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03 September 2019

Teeth grinding — what really happens when you sleep

Helen Rumbelow at the Times UK.

Does your dentist want you to wear a mouthguard? You’re not alone. Bruxism is on the rise. It’s not necessarily a bad thing, the experts tell Helen Rumbelow at the Times UK.

Dentist and patient

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There is a scene in the movie Date Night, starring Tina Fey and Steve Carell, that tries to depict the reality of a long-term relationship. Fey approaches the bed in her baggy T-shirt and puts her mouthguard in. Carell says: “Oh, you just put in your mouthguard, that means we’re not going to . . .” Fey responds to this line of seduction by reaching up and plucking her mouthguard out, with a wet suction sound and a long line of drool spooling to the floor.

I watched this scene with something of a clenched jaw. You see I, like Fey’s character, am a grinder. When I met my boyfriend, sometimes in the morning he would watch me wake up and then whisper: “You were grinding last night.” He did not mean this in a “sexy times” way. He meant that he heard the sound of my upper and lower jaw gnashing so forcefully in my sleep that it was like two tectonic plates of enamel colliding in a sickening dental earthquake.

Gnashing! Who in their right mind gnashes? Other than dogs and the people, Jesus tells us repeatedly in the Bible, who will spend their time in hell weeping and gnashing teeth? This suggests to me, by the way, that Jesus knew of what he spake; that Mary Magdalene kept Jesus up at night with horrible crunching noises and Jesus struggled to turn the other cheek.

But, says the latest research, we may all grind in bed and for good reasons. One in ten of us reports that we grind our teeth at night, which means a good six and a half million people in the UK are killing the relaxing bedtime vibe. It is probable that many more of us are doing this mysterious thing, and I don’t just mean shoving in a mouthguard. But yes, falling asleep requires us to armour up for something like a fierce bout of ice hockey.

For something so common, and so troubling, the understanding of bruxism — to give it its medical term — is still in its dark ages. (By the way, some stressy people grind while awake, but for this article I will use the term bruxism to talk about the nocturnal variety.) I spoke to several of the most distinguished professors in the field and the common theme is that many dentists, like so many of the public, still believe too many antiquated myths about bruxism, and that the treatments are more basic still.

That’s a shame, because the cutting-edge research on bruxism is fascinating. Why do humans grind in their sleep? Because grinding isn’t just a self-destructive, crunch-your-molars aberration. It is likely, researchers say, that grinding evolved because it had positive outcomes, including fighting bacteria in the mouth and possibly improved mental capacity.

Frank Lobbezoo is as close to a world expert on bruxism as you can get. He is a professor at the Academic Centre for Dentistry in Amsterdam, is chairman of the Netherlands Institute for Dental Sciences, and has been researching and publishing on the topic for decades. When I ask him for the biggest myth about bruxism he surprises me. “That bruxism is always the bad guy,” he says.

Evidence is growing that bruxism keeps the airway open for snorers and helps, by stimulating saliva, to reduce tooth decay, he says. “And there are even suggestions that it may be beneficial for cognition and concentration abilities.”

There is a lack of understanding on the causes of bruxism among dentistsThere is a lack of understanding on the causes of bruxism among dentists

What? That last bit sounds bizarre. But Lobbezoo says that there have been many studies showing a link between chewing and all kinds of positive brain functions, such as attention and learning. Why would these stop if we chew when asleep? Could we be using the night to “chew over” the difficult problems of the day?

“Since both chewing and bruxism are jaw-muscle activities that increase cerebral blood flow, my hypothesis is that also bruxism is beneficial for cognition,” Lobbezoo says. “We are currently running studies in which we try to find evidence for this.”

Let’s take us back a step to what we know about bruxism. I spoke to Professor David Bartlett at the King’s College London's Faculty of Dentistry, Oral & Craniofacial  Sciences. He is a bruxer and so is his wife, who is also a dentist. “Some people grind so strongly they break their teeth,” he says. “I have bruxism, I’ve lost back teeth and crowns.”

It’s easy to spot a bruxer if they are extreme. Some have ground their teeth smooth, like pebbles in a stone-polishing machine. Bartlett has seen “teeth that are absolutely flat, like someone has filed them down”. I have filed my canines away, practically forcing me to become a vegetarian.

There is a cloud of mystery over this field, Bartlett says. Data on prevalence is lacking: Bartlett says that studies point to maybe 30 per cent of people in the UK showing minor signs of bruxism damage. That’s triple the number who seem to know they are grinding. They may have headaches, gum recession and cracked teeth and never realise the cause.

The true number of bruxers could be much higher. Peter Svensson is a professor of dentistry at the University of Aarhus in Denmark and is another elder statesman of bruxism who has been publishing research on it for the past 25 years. I ask him if he is a bruxer and he calmly says: “Yes I am, most people will be. If you put people in a sleep lab and electrodes on their jaw muscles, nearly everyone will have activation in those muscles.”

Humans could be born bruxers. In one study 60 per cent of normal sleepers chewed in their sleep once or twice an hour. “Most people will live happily without any problems from some infrequent grinding or clenching of teeth,” Svensson says. “It’s not a disease or a condition, more a common behaviour.”

Let’s examine snorers versus grinders. Snorers are relaxed. It’s easy to pretend to snore while awake. But grinders are tense. It is hard for me to make the crunching noise I apparently make when grinding in my sleep; I worry I’ll crack a tooth. Grinders, in one study, applied more force asleep than they would when asked to replicate it during the day.

Snoring increases with age. Bruxism seems to be the reverse. Reports of bruxism are twice as high in children and adolescents, up to about 20 per cent, and dwindle to next to nothing in the elderly. “That’s not necessarily the truth,” Svensson says, because of the bias of self-reporting. The very old could be too deaf, toothless or stoic to make a fuss about bruxism. Still, this association between youth and bruxism encourages those researchers who suspect it could have a positive role to play in learning. There is an intriguing correlation between tooth loss and dementia.

Teeth grinding will probably turn out to be multipurpose. Svensson says that when we are awake, we commonly clench our jaws in anger or stress. That may be because the clenching seems to bring out our best game in terms of physical effort; our bodies may be gearing up for trouble. If you look at weightlifters, their jaw is a clenched grimace. “The photo-finish at the Olympics shows athletes at the finish line biting firmly,” says Svensson, so much so that elite athletes have more problems connected to over-clenched teeth.

But why in sleep? First, he says, our mouths are vulnerable to decay at night because protective saliva dries out. “Touching the teeth together activates saliva secretion, so it is pretty smart to have some tooth activity once in a while.”

Second, grinding “moves the jaw forward, leading to easier breathing”. There is a correlation between sleep apnoea and bruxism. Our jaws could be moving around in an attempt to compensate for restricted airways.

Third, we know that you are more likely to grind if you have drunk coffee or alcohol, or taken recreational drugs or some kinds of antidepressants — “all substances that change reactions in the central nervous system”. Grinding also gets worse when you have a poor night’s sleep. Of course, alcohol or caffeine and poor sleep often go together.

Chewing movements at night peak in light sleep and in the transitions between sleep stages, not so much in our dreams. We don’t yet know why: does the chewing help to wake us up or provide some kind of physical nudge to the brain?

Patients often encounter dentists who are in the dark when it comes to this new research on bruxism. These dentists might still think that it is a problem with a patient’s “bite” and waste months fiddling around with dental work. This theory started in the 1960s. It was a nice idea, since discredited. “It’s not true,” Bartlett says. However, many dentists still believe it. I spoke to a few dentists for this article who advocated this very line of treatment and were surprised when I told them this was an old-fashioned theory. “Many dentists are stuck in these old paradigms,” Svensson says.

Of course, eventually, if the problem gets too bad, grinders will end up using a mouthguard at night, the only treatment so far that definitely works. “At least it protects the teeth against tooth wear,” Lobbezoo says. “But it only reduces muscle activity during the first few weeks.”

So bruxers may easily bite through their mouthguards like a dog with a chew toy. Which leads to the other most popular theory about bruxism: it’s a stress thing. People like to connect worrying times to their mouths. Let’s call it Brexit bruxism. Lots of dentists have looked at my mouth and said that my teeth are telling me to give up the rat race and live in a caravan in the Highlands. But as with so many things to do with bruxism, it’s not clear. Some people grind severely all their lives, no matter their stress levels. Perhaps when we are stressed we are also drinking more caffeine and sleeping less? Or maybe we’re chewing in sleep as a way to help our brains to cope? At least two studies have found no link between stressful events and grinding. And there is no evidence as yet that all the mindfulness in the world will help your grinding.

Some medications work, but the side-effects are unpleasant. Botox in the jaw muscles is a possible treatment; in one study about half of people treated with Botox had relief from bruxism pain. But again, the side-effects aren’t great, it weakens those muscles that are nice to have for eating and so on. “For sure you’ll feel less force when eating a steak,” Svensson says.

“In other words, we are still empty-handed as far as treatment is concerned,” Lobbezoo says.

Lobbezoo and Svensson have worked as consultants at various times on a new idea: devices that work by giving you a little electrical “zap” — not enough to wake you up — when you clench too hard. There are commercial products like this out there that you tape to your temple at night, but more research needs to be done. This is, of course, a common theme. There are quite a few dentist jokes about bruxism; a cartoon of teeth dancing at a nightclub with a sign saying “no grinding”. But we still don’t know enough. At least wear your mouthguard, Bartlett says. “Most people don’t.”

Does he wear his mouthguard? “Erm, once a week.” His wife, dentist and grinder, won’t wear one at all. “They’re not,” says Bartlett, and on this I think everyone who grinds or loves someone who grinds can agree, “very nice things.”

In this story

Professor Bartlett

Head of Prosthodontics and Graduate training