In recent years, as the number of adults seeking orthodontic treatment has increased, so too has the number of periodontal tissue problems, particularly regarding the impact on periodontal tissue of receiving orthodontic treatment. Orthodontic treatment improves the occlusion and appearance of teeth by moving the teeth appropriately. These movements have a significant impact on the interactions between the teeth and periodontal tissues. Orthodontic treatment can also recover tooth alignment for patients with tooth displacement caused by periodontitis; however, orthodontic treatment also often has adverse effects on periodontal soft tissue, such as gingivitis, gingival enlargement and gingival recession. The purpose of this review is to summarise the current evidence and solid knowledge of periodontal soft tissue problems in orthodontic treatment and outline some prevention strategies.