Root bifurcation lesion is a periodontitis lesion involving the root bifurcation area of multiple teeth, the incidence of which increases with age and is mainly related to plaque, root anatomical morphology, trauma and other factors.1. Plaque: The main cause of root bifurcation lesion. Plaque is selectively adhered to the tooth surface by different bacteria, forming a cell-free, homogeneous biofilm. Once plaque is involved in the root bifurcation area, the difficulty of plaque control and tartar removal will aggravate the development of root bifurcation lesions; 2, root anatomical morphology: because the bifurcation of the root bifurcation is close to the neck of the tooth, once periodontitis occurs, the root bifurcation is easily involved; 3, trauma: it is an aggravating factor of root bifurcation lesions The root bifurcation area is sensitive to occlusal forces, and when gingival inflammation enters the area, tissue destruction will be faster, often resulting in pit-like or vertical bone resorption; 4, inflammation: pulp infection and inflammation can spread to the root bifurcation area through the parapulpal canal at the base of the pulp chamber, which can cause bone resorption at the root bifurcation.