Extracurricular activities unrelated to clinical experiences/academics are highly recommended. They should reflect your passions and interests rather than your graduation or dental school requirements. While applicants do need to shadow and volunteer it is just as important to participate in extracurricular groups that express who they are outside of their professional goals.
Admissions officers are not looking for applicants who can only ace their exams and DATs, shadow, volunteer, and perform research. They are looking for bright, multi-faceted people who are not only strong students, but also unique individuals. Remember, dentists are professionals who interact with people from all different backgrounds on a daily basis. Excellent social skills and a variety of personal interests are necessary in order to adapt to the many personalities you will meet in the field.