Just been reading the new BOOTS "baby and you" magazine.
They say that the AVENT magic trainer cup is actually BRITISH DENTAL HEALTH FOUNDATION APPROVED.
Lauren
so is this one, just looked at the dental website Tommee Tippee Easyflow Drinking System
Another article goes on to say that;
Using a cup will help keep babies teeth and gums healthy because the fluid spends less time in contact with teeth and gums but, even so it's best to avoid sugary drinks because they can cause tooth decay. If you do give juice, give occasionally and dilute as much as possible.