The most common way for the Herbst appliance to “break”, is for the screw to come loose on the upper right molar. If this happens, it may be too difficult for you to replace this at home. You have been provided with a small wrench. You may loosen the screw on the lower section and remove the Herbst arm. Then you can contact the office to schedule a time to have it reattached.
Depending on the design of the Herbst, it is also possible for it to come apart. If you open too wide, the little plunger attached to your lower jaw may slip out of the sleeve that is attached to your upper jaw. Should this happen, look in the mirror, open very wide, slip the little rods or plungers into the tubes or sleeves on the upper part, and close normally.
If the crown attached to the tooth is loose, then you should contact the office to have it recemented.