Humans have one mobile jawbone known as the mandible or sometimes commonly referred to as the lower jaw. The corresponding upper bone is part of the skull and know as the maxilla, although it sometimes referred to as the upper jaw. In order for the mouth to open or to bite down or chew, the lower mandible articulates with the temporal bones of the skull at the temporomandibular joint (TMJ). This is a gliding joint on either side of the lower part of skull, just slightly in front of the ear. It is only the lower mandible that moves and not the upper maxilla as sometimes thought.
In childhood while the deciduous (milk) teeth are still present, there are 20 teeth altogether – 10 in the maxilla and 10 in the mandible. Gradually this is replaced by the permanent teeth with a full complement consisting of 32 teeth – 16 in the maxilla and 16 in the mandible. The jaw is closed tightest when biting and chewing by forceful contraction of the muscles of mastication. The teeth of the maxilla and mandible make contact in a an alignment that ensures the upper teeth fit slightly over the lower teeth. This normal alignment is known as occlusion. The contact between the upper and lower teeth when chewing occurs only for short periods of time. The teeth being hard structures do not experience much wear and tear with chewing apart from when biting and grinding hard foods. However, if the teeth are constantly in contact and grinding against each other, it can become eroded over time.
What is bruxism?
Bruxism is the clenching and grinding of the teeth beyond normal chewing when eating. Teeth grinding is largely an unconscious act and can occur during the day while awake or even at night when asleep. In order for the teeth to be grinding together, the jaws have to be clenched. Therefore the term bruxism refers to both clenching of the jaw with grinding of the teeth. It should not be confused with the medical condition known as trismus where there is an inability to open the mouth.There are different degrees of bruxism and the severity of the effects may vary accordingly. In mild bruxism there is little to no symptoms and the condition usually requires no treatment.In severe bruxism, the clenching is to the extent that the teeth wear down over time and a person experiences jaw pain and headaches.
Daytime and Nighttime Bruxism
Apart from clenching and grinding during eating which is known as chewing (mastication), humans also have a tendency to clench when experiencing emotions such as fear and anger. This is not uncommon and is not entirely a voluntary act. Although it can be initiated and stopped at will or even avoided if one is conscious, this type of stress-induced clenching and grinding is usually short lived as well. With bruxism, the cause of the clenching is not always obvious. It can happen during the day when a person is awake and usually in response to certain stimuli and is then known as awake bruxism. However, when it happens at night while asleep it tends to occur in episodes of rhythmic contraction and relaxation or can be sustained. In this instance it is known as sleep bruxism.
Grinding the teeth to the extent where it is loud and audible, either to the patient or those nearby does not often occur, with awake bruxism. Since the person is awake and conscious, the sound of the grinding often detracts from clenching. When asleep, however, the sound may not disturb the person and often loved ones report the grinding noise. Sleep bruxism is often associated with other sleep disorders particularly where there are periods of awakening (arousal). It is more common associated with obstructive sleep apnea.
Causes of Teeth Grinding
Bruxism can be classified as primary or secondary. In primary bruxism, the grinding and clenching occurs without there being any underlying medical condition. The exact cause in these instances is not clearly understood. With secondary bruxism, the clenching and grinding is associated with some underlying disorder, whether physical or psychological.
The most common causes appear to be associated with mental and emotional states like ongoing psychological stress. Depending on the situation and the cause, this may elicit a host of emotions in a person like anger, fear or sadness. It may also be associated with more aggressive and hyperactive behavior in both adults and children.
Depression should also be investigated as a possible cause. Although uncommon, bruxism can also occur as a side effect of medication such as antidepressants.
Bruxism may also be associated with ear pain which is a common feature in conditions such as otitis externa and otitis media. This should be considered as a possible cause particularly in children as ear infections are more common in childhood.
Sometimes bruxism is associated with certain neurodegenerative conditions like Parkinson’s disease and Huntington’s disease. It may not be a common symptom but can occur over time as a complication.
Malocclusion is where there is a misalignment of the upper and lower teeth where the teeth do not meet properly when the mouth is closed tightly. It may also be associated with bruxism.
Bruxism may be associated with obstructive sleep apnea and REM sleep disorders.
Causes in Children
Bruxism affects both adults and children but the causes seem to be more extensive in children. It is very common in children when the milk teeth erupt and then occurs again when the permanent teeth emerge but resolves shortly thereafter. Although it is not completely understood as to why it occurs, bruxism in children may be associated with many of the same conditions above in addition to :
- Nutritional deficiencies
- Pinworm infestation
- Certain endocrine disorders
Signs and Symptoms
The most prominent feature of bruxism is the grinding and clenching of the teeth. A grinding sound may be audible and heard by those close to the person. Due to the overactivity of the muscles of mastication and strain on the temporomandibular joint, it is not uncommon for there to be cheek and jaw pain. The muscles are often tight and sometimes tender to touch. An uncommon feature of this constant clenching particularly when it is more one sided is hypertrophy of the muscles of mastication on the affected side. This means that muscles become slightly larger than the opposite. It is usually not visible but in rare instances could be associated with a slight swelling of one side of the face.
The clenching and grinding gradually causes a host of effects on the teeth. It wears down the exposed part of the tooth known as the crown. This is coated with a layer of enamel and once worn down the underlying tissue is exposed to the environment of the mouth. It may there present as hypersensitive teeth with intense pain when consuming hot or cold foods and drinks and mouth breathing. There may also be an increased risk of dental problems such as tooth cavities.
Pain apart from being noted on the face and particularly in the areas where the muscles of mastication and temporomandibular joint (TMJ) are located may also occur at other sites. A person may notice an earache which is related to TMJ inflammation and headaches particularly at the temples. It is important to differentiate ear pain from causes such as otitis (ear inflammation) where bruxism is also a feature and an earache that occurs as a result of bruxism.
Ongoing TMJ inflammation may lead to joint dysfunction which in addition to the symptoms mentioned above may also present with a clicking sound (clicking jaw) and sometimes a popping sensation although dislocation is uncommon.
Treatment of Bruxism
No specific treatment is required in many cases, particularly where there is mild bruxism. Regular dental check ups are essential to identify any dental complications and treat it as soon as possible. Malocclusion of the teeth should be treated accordingly as well as any underlying psychological disorders that could be contributing to bruxism. Stress management is a major consideration in bruxism particularly in individuals who are prone to ongoing psychological stress, whether related to the environment and/or as part of their personality.
Mouth guards are commonly prescribed along with behavior therapy where the patient is taught to be aware of the clenching and rest the jaw in a suitable position. Hypnosis is also sometimes considered as a part of behavior therapy. Medication such muscle relaxants or even Botox injections may be utilized to ease the tightness of the muscles. Mild anti-anxiety medication may also be prescribed for sleep bruxism.
Apart from behavior therapy and stress management, patients are advised to avoid stimulants like caffeine and nicotine and limit alcohol intake.