Tooth looseness (tooth mobility) refers to the degree of movement of natural teeth or implants when subjected to forces. In the natural dentition, each tooth has a certain physiological mobility, usually not more than 0.2 mm, but if periodontitis or occlusal trauma occurs, the mobility of the tooth will increase significantly. According to the different degrees of tooth loosening, it is clinically divided into three divisions of I-III degrees, which generally need to be judged by the clinician through professional examination or measurement. I. Judgment standard of tooth Ⅲ degree loosening 1, according to the scope of tooth loosening: the tooth buccolingual direction (inside and outside direction) of the degree of movement more than 2mm; 2, according to the direction of tooth movement: teeth exist in the buccolingual direction (inside and outside direction), near and far in the direction (left and right direction) and vertical direction (up and down direction) of the three directions of the degree of tooth movement, can be judged as teeth Ⅲ degree loosening. Second, the method of judging teeth Ⅲ degree loosening 1, the traditional measurement method: the traditional is also the current domestic clinical has been used method, that is, the doctor using dental forceps or finger holding the affected tooth shaking, with the adjacent teeth or a sign of the relative position change to estimate the degree of loosening. Its diagnostic results have a large subjectivity, and poor sensitivity, only when the affected tooth in the appearance of perceptible mobility to diagnose, and is not suitable for the early diagnosis of periodontal disease tooth mobility. 2, tooth mobility measurement instrument measurement: the use of a variety of tooth mobility measuring instrument, such as LHLY type tooth mobility displacement measuring instrument, can reduce the damage of the measuring instrument to the teeth, and can more accurately observe the index, has greater clinical practical significance.