Biomaterial Database

Changes in jaw-jerk on different levels of jaw closure and teeth-clenching in humans. 2000

E Fukuyama, and Y Fujita, and K Soma

First Department of Orthodontics, Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo, Japan. e.fukuyama.orts@tmd.ac.jp

We investigated how the jaw-jerk in the human masseter muscle is modulated in relation to the level of jaw closure (JC) and teeth clenching. Electromyographic (EMG) activity was recorded with surface electrodes. Background EMG activity of the masseter muscle was kept at three low teeth clenching levels with visual feedback. The level of JC was changed in six steps along the habitual path of closure relative to the mean maximal jaw opening during gum chewing by inserting a bite block between the upper and lower molars. The jaw-jerk was evoked by applying mechanical stimulation of about 20 N with a hammer to the bite-fork placed on the lower molars on one side in each condition of combination of a level of JC with a level of teeth-clenching. At the resting condition the excitability of the jaw-jerk increased with JC, while at weak voluntary teeth clenching it then decreased and increased again as the jaw was progressively closed. It is suggested that the excitability of the jaw-jerk would increase toward the occlusal position, which in turn would contribute to smooth masticatory movements. In addition, the mode of modulation of the jaw-jerk was studied in a subject with skeletal malocclusion.

UI	MeSH Term	Description	Entries
D008297	Male		Males
D008310	Malocclusion	Such malposition and contact of the maxillary and mandibular teeth as to interfere with the highest efficiency during the excursive movements of the jaw that are essential for mastication. (Jablonski, Illustrated Dictionary of Dentistry, 1982)	Angle's Classification,Crossbite,Tooth Crowding,Cross Bite,Angle Classification,Angles Classification,Bite, Cross,Bites, Cross,Classification, Angle's,Cross Bites,Crossbites,Crowding, Tooth,Crowdings, Tooth,Malocclusions
D008334	Mandible	The largest and strongest bone of the FACE constituting the lower jaw. It supports the lower teeth.	Mylohyoid Groove,Mylohyoid Ridge,Groove, Mylohyoid,Grooves, Mylohyoid,Mandibles,Mylohyoid Grooves,Mylohyoid Ridges,Ridge, Mylohyoid,Ridges, Mylohyoid
D008406	Masseter Muscle	A masticatory muscle whose action is closing the jaws.	Masseter Muscles,Muscle, Masseter,Muscles, Masseter
D008409	Mastication	The act and process of chewing and grinding food in the mouth.	Chewing
D009119	Muscle Contraction	A process leading to shortening and/or development of tension in muscle tissue. Muscle contraction occurs by a sliding filament mechanism whereby actin filaments slide inward among the myosin filaments.	Inotropism,Muscular Contraction,Contraction, Muscle,Contraction, Muscular,Contractions, Muscle,Contractions, Muscular,Inotropisms,Muscle Contractions,Muscular Contractions
D010474	Percussion	Act of striking a part with short, sharp blows as an aid in diagnosing the condition beneath the sound obtained.	Percussions
D011930	Reaction Time	The time from the onset of a stimulus until a response is observed.	Response Latency,Response Speed,Response Time,Latency, Response,Reaction Times,Response Latencies,Response Times,Speed, Response,Speeds, Response
D012026	Reflex, Stretch	Reflex contraction of a muscle in response to stretching, which stimulates muscle proprioceptors.	Reflex, Tendon,Stretch Reflex,Tendon Reflex
D003766	Dental Occlusion	The relationship of all the components of the masticatory system in normal function. It has special reference to the position and contact of the maxillary and mandibular teeth for the highest efficiency during the excursive movements of the jaw that are essential for mastication. (From Jablonski, Dictionary of Dentistry, 1992, p556, p472)	Canine Guidance,Occlusal Guidance,Occlusal Plane,Occlusion, Dental,Dental Occlusions,Guidance, Canine,Guidance, Occlusal,Occlusal Guidances,Occlusal Planes,Occlusions, Dental,Plane, Occlusal,Planes, Occlusal