Scanning electron microscopic evaluation of the material interface of adjacent layers of dental materials

Objective

Many dental materials are used in contact with each other in sandwich techniques. Liners, bases and permanent restorative materials are placed adjacent to each other and allowed to set under the same conditions. The same applies for endodontic materials where irrigating solutions and root canal dressings come in contact with root canal obturating materials and root-end fillers. The aim of this research was to investigate the material interface of mineral trioxide aggregate (MTA) in contact with non-setting calcium hydroxide paste (CH), glass ionomer cement (GIC) and intermediate restorative material (IRM).

Methods

All materials were mixed according to manufacturer's instructions. Freshly mixed MTA (Dentsply) was placed in a plastic container and another dental material was compacted on it while still unset. These materials included GIC (Fuji IX), non-setting calcium hydroxide (Calasept) and IRM (Dentsply). The materials were allowed to set for 28 days at 37 °C and 100% humidity. The layered materials were sectioned longitudinally embedded in resin and polished to expose the interface between the two materials. Scanning electron microscopy (SEM) was performed of the interface and X-ray energy dispersive analysis (EDX) was conducted at 50 μm intervals to establish elements present at specific distances from the material interface.

Results

The calcium hydroxide paste did not affect the hydration of MTA. Migration of silicon, aluminum and bismuth from the MTA to the CH occurred. The GIC exhibited a high degree of micro-cracking and some porosity in the interfacial region. Strontium from the GIC was detected at 200 μm within the MTA. The zinc from the IRM cement was detected at 100 μm within the MTA. The zinc affected the hydration of the MTA leading to retardation of setting and increased porosity.

Conclusions

MTA interacts with other dental materials with resultant elemental migration in adjacent materials. Zinc oxide eugenol based cements should be avoided in the presence of MTA as zinc causes retardation of cement hydration with increased porosity. Glass ionomer cements absorb the water of hydration from the MTA also resulting in increased porosity and incomplete hydration of MTA.