The inferior alveolar nerve block (shot) is the most frequently used injection technique for achieving local anesthesia (numbness) for the teeth in the lower jaw. However, this injection does not always result in successful pulpal (tooth) anesthesia (patient felt pain). No study has combined mepivacaine and lidocaine anesthetics (numbing solutions) for this type of injection (shot). The investigators propose to compare an injection of mepivacaine followed by lidocaine to an injection of lidocaine followed by lidocaine to determine if there is a difference in effectiveness.