Dental formulations of LAs are available in glass cartridges, which contain either 1.7 ml or 1.8 ml of local anesthetic solution.21-25 The cartridges are sealed with a plunger at one end and a diaphragm at the opposite end. The plunger is a filler, coloring agent, and paraffin-impregnated rubber compound. A lubricant is added to allow for greater ease of plunger movement during aspiration. The diaphragm is a rubber-filler compound sealed with an aluminum cap that accommodates the disposable needle.
Cartridges should be stored at room temperature, i.e., about 25°C (77°F).21-25 Solutions that are pinkish or darker than slightly yellow, those that are cloudy; and solutions that contain crystal precipitates or particulate contaminants suggest exposure to extreme temperatures and manufacturing problems, and potential loss of sterility.21-25,33 To minimize oxidation and changes in pH, LAs with a vasoconstrictor should be protected from sunlight, ultraviolet or infrared radiation, or fluorescent light.21-25
Cartridges should not be sterilizer or immersed in chemicals.21-25 They cannot withstand temperatures and pressures associated with steam sterilization; many disinfectants/sterilants contain and release metallic ions (e.g., mercury, zinc, copper, etc.), which may produce swelling and edema; some antirust solutions contain sodium nitrate or other similar agents, which are also capable of releasing metallic ions; and quaternary ammonium compounds are electrolytically incompatible with the aluminum cap.
If disinfection of a cartridge is desired, it can be accomplished by wiping the cap with a pledget of cotton impregnated with either 91% isopropyl alcohol (USP) or 70% ethyl alcohol (USP) just prior to use.21-25 It is of note that most commercial brands of isopropyl alcohol (rubbing alcohol) and ethyl alcohol solutions are not USP grade; such formulations often contain denaturants, which can adversely affect the rubber components of the diaphragm and plunger.
When loading the syringe the needle should penetrate the center of the diaphragm. An off-center penetration produces an oval shaped puncture, which under pressure allows leakage around the needle.21-25 Leakage may also result when using a badly worn syringe, an aspirating syringe with a bent harpoon, a syringe not intended to take 1.8 mL cartridges, or inadvertent freezing of a cartridge.21-25 Cracking of a cartridge is often the result of an extruded plunger being forced back into the cartridge.21-25