persistence of virulent microorganisms and their byproducts in the root canal system , or the surrounding tissues , following initial endodontic treatment , is the main cause for treatment failure .
it has been reported that failing root canal treatments associated with periradicular pathosis frequently demonstrated fungi colonization .
the exact factors affecting the colonization of the root canal by fungi are not completely understood .
it seems that the most common predisposing factors are certain intracanal medicaments , local and systemic antibiotics , and previous unsuccessful endodontic treatment .
it has been hypothesized that the reduction of specific strains of bacteria in the root canal during endodontic treatment may allow fungi overgrowth in the low nutrient environment .
in addition , it is possible that fungi , such as c. albicans , may gain access to the root canal from the oral cavity as a result of poor asepsis during endodontic treatment procedures or because of coronal leakage .
in fact , the presence of c. albicans in root canals was found to be directly associated with its presence in the oral cavity of the same patients .
failure of initial endodontic treatment can often be treated successfully by retreatment or endodontic surgery .
elimination of the microbial flora and infected tissues as well as a complete seal of the root canal system , to prevent future recontamination , will enhance treatment success . in this
regard , mineral trioxide aggregate ( mta ) has become a popular material to seal off communications between the root canal system and the external surface of the root .
it has been mostly used as a retrograde filling material during apical surgery and as a sealant of root perforations .
however , mta is difficult to use because of its longer setting time and poor handling properties .
mta ( proroot mta , dentsply / tulsa dental , tulsa , ok ) is marketed in gray - colored and white - colored preparations ; both are 75% portland cement , 20% bismuth oxide , and 5% gypsum by weight .
recently , the use of the white - colored preparation became more popular because of esthetic considerations .
mta is a powder that consists of fine hydrophilic particles that in the presence of water , or moisture , forms a colloidal gel that solidifies to form hard cement within approximately 4 h. the principal constituents of the gray - colored formula are tricalcium oxide , tricalcium silicate , bismuth oxide , dicalcium silicate , tricalcium aluminate , tetracalcium aluminoferrite , and calcium sulfate dihydrate .
it has been reported that a fixed concentration of white - colored mta was effective against c. albicans 
 in vitro for periods of up to 3 days .
it has also been shown that white - colored mta in concentration of 50 mg / ml was effective in killing c. albicans for periods of up to 3 days , whereas lower concentrations were not as effective . in another study ,
fungal growth occurred during 1-h incubation in both freshly mixed and 24-h set gray and white mta cements , whereas by increasing the incubation time , no fungal growth was observed in 24 and 72 h. it was also reported that both gray - colored and white - colored mta in concentrations of 50 mg / ml and 25 mg / ml were effective in killing c. albicans for periods up to 1 week .
lower concentrations of gray - colored mta might still be effective , whereas lower concentrations of white - colored mta might not .
however , the antifungal effect of mta on multiple strains of c. albicans over longer periods of time is less investigated .
the purpose of this study was to evaluate the antifungal action of various concentrations of white - colored mta against seven different c. albicans strains for various exposure periods using the tube dilution test .
fresh mix of white - colored mta ( pro - root mta , batch # 05002015 , dentsply / tulsa dental , tulsa , ok ) was prepared at concentrations of 100 , 50 , 25 , and 12.5 mg / ml by dilution with distilled water .
each freshly prepared mix was added to a broth tube containing sabouraud 's liquid medium ( hi - media laboratories , mumbai , india ) .
a total of 1287 broth tubes were prepared and divided into seven sets with experimental groups of 11 tubes each and control groups .
broth tubes without mta served as positive control and tubes without c. albicans served as negative control .
the antifungal action of mta against c. albicans was evaluated by using the tube dilution test .
stock cultures of six strains of c. albicans clinically isolated from the oral cavity ( strains 1 - 6 : c-89 , e-175 , c-304 , e-259 , c-176 , and e-170 ) and a standard strain ( strain 7 : microbial type culture collection ( mtcc ) 3017 ) were obtained .
fresh inoculate of the microorganism was prepared by growing overnight cultures until a complete suspension of growth was achieved .
the cultures were diluted in a pre - warmed broth to achieve a final density of 10 colony - forming unit ( cfu)/spot .
one - milliliter aliquots of the test c. albicans were taken from the broth culture and added to sterile capped test tubes of each experimental and positive control group .
all experimental and control groups were then incubated at 37c and evaluated at 1- , 24- , 72- , and 168-h ( 7 days ) time periods . at each time period
, 0.1 ml of samples from each tube was subcultured on sabouraud 's dextrose agar plates ( hi - media laboratories , mumbai , india ) .
differences among the groups were statistically analyzed using kruskal  wallis and mann  whitney u tests ( statistical package for the social sciences ( spss ) 7 software ) .
if the calculated critical values were at least as large as the respective critical values at the 0.05 level , then calculations were considered statistically significant in this study .
generally , a direct correlation was found between mta concentrations and its inhibition effect on c. albicans growth .
differing behavior patterns of various strains of c. albicans were also seen [ table 1 ] .
strains 5 , 6 , and 7 displayed intermediate resistance to mta , whereas strains 3 and 4 appeared to be most resistant .
the negative controls showed no fungal growth at any time period , whereas the positive controls always showed fungal growth .
effect of various mta concentrations on growth of c. albicans strains statistically , a significant difference was found between tubes containing either strain 3 or 4 and tubes containing other strains at all mta concentrations at the 1-day time period ( p < 0.001 ) .
a significant difference was found between tubes containing strain 3 and tubes containing other strains at mta concentrations of 12.5 and 25 mg / ml at the 3-days time period ( p < 0.001 ) .
a significant difference was also found between tubes containing 12.5 mg / ml and tubes containing higher concentrations of mta at the 7-days time period ( p < 0.001 ) .
the method used in the present study was the tube dilution test , which is an effective method to evaluate the antifungal and antibacterial properties of any filling material or solution .
it was considered appropriate for evaluating the antifungal activity of mta , which has a low solubility and diffusibility . c. albicans was the test organism in this study .
it is a frequent colonizer of the oral cavity , and multiple unrelated strains showing varying pathogenicity may be present in the same individual . mechanisms of pathogenicity of different strains may include the power of adaptability to a variety of environmental conditions attributable to the switching of gene expression dictated by environmental changes and evasion and immunomodulation of the host defenses by different mechanisms . c. albicans is frequently associated with failing root canal treatments and has the ability to form biofilms on different surfaces , which makes it more pathogenic than species that are less able to form biofilms .
as it may be involved in cases of persistent and secondary infections , usually present during apical surgery and perforation repair procedures , the antifungal action of the repair material may further assist in the management of such infections and enhance tissue healing . in this study ,
growth of seven strains of c. albicans in four concentrations of mta was assessed for periods of up to 7 days .
only one strain showed relative resistance even after 3 days at the lower mta concentration of 12.5 and 25 mg / ml .
recurrence of fungal growth was seen with three strains at mta concentration of 12.5 mg / ml after 7 days .
it might indicate that mta only exhibits a fungistatic action at lower concentrations , whereas a fungicidal action may be expected at higher concentrations .
this highlights the significance of using seven strains in the present study . in a previous study ,
al - nazhan and al - judai reported white - colored mta to be effective in killing c. albicans 
 in vitro for a period of up to 3 days .
however , in that study a higher concentration of mta was used . in another in vitro study , al - hezaimi et al .
, assessed the antifungal action of different concentrations of white - colored mta against c. albicans 
 in vitro .
white - colored mta in concentration of 50 mg / ml was effective in inhibiting c. albicans for periods of up to 3 days , whereas lower concentrations were not effective .
mohammadi et al . , observed fungal growth during 1-h incubation in both freshly mixed and 24-h set gray and white mta cements , whereas by increasing the incubation time , no fungal growth was observed in 24 and 72 h. another study also showed that both white and gray mta in concentrations of 50 and 25 mg / ml were effective in inhibiting c. albicans for periods of up to 7 days .
kangarlou et al . , assessed the antifungal activity of proroot mta and mta - angelus and concluded that mta - angelus was a more effective antifungal agent compared with proroot mta at concentrations of 50 and 100 mg / ml .
regarding the antifungal action of mta , it has been shown that the mechanism of action of mta involves the dissolution of calcium oxide , which increases ph by releasing ca and oh . the high ph increases the permeability of cell membranes with leakage of intracellular components .
waltimo et al . , reported that c. albicans survived incubation in calcium hydroxide solution for 1 and 6 h and was killed after 6 h of incubation .
ferguson et al . , found that an aqueous solution of calcium hydroxide had no activity against c. albicans .
however , when maintained in direct contact with c. albicans cells , calcium hydroxide paste was very effective in killing this fungus .
therefore , it can be assumed that mta is more effective in killing c. albicans when placed in direct contact with the fungus .
in addition , samiei et al . , reported that adding silver nanoparticles to mta improved its antimicrobial efficacy . in conclusion
, it appears that under the conditions of this study , white - colored mta in concentrations of 100 and 50 mg / ml is effective in inhibiting the seven tested strains of c. albicans for periods up to 1 week .
however , the antifungal activity of white - colored and gray - colored mta over longer periods of time on more number of strains merits further investigation .
 aim : the purpose of this study was to evaluate the antifungal action of various concentrations of white mineral trioxide aggregate ( mta ) against seven different strains of candida albicans using the tube dilution test.materials and methods : fresh mix of mta was prepared at concentrations of 100 , 50 , 25 , and 12.5 mg / ml and added to a broth tube containing sabouraud 's liquid medium . 
 a total of 1287 broth tubes were prepared and divided into experimental and control groups . 
 stock cultures of seven strains of c. albicans were obtained . 
 fresh inoculate of the microorganism was prepared by growing overnight cultures . 
 aliquots of the test c. albicans were taken and added to the test tubes . 
 all tubes were incubated at 37c for 1- , 24- , 72- , and 168-h time periods . at each time period , the presence of c. albicans colonies was assessed.statistical analysis used : differences among the groups were statistically analyzed using kruskal  wallis and mann  whitney u tests.results:results showed that one strain showed resistance even after 3 days at the lower mta concentrations of 12.5 and 25 mg / ml . growth reoccurred with three strains at mta concentration of 12.5 mg / ml after 7 days . 
 a significant difference was found between strain 3 and other strains at mta concentrations of 12.5 and 25 mg / ml at the 3-days time period and between tubes containing 12.5 mg / ml and tubes containing higher concentrations of mta at the 7-days time period.conclusion:white mta in concentrations of 100 and 50 mg / ml is effective in inhibiting the seven tested strains of c. albicans for periods up to 1 week . 