Side effects of chewing tobacco are many but since we are talking about your teeth here are the side effects retlaided to just your mouth.
1) Stained teeth
2) Bad breath
3) Sores on the gums and in the mouth that are stubborn to heal
5) Risk of developing oral cancer
If you can you may wish to rethink chewing even just if as you said it is not every day. I say the risk is not worth taking.