Terminology and Definitions
- Anatomical terms: Teeth have two sections - crown and root. The line where these sections join is called the cementoenamel junction. The roots are surrounded by alveolar bone and covered by gingival tissue.
- Clinical terms: The terms 'relative crown' and 'relative root' describe how much tooth remains surrounded by bone. In periodontal disease, bone loss reveals more of the root structure, reducing the crown-to-root ratio.

Clinical Importance
- The crown-to-root ratio is important for tooth support within the bone.
- Root length is longer than crown length, providing stability.
- Bone loss affects root support and increases the height of exposed tooth structure.
- A minimum 1:1 ratio is necessary for a favorable prognosis.

Models of Human Teeth
- Teeth in the alveolar bone have longer roots than crowns.
- Teeth experience horizontal and vertical occlusal forces, leading to bone resorption or apposition.

Gingival Tissue and Gingival Recession
- The gingival tissue covers the roots and is about 1 millimeter thick.
- Gingival recession is related to decreased crown-to-root ratio.

Related Dental Procedures and References
- Crown lengthening is a dental procedure related to the crown-to-root ratio.
- Post and core is another dental procedure relevant to the ratio.
- References such as Czochrowska et al., Carranza's Clinical Periodontology, Trauma from Occlusion Handout, and others provide additional information on the topic.

Crown-to-root ratio (Wikipedia)

Crown-to-root-ratio is the ratio of the length of the part of a tooth that appears above the alveolar bone versus what lies below it. It is an important consideration in the diagnosis, treatment planning and restoration of teeth, one that hopefully guides the plan of treatment to the proper end result.