H. N Handsworth signed the patent for the toothbrush only in 1857 with in the USA. Before this incident the toothbrushes were made of animal hair and didn't actually fight the bacteria affectively. Only in 1938 were the first toothbrush with nylon or synthetic bristles invented and most Americans did not brush their teeth every day until after World War II!
During WWII, the military required that soldiers brush twice a day to keep their teeth healthy. The soldiers brought the habit home after the war.
You can read more about the history of toothbrush and what changed since in our blogette.