Contribution of the digastric muscles to the control of bite force in man.
The contribution of the (co-contracting) digastric muscles to the rapid decline in bite-force magnitude after unloading of a static bite was investigated by asking participants to perform two different biting tasks with sudden unloading, and correlating the degree of co-contraction of the digastrics (as derived from their electromyograms) with the impact force, the impact velocity (as measured after a travel distance of 5 mm), and the residual force when the jaw system was in static conditions again after the impact. Co-contraction of the digastrics was varied by asking participants to perform the biting task while controlling bite force (force-controlled experiments) or jaw position (position-controlled experiments). In half of the experiments, participants co-contracted their digastrics more strongly in the position-controlled than the force-controlled experiments. However, there was no clear relation between the level of co-contraction and the magnitude of the impact force, the impact velocity and the residual force. The results imply that co-contraction of the digastric muscles is not sufficient to explain the reduction in bite force and the low impact velocity after an unexpected jaw-closing movement. Two other possible mechanisms that reduce forces in an unloaded jaw system are: (1) force velocity properties of the activated jaw muscles in conjunction with creep of the aponeurotic sheets of the jaw muscles, resulting in a slow partial recovery of the biting force after impact: (2) force length properties of jaw-opening muscles, an activity not recorded here.
van Willigen
J D
JD
Department of Medical Physiology, University of Groningen, The Netherlands.
Otten
E
E
Slager
G F
GF
Broekhuijsen
M I
MI
D001732:Bite Force; D003799:Dental Stress Analysis; D004576:Electromyography; D006801:Humans; D008406:Masseter Muscle / Q000502:physiology; D009119:Muscle Contraction; D009334:Neck Muscles / Q000502:physiology*; D011187:Posture; D011930:Reaction Time; D012018:Reflex / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D014159:Transducers