California Registered Dental Assistant (RDA) Written Practice Exam

The water/powder ratio of plaster for pouring a model is

1. 100/30

2. 100/40

3. 100/50

4. 100/60

The correct answer is: 100/50

The water/powder ratio of plaster for pouring a model is important because it affects the consistency and setting time of the plaster. A ratio that is too high, like A or B, will create a thinner mixture which can lead to weaker and more fragile casts. Similarly, a ratio that is too low, like D, will create a thicker mixture that may take longer to set and can result in a rougher surface texture on the cast. A 100/50 ratio, as in option C, is generally considered the standard for pouring a model. This creates a creamy mixture that pours easily and produces a smooth and strong cast.