visually for any air voids or chipped edges .
all defective specimens were discarded , and 10 accepted samples were prepared for each time interval .
the specimens were immersed in distilled water for 24 h , 3 days , and 7 days and maintained at 37c .
setting time was determined using a vicat apparatus ( aimil , new delhi , india ) .
the vicat indenter is 400  5 g in weight containing a needle with a flat end and 1.0  0.1 mm in diameter .
ninety seconds after mixing , the indenter needle was lowered vertically onto the surface of the test material .
the process was repeated every 10 s until the needle failed to make a complete circular indentation in the test material .
setting time was defined as the time elapsed between the end of mixing and the time when the needle failed to make a complete circular indentation on the test material .
after 24 h , the immersed solution was mixed by vortexing for 30 s and ph was measured using a phmeter ( si , mainz , germany ) , which was calibrated using standard solutions of ph 4.0 , 7.0 , and 12.0 .
compressive strength was measured by using a universal testing machine ( instron 1195 , norwood , ma , usa ) at a crosshead speed of 1.0 mm / min . the maximum load needed to fracture each specimen
was measured , and the compressive strength ( c ) was calculated in megapascals ( mpa ) according to formula : where p is the maximum load applied in newton and d is the mean diameter of the specimen in millimeters .
comparison of mean values was done using analysis of variance ( anova ) with post - hoc games - howell test .
the setting time of mta mixed with the additives was significantly shorter than that of mta mixed with water ( p < 0.001 ) [ table 1 ] . setting time observed was shortest for group 3 . setting time of the test materials in minutes ( n = 10 for each group ) the ph of mta mixed with cacl2 was lower than that of the control group ( p < 0.001 ) ; however , when caf and na2hpo4 was added to mta , ph value obtained was higher than that of the control group ( p < 0.001 ) [ table 2 ] .
ph of test materials ( n = 10 for each group ) the compressive strength of all the groups increased during a 7-day period .
the compressive strength of mta mixed with the additives was lower than that of mta mixed with water ( p < 0.001 ) [ table 3 ] . for
however , on day 3 the compressive strength of group 4 was found higher than other groups .
compressive strengths of test materials in mpa ( n = 10 for each group at each time interval )
it was the intent of this research to incorporate additives used by the cement industry to mta to try to decrease its setting time and improve its compressive strength , without affecting its ph .
the various additives used included 10% cacl2 , 20% caf , and 15% na2hpo4 . in this study ,
however , the setting time observed in this study was significantly shorter than the 2 h and 45 min as reported by torabinejad et al . this difference can be attributed to changes that may have been incorporated into the mta powder since it was first introduced .
asgary et al . , found that a significant change in composition has occurred since mta was first introduced .
according to bortoluzzi et al . , the penetration of cacl2 in the pores of cements could accelerate the reaction due to the hydration of silicates which reduces their crystallization time , thus hastening the final setting time of the material .
cacl2 mixed with portland cement has already been confirmed to be nontoxic to human cells in vitro .
addition of na2hpo4 reduced the setting time of mta to 31.60  2.91 min , a result similar to that obtained by ding et al . , and
na2hpo4 solution can be used as a cement liquid to accelerate the setting of the cement prepared from tricalcium phosphate as a cement powder .
strong ionic interactions between phosphate and calcium ions lead to the formation of calcium silicate hydrate phase .
caf resulted in markedly decreased setting time , that is , 12.40  2.07 min .
caf is a highly soluble calcium compound that completely dissociates in solution to produce calcium ions .
this might accelerate the dissociation step in hydration of cement , thus accelerating its setting time .
this decrease may be because of the addition of calcium - based electrolytes like cacl2 which tends to suppress ionization of ca(oh)2 , thus the percentage dissociation of ca(oh)2 decreases .
however , such ph difference at an alkaline condition , might not affect the antimicrobial property of modified mta .
mta mixed with na2hpo4 resulted in a ph value of 12.77  0.09 , which is similar to result obtained by ding et al . , and when mixed with caf the ph is 12.56  0.19 , which is similar to result of wiltbank et al . the compressive strength for mta mixed with water after 7 days was 36.24  3.33 mp a. this result is contrary to those obtained originally by torabenajed et al . ,
which maybe because of change in composition of mta since the time it was first introduced . with the addition of cacl2 to mta
, compressive strength obtained was 33.37  3.18 , this result was similar to that obtained by lee et al .
the compressive strength of mta obtained with the addition of caf was 30.05  1.02 and that with addition of na2hpo4 was 29.32  1.13 .
huang et al . , observed that 15% na2hpo4 used as liquid phase for mta resulted in a good diametral tensile strength value .
although these additives reduced the setting time , they also reduced the compressive strength of mta ; which could be a disadvantage of these additives .
compressive strength is an important parameter to consider when placing a filling material in a cavity that bears occlusal pressure . on the contrary ,
when used as root - end filling where minimal forces are applied , reduced compressive strength will not be a major drawback .
one drawback of our study is that distilled water has been used as a storage medium for modified mta samples .
however , previous studies have shown that different storage methods and media can influence dentine characteristics as well as physical properties of dental materials .
parirokh et al . , and and asgary et al . , have shown that placing mta in tissue fluids such as phosphate buffer saline(pbs ) storage medium results in formation of hydroxyapatite crystals over mta and causes a significant decrease in bacterial penetration .
hence , future in vitro studies can use pbs as a storage medium to simulate environment in human body .
within the limitation of this study , 10% cacl2 , 20% caf , and 15% na2hpo4 significantly reduced the setting time of white mta and also maintained the ph at a high value .
however , there was no improvement in the compressive strength of the material . based on the results ,
mta mixed with these additives can be recommended for single - visit procedures where compressive strength is not a major concern .
however , further studies regarding their biocompatibility , antimicrobial properties , sealing abilities , dimensional stability , etc . , are indicated before any recommendation for clinical use .
 aims : this study examined the setting time , compressive strength , and ph of white mineral trioxide aggregate ( mta ) mixed with various additives : calcium chloride ( cacl2 ) , calcium formate ( caf ) , disodium hydrogen orthophosphate ( na2hpo4).materials and methods : group 1 ( control ) was obtained by mixing mta with distilled water . in groups 2 and 3 , 
 mta containing 10% cacl2 and 20% caf , respectively , was mixed with distilled water . in group 4 , mta was mixed with 15% na2hpo4 . setting time , compressive strength , and ph of each group were examined.statistical analysis used : analysis was done using statistical package for social sciences ( spss ) version 14 . 
 a p - value < 0.05 was considered statistically significant . 
 comparison of mean values was done using analysis of variance ( anova ) with post - hoc games - howell test.results:the setting time of test groups were significantly shorter than that of control group ( p < 0.001 ) . 
 the compressive strengths of test groups were lower than that of control group ( p < 0.001 ) . 
 the ph value obtained for groups 3 and 4 were higher than that of the control group ( p < 0.001).conclusions : study result showed that additives significantly reduced the setting time of mta and also maintained the ph at a high value . 
 however , there was not much improvement in the compressive strength of the material . 
INTRODUCTION
MATERIALS AND METHODS
Sample preparation
Setting time
pH
Compressive strength
Statistical analysis
RESULTS
DISCUSSION
CONCLUSIONS