This clinical trial aimed to evaluate the effect of Khat chewing on the gingival health of patients with fixed orthodontic appliances (FOAs) by measuring some periodontal parameters before and during 6-time intervals of orthodontic therapy. It also aimed to evaluate this effect regarding gender. The study included 39 Yemeni orthodontic patients with a mean age of 25.7±4.5; divided into two groups, a control (non-chewers) with a mean age of 25.81±4.3 and an experimental (chewers) group with a mean age of 25.61±4.8. An examination sheet was used for data collection, including the patient’s personal information, oral health status, and three periodontal parameters: plaque index (PI), gingival index (GI), and pocket depth (PD). These data measurements were analyzed using SPSS v.24. The study showed an increase in mean plaque, gingival, and pocket depth indices at all-time visits after the appliance insertion compared to all patients’ pre-treatment status. It indicates that Khat chewing harms all periodontal parameters during the orthodontic treatment period. Mean PI, GI and PD were lower in female patients than male patients after the appliance insertion. The khat chewing process mechanically removes the dental plaque, decreasing PI and GI, while PD was worse in Khat chewers than non-chewers. Finally, it is recommended that chewing Khat should be avoided during orthodontic therapy.

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