How can prolonged setting time of glass ionomer cement be achieved?

Prolonged setting time of glass ionomer cement can effectively be achieved by cooling down the slab on which the cement is mixed. This method works because lower temperatures can slow down the chemical reactions that occur during the setting process of the cement. As a result, the overall setting time increases, allowing for more working time before the cement begins to harden.

When considering the other methods, increasing the amount of distilled water might actually influence the consistency and properties of the cement, but it doesn't necessarily extend the setting time effectively. Mixing more vigorously tends to promote faster reactions, thereby decreasing the setting time, rather than prolonging it. Using less powder would alter the composition and could lead to insufficient strength and performance, also not extending the setting time effectively. Thus, cooling the mixing slab is the most effective and reliable way to achieve a prolonged setting time in this scenario.