What does crown-to-root ratio on a radiograph indicate?

• A. An indication of a tooth's prognosis
• B. The color of the tooth
• C. The depth of the pulp chamber
• D. The mass of surrounding bone

Answer: (A)

The main idea is that crown-to-root ratio on a radiograph is used to gauge prognosis by looking at periodontal support. It compares how much tooth is above bone to how much root is embedded in bone. A favorable ratio—root length equal to or longer than the crown height—indicates solid periodontal support and a better prognosis. If bone loss or root shortening makes the crown appear tall relative to the root, the prognosis worsens because there’s less root surface in bone to stabilize the tooth under function. Radiographs help by showing root length and bone levels to estimate this ratio. It does not measure tooth color, depth of the pulp chamber, or overall bone density—the crown-to-root ratio is specifically about periodontal support and prognosis.