The microstructure and surface morphology of radiopaque tricalcium silicate cement exposed to different curing conditions

Formosa, L.M., Mallia, B., Bull, T. and Camilleri, J. (2012) The microstructure and surface morphology of radiopaque tricalcium silicate cement exposed to different curing conditions. Dental Materials, 28 (5), 584-595. (doi:10.1016/j.dental.2012.02.006).

Abstract

Objective - Tricalcium silicate is the major constituent phase in mineral trioxide aggregate (MTA). It is thus postulated that pure tricalcium silicate can replace the Portland cement component of MTA. The aim of this research was to evaluate the microstructure and surface characteristics of radiopaque tricalcium silicate cement exposed to different curing conditions namely at 100% humidity or immersed in either water or a simulated body fluid at 37 °C.
Methods - The materials under study included tricalcium silicate and Portland cements with and without the addition of bismuth oxide radiopacifier. Material characterization was performed on hydrated cements using a combination of scanning electron microscopy (SEM) with X-ray energy dispersive (EDX) analyses and X-ray diffraction (XRD) analyses. Surface morphology was further investigated using optical profilometry. Testing was performed on cements cured at 100% humidity or immersed in either water or Hank's balanced salt solution (HBSS) for 1 and 28 days at 37 °C. In addition leachate analysis was performed by X-ray fluorescence of the storage solution. The pH of the storage solution was assessed.
Results - All the cements produced calcium silicate hydrate and calcium hydroxide on hydration. Tricalcium silicate showed a higher reaction rate than Portland cement and addition of bismuth oxide seemed to also increase the rate of reaction with more calcium silicate hydrate and calcium hydroxide being produced as demonstrated by SEM and XRD analysis and also by surface deposits viewed by the optical profilometer. Cement immersion in HBSS resulted in the deposition of calcium phosphate during the early stages following immersion and extensive calcification after 28 days. The pH of all storage solutions was alkaline. The immersion in distilled water resulted in a higher pH of the solution than when the cements were immersed in HBSS. Leachate analysis demonstrated high calcium levels in all cements tested with higher levels in tricalcium silicate and bismuth replaced cements.
Significance - Tricalcium silicate cement is more bioactive than Portland cement as demonstrated by various characterization techniques. The bioactivity was monitored by measuring the production of calcium hydroxide and the formation of calcium phosphate when in contact with simulated body fluids.
Keywords - Mineral trioxide aggregate, Portland cement, Tricalcium silicate, Microstructure, Surface morphology

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