How quickly can secondary caries develop?

Immediately: Secondary caries can start as soon as bacteria have a food source to produce acids and therefore cause demineralization of the tooth. That is why it is important to brush and floss after every meal and after any snacks. At least rinse out thoroughly when you cannot brush or floss and avoid foods and liquids high in sugar. Many sports and energy drinks are very acidic and can also be problematic.

3-4 months: Cavities of any kind can develop in as little as 3-4 months once they start. If you are asking how long a restoration should last, the average lifespan of a filling is 5-7 years and a crown is 10 years.