Effect of acid‐etching procedure on selected physical properties of mineral trioxide aggregate

<jats:title>Abstract</jats:title><jats:p><jats:bold>Aim </jats:bold> To evaluate the effect of acid‐etch procedures on the compressive strength and surface microhardness of tooth‐coloured mineral trioxide aggregate (MTA).</jats:p><jats:p><jats:bold>Methodology </jats:bold> White ProRoot MTA (Dentsply Tulsa Dental) was mixed and packed into cylindrical tubes of 4 mm in diameter and 6 mm in height. Three groups, each of 15 specimens were subjected to an acid‐etch procedure either 4, 24 or 96 h after mixing. The compressive strength was measured and compared with unetched control groups. Differences between groups were analysed using the Kruskall–Wallis test. A further batch of cylindrical specimens of 6 mm in diameter and 12 mm in height were prepared for testing surface microhardness. Three groups of 15 specimens were subjected to the acid‐etch procedure at either 4, 24 or 96 h following mixing. Data were subjected to one‐way <jats:sc>anova</jats:sc>. Changes in the surface microstructure before and after the acid‐etch procedures were analysed using a scanning electron microscope (SEM).</jats:p><jats:p><jats:bold>Results </jats:bold> There was a general trend for the compressive strength and surface microhardness of specimens to increase with time. In terms of compressive strength, the increase was significant between 4 h and the other time periods for both experimental and control groups (<jats:italic>P </jats:italic>< 0.0001); however, there was no significant difference between 24 and 96 h. The increase in surface microhardness was significant between 4, 24 and 96 h (<jats:italic>P </jats:italic>< 0.0001). In addition, there was a significant difference between experimental and control groups at all time periods (<jats:italic>P </jats:italic>< 0.0001). SEM examination revealed morphological differences between the intact and the etched MTA surfaces.</jats:p><jats:p><jats:bold>Conclusions </jats:bold> Acid‐etch procedures affected the compressive strength and surface microhardness of ProRoot MTA. This indicates that it may be better to postpone restorative procedures for at least 96 h after mixing MTA. Etching created surface changes that might have the potential to enhance bonding of resinous materials.</jats:p>