Bruxism is excessive teeth grinding or jaw clenching. It is an oral parafunctional activity;[1] i.e., it is unrelated to normal function such as eating or talking. Bruxism is a common problem; reports of prevalence range from 8–31% in the general population. Several symptoms are commonly associated with bruxism, including hypersensitive teeth, aching jaw muscles, headaches, tooth wear, damage to dental restorations (e.g. crowns and fillings) and damage to teeth.However it may cause minimal symptoms, and therefore people may not be aware of the condition. There are two main types of bruxism: that which occurs during sleep (sleep bruxism) and that which occurs during wakefulness (awake bruxism). Dental damage may be similar in both types, but the symptoms of sleep bruxism tend to be worse on waking and improve during the course of the day, and the symptoms of awake bruxism may not be present at all on waking, and then worsen over the day. The causes of bruxism are not completely understood, but probably involve multiple factors.Awake bruxism is thought to have different causes from sleep bruxism, and is more common in females, whereas males and females are affected in equal proportions by sleep bruxism.Several treatments are in use, although there is little evidence of robust efficacy for any particular treatment.

Classification Definition Bruxism is derived from the Greek word βρύκειν (brúkein), meaning bite/gnash.People who suffer from bruxism are called bruxists or bruxers and the verb itself is to brux. There is no widely accepted definition of bruxism, but some suggested definitions include: Bruxism is a repetitive jaw-muscle activity characterized by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible. Bruxism has two distinct circadian manifestations: it can occur during sleep (indicated as sleep bruxism) or during wakefulness (indicated as awake bruxism) All forms of bruxism entail forceful contact between the biting surfaces of the upper and lower teeth. In grinding and tapping this contact involves movement of the mandible and unpleasant sounds which can often awaken sleeping partners and even people asleep in adjacent rooms. Clenching (or clamping), on the other hand, involves inaudible, sustained, forceful tooth contact unaccompanied by mandibular movements. A movement disorder of the masticatory system characterized by teeth-grinding and clenching during sleep as well as wakefulness. Non-functional contact of the mandibular and maxillary teeth resulting in clenching or tooth grinding due to repetitive, unconscious contraction of the masseter and temporalis muscles. Parafunctional grinding of teeth or an oral habit consisting of involuntary rhythmic or spasmodic non-functional gnashing, grinding or clenching of teeth in other than chewing movements of the mandible which may lead to occlusal trauma. Periodic repetitive clenching or rhythmic forceful grinding of the teeth. Classification by temporal pattern Bruxism can be subdivided into two types based upon when the parafunctional activity occurs – during sleep (sleep bruxism), or while awake (awake bruxism). This is the most widely used classification since sleep bruxism generally has different causes to awake bruxism, although the effects on the condition on the teeth may be the same. The treatment is also often dependent upon whether the bruxism happens during sleep or while awake, e.g., an occlusal splint worn during sleep in a person who only bruxes when awake will probably have no benefit.Some have even suggested that sleep bruxism is an entirely different disorder and is not associated with awake bruxism. Awake bruxism is sometimes abbreviated to AB, and is also termed diurnal bruxism, DB, or daytime bruxing. Sleep bruxism is sometimes abbreviated to SB,and is also termed sleep-related bruxism, nocturnal bruxism,or nocturnal tooth grinding.According to the International Classification of Sleep Disorders revised edition (ICSD-R), the term sleep bruxism is the most appropriate since this type occurs during sleep specifically rather than being associated with a particular time of day, i.e., if a person with sleep bruxism were to sleep during the day and stay awake at night then the condition would not occur during the night but during the day.[13] The ICDS-R defined sleep bruxism as a stereotyped movement disorder characterized by grinding or clenching of the teeth during sleep,[13] classifying it as a parasomnia. The second edition (ICSD-2) however reclassified bruxism to a sleep related movement disorder rather than a parasomnia. Classification by cause Alternatively, bruxism can be divided into primary bruxism (also termed idiopathic bruxism), where the disorder is not related to any other medical condition, or secondary bruxism, where the disorder is associated with other medical conditions.Secondary bruxism includes iatrogenic causes, such as the side effect of prescribed medications. Another source divides the causes of bruxism into three groups, namely central or pathophysiological factors, psychosocial factors and peripheral factors. The World Health Organization's International Classification of Diseases 10th revision does not have an entry called bruxism, instead listing tooth grinding under somatoform disorders. To describe bruxism as a purely somatoform disorder does not reflect the mainstream, modern view of this condition (see causes). Classification by severity The ICSD-R described three different severities of sleep bruxism, defining mild as occurring less than nightly, with no damage to teeth or psychosocial impairment; moderate as occurring nightly, with mild impairment of psychosocial functioning; and severe as occurring nightly, and with damage to the teeth, tempormandibular disorders and other physical injuries, and severe psychosocial impairment. Classification by duration The ICSD-R also described three different types of sleep bruxism according to the duration the condition is present, namely acute, which lasts for less than one week; subacute, which lasts for more than a week and less than one month; and chronic which lasts for over a month. Signs and symptoms Most people who brux are unaware of the problem, either because there are no symptoms, or because the symptoms are not understood to be associated with a clenching and grinding problem. The symptoms of sleep bruxism are usually most intense immediately after waking, and then slowly get better, and the symptoms of a grinding habit which occurs mainly while awake tend to slowly get worse throughout the day, and may not be present upon waking. Bruxism may cause a variety of signs and symptoms, including: Bruxism is usually detected because of the effects of the process (most commonly tooth wear and pain), rather than the process itself. The large forces that can be generated during bruxism can have detrimental effects on the components of masticatory system, namely the teeth, the periodontium and the articulation of the mandible with the skull (the temporomandibular joints). The muscles of mastication that act to move the jaw can also be affected since they are being utilized over and above of normal function. Causes The muscles of mastication (the temporalis, masseter, medial and lateral pterygoid muscles) are paired on either side and work together to move the mandible, which hinges and slides around its dual articulation with the skull at the temporomandibular joints. Some of the muscles work to elevate the mandible (close the mouth), and others also are involved in lateral (side to side), protrusive or retractive movements. Mastication (chewing) is a complex neuromuscular activity that can be controlled either by subconscious processes or by conscious processes. In individuals without bruxism or other parafunctional activities, during wakefulness the jaw is generally at rest and the teeth are not in contact, except while speaking, swallowing or chewing. It is estimated that the teeth are in contact for less than 20 minutes per day, mostly during chewing and swallowing. Normally during sleep, the voluntary muscles are inactive due to physiologic motor paralysis, and the jaw is usually open. Some bruxism activity is rhythmic with bite force pulses of tenths of a second (like chewing), and some have longer bite force pulses of 1 to 30 seconds (clenching). Some individuals clench without significant lateral movements. Bruxism can also be regarded as a disorder of repetitive, unconscious contraction of muscles. This typically involves the masseter muscle and the anterior portion of the temporalis (the large outer muscles that clench), and the lateral pterygoids, relatively small bilateral muscles that act together to perform sideways grinding. The cause of bruxism is largely unknown, but it is generally accepted to have multiple possible causes.Bruxism is a parafunctional activity, but it is debated whether this represents a subconscious habit or is entirely involuntary. The relative importance of the various identified possible causative factors is also debated. Disturbance of the dopaminergic system in the central nervous system has also been suggested to be involved in the etiology of bruxism.Evidence for this comes from observations of the modifying effect of medications which alter dopamine release on bruxing activity, such as levodopa, amphetamines or nicotine. Nicotine stimulates release of dopamine, which is postulated to explain why bruxism is twice as common in smokers compared to non-smokers. Psychosocial factors Many studies have reported significant psychosocial risk factors for bruxism, particularly a stressful lifestyle, and this evidence is growing, but still not conclusive. Some consider emotional stress to be the main triggering factor. It has been reported that persons with bruxism respond differently to depression, hostility and stress compared to people without bruxism. Stress has a stronger relationship to awake bruxism, but the role of stress in sleep bruxism is less clear, with some stating that there is no evidence for a relationship with sleep bruxism. However, children with sleep bruxism have been shown to have greater levels of anxiety than other children.[5] People aged 50 with bruxism are more likely to be single and have a high level of education. Work-related stress and irregular work shifts may also be involved. Personality traits are also commonly discussed in publications concerning the causes of bruxism,e.g. aggressive, competitive or hyperactive personality types. Some suggest that suppressed anger or frustration can contribute to bruxism. Stressful periods such as examinations, family bereavement, marriage or relocation have been suggested to intensify bruxism. Awake bruxism often occurs during periods of concentration such as while working at a computer, driving or reading. Animal studies have also suggested a link between bruxism and psychosocial factors. Rosales et al. electrocuted lab rats, and then observed high levels of bruxism-like muscular activity in rats that were allowed to watch this treatment compared to rats that did not see it. They proposed that the rats who witnessed the electrocution of other rats were under emotional stress which may have caused the bruxism-like behavior. Occlusal factors Occlusion is defined most simply as contacts between teeth,and refers to the meeting of teeth during biting and chewing. The term does not imply any disease. Malocclusion is a medical term referring to less than ideal positioning of the upper teeth relative to the lower teeth, which can occur both when the upper jaw is ideally proportioned to the lower jaw, or where there is a discrepancy between the size of the upper jaw relative to the lower jaw. Malocclusion of some sort is so common that the concept of an ideal occlusion is called into question, and it can be considered normal to be abnormal. An occlusal interference may refer to a problem which interferes with the normal path of the bite, and is usually used to describe a localized problem with the position or shape of a single tooth or group of teeth. A premature contact is a term that refers to one part of the bite meeting sooner than other parts, meaning that the rest of the teeth meet later or are held open, e.g., a new dental restoration on a tooth (e.g., a crown) which has a slightly different shape or position to the original tooth may contact too soon in the bite. A deflective interference refers to an interference with the bite that changes the normal path of the bite. A common example of a deflective is an over-erupted upper wisdom tooth, often because the lower wisdom tooth has been removed or is impacted. In this example, when the jaws are brought together, the lower back teeth contact the prominent wisdom tooth before the other teeth, and the lower jaw has to move forward to get the rest of the teeth to meet. The difference between a premature contact and a deflective interference is that the latter implies a dynamic abnormality in the bite. Historically, many believed that problems with the bite were the sole cause for bruxism.It was often claimed that a person would grind at the interfering area in a subconscious, instinctive attempt to wear this down and self equiliberate their occlusion. However, occlusal interferences are extremely common and usually do not cause any problems. It is unclear whether people with bruxism tend to notice problems with the bite because of their clenching and grinding habit, or whether these act as a causative factor in the development of the condition. In sleep bruxism especially, there is no evidence that removal of occlusal interferences has any impact on the condition. People with no teeth at all who wear dentures can still suffer from bruxism,although dentures also often change the original bite. Most modern sources state that there is no relationship, or at most a minimal relationship, between bruxism and occlusal factors.The findings of one study, which used self-reported tooth grinding rather than clinical examination to detect bruxism, suggested that there may be more of a relationship between occlusal factors and bruxism in children.However, the role of occlusal factors in bruxism cannot be completely discounted due to insufficient evidence and problems with the design of studies.A minority of researchers continue to claim that various adjustments to the mechanics of the bite are capable of curing bruxism (see Occlusal adjustment/reorganization).

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