The interdental spaces

Two teeth do not touch at a point but across a surface. Above and below it a space remains in which plaque settles undisturbed: sheltered, moist, out of reach of any bristle and not wiped by the tongue. Adding all these surfaces together comes to about a third of the entire tooth surface.

That explains two things. First: why gum inflammation almost always begins between the teeth. Second: why caries in adults arises more often between the teeth than on the chewing surfaces — for many people the chewing surfaces are sealed or rounded off, while the interdental spaces remain untouched.

Interdental brush or dental floss?

For most people and most interdental spaces the interdental brush is the more effective choice. It fills the space, also reaches the concave surfaces of the roots and is easier to handle than a thread. Studies show a clearer effect for it on bleeding and plaque.

Dental floss remains right where the teeth stand so close together that no brush goes in without injuring — often in the area of the front teeth. Many people need both: brushes for the molars, floss for the front.

The size decides

A brush that is too small moves in the interdental space without touching the walls — it acts as if it were cleaning. One that is too large can only be introduced by force and injures the gum. The right size can be pushed in with slight resistance and fills the space.

The interdental spaces of a mouth are of different sizes. Anyone working with a single size cleans some spaces well and others not at all. Have the sizes determined at the practice with measuring probes — that is a matter of minutes and the most effective single piece of advice there is on this subject.

Use

• Interdental brush: insert horizontally, not at an angle. Two or three times back and forth, without twisting. Rinse under water between two spaces. A brush lasts about a week; once the wire is bent, it is replaced.
• Dental floss: unroll about 40 centimetres, wind it around both middle fingers, and guide a short taut piece with thumbs and index fingers. Move it carefully through the tight spot — do not let it snap in — then draw it up and down in a C shape against both tooth surfaces. A fresh piece for every interdental space.

Waxed floss slides more easily through tight spots; unwaxed grips a little better. Anyone with bridges needs special floss with a stiffened end, introduced from the side beneath the bridge element. Sticks of plastic or wood are a stopgap when you are out; they reach the surfaces only incompletely.

How often, and when

Once a day is enough. The plaque needs about 24 hours to organise itself into a harmful layer — anyone who interrupts this rhythm once a day prevents it from establishing itself. Twice is not better, only more work.

The evening is the better time: at night less saliva flows and the plaque works undisturbed. And cleaning before brushing afterwards distributes the fluoride toothpaste into the opened interdental spaces as well.

It bleeds — should I stop?

No. Bleeding when cleaning the interdental spaces for the first time means that the gum is inflamed there. It is the indication of a condition that already existed, not an injury. Anyone who stops because of it leaves the inflammation in place.

With daily cleaning the bleeding usually recedes within one to two weeks — that is the fastest visible feedback oral hygiene has to offer. If it remains unchanged after two to three weeks, the findings belong at the practice: there may then be more behind it than a superficial inflammation.