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 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 contact/interference is an interference with the bite that changes the normal path of the bite. A common example of a deflective interference is an over-erupted upper wisdom tooth, often because the lower wisdom tooth has been removed or is impacted.
One study reported that sleep arousals which were experimentally induced with sensory stimulation in sleeping bruxists triggered episodes of sleep bruxism. Sleep arousals are a sudden change in the depth of the sleep stage, and may also be accompanied by increased heart rate, respiratory changes and muscular activity, such as leg movements. Initial reports have suggested that episodes of sleep bruxism may be accompanied by gastroesophageal reflux, decreased esophageal pH (acidity), swallowing, and decreased salivary flow. Another report suggested a link between episodes of sleep bruxism and a supine sleeping position (lying face up).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. Historical focus
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.