title: Preconditions for estimation of masticatory forces from dynamic EMG and isometric bite force-activity relations of elevator muscles.
abstract: OBJECTIVE
  Previous studies proposed to estimate masticatory forces from electromyograms (EMG) by substituting chewing activities of a particular muscle into bite force-activity relations obtained from isometric clenching. For biomechanical reasons, this method requires that ratios between muscle forces in chewing be the same as in clenching. The purpose of this study was to investigate whether this assumption is valid.
  
  
  METHODS
  In 32 asymptomatic subjects, EMGs of bilateral temporal and masseter muscles were registered in unilateral clenching on a bite fork and in chewing. Ratios of peak activities of different muscles were compared between the two biting tasks.
  
  
  RESULTS
  In clenching, the working: balancing ratio of the masseters amounted to 0.92, while in chewing this ratio increased to 1.9. The working:balancing ratio of the temporalis was 1.8 in clenching and dropped to 1.3 in chewing. The temporalis:masseter ratio on the balancing side increased from 0.65 in clenching to 1.1 in chewing.
  
  
  CONCLUSIONS
  The finding that ratios of muscle activities in chewing differed from corresponding ratios in clenching implies different combinations of muscle forces and/or different bite force-activity relations in the two biting tasks. In any of these cases, prediction of chewing force from the EMG of a particular muscle could lead to indefinite overestimations.
authors.affiliation: University Dental Clinic, Department of Prosthodontics, Friedrich-Alexander-University of Erlangen-Nürnberg, Erlangen, Germany. peter.proeschel@rzmail.uni-erlangen.de
authors.forename: P A
authors.initials: PA
authors.lastname: Pröschel
authors.forename: J
authors.initials: J
authors.lastname: Raum
mesh_terms: D000328:Adult; D000703:Analog-Digital Conversion; D001696:Biomechanical Phenomena; D001732:Bite Force; D016001:Confidence Intervals; D004576:Electromyography / Q000379:methods; D005260:Female; D005544:Forecasting; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D016014:Linear Models; D008297:Male; D008406:Masseter Muscle / Q000502:physiology*; D008409:Mastication / Q000502:physiology; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013703:Temporal Muscle / Q000502:physiology*