As you can see, there are many reasons why you can get tooth decay problems without sugar. If you read the whole list, you may have noticed that many of these surprising reasons had to do with your saliva and whether it is thin or thick. Still, if you cover everything and still experience this problem, keep in mind there are also genetic factors and nutritional deficiencies that may be behind this problem.
The best idea to find a fitting solution for yourself is to talk to your dentist about your concerns and follow his instructions on how to brush correctly, what sort of treatments you need to prevent cavities and tooth decay, and follow his advice on the type of foods and drinks you should avoid, and your oral hygiene routine.