Immediate versus conventional loading in users of mandibular overdentures retained by narrow-diameter implants: results from a 5-year randomized clinical trial.

OBJECTIVES: This randomized clinical trial (RCT) aimed to evaluate clinical, radiographic, functional, and patient-centered outcomes in users of mandibular two-implant overdentures (2-IMO) subjected to immediate loading (IL) and conventional loading (CL) protocols over a five-year follow-up period. METHODS: Twenty participants were randomly allocated to the CL (n = 10) and IL (n = 10) groups. Clinical peri-implant health parameters, radiographic assessments of marginal bone loss (MBL) and posterior area index (PAI), functional outcomes through masticatory performance (MP), patient-reported outcomes using the Daily Impact on Daily Life (DIDL) questionnaire, and prosthetic maintenance events were evaluated at 1, 3, and 5 years post-treatment. Data were analyzed using multilevel mixed-effects linear regression models, and differences in prosthetic maintenance events over the 5-year follow-up were assessed using binary logistic regression, with the significance level set at 5%. RESULTS: At the five-year follow-up, MBL and the masticatory domain scores were significantly lower in the IL group (p = 0.01; p = 0.03, respectively). No statistically significant differences between groups were observed for MP, PAI, or the remaining DIDL domains (p > 0.05). Intragroup comparisons revealed significant differences (p < 0.05) in peri-implant health, with a reduction observed in the IL group between the first and fifth years. A slight increase in MBL was noted in the CL group, while stability was maintained in the IL group. PAI demonstrated a progressive increase in both groups across all time points. For DIDL scores, the IL group exhibited a significant deterioration in all domains from the third year onward. Over the 5-year period, overall maintenance requirements were comparable between the CL and IL groups (136 vs. 159 events). Nylon O-ring replacement, matrix recapture, and prosthesis adjustments were the most frequent interventions. The IL group was significantly more likely to require nylon O-ring replacement (OR: 1.68; P = 0.03), while showing a markedly lower need for keratinized tissue removal (OR: 0.11; P = 0.04). CONCLUSIONS: Users of 2-IMO subjected to immediate loading tend to report decreased satisfaction with treatment outcomes from the third year of function onward. CLINICAL RELEVANCE: The IL protocol resulted in better peri-implant health parameters, reduced marginal bone loss, and fewer prosthetic maintenance events at the final assessment, while masticatory performance and PAI outcomes were comparable between groups.