There are no specific fruits and vegetables which can strengthen the teeth. Teeth remain strong by proper plaque removal to prevent acid formation and by the proteins present in the saliva. Although the fibrous content of the fruits and vegetables can help in keeping the teeth clean, they are not a replacement for tooth brushing which is the most efficient way of removing the plaque. Still a good amount of fruits and vegetables should be consumed so that the general health is maintained for an overall healthy body. Regards.