Breathing through the mouth a lot can apparently contribue to increased plaque (and gunk generally adhering more vigorously to the teeth in the front). I don't know if others primarily mouth breath while cycling or working out, but I do due to allergic congestion 95% of the year. My dentist noticed that I have plaque buildup on the front teeth rather than the rear like most people and she attributed it to my mouth breathing.

not sure this is relevant to the OP, but am throwing it our there.