Injectable foreign matter may originate in part from: anesthetic cartridge diaphragm surfaces, diaphragm polymer materials, and debris in the lumen of sterile, manufacturer-sealed needles. Particles ranging from 30 to 305 microns were collected from four brands of dental anesthetic cartridges (320 cartridges/brand). Results of this study suggest that rubber and aluminum debris may commonly be injected with anesthetic solutions. Debris on the outer surface of the needle may also be drawn into injection sites. Possible health implications of injectable matter are discussed and remain conjectural.