What is added to an anesthetic agent to lengthen the effect by decreasing blood flow?

Vasoconstrictors are substances that narrow the blood vessels, which reduces blood flow to the area where the anesthetic has been administered. By decreasing blood flow, vasoconstrictors help to prolong the anesthetic effect. This is particularly important in dental procedures where sustained numbness is desired for patient comfort and to facilitate the dental work being done.

In contrast, vasodilators would increase blood flow, which can lead to a quicker washout of the anesthetic, diminishing its effectiveness. Lidocaine and Septocaine are both types of anesthetic agents that may be used in dentistry, but they do not inherently affect blood flow; rather, they are the medications being modified by the addition of vasoconstrictors to prolong anesthetic action.