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 .