The enamel-osseous boundary is the location where the enamel and the bone of the tooth meet, the bone is the hard tissue covering the surface of the tooth root, and the enamel is the hard tissue attached to the surface of the tooth crown, the two are generally connected to each other end to end, there are also many cases where the bone of the tooth has little part and covers the top of the enamel; there are also two discontinuous contact with each other, there is a section in the middle where the dentin is exposed. The position of the enamel bone boundary is at the level of the gingival margin. If there is periodontal disease, the gums are inflamed and swollen, the position of the gums may be higher than the enamel bone boundary. If the gums are receding, the enamel-bone boundary is exposed and the gums are positioned below the position of the enamel-bone boundary. Therefore, the position of the enamel-bone boundary, which is where the enamel and bone join, is usually clinically flush with the level of the gums under normal circumstances because of its position in the cervical region of the tooth, and may change in position if there is periodontal disease.