Interdental cleaning instrument

1. An interdental cleaning instrument comprising:

a base part having a shape extending from a base end to an insertion end section in an axial direction of the interdental cleaning instrument, and having a first hardness; and

a cleaning part that is composed of an elastomer having a second hardness lower than the first hardness of the base part, covers at least a portion of the base part from the insertion end section, and is capable of cleaning an interdental space, wherein

the base part has:

a grip part that extends from the base end along the axial direction and has a shape to receive a grasp of fingers; and

a shaft part which has a shape that is insertable to an interdental space between neighboring teeth, and has the insertion end section and a base end section at which the grip part is connected to the shaft part;

the shaft part has a shape that can be flexurally deformed to displace the insertion end section in a direction which is perpendicular to the axial direction of the shaft part with respect to the base end section;

the cleaning part has a shape that covers the insertion end section to form a tip end of the cleaning part and a portion of the shaft part extending from the insertion end section by a length equal to or less than the entire axial dimension of the shaft part;

the base part has an in the axial dimension of 35 mm or more; and

the shape of the base part is set to obtain a first pressing force ranged from 0.3 N to 1.4 N to cause 10 mm of displacement at a first portion distant by 2.5 mm from the tip end of the cleaning part when the first pressing force is applied to the first portion in a state in which the interdental cleaning instrument is fixedly held at a portion 10 mm apart from the tip end of the cleaning part to the grip part side; and

a second pressing force ranged from 0.5 N to 2.5 N to cause 10 mm of displacement at a second portion distant by 8.0 mm from the tip end of the cleaning part when the second pressing force is applied to the second portion in a state in which the interdental cleaning instrument is fixedly held at a portion 35 mm apart from the tip end of the cleaning part to the grip part side.

2. The interdental cleaning instrument according to claim 1 , wherein

the shaft part as a shape that allows a displacement of the insertion end section at a point of an intermediate portion located between the insertion end section and the base end section of the shaft part between a steady-state posture in which no external force acts on the shaft part and a curved posture in which an angle between a first straight line connecting the deformed point of the intermediate portion and the insertion end section and a second straight line connecting the deformed portion of the intermediate portion and the base end section is 90 degrees.

3. The interdental cleaning instrument according to claim 1 , wherein

the grip part has such a shape that buckling occurs in the shaft part when a compressive load is applied to the base part from both sides in the axial direction; and

the cleaning part covers a maximum displacement portion of the shaft part at which the maximum amount of displacement from an initial position of a center axis of the shaft part occurs during buckling of the shaft part.

4. The interdental cleaning instrument according to claim 3 , wherein

the maximum displacement portion is located between a portion of the shaft part which is at 1.0 mm apart from the insertion end section toward the base end section side and a portion of the shaft part which is at 9.0 mm apart from the insertion end section toward the base end section side.