To assess the roles of glutamate and its ionotropic receptor in processing noxious sensory input from dental pulp,glutamate NMDA receptor subtype antagonist,MK-801 and non-NMDA receptor subtype antagonist,CNQX were administrated separately into left lateral cerebral ventricle prior to exposing pulp cavity of left maxillary first molar tooth.The number of Fos-positive neurons in medulla oblongata was measured and compared with that of the group with simple exposure of dental after same survival time pulp.Fos protein expression was reduced dose-dependently by an administration of MK-801,but CNQX had little effect.The results showed that glutamate may be an excitatory transmitter of noxious dental pulp sensory input to neurons in medulla oblongata.In pain nodel of mechanical exposing dental pulp,NMDA receptor subtype has an important role in this process.

Objective To evaluate the clinic effect of dental operating microscope ( DOM) and ul-trasonic root canal technique in removing fractured root canal instruments .Methods Eight cases with frac-tured instruments located in different parts of root canals were treated with ultrasonic technique under DOM and the results were analyzed .The fractured instruments were divided into stainless steel file , Ni-Ti file and post according to material type .Results Twenty-seven fractured instruments were removed and the total success rate was71.1%.Among them, the success rate of stainless steel file was 71.4%,of Ni-Ti file was 37.5%and of post was 100%.No root canal perforation occurred .According to the place fractured instru-ments located , the success rate of stainless steel file located at upper 1/3 root canals was 100%,at middle 1/3 was 81.8%and at apex 1/3 was 33.3%;the success rate of Ni-Ti file located at middle 1/3 was 60%and at apex 1/3 was 0.In bent root canals , the success rate of stainless steel file located at bent part crown square was 86.7%and at bent part apex square was 20%;the success rate of Ni-Ti file located at bent part crown square was 60%and at bent part apex square was 0.Conclusion DOM combined with ultrasonic root canal technique in removing fractured instruments is effective , but the success rate is relatively low for Ni-Ti files and the cases fractured instruments located at root canal apex 1/3 or bent part apex square .