To determine the effect of a dynamic impression lining material (DIL) on the retention and stability of mandibular complete dentures (LCD), masticatory performance, and the oral health-related quality of life (OHRQoL) of the patients wearing complete denture (CD) compared with those wearing a denture with conventional hard denture liner (HL). Twenty-five patients who wore CD with an ill-fitting LCD were randomly assigned to two groups: LCD relined with DIL (Dynamic impression lining material) or HL (Tokuyama® Rebase II (fast)). Three objective measures (denture retention, stability, and masticatory performance) were measured. The OHRQoL was also measured using the Thai version of oral impacts on daily performance. Outcomes were measured at six time points: baseline, 3 days, 1 week, 1 month, 3 months, and 6 months after relining. Outcome changes were analyzed using a generalized estimating equation, and all models were adjusted for age, mandibular ridge form, and CD age at a 5% significance level. After LCD relining, the frequency and severity of adverse oral impacts significantly decreased. In the DIL group, denture pain occurred on and off over six months, and an ill-fitting denture impacted at one month. In the HL group, denture pain continuously decreased over time. At 3 months, changes in the clinical properties of DIL were observed, including perceived odor. The material also peel-off from the denture base, and plaque accumulation was observed. In contrast, the HL properties remained stable for over 6 months. Although DIL improves denture retention and stability, masticatory performance, and the OHRQoL of the patients who wear CD, oral adverse effects were not eliminated. The clinical properties of DILs changed at 3 months, while the HL remained relatively stable for up to 6 months.(The clinical trial registration number: Thai Clinical Trials Registry (TCTR) number TCTR20210625005.).