Effect Of Additives To MTA On Setting Reaction And Time

Mineral Trioxide Aggregate (MTA) sets via hydration of calcium silicate components to yield hydrated calcium silicates and calcium hydroxide (Ca(OH)₂).  A drawback of MTA, however, is its long setting time.  Therefore, many additives have been suggested to reduce setting time.  The effect those additives have on setting reaction product formation has been largely ignored. 

Objective: To examine the effect additives have on MTA’s setting time and setting reaction using differential scanning calorimetry (DSC). 

Method: ProRoot MTA (Dentsply Tulsa Dental) powder was prepared with distilled water, phosphate buffered saline (PBS), CaCl₂, 3% NaOCl, or lidocaine in a 3:1 mixture and sealed in crucibles for DSC evaluation.  The setting reaction exotherms were evaluated at 37°C for 8 hours to determine setting time.  Separate samples were stored and evaluated by dynamic scan DSC (37-640°C @10°C/min) at 1 day, 1 week, and 1 month (n=9/group/time).  Dynamic DSC quantifies reaction product formed from the amount of heat required to decompose it.  Thermogram peaks were integrated to determine enthalpy which was analyzed with ANOVA/Tukey (a=.05).

Result: Isothermal DSC identified two main peaks occurring at 25-50 minutes and 4.5-6 hours for the control, while additive groups had earlier peaks indicating a decreased setting time.  The dynamic DSC scans produced an endothermic peak around 450-600°C attributed to Ca(OH)₂ decomposition.  Enthalpy values were:

Group	Ca(OH)2 Decomposition Enthalpy (J/g)
	1 Day	1 Week	1 Month
Control	70.1±17.5 C	138.5±13.5 A	98.8±8.6 A
CaCl2	100.3±8.6 A	117.4±6.9 B	96.0±11.0 AB
NaOCl	24.1±8.0 D	39.2±6.8 D	22.9±8.3 D
PBS	93.9±16.1 AB	116.8±12.4 B	82.1±14.4 B
Lidocaine	74.1±29.7 BC	87.2±6.6 C	59.6±11.7 C

Different letters denote significant (p˂0.05) differences. The use of a few additives (NaOCl/Lidocaine) resulted in significantly less Ca(OH)₂ product formation.

Conclusion: Consideration of the chemistry of MTA hydration is needed when certain additives are contemplated when mixing MTA.