Background Dental caries (tooth decay) and periodontal diseases (gingivitis and periodontitis) affect the majority of people worldwide, and treatment costs place a significant burden on health services. Decay and gum disease can cause pain, eating and speaking difficulties, low self-esteem, and even tooth loss and the need for surgery. As dental plaque is the primary cause, self-administered daily mechanical disruption and removal of plaque is important for oral health. Toothbrushing can remove supragingival plaque on the facial and lingual/palatal surfaces, but special devices (such as floss, brushes, sticks, and irrigators) are often recommended to reach into the interdental area. Objectives To evaluate the effectiveness of interdental cleaning devices used at home, in addition to toothbrushing, compared with toothbrushing alone, for preventing and controlling periodontal diseases, caries, and plaque. A secondary objective was to compare different interdental cleaning devices with each other. Search methods Cochrane Oral Health’s Information Specialist searched: Cochrane Oral Health’s Trials Register (to 16 January 2019), the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library, 2018, Issue 12), MEDLINE Ovid (1946 to 16 January 2019), Embase Ovid (1980 to 16 January 2019) and CINAHL EBSCO (1937 to 16 January 2019). The US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials. No restrictions were placed on the language or date of publication. Selection criteria Randomised controlled trials (RCTs) that compared toothbrushing and a home-use interdental cleaning device versus toothbrushing alone or with another device (minimum duration four weeks). Data collection and analysis At least two review authors independently screened searches, selected studies, extracted data, assessed studies’ risk of bias, and assessed evidence certainty as high, moderate, low or very low, according to GRADE. We extracted indices measured on interproximal surfaces, where possible. We conducted random-effects meta-analyses, using mean differences (MDs) or standardised mean differences (SMDs). Main results We included 35 RCTs (3929 randomised adult participants). Studies were at high risk of performance bias as blinding of participants was not possible. Only two studies were otherwise at low risk of bias. Many participants had a low level of baseline gingival inflammation. Studies evaluated the following devices plus toothbrushing versus toothbrushing: floss (15 trials), interdental brushes (2 trials), wooden cleaning sticks (2 trials), rubber/elastomeric cleaning sticks (2 trials), oral irrigators (5 trials). Four devices were compared with floss: interdental brushes (9 trials), wooden cleaning sticks (3 trials), rubber/elastomeric cleaning sticks (9 trials) and oral irrigators (2 trials). Another comparison was rubber/elastomeric cleaning sticks versus interdental brushes (3 trials). No trials assessed interproximal caries, and most did not assess periodontitis. Gingivitis was measured by indices (most commonly, Löe-Silness, 0 to 3 scale) and by proportion of bleeding sites. Plaque was measured by indices, most often Quigley-Hein (0 to 5). Primary objective: comparisons against toothbrushing alone Low-certainty evidence suggested that flossing, in addition to toothbrushing, may reduce gingivitis (measured by gingival index (GI)) at one month (SMD-0.58, 95% confidence interval (CI)-1.12 to-0.04; 8 trials, 585 participants), three months or six months. The results for proportion of bleeding sites and plaque were inconsistent (very low-certainty evidence). Very low-certainty evidence suggested that using an interdental brush, plus toothbrushing, may reduce gingivitis (measured by GI) at one month (MD-0.53, 95% CI-0.83 to-0.23; 1 trial, 62 participants), though there was no clear difference in bleeding sites (MD-0.05, 95% CI-0.13 to 0.03; 1 trial, 31 participants). Low-certainty evidence suggested interdental brushes may reduce plaque more than toothbrushing alone (SMD-1.07, 95% CI-1.51 to-0.63; 2 trials, 93 participants). Very low-certainty evidence suggested that using wooden cleaning sticks, plus toothbrushing, may reduce bleeding sites at three months (MD-0.25, 95% CI-0.37 to-0.13; 1 trial, 24 participants), but not plaque (MD-0.03, 95% CI-0.13 to 0.07). Very low-certainty evidence suggested that using rubber/elastomeric interdental cleaning sticks, plus toothbrushing, may reduce plaque at one month (MD-0.22, 95% CI-0.41 to-0.03), but this was not found for gingivitis (GI MD-0.01, 95% CI-0.19 to 0.21; 1 trial, 12 participants; bleeding MD 0.07, 95% CI-0.15 to 0.01; 1 trial, 30 participants). Very-low certainty evidence suggested oral irrigators may reduce gingivitis measured by GI at one month (SMD-0.48, 95% CI-0.89 to-0.06; 4 trials, 380 participants), but not at three or six months. Low-certainty evidence suggested that oral irrigators did not reduce bleeding sites at one month (MD-0.00, 95% CI-0.07 to 0.06; 2 trials, 126 participants) or three months, or plaque at one month (SMD-0.16, 95% CI-0.41 to 0.10; 3 trials, 235 participants), three months or six months, more than toothbrushing alone. Secondary objective: comparisons between devices Low-certainty evidence suggested interdental brushes may reduce gingivitis more than floss at one and three months, but did not show a difference for periodontitis measured by probing pocket depth. Evidence for plaque was inconsistent. Low-to very low-certainty evidence suggested oral irrigation may reduce gingivitis at one month compared to flossing, but very low-certainty evidence did not suggest a difference between devices for plaque. Very low-certainty evidence for interdental brushes or flossing versus interdental cleaning sticks did not demonstrate superiority of either intervention. Adverse events Studies that measured adverse events found no severe events caused by devices, and no evidence of differences between study groups in minor effects such as gingival irritation. Authors' conclusions Using floss or interdental brushes in addition to toothbrushing may reduce gingivitis or plaque, or both, more than toothbrushing alone. Interdental brushes may be more effective than floss. Available evidence for tooth cleaning sticks and oral irrigators is limited and inconsistent. Outcomes were mostly measured in the short term and participants in most studies had a low level of baseline gingival inflammation. Overall, the evidence was low to very low-certainty, and the effect sizes observed may not be clinically important. Future trials should report participant periodontal status according to the new periodontal diseases classification, and last long enough to measure interproximal caries and periodontitis.