Many people nowadays have to wear false teeth when they was middle-aged.
Since the begining of this century(1) ........ decay has greatly increased .The amount(2) ......... sugar in our food has also increased .Doctors and dentists now know that(3) ...... is the chief cause of tooth (4) ............. Eskimos' teeth for example started to(5) ............ when they began to eat sweet (6)..........