SOLUBILITY AND SORPTION
The solubility of materials in the mouth and the sorption (adsorption plus absorption) of oral fluids by the material are important criteria in their selection. Frequently, laboratory studies have have evaluated materials in distilled water. At times these studies gave results inconsistent with clinical obsevations becaused materials in the mouth are covered with plaque and therefore are exposed to various acids and organic materials. An example of the inconsistency is that zinc phosphate cements are considerably more soluble in the mouth than laboratory tests in water indicate. Also, the loss of zinc phosphate cements retaining a gold crown is a result of dissolution followed by and accompanied by disintegration. Nevertheless, laboratory tests usually rank materials correctly, so only the actual magnitude of the numbers should be taken with grain of salt.
Solubility and sorption are reported in two ways : (1) in weight percent of soluble or sorbed material, and (2) as the weight of dissolved or sorbed material per unit of surfaces area (e.g., miligram per square centimeter).
Absorption refers to the upteke of liquid by the bulk solid; for example, the equilibrium absorption of water by acrylic plastics is in the range of 2%. Adsorption indicates concentration of molecules at the surface of a solid or liquid, an example being the adsorption of components of saliva at the surface of tooth structure, or of a detergent adsorbed an the surface of a wax pattern.
Taken from : Dental Material, Robert G. Craig
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