Effect of Decreasing Water:Powder on the Setting Expansion of MTA

OBJECTIVE: Mineral trioxide aggregate (MTA) is used in Endodontic procedures to repair and seal defects in the root and for root end surgery. Clinicians commonly mix this material to a desired consistency rather than apportioning recommended amounts of MTA powder and water. This comparative study evaluated how varying water to powder (WP) ratios affected the linear setting expansion of white and gray MTA. METHOD: Using sterile water, 8 treatment combinations (n=5) of white and gray MTA samples were mixed using WP ratios of 0.26, 0.28, 0.30, and 0.35. Immediately following mixing, all samples were placed in a linear variable displacement transformer and submerged under Hank's balanced salt solution. Linear setting expansion was continually measured for 25 hours. The mean percent linear expansion of all treatment combinations were compared using 2-way ANOVA and Tukey post hoc tests (a=0.05). RESULTS: Mean expansions of white MTA were 0.084±0.012%, 0.058±0.044%, 0.093±0.013%, and 0.086±0.029% and gray MTA were 2.42±0.33%, 2.38±0.033%, 2.56±0.39%, and 2.15±0.34% for WP ratios of 0.26, 0.28, 0.30, and 0.35 respectively. No significant interaction was found between factors (p=0.228). When looking at main effects, a highly significant difference in expansion occurred between the MTA's (p<0.001) but not the WP ratios. No significant differences were found between the WP ratios of either material. CONCLUSIONS: Gray MTA undergoes significantly more linear setting expansion compared to white MTA. However, varying the WP ratio from that recommended by the manufacturer did not affect the setting expansion. Future studies should investigate the effect of MTA expansion on dentin. Support for this study was provided by NNMC.