When homo sapients evolved from chimpanzees, initially they did not need to brush their teeth. Cavities evolved concurrently with dietary changes. Wild animals never brushed teeth and had no problems with cavities.
( Pets of course are a different story. We invented Whiskas and Pedigree Pal, which created demand for for the Pet Dentistries).
In early ages, people used rag with soot and salt, to do their occasional teeth maintenance.
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An English guy named William Addis, while serving term in prison, had nothing else to do but think about teeth. The result — tooth brush invention.
171 years later, an outfit named Frank bluntly stole this idea and patented it.
Colgate, Procter and Gamble and others monetized that invention later on.
Cool handle designs to compensate for less bristles.
The reason why every year we see less and less bristles on our brushes is the result of cost savings. Bristles are the most expensive part of the toothbrush.
