Objective: To observe the movement of posterior teeth after losing the interproximal and occlusal contacts in adults from the amount and speed of mesial-distal, buccal-lingual, occlusal-gingival and three-dimensional movements. Methods: Twenty cases of metal post-core restoration from the Department of Prosthodontics, Peking University School and Hospital of Stomatology were recruited into this study, which was an observational study. The restored teeth had complete mesial, distal, and occlusal contacts before treatment. All the interproximal and occlusal contacts were removed during the preparation for the post-core. The three-dimensional positions of the post-core preparation were obtained by the intraoral scanner at the day of tooth preparation and that of post-core placement. The amounts of mesial-distal, buccal-lingual and occlusal-gingival tooth movement were measured in the software. On this basis, the amount of three-dimensional tooth movement was calculated. The speed of tooth movement was calculated based on the elapsed time between the two scans. Results: Ten females and ten males with an average age of (29.5±4.9) years were recruited. The average elapsed time was (10.9±2.7) days. The amount of the mesial-distal tooth movement was (134.8±61.2) μm, of the buccal-lingual tooth movement was (110.3±39.5) μm, of the occlusal-gingival tooth movement was (104.8±57.5) μm, and of the three-dimensional tooth movement was (211.4±71.0) μm, respectively. The amounts of mesial-distal, buccal-lingual and three-dimensional tooth movements were larger in female than in male (P<0.05). The speed of the mesial-distal tooth movement was (13.1±7.8) μm/d, of the buccal-lingual tooth movement was (10.6±4.5) μm/d, of the occlusal-gingival tooth movement was (10.1±6.8) μm/d, and of the three-dimensional tooth movement was (20.5±9.7) μm/d, respectively. The speed of mesial-distal and buccal-lingual tooth movements were larger in female than in male (P<0.05). The speed of three-dimensional tooth movement was slightly larger in female than in male, while there was no significant difference between different genders (P>0.05). Conclusion: The three-dimensional position of posterior teeth changed after losing the interproximal and occlusal contacts in adults. The female had more significant and faster tooth movement than the male.