Professional perspective
Clinical relevance
- Individual size determination as the central precondition for effectiveness and tissue tolerance
- Patient education on the absence of a manufacturer-independent color standard
- Instruction on insertion angle and force to avoid tissue trauma
- Accounting for multiple sizes per dentition given variable interdental space geometry
- Motivating patients toward regular interdental care as a core part of practice work
Sizing: PHD and ISO 16409
Sekundo and Staehle (2020) examined 2,320 interdental brush samples from 24 manufacturers for their passage hole diameter (PHD) under ISO 16409:2016. PHD determination proved to be a reproducible classification instrument with excellent inter- and intra-rater reliability (ICC ≥ 0.973), though variability increased for larger brushes. The commercial range spanned a PHD of 0.6 to 5.2 mm, with 90 percent of products at a PHD of ≤ 2.0 mm. Only 33 percent of manufacturers stated the ISO size, and only 25 percent the exact PHD value, an inconsistent labeling practice that complicates product selection for patients.
Color coding: no manufacturer-independent standard
Turner (2022) notes in the British Dental Journal that color coding of interdental brushes can denote different diameters depending on manufacturer. Patients who reorder, for instance online, based on color alone rather than brand and millimeter measurement risk purchasing an ill-fitting size. A recommendation should therefore always include the specific manufacturer's exact diameter or ISO size, not color alone.
Insertion forces and tissue protection
In the same in vitro study, Sekundo and Staehle (2020) measured insertion forces averaging 1.58 N (SD 1.27 N) for cylindrical and conical brushes, and 2.31 N (SD 0.81 N) for waist-shaped designs, values classified as predominantly moderate and therefore an unlikely cause of periodontal trauma on their own. The authors caution, however, that in vitro forces do not permit direct conclusions about clinical trauma outcomes, and corresponding in vivo studies are still lacking.
Efficacy evidence
A 2019 Cochrane review (Worthington et al.), incorporating and expanding earlier reviews on flossing and interdental brushing, evaluated 35 studies with 3,929 adult participants. It found that using floss or interdental brushes in addition to toothbrushing may reduce gingivitis, plaque, or both, more than toothbrushing alone, and that interdental brushes may be more effective than floss for gingivitis specifically, though evidence for plaque was inconsistent. The certainty of this evidence was rated low to very low throughout, and the review's authors note that observed effect sizes may not be clinically important; most trials were short-term, and participants generally had low baseline gingival inflammation.
What current evidence does not show
- No in vivo studies directly linking measured insertion forces to clinical trauma outcomes such as papilla compression or recession
- No binding, manufacturer-independent color standard, despite widespread de facto use of similar color schemes
- Limited evidence on the superiority of specific brush shapes (cylindrical, conical, waist-shaped) for plaque removal
- No high-certainty evidence establishing interdental brushes as more effective than floss across all measured outcomes; the low- to very low-certainty advantage found is specific to gingivitis
Evidence summary
What current evidence supports
- The PHD classification system under ISO 16409 is a reproducible, internationally standardized sizing method with excellent inter- and intra-rater reliability (Sekundo & Staehle, 2020)
- Color coding is not standardized across manufacturers, a labeling gap confirmed by both the Sekundo and Staehle product survey and Turner's commentary
- Using interdental brushes in addition to toothbrushing may reduce gingivitis and plaque more than toothbrushing alone, and interdental brushes may be more effective than floss for gingivitis specifically (Worthington et al., 2019), though the certainty of this evidence is low to very low
- Measured insertion forces for standard interdental brush designs are generally moderate, though this does not directly establish clinical safety without in vivo confirmation
Why this matters
Because effectiveness depends so heavily on correct sizing, and because sizing systems and color codes are not standardized across manufacturers, patient guidance needs to go beyond simply recommending an interdental brush: it needs to include a specific size, ideally verified through professional measurement, especially given that switching brands by color alone risks an ill-fitting size.
What remains uncertain
- Whether specific brush shapes offer a meaningful clinical advantage in plaque removal, given limited comparative evidence
- How in vitro insertion force measurements translate into real-world tissue trauma risk, absent in vivo studies
- The magnitude of interdental brushes' advantage over floss for gingivitis in larger, longer-term, higher-certainty trials
Sekundo, Staehle (2020): Mapping the Product Range of Interdental Brushes: Sizes, Shapes, and Forces. Oral Health & Preventive Dentistry, 18(2), 343-354. Examination of 2,320 product samples; establishes PHD under ISO 16409 as a reproducible classification instrument and analyzes insertion forces in vitro.
Turner (2022): Interdental brushes and ISO standards. British Dental Journal, 232, 761-762. Commentary; problematizes the absence of a manufacturer-independent color standard and its consequences for patient counseling.
Worthington, MacDonald, Poklepovic Pericic, Sambunjak, Johnson, Imai, Clarkson (2019): Home use of interdental cleaning devices, in addition to toothbrushing, for preventing and controlling periodontal diseases and dental caries. Cochrane Database of Systematic Reviews, 2019(4), CD012018. Incorporates and supersedes the earlier, since-withdrawn interdental brushing review (Poklepovic Pericic et al., 2013); 35 studies, 3,929 adult participants; low to very low certainty evidence throughout.
