Pressure sensors have moved from premium models to mainstream ones, and the feature addresses a specific and well-recognised way that brushing causes harm.
More force does not clean more
Plaque is a soft film held to the tooth by material the bacteria produce, and disrupting it requires contact and movement rather than pressure.
Beyond a modest force the bristles splay outward, so their tips no longer meet the surface and the working part of the brush stops contacting the tooth.
Cleaning effectiveness therefore rises with force up to a point and then falls, which is the opposite of most people's intuition about scrubbing.
Excess force damages gum and root surface
Gum tissue at the margin is thin, and repeated heavy brushing against it contributes to recession, particularly on prominent teeth on the cheek side.
Once the root is exposed, its covering is far softer than enamel and abrades under the same force that enamel would tolerate.
The characteristic result is a notched groove at the neck of the tooth, often accompanied by sensitivity to cold and to air.
The sensing mechanism is mechanical
Most designs measure deflection of the brush head relative to the handle, using either a small displacement sensor or a change in the motor's electrical load.
When the measured value crosses a set threshold, the handle responds by illuminating a light ring, altering the vibration pattern or reducing motor power.
The threshold is a manufacturer's choice rather than a clinical standard, which is why brushes differ in how readily they trigger.
What the feature does not do
A sensor reports force along one axis and cannot detect brushing at the wrong angle, missing sections entirely, or scrubbing horizontally across the gum margin.
It also cannot distinguish force applied to the tooth from force applied to soft tissue, so it offers no protection against poor placement.
Technique still has to come from somewhere, and a hygienist watching a person brush identifies errors that no handle can measure.
Interpreting the feedback usefully
A sensor triggering constantly is worth acting on rather than ignoring, since it indicates a habit that is likely already affecting the gum margin.
Bristles that splay within weeks are a comparable signal, and they suggest force high enough to shorten the useful life of every head.
Existing recession, notching or persistent sensitivity should be assessed by a dentist, because the cause may be brushing force, grinding, acid exposure or a combination.