I've never 'got'

Changing toothbrushes.

There's contradictory reasons given, as in

• the bristles wear out, so they'll no longer be effective
  
• the bristles wear out and so become too
  abrasive
  
  

I've never had great teeth, though in the last decade things have improved. I brush twice daily and floss once. Having done experiments on the sly, it certainly hasn't made any difference in my gum health or tooth decay.