Diagnostic Criteria for Bruxism on Polysomnography
Sleep bruxism is diagnosed on PSG when there are more than 2 rhythmic masticatory muscle activity (RMMA) episodes per hour of sleep, scored on masseter and/or temporalis muscle EMG recordings. 1, 2
Core Diagnostic Parameters
RMMA episodes are the fundamental unit for diagnosing sleep bruxism on polysomnography and must be distinguished from other mandibular movements associated with arousals, limb movement disorders, or obstructive sleep apnea. 3
Required PSG Channels for Bruxism Assessment
- Masseter muscle EMG (bilateral or unilateral recording) 2, 4
- Temporalis muscle EMG (optional but recommended) 3
- Standard sleep staging channels: EEG, EOG, submental EMG 4
- Audio-video recording (strongly recommended to improve diagnostic accuracy and reduce false positives by approximately 24%) 2
Quantitative Diagnostic Thresholds
The diagnostic cut-off is >2 RMMA episodes per hour of sleep, though this represents a binary threshold in what is increasingly recognized as a continuum spectrum of jaw motor behaviors. 1, 5
- Sensitivity: 83.3% when using portable devices at 2 events/hour threshold 1
- Specificity: 72% at the same threshold 1
- Event-by-event concordance: Approximately 68% between scoring with and without audio-video, with a tendency to overestimate RMMA by 24% when audio-video is absent 2
Scoring Methodology
RMMA Episode Characteristics
RMMA episodes are scored based on stereotyped movement patterns characterized by rhythmic masticatory muscle contractions during sleep, distinct from random muscle activity or movements associated with other sleep events. 3
Technical Considerations
- Intra-class correlation coefficient for RMMA scoring is good (ICC = 0.91) even without audio-video, though audio-video improves accuracy 2
- Intra-examiner reliability is high (ICC = 0.97) for experienced scorers 2
- Scoring should follow AASM Manual for the Scoring of Sleep and Associated Events standards for consistency 6
Clinical Context and Limitations
Important Caveats
The 2 episodes/hour threshold is somewhat arbitrary and may not correlate directly with clinical consequences such as tooth wear, TMJ pain, or muscle pain. 5 The field is moving toward recognizing bruxism as a continuum rather than a present/absent phenomenon.
Portable PSG systems (Type 2) can be used for bruxism assessment in home environments, offering a cost-effective alternative to laboratory studies, though they carry a moderate risk of overestimation when audio-video is unavailable. 2, 4
Differential Diagnosis
Mandibular movements during sleep must be differentiated from:
- Arousal-related movements 3
- Periodic limb movements (which may co-occur; mean leg movement index is higher in bruxism patients at 21.36 vs 8.42 in non-bruxism patients) 3
- Respiratory event-related movements (respiratory event index tends to be lower in confirmed bruxism patients: 13.17 vs 17.95) 3
Epidemiological Context
Sleep bruxism prevalence varies by age: 14-20% in children, 8% in adults <60 years, and 3% in adults >60 years, which should inform pretest probability. 3