Evaluation of Additives on MTA Setting and Product Formation

Mineral Trioxide Aggregate (MTA) is an endodontic material indicated for many applications.  Hydration of the calcium silicates in MTA powder produce several hydrated silicate species as well as calcium hydroxide that are pertinent to the physical and biological performance of MTA.  Various additives have been suggested to improve the long setting time and poor handling properties of MTA.

Objectives:  To evaluate MTA setting reaction and products using differential scanning calorimetry (DSC) when MTA is prepared conventionally or with additives.

Methods:  ProRoot MTA powder was prepared with distilled water (control), phosphate buffered saline (PBS), or a 3% sodium hypochlorite (NaOCl) solution (ChlorCid V, Ultradent) in a 3:1 mixture and sealed in an aluminum crucible for DSC evaluation (n=3/group).  The setting reaction exotherms were monitored at 37^oC for 8 hours followed by a 37-640°C dynamic scan at 10^oC/min.  DSC dynamic thermogram peaks were identified and integrated to yield enthalpy to serve as an indicator of reaction product formed.  Quantitative results were analyzed with ANOVA/Tukey (a=.05).

Results:  Isothermal setting reaction monitoring generally identified two main exothermic peaks occurring around 25-50 minutes and 4.5-6 hours.  The dynamic DSC scan produced an endothermic peak at 450-550°C attributed to Ca(OH)₂ decomposition.  The observed enthalpy (mean ± standard deviation) associated with this peak is shown in the table.  Different letters denote significant (p<0.05) differences.  The use of NaOCl in mixing MTA resulted in significantly decreased formation of Ca(OH)₂.  Qualitative differences in the dynamic scan were also observed in the NaOCl group compared to the others.

Group	Ca(OH)2 Decomposition Endotherm Enthalpy (J/g)
Control	31.3±4.6 a
PBS	29.0±12.9 a
NaOCl	4.7±2.5 b

Conclusion: Consideration of the chemistry of MTA hydration is strongly suggested when certain additives are contemplated in MTA preparation.