[knodi123]

as a child, I was told that my teeth were fairly well protected against cavities on the open surfaces by cursory brushing, by virtue of my sealants- but that flossing was equally if not more important since those inter-tooth pockets were the only places where food could hang out, firmly pressed against the enamel.

[Otik]

There actually hadn't been much research done on it until relatively recently (and probably still not enough), so your dentist was just following the common knowledge of the time.

Here's a link: http://www.cochrane.org/CD008829/ORAL_flossing-to-reduce-gum...