If they were popping out doesn't that indicate they didn't fit your teeth properly? These people aren't sounding very reliable to me lol.
Gah, I explained myself badly. The wire that held my traintracks together was suspended across the gaps to reach the molars at the back of my mouth. If I ate something like apple, there was a chance that the food would cause the wire to bend and slip out of the clamp that was attached to my back molars. It took ages to bend the wire back into it's original position.