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The Greeks had a word for what we now refer to as bruxism: brychein—the grinding or gnashing of teeth. With references to this “gnashing of teeth” in both Dante’s “Inferno” and the Bible, the condition may be as old as mankind. Its causes, mechanisms and treatment, however, are still largely unknown, and misinformation continues to confuse both patients and dental professionals. In order to shed light on the topic, prevention spoke with Belgian dentist Dr François Mathonet. A bruxer himself, Mathonet specialised in temporomandibular disorders and orofacial pain and, as such, is the perfect person to offer in-depth information on the condition and a holistic approach to the problem.
“Above all, I am interested in the human body,” Mathonet explains. “And if I could, I would sweep away the boundaries that exist between individual disciplines and their specialists. I became interested in bruxism because I wanted to understand why I was doing it myself. Also, what I had learnt about it at university did not seem quite complete, and I wanted to be able to offer different solutions to my patients. So, after studying dentistry at the University of Liège, I studied occlusion, temporomandibular disorders and chronic pain to get a better understanding of dental health in relation to the rest of the body. I like the fact that bruxism requires dentists to look beyond the mouth and take the entire body into account in addition to psychological and emotional factors. The subject fascinates me, because it is vast and still full of questions.”
Dr Mathonet, bruxism is a so-called parafunction. What does this mean?
The activities of the masticatory muscles are classified into two categories. The first is functional muscle activity, which includes chewing, speaking and swallowing. If we add up the only moments where the teeth normally touch each other—during swallowing and at the end of chewing—it comes to no more than 20 minutes per day. For the rest of the day, a small space separates the teeth and the muscles have minimal tension—just enough to counteract gravity and keep the mouth shut.
The second category is parafunctional activity, which includes bruxism—the repetitive jaw muscle activity of clenching or grinding the teeth, or bracing or thrusting the mandible, with or without the tongue muscles. During parafunction, the muscles work together in activities that the body has not evolved for. Other than bruxism, examples of parafunction include habits such as the biting of the cheeks, lips or tongue, chewing gum, thumb-sucking, nail-biting and so on. Sometimes, the body adapts very well to these parafunctions, but often they cause damage to some or other structure. We also use the term “muscular hypertonicity” to describe an activity or habit that goes beyond vital functions.
What proportion of the population suffer from bruxism?
The International Classification of Sleep Disorders estimates that 85–90 per cent of the general population grind their teeth to some degree at some point in their life, although only 5 per cent develop a clinical condition. The last systematic review of the epidemiologic report of bruxism concluded a prevalence of about 22.1–31.0 per cent for awake bruxism, 9.7–15.9 per cent for sleep bruxism and an overall prevalence of about 8.0–31.4 per cent. The review also concluded that bruxism affects men and women equally, but affects elderly people less.
These numbers must be taken with a grain of salt though, because they rely on self-reporting. For a more reliable assessment of nocturnal bruxism, more controlled, randomised, longitudinal and large-scale studies with polysomnographic tools are required. This is becoming possible thanks to the development of simple measuring devices that can be used at home and are capable of collecting an increasing variety of data.
What are the consequences of bruxism for teeth and gingivae?
Consequences for the teeth are excessive tooth wear on the occlusal surfaces and at the necks, increased tooth mobility, fracture and hypersensitivity. For the gingivae, bruxism is an increasing factor for periodontal disease. Other consequences of bruxism are increased muscle fatigue, jaw, neck and back pain and headaches—bruxism can act as a trigger for migraines—as well as overuse and inflammation of the temporomandibular joint with pain around the ears, tinnitus and tiredness. This tiredness can even affect other people as well, because some people grind their teeth loud enough in their sleep to wake up their partners.
Symptoms may vary from patient to patient, but so does a patient’s tolerance. Some people can clench their teeth all day and night without experiencing pain until they start to show tooth wear and gingival recession. Others may have a difficult week, clench or grind more than usual and immediately get jaw pain and tension headaches. Patients’ symptoms will show at their weak points. For example, patients who have had their third molars removed under general anaesthesia have a higher risk of dislocation of their temporomandibular joints, so when they start grinding as a reaction to a stressful event, the first symptoms will probably be pain or the temporomandibular joints clicking louder than usual.
Why do people grind or clench their teeth? Are there genetic factors?
Until recently, many dentists thought that occlusion was the main factor in bruxism, but scientific evidence has shown no link—or a very minimal link at best—between bruxism and occlusal factors. This shows that the mechanisms of bruxism are still largely unknown. There are, however, several known causes.
Awake bruxism is often done unconsciously due to habit and ignorance. Many people can spend years unconsciously contracting their jaw muscles without making the connection between muscle tension and the pain they are experiencing as a consequence. This muscular hypertonia, with or without dental contact, is linked to an over-activation of the sympathetic system. Any signal that is perceived as an aggression by the body has the effect of activating our defence system and contracting certain muscles in the body. In acute situations or when it is quickly counterbalanced by the parasympathetic rest system, it is actually very useful and even indispensable. However, when the body chronically perceives aggression, it drains its reserves until it snaps. A stressful environment, an increased reaction to life events, chronic pain or a unhealthy lifestyle are all responsible factors. I think this regulation of the autonomic nervous system is both genetic and acquired. On the one hand, it is genetic, but on the other hand, it evolves in response to the environment in which a person grows up.
Regarding sleep bruxism, information on prevalence, pathophysiology and valid treatment is limited. Most periodic movements of the body, legs or arms and jaw (such as sleep bruxism) are observed during phase two of sleep—non-REM, light sleep. This phase includes micro- awakenings that are associated with increased brainstem and autonomic ortho-sympathetic activity, faster breathing and increased heart rate and muscle contractions, especially in the jaw. A number of other problems are linked to sleep bruxism: certain respiratory disorders, such as obstructive sleep apnoea; insomnia and parasomnias; restless leg syndrome; faciomandibular myoclonus; epilepsy and gastroesophageal reflux.
The activity of the sympathetic nervous system has been shown to be related to pain and psychological stress. Dopamine is a marker of this activity, along with an increased heart and respiratory rate. Together with serotonin, it plays a role in peripheral sensitisation and an increased perception of painful stimuli. Substances that have an influence on the dopaminergic system, such as levodopa, amphetamines or nicotine, have consequences for bruxism. Nicotine stimulates the production of dopamine, which helps explain why bruxism is twice as prevalent in smokers compared with non-smokers. Genetics also play a role in the production of dopamine and serotonin. A study has shown that 21–50 per cent of people who suffer from nocturnal bruxism have a direct family member who suffered the same problem during childhood. The mechanisms involved are still very unclear, and many hypotheses suggest personality types, stressful environments, repressed emotions and frustration. One hypothesis I like is that of the tension between the conscious and the unconscious. The hypothesis states that, during light sleep, the differences that may exist between our dreams and our daily lives would materialise in muscle tension.
"One hypothesis I like is that of the tension between the conscious and the unconscious. The hypothesis states that, during light sleep, the differences that may exist between our dreams and our daily lives would materialise in muscle tension."
How does daytime bruxism differ from nocturnal bruxism?
Both terminologies—day and night bruxism and awake and sleep bruxism—are used, but I prefer the latter, because people who nap during the day can also brux. The difference between awake and sleep bruxism is the fact that one can become aware of awake bruxism. By attention and will, patients can consciously relax the muscles. While asleep, things get a little more complicated. As I said before, other factors may be responsible at night, so treatment there may also differ.
Can bruxism be reduced? How?
I have the opportunity to work in an interdisciplinary practice where dentists, physiotherapists, osteopaths and speech therapists rub shoulders. Each specialty allows its own optimal take on the problem. For example, the dentist will specify the diagnosis, explain the responsible factors, help raise the patient’s awareness and establish a treatment plan. The physiotherapist will work at a muscular level and help the muscles to relax and return to their normal length. The myofunctional speech therapist can retrain the masticatory system and offer tools for self-management. The osteopath focuses on the musculoskeletal system and the nutritional aspect of the problem. Sleep tests can also be done at home or at the hospital. Outside the office, we work with sleep doctors, psychologists, neurologists and orthodontists. In some cases, self-hypnosis or meditation tools can also be taught.
There is no ready-made, miracle treatment for bruxism—the treatment plan is defined according to each patient’s situation. The goal is to empower patients by providing them with treatment, and knowledge and tools they can use. In a study that has not yet been published, which followed about a hundred people suffering from dysfunction of the masticatory apparatus (with pain and/or functional limitations) related to bruxism, 80.11 per cent of the subjects presented an overall relief of 60–100 per cent thanks to an approach based on a self-management philosophy. In this approach, patients—although aided by professionals—played a role in their own health.
What is the link between stress and bruxism? Why does stress cause bruxism in some people and not in others?
I wouldn’t say that stress in itself is bad. Personally, I like to imagine it as an energy. When there is stress, the body gets ready, wakes up and makes energy available. This energy can either put someone in motion, or alternatively, create tension. Either energy is used to create, to do something—like run, take action—or it is stored in the body. This second option results in bruxism, but also symptoms such as hypertension, irritable bowel syndrome, fatigue and an increase in the muscle tone in the head, neck and back. The place where this tension will express itself differs from person to person.
What is the best way for bruxism sufferers to alleviate stress?
It is difficult to give an exact answer to this question. For me personally, a good way to reduce stress is to take some time, listen to myself and observe myself, and do those things that make me feel good. Relieving stress
depends on one’s own tastes and personality.
Is bruxism always caused by stress? How about temporomandibular joint disorders?
No, during the day, a patient can also show hypertonicity of the jaw even during a moment of relaxation. He might just not be aware of this bad habit, because he is not aware of this tension. At night, other factors intervene, such as gastrointestinal reflux, respiration or others. Some are stress-related, others are anatomical and genetic. Temporomandibular disorders are a vast subject because they depend on many factors, such as occlusion, trauma and the adaptability of the individual. For example, bruxism causes chronic micro-traumas in musculoskeletal structures and can lead to orthopaedic instability, and sometimes pain associated with temporomandibular disorders can reinforce bruxism.
Is there a possible link between bruxism and tongue position?
That is a very good question. The first step of the self-management approach is sensorimotor awareness. The patient becomes aware of the hypertonia of the jaw muscles that the tongue is part of. The hypertonia we are talking about is related to stress and—depending on the patient—when these forces are prolonged, symptoms could appear in the temporomandibular system.
The correct resting position of the jaw is a neutral position in which muscle tension is minimal—just enough to counteract gravity. Thus, the lips are closed, there is no visible mimicry and the muscles are relaxed. A small space separates the teeth. The tongue can have different resting positions in adulthood: at the bottom or in the middle of the mouth or gently touching the palate—the tongue is and is not tense. It is a mistake to advise patients to actively push the tongue against the palate, because they will have to make an effort, which in turn leads to increased tension for the entire musculature. So, the correct advice would be that the tongue should be completely relaxed and soft, and it may touch the palate if it moves there naturally.
Some dentists think bruxism does not cause abfractions and that abfractions are only caused by brushing teeth too hard. What is your opinion on this?
I think abfractions have multifactorial origins, including erosion (chemical wear), abrasion (brushing and chewing) and attrition (bruxism). These three components will be found to varying degrees in a person. This corresponds to the situations I’ve found in patients. The enamel at the limit between crown and root is very thin, so with little force of flexion it can chip easily. I find abfractions very often in patients with recessions.
"The goal is to empower patients by providing them with treatment, and knowledge and tools they can use."
Does a mouthguard protect against tooth wear and receding gingivae?
One of the only proven effects of mouthguards is protection and consequently the slowing down of tooth wear. They can also reduce the occlusal forces. The more open your mouth is, the less force you have to bite down. This is the same principle as a crocodile’s bite: with a small piece of wood in its mouth, it cannot bite down. For the periodontium, mouthguards allow better distribution of the occlusal forces, especially in cases of missing teeth or untreated malpositions, thus, better balancing the constraints related to recessions. Bruxism is an aggravating factor of periodontal problems, and a mouthguard can prevent significant damage in some people at risk and extend the life of loose teeth. However, one must be vigilant in cases of difficulty of breathing and sleep apnoea. In these cases, a mouthguard causing mandibular loosening may increase the number of obstructive episodes. In these cases—and they are very common—it is essential to do a more complete analysis of sleep.
I’ve heard people say that biofeedback is the only thing that helped them. Could you tell me more about this?
Yes, biofeedback is the principle that I mentioned before that allows awareness throughout the day. There are various feedback possibilities. It can either be a reminder on your phone or a visual cue, such as sticky notes, to remind you of the correct jaw position.
However, being aware at night is of course an entirely different matter. Luckily, there are functional devices, such as labial interceptors, that stimulate a suction reflex. This reflex stimulates nasal breathing and causes muscle relaxation. Other functional devices, such as Bionator appliances, have remarkable effects in children when the dental structures are still in development. I am currently looking into the possible benefits they could have for adults too. Lastly, I am experimenting with bilaterally stimulating certain points on the cranium to help calm down the limbic system and am looking forward to the results it may have.
Finally, do you know of cases of bruxism where it was healed or simply disappeared? And, how?
Yes, a multidisciplinary team that approaches bruxism from multiple perspectives and allows patients to be active participants in their own health can reduce bruxism to a normal, non-iatrogenic degree. In the case of sleep bruxism associated with respiratory disorders, surgery or mandibular advancement orthoses give good results while improving the patient’s quality of life.
Editorial note: A list of references can be obtained from the publisher.