The effect o f two accelerants on properties of Portland cement, Grey and White ProRoot MTA
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Introduction. Mineral trioxide aggregate (MTA) was initially developed as a perforation repair material. Subsequently, its uses expanded to include root-end filling material, an apical barrier in apexification, and a capping material in vital pulp therapy. Recently, different accelerants have been developed that provide faster setting time and greater compressive strength when combining certain additives with the powder. The best setting time and compressive strength results were obtained when the composition of the accelerant formulation included CaCl 2 , fumed silica, and CaHPO 4 or Ca 10 (PO 4 ) 6 (OH) 2 . Objective. To test two accelerant formulations in form of aqueous suspensions and determine their effect on the properties of Portland cement (PC), Grey ProRoot MTA (GMTA) and white ProRoot MTA (WMTA) in terms of setting pH, compressive strength, solubility, and internal surface morphology of the set specimens. Materials and methods. Three types of cements were tested: PC, GMTA, and WMTA. These cements were mixed with either distilled water (control) (PC-W, GMTA-W, and WMTA-W), accelerant formulation L (PC-L, GMTA-L, and WMTA-L), or accelerant formulation J (PC-J, GMTA-J, and WMTA-J). The pH of 5 samples from each composition was monitored during 30 minutes from the start of mixing. The setting time was measured on 5 samples from each group using a Gilmore needle apparatus. The compressive strength was measured on 10 samples from each formulation at 24 hours after mixing the cement. The solubility of the material was tested at five time periods: 24h, 72h, 7d, 14d, and 28d. Six specimens from each formulation were prepared for the solubility test. The solubility values obtained at different periods of time were recorded and represented graphically as cumulative solubility and solubility rate. Precipitates formed on the surface of the specimens at the end of the solubility experiment and precipitates collected from bottles in groups GMTA-W and GMTA-L were analyzed using X-Ray Diffraction. The internal morphology of fractured specimens from each of the setting time groups was analyzed using Scanning Electron Microscopy. Comparisons between the control and experimental groups of the same cement type were performed using the student's t-test at a 5% level of significance that was adjusted using Bonferroni's method. Results. The setting pH of WMTA-L was significantly lower than WMTA-W (p < 0.0056). The final setting time of cements mixed with formulation L or J was significantly shorter than that of cements mixed with water (p < 0.0056). In addition, WMTA-L showed significantly shorter final setting time than WMTA-J (p < 0.0056). The compressive strength values of cements mixed with formulation L or J were significantly greater than that of cements mixed with water (p < 0.0056). Specimens in WMTA-L and WMTA-J were significantly more soluble than WMTA-W at the first three and seven days respectively (p < 0.0056). The crystals precipitated on the surface of all cements appeared to be a mixture of chemicals primarily containing calcium carbonate. Some peaks identified as calcium hydroxide were found in WMTA-L. The precipitates collected from the bottles were identified as calcium carbonate for GMTA-W and calcium carbonate and hydroxyapatite for GMTA-L. Using SEM, all accelerated cements exhibited a highly consolidated and dense structure compared to their respective non-accelerated cements, which exhibited a more porous and loosely packed structure. Conclusion. The addition of formulation L or J to PC, GMTA and WMTA significantly reduced the setting time. This reduction in setting time was accompanied by a desirable increase in the compressive strength. Although a statistically significant decrease in immediate pH of WMTA was observed after the addition of formulation L, this change seems to be clinically irrelevant. The addition of formulation L and J resulted in greater levels of cumulative solubility of WMTA at the first three to seven days. SEM observations were in agreement with the compressive strength findings.