Influence of an acid environment on hardening of SuperEBA and MTA

Background. Super EBA (SE) and MTA are considered to be among the best retrograde filling materials used in endodontic surgery. Since the post-operative course is characterised by phlogosis and an acid pH, it is worth asking whether this environment influences the hardening of these materials. The aim of this study was to evaluate in vitro the influence of pH on the Vickers hardness of MTA and SuperEBA. Methods and materials. Twelve MTA and 12 SuperEBA disks were prepared and left to harden, for 24 hours and 1 hour respectively, in pH5 and pH7 buffer solutions (n. 6 for each group). After careful polishing of the free surface the final hardness was evaluated using a micro-hardness meter; an optical microscopy assessment was also performed as a qualitative analysis to evaluate the indentations. Data were analysed with one-way ANOVA and Scheffe post hoc test. Results. Means of Vickers values and standard deviation were: pH7 MTA 38,59(2,59); pH5MTA 4,02(1,57); pH7 SE 18,46(5,38); pH5 SE 20,65(5,49). MTA at neutral pH is associated with the best hardness; this is dramatically reduced if the samples are exposed to an acid solution. Instead, SuperEBA, characterised by a lower hardness, is practically unaffected by changes in the pH level, showing only a slight increase in an acid pH environment. The differences were statistically significant (p<0,001) except for the groups of ph7 SE vs pH5 SE. Conclusions. An acid pH significantly influences the hardness of MTA but not of SuperEBA.