When you get a second opinion keep inmind that tooth decay is a selective thing. What one dentist wants to fill another will be happy to watch. Did anyone ask how big these cavities are? And what teeth are they talking about. Also are they talking fillings or fissure seals? Sealants are done to 'seal' fissures that may otherwise decay. They are a preventative rathr than restorative.
Also fruitjuice hs a high sugar content even with no added sugar.