Based on the clinical scenario above:
P: bad breath, male, adult
I: tooth-brushing
C: doing nothing
O: reduction in bad breath
Not all of these terms will be used directly in the search, but it's good to be aware of all potential search terms.
Here's the question that you'd base your search on:
Does tooth-brushing, in comparison with doing nothing [i.e., what the patient is currently doing], decrease bad breath in older male adults?