Comparison of Stiffness Determinations for Toothbrushes by Varying Vertical Load

Objectives: Toothbrush bristle stiffness can potentially contribute to dental abrasion. Current ISO and ANSI/ADA standards contain informative methods that require a vertical load (VL) of 5±0.05N for determining resistance to deflection and stiffness of toothbrushes, but these methods are only applicable to manual flat-trim-profile toothbrushes. With the introduction of modern manual and power toothbrushes, there is a need to modify the methods as new toothbrushes can collapse under this VL and cannot be evaluated for safety. Hence, the objective of this study was to determine if applying different VLs affected the stiffness determination of manual and power toothbrushes.
Methods: 17 different manual and power toothbrushes were tested according to ISO 22254 and ANSI/ADA 119, with modification with each toothbrush tested at VLs ranging from 2-5N (n=5 for each toothbrush at each VL). Toothbrush heads were cut at the neck, conditioned in water (37±2°C, 90s), and attached to the test machine. Resistance to deflection was measured at each VL, and stiffness was calculated.
Results: For each toothbrush, lowering the VL typically lowered the stiffness determination. A comparison of the stiffness obtained from each VL was performed for each toothbrush by Student’s t test (95% confidence level). Generally, there was a statistically significant difference in the stiffness when comparing one VL to the next for each toothbrush. Some toothbrushes collapsed under higher VLs and were only tested under lower VLs.
Conclusions: As the VL applied to the toothbrushes was decreased, statistically significant lower stiffness values were generally obtained. Some differences could be due to partial collapse of the bristles (higher VLs) or poor contact between the bristles and brushing table (lower VLs). These results indicate that while the VL in ISO and ANSI/ADA standards is too high for some modern manual and power toothbrushes, further research is needed to determine more suitable VLs for various brush types.