Eight out of 10 dentists prefer Crest toothpaste. What is the ratio of dentists who do not prefer Crest to those who do?

Step 1 ：The problem states that 8 out of 10 dentists prefer Crest toothpaste. This implies that 2 out of 10 dentists do not prefer Crest toothpaste.

Step 2 ：We are asked to find the ratio of dentists who do not prefer Crest toothpaste to those who do. This is equivalent to the ratio of 2 to 8.

Step 3 ：We simplify the ratio 2:8 to 1:4.

Step 4 ：\(\boxed{1:4}\) is the final answer.