In dentistry, a furcation defect is a term used to describe bone loss, usually a result of periodontal disease, affecting the base of the root trunk of a tooth where two or more roots meet. The extent and configuration of the defect are factors in both diagnosis and treatment planning. A tooth with a furcation defect has typically reduced prognosis owing to the difficulty of rendering the furcation area free from periodontal pathogens. For this reason surgical periodontal treatment may be considered to allow vision and access to the furcation. Because of its importance in the assessment of periodontal disease, a number of methods of classification have evolved to measure and record the severity of furcation involvement; most of the indices are based on horizontal measurements of attachment loss in the furcation...