Is there a first night effect on sleep bruxism? A sleep laboratory study

J Clin Sleep Med. 2013 Nov 15;9(11):1139-45. doi: 10.5664/jcsm.3152.


Study objectives: Sleep bruxism (SB) is reported to vary in frequency over time. The aim of this study was to assess the first night effect on SB.

Methods: A retrospective polysomnographic (PSG) analysis was performed of data from a sample of SB patients (12 females, 4 males; age range: 17-39 years) recorded in a sleep laboratory over 2 consecutive nights. Sleep parameters and jaw muscle activity variables (i.e., rhythmic masticatory muscle activity [RMMA]) for SB were quantified and compared between the 2 nights. Subjects were classified into groups according to severity of RMMA frequency, such as low frequency (2-4 episodes/h and/or < 25 bursts/h) and moderate-high frequency (≥ 4 episodes/h and ≥ 25 bursts/h).

Results: Overall, no first night effects were found for most sleep variables. However, total sleep time, sleep efficiency, and stage transitions showed significant time and group interactions (repeated measures ANOVAs, p ≤ 0.05). The RMMA episode index did not differ between the 2 nights, whereas the second night showed significantly higher burst index, bruxism time index, and mean burst duration (repeated measure ANOVAs, p ≤ 0.05). Five patients of 8 in the low frequency group were classified into the moderate-high frequency group on the second night, whereas only one patient in the moderate-high frequency group moved to the low frequency group.

Conclusions: The results showed no overall first night effect on severity of RMMA frequency in young and healthy patients with SB. In clinical practice, one-night sleep recording may be sufficient for moderate-high frequency SB patients. However, low RMMA frequency in the first night could be confirmed by a second night based on the patient's medical and dental history.

Keywords: Sleep bruxism; first night effect; polysomnography; rhythmic masticatory muscle activity; sleep laboratory.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Analysis of Variance
  • Electrocardiography / methods
  • Electroencephalography / methods
  • Electromyography / methods
  • Female
  • Humans
  • Male
  • Masticatory Muscles / physiopathology
  • Muscle Contraction / physiology
  • Periodicity*
  • Polysomnography / methods
  • Retrospective Studies
  • Severity of Illness Index
  • Sleep / physiology*
  • Sleep Bruxism / diagnosis
  • Sleep Bruxism / physiopathology*
  • Sleep Stages / physiology
  • Surveys and Questionnaires
  • Young Adult