The performance of different disposable needle syringe systems was determined by measuring needle-puncture pain, needle-bending forces, and the fluid dynamics of the systems. Thirty-gauge needles cause less needle-puncture pain than any other needle. The force required to bend the 30-gauge needle irreversibly was lower than that for the other needles. Studies of the fluid dynamics of different needle syringe assemblies demonstrated that the flow rate can be limited by using large-size syringes (30 mL) and needles with the smallest internal diameter. On the basis of the results of this study, 30-gauge needles attached to 10-mL syringes are recommended for infiltration anesthesia, and 25-gauge needles with 10-mL syringes are advocated for regional nerve blocks. In infiltration anesthesia, the local anesthetic agent should be injected slowly into the subdermal tissue over a 10-second period. When performing regional nerve blocks, it is also advisable to inject the local anesthetic agent over a 10-second time interval.