Brushing manually with the wrong technique and not for long enough does not remove plaque effectively. This allows harmful bacteria in the plaque to damage teeth and irritate gums.

Brushing properly before bed keeps harmful bacteria under control and helps good bacteria maintain a healthy mouth while you sleep. Philips Sonicare is the #1 dental professional recommended sonic toothbrush brand worldwide.
At night, our mouths are vulnerable. While we sleep, saliva flow slows down, allowing bacteria left behind to multiply more easily.

Sonicare Fluid Action supports the bristles to clean by driving fluid between teeth & along the gumline.
Slot DE et al, Int Dent Hygiene (2012):187-97
vs. a manual toothbrush
DiamondClean range with A3 brush head, vs. a manual toothbrush