Brush plaque removing ability

[Bibilui]

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? 3 month? 4? 5? or 6 month?

[funnywebsite]

Toothbrushes should be changed at least every 3 months, no longer. I do not know anything about a 30 per cent reduction whatever you are going on about, so I don't know if you are wondering about changing your toothbrush or if this is a maths question. I just know you need to change your toothbrush regularly and keep it no more than 3 months.