Sahaprom Namano, Yuriko Komagamine, Bui Ngoc Huyen Trang, Maiko Iwaki, Kaho Hoteiya, Terumi Sakaguchi, Shunsuke Minakuchi, Manabu Kanazawa
Background/Objectives: Metabolic syndrome (MetS) causes significant oral manifestations that negatively impact oral health-related quality of life (OHRQoL). This randomized controlled trial evaluated the effects of combined dental interventions and lifestyle guidance on OHRQoL in patients with MetS. Methods: In total, 82 participants with MetS were randomized into an intervention group (IG; n = 39), receiving dental treatment plus lifestyle guidance, or a control group (CG; n = 43), receiving lifestyle guidance only. OHRQoL was assessed using GOHAI and OHIP-14 at baseline, 1 month, and 3 months. Data were analyzed using repeated-measures ANOVA and multivariable ANCOVA, adjusting for age, sex, baseline OHRQoL, and waist circumference. Pearson correlations examined the relationship between metabolic changes (Δ) and OHRQoL. Results: At 3 months, the IG demonstrated significantly superior OHIP-14 scores (p = 0.020) and a large effect size in social disability (ηp2 = 0.148, p < 0.001) compared to the CG. Within-group analysis showed the IG achieved highly significant longitudinal improvements in pain and psychological discomfort (all p < 0.001). Subgroup analysis confirmed these gains were primarily driven by participants with missing teeth (ηp2 = 0.447, p < 0.001), whereas the periodontitis-only subgroup showed non-significant shifts. Multivariable analysis identified age and baseline scores as primary predictors. Notably, OHRQoL improvements significantly correlated with reductions in body weight (r = 0.355, p = 0.001) and waist circumference (r = 0.238, p = 0.031). Conclusions: Integrated dental and lifestyle interventions significantly improved OHRQoL in MetS patients by enhancing psychosocial well-being and social reintegration. Gains were functionally driven by systemic metabolic success. Addressing “nutritional barriers” through dental rehabilitation, while targeting weight loss goals, was essential for holistic MetS management.