**Core Concept**
Gypsum products are widely used in dentistry as impression materials and dental casts due to their dimensional stability, ease of manipulation, and cost-effectiveness. The setting expansion of gypsum products is a critical property that affects the accuracy and fit of dental restorations. The expansion is primarily due to the crystallization of hemihydrate to dihydrate, which releases water vapor and causes the material to expand.

**Why the Correct Answer is Right**
The setting expansion of gypsum products can be reduced by controlling the amount of water incorporated into the powder. Excess water leads to a higher degree of crystallization, resulting in increased expansion. By limiting the water content, the expansion can be minimized. Another factor that influences setting expansion is the temperature of the environment. Warmer temperatures can accelerate the crystallization process, leading to greater expansion. Therefore, it is essential to control the temperature and water content to achieve the desired level of expansion.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the setting expansion of gypsum products.
* **Option B:** This option may be related to other properties of gypsum products, such as their mechanical strength, but it does not directly affect setting expansion.
* **Option C:** This option is incorrect because it is actually a factor that increases setting expansion, not reduces it.

**Clinical Pearl / High-Yield Fact**
To minimize the setting expansion of gypsum products, it is essential to use the correct amount of water and control the temperature of the environment. A general rule of thumb is to use a water-powder ratio of 0.25-0.30 to achieve optimal expansion.

**Correct Answer:** C.