In most instances you will know what to avoid. One should avoid everything that is hard and tough, as such food can damage the appliances.
Here is a list of the most common ones:
Apples – it pays to cut them into pieces
Carrots – shred them or cut them into very small pieces
Sweet corn – scrape the corn of the stalk and do not gnaw
Do not crunch ice cubes
Lollipops, rock candy, toffee and caramel are also on the ban list.
Popcorn is on the banned list as the husk gets under the skin at the teeth
Sugarcoated chewing gum is also banned as it sticks to all appliances
Dried fish is banned as it breaks the appliances
One should also avoid the chewing pencils and pens.