The chemical properties of light- and chemical-curing composites with mineral trioxide aggregate filler.
OBJECTIVE
One of the challenges encountered with composite restorations is their inability to prevent secondary caries. Alternative fillers that initiate remineralization have been proposed but poor mechanical strength limits their use to lining and support materials. Mineral trioxide aggregate (MTA) is a material with many dental applications including root-end filling and pulp capping. MTA is capable of encouraging remineralization by leaching calcium in solution, and has the ability to form apatite in physiological solution. The aim of this study was to characterize and investigate the chemical properties of MTA-filled composite resins.


METHODS
Composite resins composed of light-cured (Heliobond) and chemical-cured (Superbond) dental resins filled with MTA Plus (MTA-Light, MTA-Chem) respectively, and MTA Plus mixed with water (MTA-W), were investigated. Un-hydrated and set materials were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) analysis and Fourier transform infrared (FT-IR) spectroscopy after being stored dry or immersed in Hank's balanced salt solution (HBSS). The chemical properties of the set materials were then investigated.


RESULTS
XRD and FT-IR analyses revealed that MTA powder remains unhydrated within the composite, even after 28 days of immersion in HBSS. Furthermore neither resin appeared to chemically react with the MTA. EDX revealed minimal diffusion of bismuth oxide through the polymer network. Apatite formation on the material surfaces was demonstrated by SEM. Significantly less apatite deposition was exhibited on the composites compared to MTA-W. All materials leached calcium and produced an alkaline pH in physiological solution. The pH at 28 days was: MTA-W 12.7, MTA-Light 11.4, and MTA-Chem 10.8. Calcium ion concentration followed the same trend, with MTA-W>MTA-Light>MTA-Chem.


SIGNIFICANCE
The novel composites exhibited calcium ion release, alkalinizing pH and formation of apatite, although in each case not as strongly as the control (MTA-W). MTA-Chem fared less favorably than MTA-Light in these aspects. Thus they are recommended for applications where bioactivity is desirable but not critical, and only they have a significant advantage over ordinary MTA in some other aspect.