Your teeth are more vulnerable to problems such as decay during treatment. You should avoid sweet and/or sticky foods, and acidic drinks such as fizzy drinks and fruit juices. You particularly need to avoid snacking between meals.
Each time you eat or drink, your teeth are attacked by acids for around 40 minutes, which leads to decay. Your saliva washes this acid away and re-mineralises your teeth, but it needs time to do this. If you snack frequently the acid is never washed away and your teeth become damaged.