Soft drink is bad for your teeth for two reasons:
1. The high sugar content provides food for the bacteria that cause decay, leading to holes in your teeth
2. The high acid content wears away the outer surface of your teeth, exposing the inner surface which is closer to the nerve. This can lead to sensitivity and if severe, can damage the nerve, and may lead to needing root canal treatment. To prove how highly acidic coke is, the pH of water is 7 (neutral) but the pH of coke is 2.63 which is only one point higher on the pH scale than battery acid.