Definition.
Bruxism has been defined as an involuntary activity of the jaw musculature characterized by jaw clenching, bracing, gnashing and grinding of the teeth while asleep.
This behaviour can be also observed during the night in the so-called “ sleep bruxism ”; according to the “International Classification of Sleep Disorders”, it can be classified as a parasomnia, a group of sleep disturbances that includes sleep walking, nightmares, sleep talking and enuresis.
Many factors can develop this pathology:
| Exogenous | Endogenous |
|---|
| Stress-anxiety; | Personality; |
| Environmental influences (e.g., familial, jaw-clenching reactions, tongue habits); | Genetic (no proven transmission); |
| Occlusal interferences (controversy); | Neurochemicals (e.g., dopamine, noradrenaline, serotonin); |
| Medication (e.g., L-dopa, neuroleptics, amphetamine); | Neurological disorders (e.g., Parkinson, Meige syndrome , oral tardive dyskinesia, RBD, olivopontocerebellar atrophy, cerebellar hemorrhage); |
| Substance abuse (e.g., cocaine, alcohol); | Psychiatric-related disorders (e.g., dementia, mental retardation,tics/ Tourette syndrome); |
| Sleep disorders (e.g., PLMS, apnea, RBD); |
Prevalence: it ranges from 14-20% in children (5-8% in adults but decreases) to 3% in those 60 and over. There’s no gender predilection.
Characteristics.
Bruxists present the same characteristics, both in the nocturnal and diurnal disturb.
In the former, the patient shows an abnormal EMG activity of masseter and anterior temporal muscles during the sleep, equally distributed in non-REM and REM sleep, but are more frequent in stages 1 and 2 than in slow-wave sleep.
The great majority of bruxism episodes detected in non-REM sleep are associated with the cyclic alternating pattern and always occurred during a transient arousal. The framework of this cyclic alternating pattern offers a unified interpretation for sleep bruxism and arousal-related phenomena.
Besides, other physiologic changes can be observed during the sleep arousal-related phenomena:
- gross body movements (such as involuntary leg movement or turning),
- increases in heart rate,
- altered respiratory patterns,
- peripheral vasoconstriction.
Although the exact neural mechanisms underlying repetitive masticatory muscle activity during sleep have not been elucidated, they may involve alterations in brain neurochemistry.
Symptoms and Consequences.
Myofacial pain and muscular hypertrophy, TMJ structural damage and non-restorative sleep are striking symptoms of bruxism.
Trauma to dentition and supporting tissues include thermal hyper-sensitivity, tooth hypermobility, injury to the periodontal ligament and periodontium.
According to some literature, bruxism is correlated with temporo-mandibular disorders (TMDs) and malocclusion; the prevalence of TMDs in children varies from 16% to 90%.
The most prevalent clinical signs of TMD are: TMJ sounds, limitation of mandibular movements, TMJ and muscle tenderness, headache, earache.
The etiology of TMD is considered to be multifactorial (however controversial); causal factors include different structural parameters, psychosocial variables, acute trauma, occlusal interferences, stress and functional mandibular overload variables (e.g., parafunctional habits, grinding).
Risk factors.
Among risk factors, age seems to be the dominant one (bruxism declines from childhood to old age), while smoking is a modest risk for the develop of this disturb.
An important role has been given to drugs such ecstasy, ketamines, methamphetamines because of their effects on the alteration on mood regulation, impulse control and sleep.
It seems that antipsychotic and antidepressant medications like fluorexetine, fluvoxamine, paroxetine or sertraline) may trigger sleep bruxism in non-bruxers. In fact, these substances can induce movement disturbs like dystonia and dyskinesia.
Other analyses about behaviours revealed that the amount of alcohol and an aggressive personality are positively associated with bruxism; in male subjects a self transcendence is also positively associated with bruxism, while in female subjects escaping from stressful events is negatively associated with it.
Recent studies with twins support an old hypothesis that this disturb could be characterized by a familial predisposition.
Treatments.
It is often recommended by specialists to use splints so as to prevent tooth surface loss, due to grinding, and pain and overload on the temporomandibular joint.
An alternative is represented by the NTI appliance, that inhibits jaw’s nociceptors during bruxism episodes.
Finally, also the use of the botulinum toxin A seems to be a safe and effective treatment for severe tooth grinding: it inhibits the release of acetylcholine in neuromuscular junctions; it is intramuscular injected and its effects last for three-six months. The target muscle usually is the masseter.
