The pulp is usually acidic, but also can be sweet, and even pulpless varieties are found.

Between the pulpless are also some fingered varieties and the Yemenite citron.

Yemenite citron - a pulpless citron.

Price initially did dental research on the relationship between endodontic therapy and pulpless teeth and broader systemic disease, known as focal infection theory, a theory which resulted in many extractions of tonsils and teeth.

Price spent 25 years of his career performing research on pulpless and endodontically-treated teeth, which supported the theory of focal infection, which held that systemic conditions, including complexion, intestinal disorders, and anemia could be explained by infections in the mouth.

One researcher in 1940 noted "practically every investigation dealing with the pulpless teeth made prior to 1936 is invalid in the light of recent studies" and that the research of Price and others suffered from technical limitations and questionable interpretations of results.