- The primary role of a retarder when added to gypsum products in dental practice is to prolong the setting time.
- Gypsum products, such as dental stone and plaster, undergo a chemical reaction called hydration when mixed with water, leading to the setting and hardening of the material.

- A retarder functions by slowing down this chemical reaction, which allows for increased working time.
- This is particularly important in clinical and laboratory settings where precise manipulation and detailed shaping of the gypsum are required before the material hardens.
- Without a retarder, the gypsum might set too quickly, making it difficult to form accurate impressions or models.

It is important to note that:
- Option 1 (To accelerate the setting process) is incorrect because a retarder slows down, not speeds up, the setting.
- Option 2 (To increase the final strength) is not the main function of a retarder; strength is more influenced by the gypsum type and powder-to-water ratio.
- Option 4 (To improve the surface hardness) is unrelated to retarders; surface hardness depends on the proper setting and composition of the gypsum itself.

In summary, the key point is that retarders extend the setting time to facilitate better handling and accuracy in dental gypsum applications.

Reference: Craig’s Restorative Dental Materials, 13th Edition, Chapter 4, pp. 68-70