Toothbrushing, inflammation, and risk of cardiovascular disease: results from Scottish Health Survey

Two questions:

The researchers control for factors such as class, smoking and
physical activity; but it seems unlikely that the group of non-smoking
physically-active middle-class people who don't brush their teeth is a
large one. Wouldn't this undermine the comparison?

Wouldn't the same findings result from a survey comparing those who
did and did not say they looked after themselves?

Competing interests:
None declared