Investigation of the effect of the water to powder ratio on hydraulic cement properties

Koutroulis, A. and Batchelor, H. and Kuehne, S. A. and Cooper, P. R. and Camilleri, J. (2019) Investigation of the effect of the water to powder ratio on hydraulic cement properties. Dental Materials, 35 (8). pp. 1146-1154. ISSN 0109-5641 (https://doi.org/10.1016/j.dental.2019.05.011)

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Abstract

Objective: The use of rheological properties to determine the optimal water: powder ratio of tricalcium silicate-based prototype materials incorporating alternative radiopacifiers and fillers. Determination of how the proportion of water incorporated affected the physicochemical behaviour of the materials. Methods: Endodontic cements replaced with 30% radiopacifier, and additions of calcium phosphate and micro-silica were tested. The unmodified cements were mixed with a 0.35 water: powder ratio which served as control. At this water: powder ratio, unmodified Portland cement without any addition had an adequate consistency and furthermore it has been well characterized. Assessment of material rheological properties enabled adjustment of the water: powder ratio in each material to provide comparable viscosity values to those of the pure cement. The flowability, phase analysis and calcium release were measured for both viscosity-matched and the standard 0.35 water: powder ratio blends. The prototype materials with the adjusted water: powder ratios were also characterized by scanning electron microscopy, energy-dispersive spectroscopy and evaluated for radio-opacity. Results: The use of the 0.35 water: powder ratio is not appropriate when changing the radiopacifier and incorporating additives. Zirconium oxide did not vary the water: powder ratio but tantalum oxide and calcium tungstate resulted in an increase and decrease in water demand respectively. Using the standard 0.35 ratio when the mixture had a low water demand resulted in higher flowability values and calcium release in solution. Micro-silica and calcium phosphate altered the hydration of the materials. All materials were adequately radiopaque. Significance: Rheological assessment is an easy reproducible way to determine the water: powder ratios of materials with varying amounts of additives and radiopacifiers during development. Modifications to the water: powder ratio affects material properties.

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