Why does smoking lead to tooth decay, gingivitis and periodontal disease?

Not decay perhaps: Smoking is a cause of many problems. Not so much tooth decay, but it can lead to gingivitis and periodontal disease. This is because the smoke has so many chemicals in it they aren't healthy for any oral structure. Also, just the heat of the smoke can cause lots of problems. Simply put...If you can quit smoking...Do so. You'll save your health, others health and save $$$.

Indirectly: Smoking indirectly leads to tooth decay because of the increased heat of the cigarette or cigar etc. Causing the bacteria that cause the decay to be more active, this also applies to gingivitis and periodontal disease. The other component chemicals from the smoke cause irritation and tissue damage.

IRRITANT: Smoking is an irritant to the entire body, especially its localized damage to the oral tissues and teeth.