Fifty years old lost several teeth does not belong to the normal situation, under normal circumstances permanent teeth can be used for life, will not automatically fall off, disease conditions, tooth loss is generally periodontitis caused by the following. 1. Under normal circumstances: the teeth are located in the alveolar bone, the teeth of the dentin and gums, periodontal membrane, alveolar bone together constitute a functional system, the system will be firmly attached to the teeth in the alveolar bone, the teeth can be lifelong existence, and to exercise the functions. 2. In case of disease: when periodontitis occurs, the combined epithelium proliferates to the root side, and its crown side separates from the tooth surface to form a periodontal pocket, i.e. attachment loss occurs. At the same time, the alveolar bone will be resorbed, so that the supporting tissues of the teeth are lost, and the teeth gradually loosen and eventually fall off. If the above symptoms occur, it is recommended to go to the hospital in time to receive early formal treatment.