If you think your teeth are as white as they've always been, go and find a small child and ask it to open its mouth. Compare and contrast. See how its teeth look like little sparkly white pearls. See how your teeth are actually yellow. Dull and yellow. Especially if you are over 30, and especially if you indulge in those three great staples of modern life - red wine, tobacco and coffee.

It won't kill you - but there's no denying that shiny white teeth are covetable. On television, yellow teeth are only sported by peasants, serial killers and Shane McGowan. All movie stars and pop singers now have dazzlingly white teeth. They call it the Hollywood smile, and in America, people go to great lengths to acquire one. The thesis is that white teeth make you look younger and, therefore, more lovely.

Given that the effect of whitening toothpastes is extremely limited (they can only remove surface stains), there has traditionally been only one real solution: home bleaching, which takes about a fortnight. But now along comes a new generation of light-activated bleach treatments with one major advantage: they can take as little as half an hour. From icky yellow to baby-teeth white in 30 minutes: you can have it done in your lunchbreak. And it lasts for (a rather vague number of) years. And although even the insides of your teeth are leeched of colour, it won't damage them: it is approved by the US Food and Drug Administration (and they never get anything wrong, oh no).

The British Dental Association remains uncertain about the effectiveness of these speedier treatments, which have been around a very short time and are constantly being updated. Spokesman Dr Jonathan Portner, who has a private practice in north London, says he finds the home bleaching options more reliable and more controllable, not to mention far more economical. But on one point he is reassuring: home-bleaching has been used safely for more than 30 years, and does not damage your teeth. And these new methods, using light-activated bleach, are just as safe.

I jump at the chance to try it, but find myself nervous and regretful as I make my way to the Capital Dental Centre in south-west London for a complimentary treatment. My teeth are plenty white enough; I've never given a thought to their colour before. And I hate going to the dentist. So why am I going to the dentist for vanity's sake alone?

Dr Sunny Luthra is friendly and informal - "Hi, I'm Sunny" - and he is a salesman: he tells me that the treatment is the quickest and most advanced in Britain. Of course he is a salesman - he has just bought an expensive new lamp, and he has to make his money back. (Later, I talk to another cosmetic dentist, Dr Phil Stemmer at London's Teeth for Life Clinic; he offers a slightly different light-activated treatment, which takes about twice as long, with the teeth being done one at a time, and of course he thinks that one is the best. Later still, Luthra hints that Stemmer's treatment is old hat now. It becomes increasingly clear that, in the world of private cosmetic dentistry, you should shop around before shelling out.)

I tick through Luthra's health questionnaire - malaria, no, anthrax, no, etcetera - and then we go through to the treatment room. I am so nervous by now that all I will later be able to remember of the room are some child's toys and news of the war on a wall-mounted TV. My teeth shade is "A3.5". That's at the "darker end of above average". ("It's not the end of the world," as Luthra puts it.)

I tell him I have two worries. The first is that the treatment will damage my teeth. He assures me that it won't. My second worry is that the treatment will go too far. That in just 30 minutes I will be transformed into a fairground freak. But he tells me that those humdinger glow-in-the-dark Hollywood smiles are not achieved by tooth whitening. "They have veneers," he says. "Like stick-on nails, but for teeth. That's the only way you can get that effect." The effects of tooth whitening are more subtle, apparently - the process can only go so far.

Then to business. And it is a bit of a business - when Luthra later attempts to suggest that some of his patients find the process "soothing", I am forced to snap: "It was traumatic."

First a plastic "cheek retractor" is forced into my mouth, to keep my jaw wide open and my lips back from my teeth. It turns out that I have a very small mouth, which means it's something of a palaver, and the retractor doesn't quite do its job (Luthra's assistant has to stand with one finger on my bottom lip throughout the procedure to stop peroxide burning my skin). My new space-alien look is completed by a pair of dark plastic specs.

Next, Luthra applies a gel to my gums and sets it hard with a special light; this to protect my flesh from the nasty bleaching agent. Then a "wavelength-specific" light-activated hydrogen peroxide paste is daubed on my teeth - it is about 35% peroxide - and an extremely bright lamp is positioned in front of my jaw. The inside of my mouth is lit up by cool, white light.

Luthra gives me two 15-minute sessions with this lamp, the second time around applying a weaker gel. Thirty minutes with your mouth wedged wide doesn't exactly fly by, but there are small distractions, mainly involving tiny scraps of peroxide finding their way onto my tongue or bottom lip followed by a sudden burning sensation. Cue frantic hand signals and gargling sounds before Luthra or his assistant dab it away with wet cotton wool.

Every now and again there is also a moment of burning, sinking discomfort to the core of my teeth: mild, but disturbing. These were only fleeting, but still, this is not a soothing experience.

When the retractor comes out, for a few moments I cannot close my mouth: I actually dribble as I attempt to wash out the scraps of gel. Dignified it was not.

Out comes the mirror. Luthra is distinctly disappointed; one of my eye teeth is still a little yellow and there is still some faint yellow around the base of my lower teeth. My teeth do look much whiter to me - but only a few shades, not the eight or nine that Luthra says can be achieved in one session. Better that than scary, I reassure him. (It's worth making sure you've talked through in advance what's going to happen if some teeth haven't gone white or if you're not completely happy with the result, because this is an expensive business, and one session on such a lamp will set you back between £600 and £700.)

I suck my teeth tentatively on my journey back to work, where nobody can see a blind bit of difference. "You had white teeth to start with, you muppet," says one colleague. During the afternoon my teeth begin aching. Luthra had warned me that this would happen: my teeth might feel a bit sore for 24 hours. But, all the same, I fantasise about my teeth having been weakened; about them crumbling and falling out.

All that was last Friday. The tenderness lasted just that first day. After that I completely forgot about it. Some people say that my teeth look much more white and sparkly now, but only after I have danced about before them baring my fangs and bleating: "Do my teeth look whiter?" Then again, I do constantly find myself peering at other people's teeth. And boy, do they look yellow to me now.