Elderly patients often find it challenging to remove plaque accumulated on the attachments of implant overdentures (IOD) using conventional cleaning instruments. Further, excessive plaque accumulation can lead to peri-implant diseases and occasionally to respiratory diseases. Therefore, here, we aimed to compare the effectiveness of waist-shaped interdental brushes (WIB) with that of straight-shaped ones (SIB) in plaque removal from the locator attachments of IOD. Twenty participants with two locator attachments retaining mandibular IOD participated in this study. After the baseline cleaning, the participants refrained from oral hygiene maintenance for 3 days. A dentist cleaned one of the attachments using the WIB and the other attachment using the SIB. The pre- and post-cleaning modified plaque index (mPLI) scores were recorded. Following another 3 days free from oral hygiene maintenance, the trained participants repeated the same cleaning procedure using the WIB and SIB. Pre- and post-cleaning mPLI scores were recorded. Regardless of the type of brush used, the post-cleaning mPLI scores were lower than the pre-cleaning ones. After the cleaning procedure, the overall mean mPLI score was lower in the WIB group than in the SIB group. The post-cleaning mPLI scores at the line-angles and on the axial surfaces of the attachments were also lower in the WIB group than in the SIB group. There was no difference in the cleaning effectiveness between the dentist and participants when they used the same type of interdental brush. The WIB was significantly more efficient in plaque removal than the SIB, especially at the line-angle sites.