Analysis of predictive factors for post-orthodontic stability: a retrospective cohort study

​​ Orthodontic relapse remains a challenge in clinical practice. This study aimed to comprehensively evaluate the independent contributions and time-dependent patterns of multidimensional factors influencing the relapse risk, to provide insights for formulating personalized stability strategies. ​​ This multi-center retrospective cohort study included 474 participants with a median follow-up of 6 years. Variables included baseline, anatomical, treatment, and retention factors. Relapse was assessed by comparing intraoral photographs at post-treatment and follow-up (≥ 3 years post-debonding). Multivariate logistic and Cox regression analyses were performed to identify relapse predictors, with stratified analyses by molar relationship. ​​ Relapse rate was 21.3%. Protective factors included female sex (odds ratio [OR] = 0.475, p = 0.013) and tooth extraction treatment (OR = 0.437, p = 0.006). Convex facial profile (OR = 2.057, p = 0.031), high-angle vertical pattern (OR = 2.086, p = 0.043) and longer follow-up duration (OR = 1.152, p = 0.010) were risk factors. Retainer adherence was strongly protective: full-time wear (OR = 0.070, p < 0.001) and nighttime wear (OR = 0.316, p = 0.004) during the first year, as well as longer total wear duration (1–2 years: OR = 0.408, p = 0.028; >2 years: OR = 0.352, p = 0.006) significantly reduced relapse risk. Cox regression confirmed that full-time wear (hazard ratio [HR] = 0.231, p < 0.001) and wear duration > 2 years (HR = 0.366, p < 0.001) significantly reduced the instantaneous hazard of relapse. Stratified analysis revealed convex profile (OR = 5.706, p = 0.006) and high-angle pattern (OR = 4.234, p = 0.015) specifically increased relapse risk in Class II patients, whereas female sex (OR = 0.101, p = 0.003) was most protective in Class III patients. ​​ Convex facial profile and high-angle pattern indicated increased relapse risk, particularly in Class II patients. Female sex (especially in Class III patients) and extraction treatment showed protective effects. ​​High retainer adherence (full-time wear and prolonged use) was the most critical stability factor.​​ Clinical practice calls for personalized retention strategies based on individual risk profiles.