A dental floss device (1) comprises a handle (2) having a head piece (3) and a disposable holder (4) for a length of dental floss (5). The holder (4) comprises a base portion (20) and a pair of spaced-apart jaws (21) extending from the base and which extend to embrace the head piece (3) of the handle (2) when the holder (4) is in a correct alignment configuration with respect to the handle (2). The device has an interlock which ensures that the holder (4) can be interengaged with the head piece (3) only when the holder (4) is correctly aligned with the head piece (3). The interlock comprises a head interlock part provided by interlock grooves (10) and a holder interlock part provided by corresponding interlock tongues (11). There are two interlock grooves (10) and corresponding interlock tongues (11) which slidably interengage when the holder (4) is correctly aligned with the head piece (3). If the holder (4) is turned so that it is not correctly aligned with the head piece (3), the interlock tongues (11) of the holder (4) prevent engagement of the holder (4) with the head piece (3). Thus there is no risk that a user will incorrectly align and engage the dental floss holder with the head piece (3).
