Mechanical Testing of Toothbrushes With Refined Pressure Control Design

Objectives: Aim of the study was to assess a manual toothbrush with a new neck design regarding the mechanical contact pressure behaviour and head deflection. To study the effect of the new design, two types of toothbrushes with similar geometry and material properties were investigated. In terms of functional performance, the two toothbrushes only differ by the presence or absence of a flex zone (ball joint) in the brush head.
Methods: Two toothbrush types were tested, with (type_1) and without flex neck (type_2). A universal testing machine (Instron E 10000) was used to realise a linear toothbrush movement against a counterpart to measure the resistance force of the brush heads while deflecting them with a roller force applicator equipped with a load cell (Dynacell 250N). Toothbrush heads were untufted, i.e. without bristles. The handles were fixated using a form-fitted holder to prevent uncontrolled bending of the toothbrush. Force-deflection-diagrams were recorded. 10 samples per toothbrush type were tested until a maximum head deflection of 10mm was reached. Additionally, video analyses were made to visualise the process.
Results: Exerting the force on the toothbrush, the head directly bent at the flex zone of type_1, whereas the entire neck and head were deflected for type_2. At a deflection of 10mm, a force of 5.6±0.1N was measured for type_1, and 12.9±0.5N for type_2. Considering the entire force-deflection-progression, toothbrush type_1 is deflected 2 to 2.5 times higher than type_2 applying the same bending force.
Conclusions: By adding a flexible ball joint to the toothbrush design, the stiffness in the neck-head region was reduced significantly; and in conclusion, less pressure is exerted in comparison to the toothbrush without a flex neck. This leads to a gentler force application and thus to an improved pressure control, and the risk of aggressive “overbrushing” can be significantly reduced by the new design.