INTRODUCTIONrnThere is an increasing number of periodontal patients seeking orthodontic treatment for improvements in function and aesthetics.1 It has been found that appropriate orthodontic-periodontal combi-nation therapies can improve periodontal conditions.2–3 However, in patients with periodontitis (PD), there can be an increased risk of alveolar bone loss due to unfavourable orthodontic conditions, e.g., poor oral hygiene due to increased difficulty in tooth brushing and formation of biofilms4 with higher periodontal pathogenicity leads to the recurrence of active PD and exacerbation of alveolar bone loss.5 In addition, orthodontic force itself can induce an inflammatory response, which may amplify the level of inflammation in the periodontium and result in elevated bone resorption.6–8 The situation may be even worse if a patient smokes or suffers from diabetes, immune disorders, osteoporosis and genetic predisposition.9–12 Thus, it is of great importance to prevent alveolar bone loss during orthodontic treatment in patients with PD.