Effectiveness of Combined Face-to-Face and Mobile-Based Motivational Interviewing on Oral Hygiene Status and Behavior Among Adolescents in Gorontalo, Indonesia: A Quasi-Experimental Study

Background/Objectives: Oral health problems among adolescents in Indonesia remain high, particularly in Gorontalo City. Conventional education approaches are often insufficient to promote sustained behavioral change. This study aimed to evaluate the effectiveness of combined face-to-face and mobile-based Motivational Interviewing (MI) on oral hygiene status (OHI-S), knowledge, and toothbrushing behavior among adolescents. Methods: A quasi-experimental study with a non-randomized control group and repeated measurements was conducted among 100 adolescents aged 15–18 years in Gorontalo, Indonesia. Participants were allocated into a combined MI group (face-to-face plus mobile application) and a face-to-face MI group. Knowledge was assessed using a validated 15-item questionnaire, and toothbrushing behavior was measured using a 24-item questionnaire; both instruments used dichotomous scoring and demonstrated good reliability (Cronbach’s alpha = 0.82 and 0.85, respectively). Oral hygiene status was evaluated clinically using the Simplified Oral Hygiene Index (OHI-S) by a calibrated examiner (κ = 0.82). Outcomes were measured at baseline and at three follow-up points over three months. Data were analyzed using the Wilcoxon signed-rank test and Mann–Whitney U test, with significance set at p < 0.05. Results: Within-group analyses showed improvements across all outcomes in both groups (p < 0.05). The combined MI group demonstrated greater improvements compared to the face-to-face group, with median knowledge scores increasing from 4 to 8 versus 5 to 7 (between-group p = 0.002), toothbrushing behavior from 10 to 15 versus 12 to 13 (p = 0.001), and OHI-S scores decreasing from 3.2 to 1.4 versus 2.8 to 2.0 (p < 0.001). These findings indicate a greater magnitude of change in the combined intervention group. Conclusions: The combined face-to-face and mobile-based MI approach was associated with greater improvements in oral hygiene status, knowledge, and toothbrushing behavior among adolescents compared to face-to-face MI alone. However, due to the non-randomized design, the findings should be interpreted as associations rather than causal effects.