An actuator for advancing a rod which enables release of the rod from an actuating mechanism by rotating the rod to allow the rod to be retreated. The actuator may also provide a mechanism for disabling the driving mechanism as the rod is fully advanced to prevent damage by excessive forces being applied to the rod. The actuating mechanism can be fully enclosed in a stock of a dispenser gun or applicator, facilitating cleaning of the dispenser gun. The disclosed dispenser gun is particularly suitable for dentistry applications.