Bruxism occasional tooth grinding. It has been shown that the majority (86%) of sleep bruxism episodes occur during periods of sleep arousal. 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
Habitual aspect The habitual aspect is a type of imperfective aspect, which does not depict an event as a single entity viewed only as a whole but instead specifies something about its internal temporal structure. Östen Dahl found that the habitual past, the most common tense context for the habitual, occurred in only seven of 60 languages sampled, including English. Especially in Turkic languages such as Azerbaijani and Turkish, he found that the habitual can occur in combination with the predictive mood. Standard English has two habitual aspectual forms in the past tense. One is illustrated by the sentence "I used to