A crown-to-root ratio of 1:3 indicates which relationship?

• A. Crown length divided by root length
• B. Crown length by alveolar crest height
• C. Length of enamel divided by root length
• D. Crown length is one-third of root length

Answer: (D)

Understanding crown-to-root ratio means comparing how tall the crown is to how long the root is along the tooth’s long axis. A 1:3 ratio means the crown height is one unit while the root height is three units, so the crown is one-third as tall as the root. In other words, crown length equals one-third of root length. This is the precise relationship conveyed by the 1:3 ratio. It isn’t about enamel length or alveolar crest height, and stating just a formula without the numerical proportion wouldn’t reflect the given ratio.