Final answer:
Altering the water temperature is the best method to control the setting time of an irreversible hydrocolloid without changing its physical properties. Warm water accelerates and cold water decelerates the setting reactions.
Step-by-step explanation:
The best method to control the setting time of an irreversible hydrocolloid without affecting its physical properties is to alter the water temperature. Changing the water to powder ratio, mixing time, or composition could indeed affect the physical properties of the hydrocolloid. On the other hand, altering the water temperature influences the rate of the chemical reaction leading to the setting of the hydrocolloid. For instance, using colder water will slow down the setting time, while warmer water will speed it up. This method allows for adjustability in clinical situations to accommodate different needs without compromising the material's inherent qualities.
It's imperative to note that the water itself remains unchanged in terms of quality when used to mix with hydrocolloid powder—meaning it neither increases nor decreases in quality. The solvent power of water facilitates such reactions by allowing substances to come into contact without altering the water's composition.