Determination of bound and unbound water in dental alginate irreversible hydrocolloid by nuclear magnetic resonance spectroscopy

ObjectivesAlginate materials are considered unsuitable for precise fixed prosthetic rehabilitation due to their tendency to undergo spontaneous syneresis. Commercial alginate impression materials were investigated using Nuclear Magnetic Resonance (NMR) Spectroscopy to probe the relation between changes in the microscopic water environment and dimensional change to obtain a better understanding of spontaneous syneresis.MethodsNMR was used to measure the spin-lattice relaxation times (T1) of 1H nuclei in water in alginate matrices to characterize changes in gel structure over time. These results were related to the dimensional stabilities of the alginate impression materials, their chemical compositions, and the Moisture Sorption Isotherms (MSI) obtained by incubation at fixed relative humidities.ResultsThe rate of change of T1 with time was found to be a better predictor of dimensional stability than MSI. The greatest dimensional stability for the alginate powders investigated was associated with a high filler:alginate ratio and a high Ca:Na ratio.SignificanceNuclear magnetic resonance spectroscopy may used to measure changes in alginate impression materials under conditions where no dimensional change can be observed directly. Changes occurred rapidly even at 100% humidity, suggesting the dimensional stability of alginate impression materials is partially independent of the rate of dehydration. The results may open a way to formulate alginate impression materials more suitable for precise fabrication of dental prostheses.