Some smokers "bite" the cig filter when they smoke, while others smoke with their lips (cig filter never touches the teeth). Smoking in such ways stains different parts of the mouth cavity.
Apart from OP, I found out that supplementing bee pollen reduces the craving for smoking. It could be due to the increased metabolism & nutrition. More energy, hence less need for smoking perk-me-ups.
How much baking soda do you use for brushing? Sometimes, I put too much & it sort of "stings" the mouth cavity & lips. Thanks.