Barbed needle and inexplicable paresthesias and trismus after dental regional anesthesia.

The tips of 100 needles that had been used clinically for the administration of mandibular block anesthesia (50 by students and 50 by staff) were examined individually under a dissecting microscope. Sixty percent of these needles were found to be barbed. With the use of an animal laboratory simulation, it has been shown that the tips of standard needles as used in general dental practice will barb if allowed to touch bone (medial aspect of the mandibular ramus) during the administration of a mandibular block for dentistry using the direct approach and that a relationship exists between the pattern of this barbing, the disposition of the bevel of the needle at the time of its insertion, and the likelihood of lingual or inferior dental nerve involvement on withdrawal of the barbed needle. Simple precautions are advanced for reducing the possibility of nerve or other tissue damage from this source.