It happened late one evening. I was sitting at my desk avoiding a deadline, procrastinating by snacking. I felt something between my two front teeth and, thinking it was a bit of food, I went to fish it out with the classy decorum one always shows when quite alone: by sliding my nail in between my teeth. Something dislodged and it felt immediately wrong, harder than any substance I might have eaten in the last few hours. I examined it, hoping it was not what I had begun to fear it might be: a tooth. But there, balanced on the fleshy part of my index finger was something definitely toothlike.

Fearing I was in one of those awful dreams, in which all your teeth fall out, I walked extremely slowly to examine myself in the bathroom mirror. The entire back of my bottom front tooth had sheared off, leaving a thin facade at the front. Panic set in as I imagined my future, toothless. What were you meant to do with a fallen-out tooth? Put it in ice? Milk?

Twenty-four hours later I was sat in the dentist's chair as he stuck something entirely man-made to the back of my tooth and heat-sealed it on. He never even asked to see my saved bit of tooth. "So have you been wearing the night-guard I gave you?" Mouth full of instruments and sucky things, eyes wide with remorse, I shook my head. No, I had not been wearing my night-guard, prescribed because I bashed my teeth violently together at night; I thought it was very unsexy and now here I was paying the price for my vanity. "This is because of the forces you're inflicting on your teeth, as you're clenching them together," my dentist said. "You really need to wear that night-guard if you want to avoid more of this."

I first became aware that I was doing something dreadful to my teeth five years ago. I'd not long moved in with my boyfriend, after we'd built our own home (a joyful but also rather stressful time); he said that, as I fell asleep, I smashed my teeth together, a bit like those joke teeth that chatter. I didn't think much of it except that my fillings kept breaking.

I had recently started going to a very progressive dentist who believed in prevention rather than reconstruction and he was the first to tell me about tooth-grinding - and prescribe me a soft, clear plastic night-guard that looked like a boxer's gumshield and fitted over my top teeth. (A night-guard as a stabilisation splint or tooth guard is the first form of defence against tooth-grinding.) It was hideous and I hardly ever wore it. Meanwhile, I was knocking more and more fillings out and it was costing me money. Then came the fallen tooth, and I realised I had to wear the darn thing or risk ending up with wooden teeth.

Many of us grind our teeth - a condition known as bruxism - yet most of us have no idea we're doing it. Even if our teeth escape damage, we may have unexplained but frequent headaches. "Apparently 60% of headaches are of dental origin, due to muscle spasm," explains Dr Anoop Maini of Park West Dental surgery. "These people have acupuncture or see a cranial osteopath who releases the tension, but the result soon returns since the cause is not corrected."

So why do we grind our teeth? It's a combination of not having a perfect bite and stress. In a perfect bite, the teeth meet evenly on closing and the jaw muscles are relaxed; with an imperfect bite there's an anomaly and, when we sleep, the mind tries subconsciously to "grind away" at the obstruction. Unfortunately the grinding is indiscriminate and, in the process, our jaw muscles become very tense and can even spasm. Stress makes us "worry away" at the imperfection in our bite even more. Although Roy Higson, president of the British Society of Occlusal Studies, thinks even having a perfect bite doesn't protect you from grinding if you suffer from stress. "A lot of people have ill-fitting teeth but I've also seen well-fitting teeth but that person is stressed so they'll grind."

The slightest thing can set you off: you may have had a filling which throws your bite out minutely; a cap replaced; your wisdom teeth may have not long come through; or you may have always had an uneven bite and something stressful in your life sets off the grinding.

There are two types of bruxism: good old-fashioned grinding, and clenching (my special form of teeth- bashing comes under clenching). "There tends to be a male/female divide in the male physiology. Muscles win over teeth so men tend to grind," explains Higson. "With women the muscles lose out, so they tend to clench rather than grind, and get sore muscles. Females get more headaches, temporal ones especially."

Although my tooth guard is a soft one, all the dentists I spoke to no longer recommend them, saying a hard acrylic version has proved to be more effective. "A hard plastic night-guard opens the bite, separates the teeth and provides a surface that is not so nice to bite on, so it can break the cycle of tooth-grinding," says Dr David Bartlett, senior lecturer and honorary consultant at King's College Dental Institute in London. "But a soft one can make the problem worse, because the shield is soft it can actually feel quite nice to bite on so there may be a tendency to do it more." I can concur with that as it is like having a mouthful of chewy sweets. The advantage is that a soft night-guard costs about a fifth of the price of a hard acrylic one (both, however, have to be specially made and fitted for each patient) and, for someone such as me who bashes, a soft night-guard can act as a shock absorber.

If a night-guard doesn't sort the problem then a patient may have to look at equilibration; simplistically this is when the teeth are minutely filed down to remove the interferences that cause bruxism in the first place.

However, any shift in your teeth and the problem can start all over again. Like most things, the key to avoiding problems is to lead as stress-free a life as possible. There seem to be those for whom tooth-grinding, especially in severe cases, is more than a matter of imperfect bite but due to psychological problems.

"Some people tend to have a lot of problems in their life," says Bartlett, "and their tooth-grinding can be difficult to manage." Anecdotally, it seems people living in cities seem to grind more. Other things can increase the problem. "Drug-taking can definitely make the problem worse," confirms Bartlett. "Ecstasy and drugs like it are related to muscle actions and those people have an increased tendency to grind."

Many mothers have noticed that even very young babies can grind their teeth. Clearly this isn't due to an excess of class A substances (although my daughter does go at her teething granules as if they were crack cocaine) or stress, so what causes their juvenile grinding? "They are usually in a transitional stage and have mixed dentition," says Higson. In other words they are in between having their milk and adult teeth or they simply haven't got all their teeth through yet and their bite is changing.

If you think you may grind, clench or bash, it's vital to find a knowledgeable dentist to treat the cause, not the symptoms. Left untreated, severe tooth-grinding can result in tooth loss, jaw spasms, or teeth so ground down they are little more than stubs.

There is one advantage to wearing a night-guard that I must point out; it has the effect of making your lips look like you've had collagen injections, so it's not all bad.

Do you grind?

The symptoms:

· Recurrent, unexplained headaches, especially in the temples

· Head, neck or shoulder pain

· Sensitive teeth

· Breakage/chipping of teeth or fillings, especially larger fillings

· Sculpting or ridging of the tongue

· Ridging on inside of the cheeks

· Tightness in jaw muscles

· Gum recession

· Clicking of jaw

· Wearing down of teeth surfaces, especially obvious in front teeth

· For a list of dentists trained in treating bruxism and occlusal disease visit www.bsos.org.uk