Hydrocolloid In Dentistry
Definition and General Properties
Hydrocolloids in dentistry are a type of colloid in which the dispersed particles (solute) are uniformly distributed and suspended within a liquid medium (solvent), typically water. Unlike solutions where solute particles dissolve completely, or suspensions where solute particles settle at the bottom, colloids maintain a stable suspension of small solute particles (< 200μm) in the solvent. When this occurs in water, it is termed as a hydrocolloid.
Imbibition and Syneresis
Imbibition refers to the absorption of water by a hydrocolloid from its environment. This occurs when the hydrocolloid is exposed to moisture, causing it to swell and increase in volume.
Syneresis, on the other hand, is the opposite process, where water molecules are expelled from the hydrocolloid due to further setting or agglomeration of the solute particles. This leads to shrinkage and the release of excess water.
Drying Shrinkage
Drying shrinkage is the reduction in volume that occurs in a hydrocolloid as a result of water evaporation. When exposed to air or a dry environment, the water within the hydrocolloid evaporates, causing it to contract and shrink.
Important Considerations
- Hydrocolloids can exist in two physical states: sol and gel. The sol state refers to a viscous liquid phase, while the gel state is a rubbery gelatinous phase. The transition between these states occurs during the setting reaction.
- In hydrocolloid impressions, the material is initially placed on the tissue in the sol state, where it flows and adapts to the contours of the oral structures. As it sets, it transitions into the gel state, forming a stable impression.
- To prevent drying shrinkage and maintain dimensional stability, hydrocolloid impressions should be stored in an environment with high humidity (ideally 100%) before casting to ensure optimal results.