Dental Materials
Volume 25, Issue 4 , Pages 486-493, April 2009

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

  • C.M. Fellows

      Affiliations

    • Key Centre for Polymer Colloids, The University of Sydney, Sydney, NSW 2006, Australia
    • Corresponding Author InformationCorresponding author. Present address: School of Biological, Biomedical, and Molecular Sciences, The University of New England, Armidale, NSW 2351, Australia. Tel.: +61 2 6773 2470; fax: +61 2 6773 3268.
    • ,
  • G.A. Thomas

      Affiliations

    • Department of Obstetrics and Gynaecology and Faculty of Dentistry, The University of Sydney, Sydney, NSW 2006, Australia

Received 17 October 2007; received in revised form 19 September 2008; accepted 7 October 2008.

Abstract 

Objectives

Alginate 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.

Methods

NMR 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.

Results

The 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.

Significance

Nuclear 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.

Keywords: Alginate, Dental impression materials, Nuclear magnetic resonance spectroscopy, Moisture sorption isotherm, Syneresis, Water behavior, Tissue engineering materials

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PII: S0109-5641(08)00251-0

doi:10.1016/j.dental.2008.10.001

Dental Materials
Volume 25, Issue 4 , Pages 486-493, April 2009

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