original_query: What is the significance of the crown-to-root ratio when evaluating a tooth for a crown-lengthening procedure?
query: What is the significance of the crown-to-root ratio when evaluating a tooth for a crown-lengthening procedure?
answer: It is not the length of the post within the root canal that provides retention for the core and crown, but rather the length of the post within the root structure surrounded by bone.  A poor crown-to-root ratio (e.g., a long post, but only extending a short way into bone-supported root structure) indicates a poor prognosis for the restoration. This ratio is essential when considering crown-lengthening procedures.