1.  Field of the Invention
The invention relates to toothbrushes. 
2.  Description of Prior Art
Toothbrushes, both manual and electrically operated, have a shank extending from a handle to a brush head on which is carried an array of bristles for brushing teeth.  Various fixed shapes and configurations for providing different overall brush-contacting surfaces are well-known.  It has been appreciated for a long time that certain shapes, concave or convex, say, are preferred for certain uses and for brushing outer surfaces of the front teeth and inner surfaces of the front teeth respectively.  Compromised design arrangements, including complicated overall bristle surfaces or mixed (concave and convex) shapes may be formed on a single brush head.  More recently, flexible brush heads have been used that can be normally altered to provide different desired bristle configurations.  In those cases, the brush head is made of flexible or deformable material that can retain different shapes, to present bristles in concave or convex configurations say, after each manual manipulation into a desired shape for use.  This requires that the user grips the brush head which may not be convenient if the bristles are wet or coated with toothpaste, and is in any event often unhygienic. 
It is an object of the invention to overcome or at least reduce this problem. 
According to the invention there is provided a toothbrush having an elongate shank with a longitudinal axis, an elongate brush head formed of flexible material joined end to end along the longitudinal axis to a remote end of the shank and carrying an array of bristles on one major surface thereof, a push rod extending along the shank coupled to a remote end of the brush head, a lever mounted to the toothbrush for moving the push rod generally along the longitudinal axis to alter an effective length of brush head and change the shape of the major surface between a concave shape and a convex shape. 
The head is preferably formed with laterally extending slots in said major surface to facilitate bending of the head into said concave and convex shape. 
The lever may be rotatably mounted to the toothbrush and formed with an arcuate surface that is mechanically coupled to one end of the push rod so that when the lever is rotated the push rod is moved along the longitudinal axis.  The arcuate surface is preferably formed with steps that determine incremental movement of the push rod as the lever is rotated. 
The lever may be mounted inside the toothbrush and extends proud of an exterior surface thereof to enable an exposed part of the lever to be conveniently thumb-operated to adjust the shape of the head.