ROLE OF PERIODONTAL MECHANORECEPTORS IN EVOKING REFLEXES IN THE JAW-CLOSING MUSCLES OF THE CAT

1. In anaesthetized cats the left maxillary and mandibular canine and incisor teeth were extracted. Nine weeks later the animals were anaest hetized again and titanium implants were placed into the edentulous ri dge of the maxilla and mandible. 2. Terminal experiments were performe d between 9 weeks and 10 months after inserting the implants. Recordin gs were made from the trigeminal ganglia and peripheral nerves of anae sthetized cats. Neurones were identified which responded to forces app lied to the maxillary teeth but none was found which responded to forc es applied to the implant. 3. The responses of motor units in the temp oralis muscle were studied in response to ramp-plateau forces applied to the maxillary canine tooth and maxillary implant using peristimulus time histograms and cumulative sum (cusum) analysis. A small amount o f inhibition of the motor units was observed in response to the applie d forces to the implant. However, the inhibition was much more profoun d when similar forces were applied to the tooth. 4. The results confir m that when forces are applied to a tooth, periodontal mechanoreceptor s are stimulated which evoke reflex inhibitions to motor units in the jaw-closing muscles. However, there is evidence that mechanoreceptors situated distant to the periodontium can also evoke such reflexes. 5. The results are discussed in relation to the overall functional role o f periodontal mechanoreceptors in the reflexes of mastication.