Purpose: Due to the cross-sectional shape of interdental spaces, it was assumed that interdental brushes having heads with a triangular cross section have an improved cleaning efficacy compared to conventional round brushes. The aim of this study was to evaluate in vitro the cleaning efficacy of triangular (TIB) compared to round interdental brushes (RIB). Materials and Methods: Extracted natural human teeth were fixed in a socket and matched to pairs in a reversible and reproducible manner, simulating two types of small interdental spaces. The proximal tooth surfaces were covered with a dye indicator to simulate plaque. After registering the baseline situation with a digital camera and a highly reproducible geometrical setup the teeth were relocated in their contact position. The interdental spaces were cleaned in a standardized manner followed by digital imaging of the proximal tooth surfaces as described above. The cleaning efficacy was quantified and related to the total proximal tooth surface by digital image subtraction. Four RIB and four prototypes of TIB, which were appropriate for application in small interdental spaces, were tested (n = 12). Results: In isocele, equilateral and both types of interdental spaces the round interdental brushes cleaned 37± 3%, 33± 3% and 35± 2% (Curaden), 50± 6%, 45± 6% and 48± 7% (Tepe), 50± 3%, 40± 2% and 45± 3% (Oral B) and 41± 6%, 33± 4% and 37± 3% (Butler), respectively. The triangular brushes cleaned 64± 7%, 49± 4% and 56± 4% (GABA #4), 67± 4%, 54± 5% and 60± 5% (GABA #5), 69± 6%, 54± 5% and 61± 5% (GABA #6), and 80± 6%, 59± 4 and 69± 3% (GABA #7), respectively. The differences between all groups were statistically significant (p Schlagwörter: interdental cleaning aid, triangular interdental brushes, cleaning efficacy