In general, dentists are committed to saving teeth! This is why dentists opt to fill a cavity, rather than pulling the tooth.
Cavities can decay so much that it gets to the point where restoration is impossible without a procedure called crown lengthening. Crown lengthening is a way to remodel the contour of the gum line. The routine surgical procedure does not actually lengthen the crown, but rather lowers the gum line. Patients opt for this procedure when there is not enough tooth structure to affix a crown. Even when a tooth has been broken below the gum line, crown-lengthening surgery can successfully expose more of the tooth.