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

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.peer-reviewe

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 (Super-bond) 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.peer-reviewe