Effects of TMJ anesthesia and jaw gape on jaw-stretch reflexes in humans.
OBJECTIVE
To study the roles of afferent sensory inputs in the temporomandibular joint (TMJ) and of muscle length in the modulation of the jaw-stretch reflex in humans.


METHODS
Reflexes were evoked in both the masseter and temporalis muscles under standardized conditions in 11 young women. The study was performed in two sessions; experimental conditions were jaw gape and injection of local anesthetics. For jaw gape, 4, 14, and 24 mm were used in random order. One milliliter TMJ injections (carbocaine, 10 mg/ml, versus isotonic saline, 0.9%) were given in a randomized, double blind manner. When a participant received carbocaine during the first session, isotonic saline was injected during the second one. A total of 480 reflexes were evoked in every participant.


RESULTS
No significant differences were found between carbocaine and isotonic saline. ANOVA and post hoc paired t tests did show, however, a significant effect of jaw gape for the left masseter and anterior temporalis muscles, with the 14 mm gape having the highest amplitude.


CONCLUSIONS
Blocking the afferent sensory input (including the mechanoreceptors) from the TMJ seems to have no influence on the sensitivity of the human jaw-stretch reflex. Instead, muscle spindles are the most likely receptors to be responsible for the reflex modulation that was observed in the present study.
Lobbezoo
F
F
Department of Oral Function, Academic Centre for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA Amsterdam, The Netherlands. f.lobbezoo@acta.nl
Wang
K
K
Aartman
I H A
IH
Svensson
P
P
D000328:Adult; D000704:Analysis of Variance; D000758:Anesthesia / Q000379:methods; D000779:Anesthetics, Local / Q000494:pharmacology*; D004311:Double-Blind Method; D004558:Electric Stimulation; D004576:Electromyography; D005246:Feedback; D005260:Female; D006801:Humans; D007568:Jaw / Q000187:drug effects* / Q000502:physiology; D008406:Masseter Muscle / Q000187:drug effects / Q000502:physiology; D008619:Mepivacaine / Q000494:pharmacology*; D009132:Muscles / Q000187:drug effects* / Q000502:physiology; D011930:Reaction Time; D012026:Reflex, Stretch / Q000187:drug effects* / Q000502:physiology; D013703:Temporal Muscle / Q000187:drug effects / Q000502:physiology; D013704:Temporomandibular Joint / Q000187:drug effects* / Q000502:physiology
D000779:Anesthetics, Local; D008619:Mepivacaine