Many people drink sugar free sodas hoping that the are healthier than regular soda. Regular soda is definitely not good for your teeth. As a boy I once did a science project and put extracted teeth into different liquids for varying amounts of time to see what would happen. The teeth that were put into a sugary soda like Coke, had large cavities within 2 weeks. Regular sodas have a lot of sugar. A single can of Coke has 39 grams of sugar. But sugar is not the main problem. The main issue is the acidity of sodas. sugar free sodas are as acidic as sugar full soft drinks.
The enamel of a tooth is made up of an inorganic matrix. The inner section of the tooth is organic as well and it is when the bacteria penetrate the inorganic outer layer that we have problems and a cavity begins that will continue to grow and damage the tooth. Anything that weakens that outer layer will make it easy for a cavity to begin. Acid is what will weaken this enamel layer and it is actually how the bacteria make their cavity.
The sugar in food is the energy for bacteria but it is the acid that does the damage. So when we drink sugar free sodas, we actually are taking in as much acid as a regular soda. In fact people tend to drink much more sugar free soda thinking that it is healthier. We all know that feeling of grittiness when we drink a soda that the teeth seem not to slide so smoothly across each other. That is the acid removing a micro layer of tooth structure.
Tray and avoid drink any soda because the extreme acidity of the citric acid component will be very aggressive to your teeth.