When a chewing gum manufacturer makes the claim, "four out of five dentists surveyed recommend sugarless gum for their patients that chew gum," how many dentists need have been surveyed for the statement to be factually accurate?

Five.

Explanation:

The scientific researches have proper methodology, observation and the interpretation of the result to explain the hypothesis as a correct theory. The hypothesis is based on the observations only.

The fact or any actual concept needs to be explained well in the scientific research. The claim that four out of five dentist are involved in the survey. This statement clearly claim that atleast five dentists are surveyed for the statement to be correct.

Thus, the answer is five.