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general::
1. Completely, fully, as in Obviously new to skiing, they were equipped to the teeth with the latest gear. This idiom dates from the late 1300s. Also see ARMED TO THE TEETH; FED TO THE GILLS. 2. Also, up to the or one's teeth. Fully committed, as in We're in this collaboration up to our teeth. [First half of 1900s] Both of these hyperbolic usages allude to being fully covered or immersed in something up to one's teeth.
American Heritage Idioms