Complications and Maintenance of Mandibular Two-implant Overdentures: A 3-year Pilot Randomized Clinical Study of Bar–Locator Versus Bar–Ball Attachments

Abstract

Abstract Objective This 3-year pilot randomized clinical study aimed to compare prosthetic complications and maintenance requirements of mandibular two-implant overdentures retained by bar–locator and bar–ball attachment systems. Materials and Methods A total of 10 completely edentulous participants were randomly allocated to receive mandibular overdentures retained by either bar–locator ( n  = 5) or bar–ball ( n  = 5) attachment systems. All participants received new complete dentures before implant placement. Two implants were inserted in the inter-foraminal region and restored with the assigned bar-retained attachment. Prosthetic complications and maintenance events were recorded during scheduled follow-up visits over 3 years. Evaluated outcomes included retentive component wear, attachment separation, screw loosening, denture tooth and base complications, opposing prosthesis fractures, and relining requirements. Statistical Analysis Descriptive statistics, Fisher's exact test, independent samples t-tests, effect sizes, and confidence intervals were used for analysis, with emphasis placed on estimation rather than formal hypothesis testing. Results No statistically significant differences were observed between attachment systems for individual prosthetic complications. Retentive component wear was the most common complication and occurred more frequently in the bar–locator group, whereas denture relining was more common in the bar–ball group. Although the mean number of complications per patient was higher with bar–locator attachments, the difference did not reach statistical significance. However, the large effect size suggested a potentially clinically meaningful increase in maintenance burden associated with bar–locator systems. Conclusion Both attachment systems demonstrated frequent but manageable prosthetic complications over the 3-year follow-up period, with no statistically demonstrable superiority between designs within the limitations of this pilot study. Bar–locator attachments were associated mainly with retentive component wear, whereas bar–ball attachments showed greater relining requirements. No catastrophic mechanical failures were observed, supporting the clinical reliability of both systems. These preliminary findings may assist in the design and sample size estimation of future adequately powered clinical trials.