I’m lying in bed, waiting for the alarm to go off.

I’ve been lying like this for half an hour, staring at the ceiling, barely moving. In ten minutes or so, I’ll jump a bit, put my hand out to find the clock, tell my husband he can go back to sleep for 20 minutes, and get up. But I’m willing that moment not to come. Once it’s here, the day has officially begun, and I’ll be just a couple of hours away from the event I’m dreading.

When I was young, there was an advert on the black and white telly that showed what goes on in your mouth if you don’t clean your teeth.

Believe it or not – and I did – there were nasty-looking monochrome cartoon workmen with pickaxes and hammers hiding in between your molars, and if you didn’t brush up and down, up and down, till they’re clean and sparkling, your teeth would soon be riddled with holes and black bits that only close encounter with the dentist’s pliers could sort out.

Wind on 30 years and, like most things, the science of dentistry had become unrecognisable. In place of the evil oral workmen, the inside of the mouth had become a playground for dental professionals who had secretly wanted to be civil engineers but suspected there wasn’t enough money in it. No more leaving gaps between teeth, no more letting people walk around with less than bright white incisors.

With the result that I, who on a weak day could be persuaded to make a donation to the Refrigeration Units for Inuits Appeal, agreed to have my left lower fifth to eighth converted into a bridge that would give the Golden Gate in San Francisco a run for its money.

For 20 years or so, the bridge and its neighbouring crowns lived happily side by side. But then, last spring, my tongue detected something strange. Hard to say what it was, exactly, but something seemed to move a bit. The nasty cartoon workmen hadn’t managed to psychologically damage me as badly as they’d obviously been meant to, for I managed to find reasons not to mention this to a dentist right through the summer, and into the autumn. Perhaps it was the cold November air, or maybe I’d never quite brushed away all the juvenile cartoons, but for some reason or other doing anything as energetic as chewing a Crunchie suddenly became unpleasant. Or excruciating, as we hypochondriacs like to put it.

I sat in the dentist’s chair, and watched his eyes above his mask while he poked around under the crown that by now was distinctly wobbly. Hmm, he said. How long has it been like this? Just a week or two, you say? His gaze strayed up from my molar, probably checking to see how much my nose had grown. Well, I’m going to have to drill across the bridge and lift the crown off, and see if I need to pull the back tooth out altogether.

Not now, you’re not, I said, spitting cotton wool everywhere. I’ve got to go now. (To have a lie down and wail, I added, but only in my head.) I’ll have to make a new appointment. And so for a fortnight I’ve indulged my tongue and let it make its way round the periphery of the peripatetic crown, and managed to dispatch any thoughts about local anaesthetic that doesn’t take or drills slipping and taking out one side of my face.

But now, as the alarm finally rings, I can dismiss those fears no longer.

I get dressed, then change my blouse to an old T-shirt in case I end up covered in blood.

I pour myself a cup of tea, but can’t drink it properly because my mouth is already trembling.

You used to be a dental assistant, my husband reminds me, in exasperation. That’s true. But that’s also half the problem. I know too much.

Five minutes before my appointment, I’m standing in front of the reception desk.

The receptionist looks at me, slightly pained. That’s nice. Sympathy. “I’m so sorry,” she begins. I know, I know.

“I’m afraid he’s called in sick today. Do you want to make another appointment?”