title: Symptoms and physiological responses to prolonged, repeated, low-level tooth clenching in humans.
abstract: BACKGROUND
  The traditional view contends bruxism, such as tooth grinding/clenching, is part of the etiology of temporomandibular disorders (TMD) including some subtypes of headaches. The purpose of this study is to investigate if a low-level but long-lasting tooth-clenching task initiates TMD symptoms/signs.
  
  
  METHODS
  Eighteen healthy participants (mean age ± SD, 24.0 ± 4.3 years) performed and repeated an experimental 2-hour tooth-clenching task at 10% maximal voluntary occlusal bite force at incisors (11.1 ± 4.6 N) for three consecutive days (Days 1-3). Pain and cardiovascular parameters were estimated during the experiment.
  
  
  RESULTS
  The task evoked pain in the masseter/temporalis muscles and temporomandibular joint after 40.0 ± 18.0 minutes with a peak intensity of 1.6 ± 0.4 on 0-10 numerical rating scale (NRS) after 105.0 ± 5.0 minutes (Day 1). On Day 2 and Day 3, pain had disappeared but the tasks, again, evoked pain with similar intensities. The onset and peak levels of pain were not different between the experimental days (P = .977). However, the area under the curve of pain NRS in the masseter on Day 2 and Day 3 were smaller than that on Day 1 (P = .006). Cardiovascular parameters changed during the task but not during the days.
  
  
  CONCLUSIONS
  Prolonged, low-level tooth clenching evoked short-lived pain like TMD. This intervention study proposes that tooth clenching alone is insufficient to initiate longer lasting and self-perpetuating symptoms of TMD, which may require other risk factors.
authors.affiliation: Department of Crown and Bridge Prosthodontics, Graduate School of Dental Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: Tamiyo
authors.initials: T
authors.lastname: Takeuchi
authors.forename: Taro
authors.initials: T
authors.lastname: Arima
authors.forename: Malin
authors.initials: M
authors.lastname: Ernberg
authors.forename: Taihiko
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Noboru
authors.initials: N
authors.lastname: Ohata
authors.forename: Peter
authors.initials: P
authors.lastname: Svensson
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001732:Bite Force; D005157:Facial Pain / Q000209:etiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000502:physiology*; D015999:Multivariate Analysis; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D017288:Pain Threshold / Q000502:physiology; D012738:Sex Hormone-Binding Globulin; D019265:Spectroscopy, Near-Infrared; D013997:Time Factors; D055815:Young Adult
chemical_list: D006454:Hemoglobins; D012738:Sex Hormone-Binding Globulin
keywords: masseter muscle; maximal voluntary occlusal bite force; tooth clenching; trigeminal physiology