Abstract:
An electrically driven toothbrush has a brush holder that is arranged to rotationally vibrate and carry a number of bristles interspaced with arcuate membranes. The membranes serve to aid cleaning of the teeth and to polish the teeth surfaces during use of the toothbrush.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a continuation of U.S. application Ser. No. 10/373,738, filed Feb. 27, 2003 now U.S. Pat. No. 6,983,507, the entirety of which is incorporated by reference herein. 

   BACKGROUND OF THE INVENTION 
   The invention relates to toothbrushes. 
   The invention relates more particularly to electrically driven toothbrushes in which brush bristles are arranged to move relative to an elongate toothbrush handle such that the bristles rotate about an axis generally at right angles to a longitudinal axis of the handle. The bristles may rotate completely or preferably oscillate as fully described for example in U.S. Pat. No. 5,625,916. 
   In certain conditions, the overall cleaning effect of such brushes is not wholly satisfactory, especially for polishing the teeth or removing stains. 
   It is an object of the invention to overcome or to at least reduce this problem. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the invention there is provided an electrically driven toothbrush having an elongate handle and a brush head mounted to a remote end of the handle, a bristle holder rotatably mounted to the brush head to rotate about an axis generally at right angles to the longitudinal axis of the handle, including an array of upstanding bristles interspaced with a number of separate upstanding flexible membranes that are arranged such as to rub against surfaces of teeth during brushing. 
   The membranes are preferably shorter than at least the longest of the bristles. 
   Each membrane is preferably arcuate in cross-section and partially surrounds a respective bristle of the bristle array. 
   Each membrane may be semi-circular in cross-section and positioned between a respective bristle and the rotational axis of the brush holder. 
   The membranes are preferably evenly distributed about the brush holder axis and each partially surround a respective peripherally sited bristle of the bristle array. 
   There are typically five membranes and at least ten bristles. 
   The membranes may be formed of plastic material. 
   According to another aspect of the invention there is provided a rotatable bristle holder for an electrically driven toothbrush having an array of upstanding bristles interspaced with a number of separate upstanding flexible membranes arranged such as to rub against surfaces of the teeth during brushing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An electric toothbrush according to the invention will now be described by way of example with reference to the accompanying drawings in which: 
       FIG. 1  is a sectional bottom view of the toothbrush; 
       FIG. 2  is a cross-sectional side view of a brush head of the toothbrush; 
       FIG. 3  is a plan view of  FIG. 2 ; 
       FIG. 4  is an enlarged top plan view of the brush head; and 
       FIG. 5  is an isometric view of  FIG. 4 . 
   

   DETAILED DESCRIPTION 
   Referring to the drawings, in  FIG. 1  the toothbrush comprises a handle portion  10  at a first end of the toothbrush, a brush head  11  at a second end of the toothbrush, a rotatable shaft  12  extending from the handle to the head, and a generally circular bristle holder  13 . The handle provides compartments for holding an electric motor  14  and two batteries  15  and  16 . A shaft coupling  17  is arranged to grip one end of the shaft  12  and allow the shaft to be pulled out for cleaning or replacement. 
   The head  11 , as is better seen in  FIG. 2  supports a post  18  which provides a rotational pivot axis  40  for the bristle holder  13 . Bristles  19  are shown for illustrative purpose only in  FIG. 2 . The shaft  12  has an integrally formed remote-most end  20  that is off-set from a central longitudinal axis  21  of the shaft. 
   The remote-most end  20  fits a slot  22  (see  FIG. 3 ) formed in a side of the bristle holder  13 . It will be noted that the end  20  points towards an intersection of the first axis  21  and a second central axis  40  of the post  18 . When the shaft  12  is rotated by the motor  14 , the remote end  20  describes a circle about the shaft  12  and drivingly engages the slot  22  to cause the bristle holder  13  to rotationally vibrate. As may be seen in  FIG. 3 , the slot  22  is closed-ended and extends radially inward from the outer circumference of the holder to less than the distance to the centre of the holder. Thus, the holder  13  pivots or rotates forwards and backwards about the centre of the post  18 . Such vibrations comprise the relative motion between the head  11  and the bristles  19  and is generally beneficial for efficient cleaning of teeth. The width of the slot  22  is preferably generally the same as the diameter of the end  20  to leave minimum play; this keeps noise to a minimum in use. 
     FIG. 1  shows a toothbrush where the holder  13  vibrates or rotates through an angle of 30°. In  FIG. 2  the angle is 35°. It will therefore be appreciated that the rotational angle can be chosen by fitting different shafts  12  and that the same bristle holder can be used for all angles. It is also possible to use the holder  13  in a toothbrush where the holder is oscillated through 60° or 120° or rotated through 360° in continuous rotation. 
   The described shaft  12  is preferably integrally formed, i.e., a single length of a thin rod and shaped as shown. However, it is possible to arrange for the remote end  20  to be separately formed or provided and fixed to a straight end part of the shaft. Such a separate part can be a brush having a central axis coinciding with the axis  21  of the shaft and an off-centre driving post. The driving post then takes up the position and function of the remote end  20 . Thus, the driving post and the slot  22  then form the driving engagement between the shaft and the holder  13  and so the driving post can be regarded as the remote end of the shaft. 
   As shown in  FIGS. 4 and 5 , the brush holder  13  carries ten bristles that are interspaced by five flexible membranes  23 . Each membrane is generally semi-circular in cross-section and partially surrounds a respective bristle mounted adjacent the periphery of the brush holder. The membranes  23  are positioned between the respective bristles and the central axis  40  of the brush holder. In such a configuration, the membranes are inherently unlikely to become clogged up with toothpaste or debris removed from the teeth. 
   The peripheral bristles are preferably thicker than the inner bristles which may be shorter in length than the peripheral bristles. The membranes  23  are generally shorter than all the bristles and typically protrude up about 50% to 90% of the height of the bristles they partially surround. The membranes are formed of food-safe plastics material such as neoprene or other synthetic rubber, but may be made of woven fabric or similar. 
   The membranes rub against the surfaces of the teeth and serve to polish surfaces of the teeth and remove stains during use. The membranes may be reasonably effective in this respect if they are generally rectangular in cross-section, or completely or more completely, surround than shown in the Figures, some or all of the bristles.