tooth brush

[yanetai]

for how long has a brush been in use that would reduce its plaque removing ability up to 30 per cent than a new one?

[buildersmate]

Clearly just a wind-up. Far too many variables in the problem. And what practical use would such info be.

[ezapf]

Popular question for a wind-up:
toothbrush

[logman]

5,4"

[aka estie]

28%

[mibn2cweus]

pi r squared,

no, pi r round,

cornbread r squared.

[lady_p_gold]

25 or 17 or a Mothercare baby stroller

[qapmoc]

Eddie, you cannot be serious, after three months the bristles would still be straight !!! I never replace my toothbrush until the bristles actually bend enough to touch the handle.