Dental decay is caused by bacteria which effectively produce acid by reacting with fermentable carbohydrates, particularly sugars, in your diet. This acid causes demineralisation of the enamel, and if present for sufficient time, will lead to an opening in the enamel which then allows destruction of the underlying dentine. This is called decay and presently this decay can only be treated by removal and restoration of the resulting cavity ie a filling.
To reduce your risk of decay, avoid snacking as much as possible. When you eat a meal, significant amounts of saliva will be produced, and this saliva will help to neutralise the acid. However, by snacking, you are starting the cycle of acid attack and demineralisation all over again.
In a normal day, your mouth can recover from 3 or maybe 4 attacks, that is at mealtimes. The highest risk time for decay is between meals, when your saliva flow is low. So, put simply, snacking is out if you want to avoid decay, and this includes snacking on "healthy" snacks, such as fruit, fruit juice or yogurts. These foods should be confined to mealtimes and ideally you should not eat or drink within 2 hours of bedtime, again because your saliva flow is lower overnight meaning that your teeth are more susceptible to decay.
Besides not snacking, how can I protect my teeth?
Fluoride will help remineralise teeth that have been attacked by acid. Fluoride occurs naturally in many water supplies and in Ireland fluoride has been added to the water supply since the 1960's. This has led to a visibly dramatic reduction in the amount and extent of decay present in teeth.
Any objection to the inclusion of fluoride is purely philosophical, and there are no known health risks as a result of the small amount of fluoride that is added. Fluoride is also contained in most toothpastes, again in minute quantities.