Symbolism, Imagery, Allegory
Like Sadie's career teaching domestic science, Bessie's career as a dentist is the perfect fit for her personality.
Dentistry was a hard career for a person of color to break into, much less a woman. Although Bessie is intimidated from the get-go, she plays the part of a "great actress" and acts like nothing fazes her (5.17.20). That's a classic Bessie move, right there.
Similarly, her approach to the actual practice of dentistry reveals further insight into her character. Although some are skeptical of this female dentist, Bessie proves herself to be full-hearted in her love for her patients and blessed with a "gentle touch" (5.19.9). As with all things involving Bessie, you just have to make it past the tough exterior to get to the warm, fuzzy goodness underneath.