Replacement of radiopacifier in mineral trioxide aggregate; characterization and determination of physical properties

Objective

Investigation of the replacement of bismuth oxide by zirconium oxide in mineral trioxide aggregate (MTA) and characterization and evaluation of the radiopacity and physical properties of varying replacements of zirconium oxide mixed at either water-powder or water-cement proportions of 0.3. The suitable filler loading of zirconium oxide for Portland cement in a MTA system for use as a root-end filling material was thus determined.

Methods

Portland cement replaced by zirconium oxide in varying amounts ranging from 0% to 50% in increments of 10 was mixed with water either at a water/powder (WP) proportion or at a water/cement (WC) proportion of 0.3. Portland cement and ProRoot MTA were used as controls. The materials’ microstructures were investigated using optical light microscopy. The radiopacity, strength, setting time, water uptake, solubility, sorption and porosity of the specimens were also evaluated. The optimum formulation was selected using the digital logic method.

Results

Portland cement replaced with 30% zirconium oxide mixed at a water/cement proportion of 0.3 resulted to have the optimum combination of properties. This material exhibited radiopacity, compressive strength, setting time, water uptake, solubility and sorption comparable to ProRoot MTA. Both microscopy and the evaluation of porosity from the solubility and sorption experiments indicated a degree of porosity consisting mainly of capillary pores and entrapped air voids.

Significance

A filler loading of 30% zirconium oxide to Portland cement mixed at a water to cement proportion of 0.3 resulted in a material with comparable properties to mineral trioxide aggregate.