Which of the following is adjusted by manufacturers to create regular and fast-set alginate impression materials?

The adjustment of alginate impression materials to create regular and fast-set variants is primarily achieved by the inclusion of sodium phosphate. Sodium phosphate acts as a reaction retarder in the setting process. In the formulation of alginate, the presence of sodium phosphate slows down the rate at which the calcium sulfate hemihydrate reacts with water, allowing for a longer working time in regular-set alginates. Conversely, in the fast-set versions, sodium phosphate is reduced or omitted to allow for a quicker reaction, leading to a faster setting time.

Understanding the role of sodium phosphate in alginate formulations is crucial for dental professionals as it directly influences the usability of the material during procedures requiring impressions, providing either more time for manipulation or a quicker setting process as needed. The other components mentioned, such as diatomaceous earth, calcium sulfate dihydrate, and potassium sulfate, contribute to different functions within the alginate composition, such as improving strength, consistency, or reducing the setting expansion, but they do not influence the setting time in the same way sodium phosphate does.