Why do some people grind their teeth when sleeping? The short and unsatisfying answer is that we don’t fully know. But there have been many possible reasons proposed. Most commonly:
- Psychosocial factors like stress and anxiety
- Malocclusion – Misaligned bite and bite interferences
- Obstructive sleep apnea
- Medications/Drugs – including illicit drugs, prescription drugs, alcohol, and caffeine
Some of these are supported by the evidence. Others are not.
Before I review the current thinking on etiology, it helps to understand a little more about this disorder.
The Clinical Term is Bruxism
Clenching, grinding, or gnashing your teeth involuntarily is called bruxism. There are two kinds:
- awake bruxism
- sleep bruxism
The names are self-defining. Though they are both characterized by the same movements, they are distinct disorders with distinct etiologies. Having one makes you no more likely to have the other.
The statistics on prevalence are all over the map. Awake bruxism has been reported to affect somewhere between 4 to 30% of the adult population.
For sleep bruxism, the only safe conclusions are that it is more common in children than in adults and that prevalence continues to decrease as you age.
Most publications cite somewhere between 8% and 13% prevalence of sleep bruxism in adults. Based on my clinical experience, that sounds reasonable.
Sleep Bruxism is Worse
More teeth damage occurs with sleep bruxism than with awake bruxism. Bruxers exert significantly more force when they’re asleep than when they’re awake.
Awake bruxism is diagnosed by self-report. Awake bruxers can present with the same signs and symptoms as sleep bruxers. But, unlike sleep bruxers, these patients can easily relate these signs and symptoms to their clenching and grinding behavior.
Sleep bruxism is not so easy to diagnose. A little detective work is required. Patients often have no idea that they are sleep bruxers. A truly definitive diagnosis requires a sleep study. But that is not practical for most patients.
We can find plenty of evidence for sleep bruxism by evaluating attrition. Attrition is tooth wear caused by tooth-to-tooth contact.
We must distinguish attrition from the three other types of non-cavity tooth wear:
- Erosion – caused by chemical exposure with no bacterial involvement
- Abfraction – caused by misaligned, repetitive bite force that fractures the thin enamel rods at the gum line of the tooth on the cheek-facing side.
- Abrasion – caused by a mechanical force from a foreign object – like hard bristled toothbrushes, tongue rings, or pencils held in the mouth
Each type of tooth wear is distinguishable by characteristic features.
Often, teeth can be compromised by more than one type of tooth wear at the same time.
Click here to watch a video that describes all four types of wear in more detail. This post is focused on bruxism-induced attrition.
Attrition can be caused by the normal functional use of our teeth as we age. And, it can be caused by bruxism. To diagnose bruxism, we compare your age to the level of attrition in your dentition.
We expect to see some attrition in older patients. They have been using their teeth for many years. But attrition should be very minimal for twenty-somethings.
Below are bitewing x-rays of patients who show no signs of bruxism. They show normal levels of wear for their age.
Compare those to flattened teeth evident on the bitewing x-rays of sleep bruxers.
Bruxism – a Parafunctional Activity
Believe it or not, teeth aren’t designed to contact very much. In normal function, they should only be touching for about five to seven minutes per day on average – mainly when chewing food.
Even while chewing, the bolus of food often separates the upper and lower teeth. When we are speaking, our teeth do not touch. And when we are at rest, our teeth should be comfortably apart.
Clenching or rubbing teeth together for extended periods is not normal function. It’s parafunction. Worse yet, the forces applied during bruxism are side-to-side grinding motions.
Our teeth are designed to absorb the mainly vertical forces of normal chewing, not the heavy lateral forces imposed by bruxism.
We diagnose bruxism when teeth show much more wear than would be expected with normal function. They’re often flattened, chipped, and missing some of their protective enamel.
The damage in the above images is pretty obvious. Often the presentation is a bit more subtle. Bruxism can occur on a spectrum of severity.
Another common feature of attrition caused by bruxism is called compensatory eruption. When we grind our teeth regularly, our body has a way to prevent us from losing vertical dimension.
Vertical dimension measures the distance from the tip of your chin to the tip of your nose when your teeth are in contact.
Bruxing triggers a process that remodels and elongates the jaw bone to preserve your vertical dimension. As a result, the front teeth appear to be erupting towards the opposing teeth.
It often results in an uneven bite plane. But, at least it does maintain your facial structure and the positioning of your jaw joints
However, if the bruxing pattern is extensive and very rapid, the body won’t have time for this bone remodeling process, and your vertical dimension will be shortened.
Unfortunately, a shortened vertical dimension causes your mouth to be over-closed. Over-closure can change the positioning of your jaw joints, reduce your airway space, and create an aged appearance.
Evaluating attrition to diagnose sleep bruxism has an obvious limitation. Excessive attrition can’t tell us if sleep bruxism is ongoing. We can only determine that parafunctional tooth-to-tooth contact has occurred at some point. In some cases, the damage was already done and now bruxing has stopped.
To determine if you are bruxing now, you can
- Ask family members or sleep partners to observe you while you sleep to confirm whether or not you grind.
- Try an app called Do I Snore or Grind. It will record the sounds you make while you’re sleeping and can distinguish snoring from grinding.
- Buy a cheap off-the-shelf “boil and bite” night guard. If it looks chewed up after a few nights of wearing it, that’s good evidence that you are a sleep bruxer.
- Have a dentist or sleep specialist send you home with a screening device like Bruxoff or StatDDS.
- Have a formal sleep study. It will offer the most comprehensive and reliable information.
Other Signs and Symptoms
Significant attrition is oftentimes the only reason we diagnose sleep bruxism. Many patients with mild or moderate, or sometimes even severe cases don’t show any other signs or symptoms. But, others aren’t so lucky.
Other signs and symptoms of bruxism include:
- Enlarged masseter muscles – Those are the muscles responsible for moving the lower jaw. All the work they are doing every night can make them bulk up.
- Headaches upon awakening
- Jaw pain
- Limited opening
- Clicking sounds in the jaw joint
- Bony growths called exostosis and tori – The pressure from grinding will trigger the body to produce more bone in some people.
- Gum recession
- Tooth mobility – Mobile teeth lead to greater susceptibility to periodontal disease.
Sleep Bruxing Pattern
Sleep bruxism events occur during microarousals. Microarousals are brief periods of awakening lasting less than 15 seconds. They are a normal part of the sleep cycle.
During a microarousal, your autonomic nervous system kicks into high gear. Your heart rate goes up, and your muscles tense. Then – if you are a sleep bruxer – you grind, gnash, and clench for a few seconds.
Most bruxing events occur during non-REM sleep.
Though microarousals are natural, they can become more frequent with some drugs, medications, or medical conditions.
Awake Bruxism Causes
There’s general a consensus that so-called psychosocial factors like stress and anxiety are the main causes of awake bruxism.
Genetics can play a role indirectly. Those with genetic variants associated with a higher level of perceived stress may be more likely to develop awake bruxism.
Drugs and medications affecting neurotransmitters may also trigger or worsen awake bruxism. The evidence is not conclusive but it’s compelling.
The same kinds of drugs are also implicated as a cause of sleep bruxism. They are discussed in greater detail in the Sleep Bruxism Causes section below.
But stress is the most common trigger for awake bruxism. There is no controversy about that.
Sleep bruxism is another story.
Sleep Bruxism Causes
Back to the original question! Why do some people grind their teeth while sleeping? I’ll review each of the most common causes proposed.
Psychosocial Factors – Stress and Anxiety or Other Mental Health Disorders
We have established that stress causes awake bruxism. But, believe it or not, there is no consensus that stress, anxiety, or other mental health disorders cause sleep bruxism.
Lending credence to the hypothesis that stress causes sleep bruxism, researchers have found elevated levels of stress hormones called catecholamines in sleep bruxers. Catecholamines are hormones that double as neurotransmitters. They include adrenaline and dopamine.
But other researchers who reviewed a wide range of studies were not convinced. They noted that most of the studies establishing a relationship between stress and sleep bruxism were based on self-report. Data taken from sleep studies did not substantiate these findings.
Many articles written for a patient audience will tell you unequivocally that stress causes sleep bruxism. But the truth is – the jury is still out on this question.
I see many patients with low-stress and super-relaxed personalities with very worn teeth. I also see the most high-strung patients show no signs of grinding.
If stress does play a role, it certainly doesn’t apply to all sleep bruxers. And, if you are experiencing high levels of stress, that does not necessarily mean you will grind your teeth when you sleep. You must be otherwise pre-disposed to this disorder.
Another area of controversy is whether or not a misaligned bite – or malocclusion – is to blame for sleep bruxism. This long-held belief has been thoroughly debunked.
It is possible that sleep bruxers who also happen to have malocclusion may suffer worse symptoms than bruxers with a normal bite relationship.
Grinding and gnashing teeth with bite interferences, a significant over-bite, or another form of malocclusion, may intensify the stress on muscles and joints. But, malocclusion does not cause sleep bruxism.
Obstructive Sleep Apnea (OSA)
You will see a theme in this post! Here is yet another area of controversy.
It has been postulated that bruxism is a protective response to a compromised airway. Are those suffering from sleep apnea grinding their teeth as a way to unconsciously open up their airway? Probably not.
OSA likely does not cause sleep bruxism. However, these two conditions are definitely correlated. An excellent review of various hypotheses accounting for the relationship between OSA and sleep bruxism is discussed in this post.
Interventions that treat OSA are shown to also reduce episodes of sleep bruxism. Both disorders are mediated by the central nervous system and likely share some of the same etiologic factors.
OSA is a serious disorder. l recommend that all of my bruxing patients with other risk factors for OSA be checked out.
Finally – an answer with confidence. Genetics does appear to be a big factor. Studies show that somewhere between 21 and 50% of bruxers have a family member with the same condition.
The bruxing motion is triggered by the autonomic nervous system. Our genes partly determine the level and morphology of hormones and neurotransmitters in our system. These variations are believed to influence our susceptibility to sleep bruxism.
Genetics – not necessarily stress – could at least partially account for why elevated levels of stress hormones are found in the urine of sleep bruxers.
This finding definitely aligns with my anecdotal clinical experience. When I see a patient with obvious signs of sleep bruxism, typically, their child or parent will show the same pattern. It is also more common in some ethnic groups than others.
Drugs and Medications
Alcohol, tobacco, and caffeine are positively correlated with sleep bruxism. For coffee lovers – don’t worry. You have to consume about eight cups a day before the effect is noticed!
Anecdotal evidence also implicates illicit drugs like methamphetamines and MDMA to awake bruxism and sleep bruxism.
Commonly prescribed prescription drugs are also associated with awake bruxism and sleep bruxism. Most notably, selective serotonin uptake inhibitors (SSRIs) – used to treat anxiety and depression – have been linked to bruxism. Medications for ADHD have also been implicated. Adderall is the most commonly known.
These drugs either cause bruxism or make it worse.
A possible mechanism for the former may come from their impact on dopamine and other neurotransmitters.
A possible mechanism for the latter is sleep disruption. As stated earlier, sleep bruxism occurs mostly during non-REM microarousals. If your sleep is disrupted by consuming these substances, you will experience more microarousals, and thus more bruxism.
These drugs could turn a mild, subclinical sleep bruxer into a heavy sleep bruxer.
My Verdict Summary
Back to the original list of potential causes of sleep bruxism and my verdict based on the available evidence:
- Psychosocial factors like stress and anxiety – I am not convinced stress causes sleep bruxism. But, it likely exacerbates symptoms for those otherwise predisposed.
- Malocclusion – Misaligned bite and bite interferences – I am convinced that malocclusion does NOT cause sleep bruxism. But bruxers with malocclusion may develop more painful symptoms.
- Obstructive sleep apnea – Technically speaking, I am convinced that OSA does not cause sleep bruxism. Though practically speaking, it does not matter. These disorders are correlated. Patients with sleep bruxism and other risk factors for OSA should be checked for OSA. And, therapies for OSA also help with sleep bruxism.
- Genetics – I am convinced that genes play a very large role in sleep bruxism. This effect is likely due to genetic variations in hormones and neurotransmitters.
- Medications/Drugs – including illicit drugs, prescription drugs, alcohol, and caffeine – Given these substances have direct impacts on hormones and neurotransmitters, I am convinced that they:
- cause bruxism and/or
- intensify it – potentially from a very mild, subclinical presentation to a symptomatic and noticeable level
My hunch is that they do both.
There are still many unanswered questions about sleep bruxism. It is now generally believed to be a multi-factorial disorder. We will have to wait for additional research to shed more light on how these factors interact to cause sleep bruxism.
If you or someone you love suffers from bruxism, you may be wondering how severe the consequences of this disorder can be and what treatments are available.
Addressing these questions is the subject of this post.
Spoiler alert – many patients seriously underestimate the trouble they’re in for – both dentally and financially – by not addressing this problem early on!
Feel free to ask me a question or share your experience with bruxism by posting in the comment section below!