Question: How does soft drink ruin your teeth?

There are two main factors – sugar and acid. Soft drinks tend to be high in both. The pH (how acid/alkaline the mouth is) of the mouth is relatively stable, and an increase in acidity will cause tooth decay because teeth are made from calcium and phosphorus (among other minerals) which are susceptible to acid. Essentially the acid eats away the mineral layers.

So excess sugar leads to bacteria on teeth (plaque) producing more acids which then accelerates tooth decay. Soft drinks are also often high in acid which can erode the mineral layer as well. Also the pH of the mouth determines which bacteria will live in your mouth, lower pH (acidic) provides an environment for the bad bacteria and higher pH (more alkaline) provides for the heather bacteria. It is also not so much about the amount of sugar you eat but the frequency (higher frequency is worse).

A persons tooth quality also plays a role as some people have have more/less tooth mineral content in their teeth and variation in the enamel layer. So less soft drink is best.