Setting expansion of gray and white mineral trioxide aggregate and Portland cement

One possible reason for the sealing ability of mineral trioxide aggregate (MTA) is its slight expansion upon setting. Both gray mineral trioxide aggregate (GMTA) and white mineral trioxide aggregate (WMTA) are composed of approximately 75% Portland cement (PC). WMTA differs from GMTA in its lower content of tetracalcium aluminoferrite. This difference in composition may affect setting expansion. The purpose of this study was to compare the hydroscopic linear setting expansions of GMTA, WMTA, and PC with a new device. Materials were mixed with water, placed into a cylindrical mold, and covered with sterile water or Hank's balanced salt solution (HBSS). Expansion changes were measured by using a linear variable displacement transformer dilatometer. One-way analysis of variance and post hoc tests (alpha = 0.05) showed the mean expansion at 24 hours was 1.02% for GMTA, 0.29% for PC, and 0.08% for WMTA in water immersion and 0.68% for GMTA and 0.11% for WMTA in HBSS immersion. GMTA expanded significantly more than WMTA in either water or HBSS immersion.