ABSTRACT Objectives To compare the effectiveness of metronidazole gel and mobile telephone short-message service (SMS) reminders on gingivitis in patients undergoing fixed orthodontic treatment. Materials and Methods The trial was double blinded (patient and investigator), and only the clinical trial unit pharmacist was unblinded. Data were collected from patients undergoing fixed orthodontic treatment for at least 6 months. A total of 66 patients were randomly assigned to either 0.8% metronidazole gel (n = 22), SMS reminder and placebo gel (n = 22), or placebo (control) group only (n = 22). Gingival index (GI), bleeding index (BI), and orthodontic plaque index (OPI) were evaluated on several teeth at baseline (T 0 ) and after 4 weeks (T 1 ). Paired-sample t -tests were used to compare mean differences of indexes at T 0 and T 1 in the groups, and independent-sample t -tests were used to determine the effects of interventions compared with the controls. Results Data from 64 patients were analyzed; there were 2 dropouts. There were statistically significant ( P < .05) reductions in GI, BI, and OPI scores from T 0 to T 1 for each intervention. However, there were no significant differences between each intervention and the control group. There were no adverse effects. Conclusions The null hypothesis could not be rejected. There is no difference between interventions (application of 0.8% metronidazole gel and SMS reminder for reinforcing oral hygiene) in reducing gingival inflammation in orthodontic patients.