There are several antonyms for the phrase "make teeth chatter," which means to cause someone to tremble or shiver with fear or cold. One antonym is "calm down," meaning to make someone feel more relaxed and less afraid or nervous. Another antonym is "warm up," which means to provide heat and make someone feel comfortable and less cold. Similarly, "soothe" is an antonym that indicates the act of comforting someone, whereas "terrify" is an antonym that means to frighten or scare someone. Depending on the context, other antonyms could include "relax," "ease," "comfort," or "reassure," among others.