Abstract:
A toothbrush for removing plaque, tarter and calculus from teeth. The toothbrush includes an elongated grip handle having a plurality of toothbrush bodies mounted on an end. The toothbrush bodies are adapted to clean various surfaces of teeth simultaneously.

Description:
This application is a division of prior application Ser. No. 09/084,098 filed May 26, 1998, now U.S. Pat. No. 6,209,164, which is a division of application Ser. No. 08/963,114 filed Oct. 28, 1997, now U.S. Pat. No. 5,842,249, which is a file wrapper continuation application of Ser. No. 08/424,314 filed on Apr. 21, 1995, now abandoned, which is a national stage application under §371 of international application PCT/JP93/01561 filed Oct. 28, 1993. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a toothbrush and an electric toothbrush for efficiently removing plaque, tartar, and calculus from teeth. 
     BACKGROUND OF THE INVENTION 
     Teeth are an important organ indispensable for the mastication of food and the utterance of speech sounds. In order for the teeth to perform their functions, it is necessary for them to be brushed after meals or before sleeping to prevent tartar and calculus from being deposited on dental necks for protection against periodontites. 
     For brushing teeth, it has heretofore been customary to use tooth brushes having bristle assemblies planted on an end of a handle. Electric toothbrushes that have been developed in recent years have also been widely used. 
     Toothbrushes and electric toothbrushes, which are respectively manually and automatically operable, are generally used by turning the bristle assemblies back and forth about the toothbrush axis. 
     However, the conventional toothbrushes and electric toothbrushes have suffered the following drawbacks: 
     When the handle of a toothbrush is rocked about its own axis in use, the bristle assemblies are angularly moved alternately upwardly and downwardly. More specifically, when the user of an electric toothbrush holds its grip cylinder and angularly moves the bristle assemblies about the axis while keeping the bristle assemblies against a tooth side or neck, a downward swinging movement of the bristle assemblies peels an end of the gum off the tooth neck, and pushes a deposit of plaque into a recess that is formed between the peeled gum and the tooth neck. Therefore, the brushing operation tends to produce a deposit of tartar and calculus, causing periodontites such as a dentoalveolitis. 
     SUMMARY OF THE INVENTION 
     Means according to the present invention for solving the above problems are as follows: 
     According to a first invention, a toothbrush comprises: 
     a grip handle; 
     a crown cap mounted on a distal end of the grip handle and having a substantially L-shaped cross section and a predetermined length; and 
     bristle assemblies planted on inner surfaces of wings of the crown cap and having tip ends inclined at a predetermined angle toward a bent corner of the crown cap. 
     According to a second invention, an electric toothbrush comprises: 
     a grip base; 
     a handle mounted on the grip base for reciprocating angular movement at least about an axis thereof by electric actuator means housed in the grip base; 
     a crown cap mounted on a distal end of the handle and having a substantially L-shaped cross section. and a predetermined length; and 
     bristle assemblies planted on inner surfaces of wings of the crown cap and having tip ends inclined at a predetermined angle toward a bent corner of the crown cap. 
     According to a third invention, in the toothbrush or the electric toothbrush according to the first or second invention, the crown cap has adjusting means for adjusting the projection of one of the bristle assemblies, and mounting means for mounting a distal end of the grip handle or the handle detachably on a longitudinal end of the crown cap. 
     The electric actuator means is not limited to any structure, but may comprise a known means such as a combination of a motor and a cam mechanism. 
     The mounting means for detachably mounting the grind handle or the handle on the crown cap is not limited any particular structure. The mounting means may be composed of known means, e.g., engaging holes defined in the opposite ends of the crown cap and an engaging body mounted on the distal end of the grip handle or the handle and engaging in one of the engaging holes, or alternatively, an engaging hole defined longitudinally through the crown cap and an engaging shaft mounted on the distal end of the grip handle or the handle and engaging in the engaging hole. 
     The bristle assemblies are inclined at an angle of 45°, for example, to the inner surfaces of the crown cap. However, the angle of inclination is not limited to 45°. The bristle assemblies are not limited to any particular length, but may have the same length or lengths that vary stepwise. 
     The adjusting means for adjusting the projection of one of the bristle assemblies is not limited to any particular structure, but may be known means, e.g., a screw for moving a base on which the bristle assembly is planted into and out of the crown cap. 
     According to a fourth invention, a toothbrush comprises: 
     a grip handle; 
     a crown cap mounted on a distal end of the grip handle and including a molar tooth fitting portion and a front tooth fitting portion which have respective inner walls corresponding to respective tooth surfaces; and 
     bristle assemblies planted on the inner walls of the molar tooth fitting portion and the front tooth fitting portion and inclined at an angle ranging from 30° to 60° toward tip ends of molar and front teeth that are fitted in the molar tooth fitting portion and the front tooth fitting portion, respectively. 
     According to a fifth invention, an electric toothbrush comprises: 
     a grip base; 
     a handle mounted on the grip base for reciprocating angular movement about an axis thereof or in the direction of a tooth axis, or in the direction normal to the direction of the tooth axis, by electric actuator means housed in the grip base; 
     a crown cap mounted on a distal end of the handle and including a molar tooth fitting portion and a front tooth fitting portion which have respective inner walls corresponding to respective tooth surfaces; and 
     bristle assemblies planted on the inner walls of the molar tooth fitting portion and the front tooth fitting portion and inclined at an angle ranging from 30° to 60° toward tip ends of molar and front teeth that are fitted in the molar tooth fitting portion and the front tooth fitting portion, respectively. 
     According to a sixth invention, in the toothbrush or the electric toothbrush according the fourth or fifth invention, the crown cap has only a molar tooth fitting portion and a bristle assembly corresponding thereto. 
     According to a seventh invention, in the toothbrush or the electric toothbrush according the fourth or fifth invention, the crown cap has only a front tooth fitting portion and a bristle assembly corresponding thereto. 
     The electric actuator means is not limited to any structure, but may comprise a known means such as a combination of a motor and a cam mechanism. 
     The bristle assemblies should preferably be inclined at an angle of 45° to the surfaces of a molar or front teeth that is fitted in the tooth fitting portion. However, the angle of inclination is not limited to 45°, but may be selected in a range from 30° to 60°. The bristle assemblies are not limited to any particular length, but may have the same length or lengths that vary stepwise. 
     According to an eighth invention, a toothbrush comprises: 
     a grip handle; and 
     a plurality of toothbrush bodies detachably mounted on a distal end of the grip handle; 
     the toothbrush bodies having bristle assemblies inclined at an angle ranging from 30° to 60° with respect to sides of teeth toward tip ends of the teeth in use. 
     According to a ninth invention, a toothbrush comprises: 
     a grip base; 
     a vibrator mounted on the grip base for vibration in predetermined directions by electric actuator means housed in the grip base; and 
     a plurality of toothbrush bodies detachably mounted on the vibrator; 
     the toothbrush bodies having bristle assemblies inclined at an angle ranging from 30° to 60° with respect to sides of teeth toward tip ends of the teeth in use. 
     The electric actuator means is not limited to any structure, but may comprise a known means such as a combination of a motor and a cam mechanism. 
     The toothbrush bodies should preferably be attached such that the bristle assemblies are inclined at an angle of 45° with respect to sides of teeth that are inserted. However, the angle of inclination is not limited to 45°, but may be selected in a range from 30° to 60°. 
     The number of toothbrush bodies may generally range from two to three though not limited to any particular value. If two toothbrush bodies are employed, then they are positioned respectively on the corresponding opposite sides of teeth, or one of them is positioned on the occlusal tooth area of the teeth and the other on one of the sides of the teeth. If three toothbrush bodies are employed, then one of them is positioned on the occlusal tooth area of the teeth and the others on the respective sides of the teeth. 
     If the angle of inclination of the bristle assemblies were less than 30° or greater than 60°, then they would not sufficiently scrape off plaque or the like because the pressure applied by the tip ends of the bristle assemblies to the tooth surfaces would be weak. 
     The bristle assemblies are not limited to any particular length, but may have the same length or lengths that vary stepwise. 
     According to tenth through sixteenth inventions, an electric toothbrush  10  comprises a bristle assembly  16  reciprocally angularly movable to swing upwardly along teeth sides while being held against the teeth sides or neighboring regions, reciprocally rocking means  18  for angularly moving the bristle assembly  16 , and an actuator  68  coupled to the reciprocally rocking means  18  (The reference numerals used in this sentence are indicated in FIG. 23, and those in sentences given below are indicated in FIG.  4 ). 
     The bristle assembly  16  may be mounted in one side of a casing  14  having a substantially inverted L shape, and a temporary positioning member  54  may be mounted on the other side of the casing  14  for temporarily positioning the bristle assembly  16  for engagement with a tooth side. 
     The temporary positioning member  54  may comprise a resilient member. 
     The temporary positioning member  54  may comprise bristles. 
     The temporary positioning member  54  may be adjustable in height. 
     The bristle assembly  16  may comprise an upper set of bristles  46  and a lower set of bristles  46 , the lower set of bristles  46  being longer than the upper set of bristles  46 . 
     The bristle assembly  16  comprises an upper set of bristles  46 , a middle set of bristles  46 , and a lower set of bristles  46 , the bristles being of longer, shorter, and medium lengths successively from the lower set through the middle set to the upper set. 
     In the first through third inventions, when the toothbrush is used, one of the bristle assemblies is held against the occlusal tooth areas of teeth and the other against the boundaries (tooth necks) between the tooth sides and the gum. If the toothbrush is a manual toothbrush, then the grip handle is manually angularly moved reciprocally about the axis thereof. If the toothbrush is an electric toothbrush, the grip handle is angularly moved reciprocally about the axis thereof by the electric actuator means. 
     If the toothbrush has the adjusting means for adjusting the projection of one of the bristle assemblies, then the projection of the bristle assembly is adjusted by the adjusting means such that the bristle assembly adjustable by the adjusting means will abut against the occlusal tooth areas of teeth and the other bristle assemblies will abut reliably against the boundaries (the tooth necks) between the tooth sides and the gum. 
     The toothbrush with the adjusting means has a particular orientation in order to keep the adjustable bristle assembly in abutment against the occlusal. tooth areas of teeth at all times. In this structure, therefore, the crown cap can be attached in a different position. to change the orientation of the toothbrush for brushing all the surfaces of teeth. Specific details will be described later with respect to embodiments given below. 
     In the fourth through seventh inventions, when the toothbrush is used, a molar tooth is fitted in the molar tooth fitting portion or a front tooth is fitted in the front tooth fitting portion. Each of the bristle assemblies is held in contact with the surface of the tooth at an angle ranging from 30° to 60°. If the toothbrush is a manual toothbrush, then the grip handle is manually angularly moved reciprocally about the axis thereof, or in the direction of the tooth axis, or in the direction normal thereto. If the toothbrush is an electric toothbrush, the grip handle is angularly moved reciprocally about the axis thereof, or in the direction of the tooth axis, or in the direction normal thereto, by the electric actuator means. 
     In the eighth and ninth inventions, when the toothbrush is used, a tooth is fitted in the space surrounded by the bristle assemblies. The bristle assemblies positioned on tooth sides are held in contact with the tooth sides at an angle ranging from 30° to 60°. If the toothbrush is a manual toothbrush, then the grip handle is manually vibrated about the axis thereof, or in the direction of the tooth axis, or in the direction normal thereto. If the toothbrush is an electric toothbrush, the grip handle is vibrated about the axis thereof, or in the direction of the tooth axis, or in the direction normal thereto, by the electric actuator means. 
     In the tenth through sixteenth inventions, when the electric toothbrush is used to brush a tooth, the bristle assembly is brought into abutment against a side or neck of the tooth while being held substantially horizontally, and angularly moved reciprocally so as to swing upwardly by the reciprocally rocking means coupled to the actuator. 
     The bristle assembly may be mounted in one side of the casing of a substantially inverted L shape, and the temporary positioning member may be mounted on the other side of the casing for temporarily positioning the bristle assembly for engagement with the tooth side. The temporary positioning member can be held against the occlusal tooth area of the tooth crown for thereby accurately holding the bristle assembly against the tooth side or the tooth neck for scraping off deposited plaque. 
     The temporary positioning member may comprise a resilient member or bristles, and may be adjustable in height. This arrangement allows the temporary positioning member to hold the bristle assembly accurately against a tooth surface ranging from the tooth side to the tooth neck without slipping over the occlusal tooth area of the tooth crown. 
     The bristle assembly may comprise an upper set of bristles and a lower set of bristles, the lower set of bristles being longer than the upper set of bristles. Alternatively, the bristle assembly may comprise an upper set of bristles, a middle set of bristles, and a lower set of bristles, the bristles being of longer, shorter, and medium lengths successively from the lower set through the middle set to the upper set. With this arrangement, the bristles of the bristle assembly can abut against a curved tooth surface along the tooth side and the tooth neck for effectively removing plaque. 
     In any of the first through sixteenth inventions, since the bristle assemblies, though they are angularly movable reciprocally, are planted so as to be inclined to the tooth surface, the frictional force is stronger upon angular movement toward the tip end of the tooth, and weaker upon angular movement in the opposite direction. Therefore, plaque, tartar, and calculus deposited on the occlusal tooth area, the tooth side, and the tooth neck are gathered toward the center of the tooth fitting portion. For the same reason, the gum is not peeled off the tooth neck, and plaque, tartar, and calculus deposited, on the tooth neck are removed without being pushed between the tooth and the gum. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a toothbrush according to an embodiment of the present invention; 
     FIG. 2 is a view illustrative of the structure and operation of bristle assemblies of the toothbrush; 
     FIG. 3 is an enlarged view of tip ends of bristles; 
     FIG. 4 is an exploded perspective view of an electric toothbrush according to the present invention; 
     FIG. 5 is a perspective view of a toothbrush according to another embodiment of the present invention; 
     FIG. 6 is a perspective view of a toothbrush according to an embodiment of the present invention; 
     FIG. 7 is a view illustrative of the structure of bristle assemblies and the manner in which the bristle assemblies abut against tooth surfaces; 
     FIG. 8 is an enlarged view of tip ends of bristles; 
     FIG. 9 is a perspective view of an electric toothbrush according to the present invention; 
     FIG. 10 is a front elevational view of the structure of another crown cap; 
     FIG. 11 is a front elevational view of the structure of still another crown cap; 
     FIG. 12 is an exploded perspective view of a toothbrush according to an embodiment of the present invention; 
     FIG. 13 is a view illustrative of the structure of bristle assemblies and the manner in which the bristle assemblies abut against tooth surfaces; 
     FIG. 14 is an enlarged view of tip ends of bristles; 
     FIG. 15 is a perspective view of an electric toothbrush according to the present invention; 
     FIG. 16 is an exploded perspective view of an electric toothbrush according to another embodiment of the present invention; 
     FIG. 17 is a fragmentary perspective view of toothbrush bodies according to a second embodiment of the present invention; 
     FIG. 18 is a fragmentary perspective view of toothbrush bodies according to a third embodiment of the present invention; 
     FIG. 19 is a cross-sectional view of one of the toothbrush bodies according to the third embodiment of the present invention; 
     FIG. 20 is a fragmentary perspective view of toothbrush bodies according to a fourth embodiment of the present invention; 
     FIG. 21 is a fragmentary perspective view of toothbrush bodies according to a fifth embodiment of the present invention; 
     FIG. 22 is a perspective view of an electric toothbrush according to an embodiment of the present invention; 
     FIG. 23 is a cross-sectional view taken along line  23 — 23  of FIG. 22; 
     FIG. 24 is a cross-sectional view taken along line  24 — 24  of FIG. 23; 
     FIG. 25 is an enlarged fragmentary vertical cross-sectional view of a bristle assembly; 
     FIG. 26 is an enlarged fragmentary front elevational view of the bristle assembly; 
     FIG. 27 is a diagram showing paths followed by the tip ends of bristles when the bristle assembly is angularly moved reciprocally; 
     FIG. 28 is a fragmentary vertical cross-sectional view of a brush assembly according to another embodiment; and 
     FIG. 29 is a view illustrative of the structure of a tooth. 
    
    
     DETAILED DESCRIPTION 
     First through third inventions will be described in detail below based on embodiments shown in the drawings. 
     FIG. 1 is an exploded perspective view of a toothbrush according to an embodiment of the present invention. FIG. 2 is a view illustrative of the structure and operation of bristle assemblies of the toothbrush. FIG. 3 is an enlarged view of tip ends of bristles. 
     A toothbrush A 1  which is manually operable in use comprises a grip handle  1 , a crown cap  2 , and bristle assemblies  3 ,  3   a.    
     The grip handle  1  is in the form of a rod of plastic and has an engaging body  10  as a mounting means on its distal end. The engaging body  10  comprises a pair of juxtaposed flexible members  11  spaced from each other and each composed of an engaging member having a curved outer side projecting outwardly. 
     The crown cap  2  comprises a member made of plastic and having a predetermined length, and has a substantially L-shaped cross section. The crown cap  2  has a vertical wing  21  for covering a tooth side and a horizontal wing  22  for covering an occlusal tooth area. The crown cap  2  has a pair of engaging holes  20  (one shown in FIG. 2) defined in the respective corners of longitudinal ends thereof, each of the engaging holes  20  serving as part of the mounting means for receiving the engaging body  10 . The engaging body  10  can easily engage in and disengage from one of the engaging holes  20  with small forces, and can be fixed in position when engaging in one of the engaging holes  20 . 
     The bristle assemblies  3 ,  3   a  are mounted on respective inner surfaces of the vertical and horizontal wings  21 ,  22  of the crown cap  2 . The bristle assemblies  3  on the vertical wing  21  are directly planted on the inner surface thereof such that their distal ends are inclined at an angle of substantially 45° toward the bent corner of the crown cap  2 . 
     As shown in FIG. 2, the bristle assembly  3   a  on the horizontal wing  22  is mounted on its inner surface such that the projection of the bristle assembly  3   a  from the inner surface of the horizontal wing  22  can be adjusted in a certain range by an adjusting means. The adjusting means comprises a bristle base  30  in the form of an elongate rectangular plate. The bristle base  30  is disposed in a rectangular guide hole  24  defined in the horizontal wing  22  for sliding movement into and out of the guide hole  24 . An adjustment screw  25  threaded through a ceiling of the guide hole  24  has a tip end rotatably mounted in a central area of an inner wall of the bristle base  30 . When the adjustment screw  25  is turned, the bristle base  30  slides into or out of the guide hole  24 , thereby adjusting the projection of the bristle assembly  3   a  in a certain range. 
     As with the bristle assembly  3 , the bristle assembly  3   a  is planted on the bristle base  30  such that their distal ends are inclined at an angle of substantially 45° toward the bent corner of the crown cap  2 . 
     As shown in FIG. 3, the bristle assemblies  3 ,  3   a  have bristles  41  whose tip ends are bent toward the bent corner of the crown cap  2  and are rounded. The bristles  41  thus shaped are sufficiently effective to remove plaque off teeth without damaging the gum when they brush the teeth. 
     A process of using the toothbrush according to this embodiment and operation thereof will be described below with reference to FIGS. 1 through 3. 
     (1) The length of tooth crowns which project from the gum varies from individual to individual. To use the toothbrush, the following adjustments are made in order to accommodate individuals&#39; differences. 
     First, the tip end of the adjustable bristle assembly  3   a  is held against the occlusal tooth areas, and the projection of the bristle assembly  3   a  is adjusted by turning the adjustment screw  25  so that the other bristle assembly  3  abuts reliably against the boundaries (tooth necks) between the tooth sides and the gum. 
     (2) The tip end of the bristle assembly  3   a  is held against the occlusal tooth areas, and the tip end of the bristle assembly  3  is held against the tooth sides and the gum, followed by manual reciprocating swinging movement of the grip handle  1  about its own axis. 
     Though the bristle assemblies  3 ,  3   a  are angularly moved back and forth at this time, since the tip ends of the bristle assemblies  3 ,  3   a  are inclined toward the bent corner of the crown cap  2 , the frictional force is stronger upon angular movement toward the bent corner of the crown cap  2 , and weaker upon angular movement in the opposite direction. Therefore, plaque, tartar, and calculus deposited on the occlusal tooth areas, the tooth sides, and the tooth necks are gathered toward the bent corner of the crown cap  2  on its inner surface. For the same reason, the gum is not peeled off the tooth necks, and plaque, tartar, and calculus deposited on the tooth necks are removed without being pushed between the teeth and the gum. 
     (3) When the brushing of tooth regions which can be brushed in one direction by the crown cap  2  is finished, the crown cap  2  is removed from the grip handle  1 , and the engaging body  10  of the grip handle  1  is caused to engage in the opposite engaging hole  20  of the crown cap  2 . The vertical and horizontal wings  21 ,  22  of the crown cap  2  are now switched around, allowing the toothbrush to brush other tooth regions that have not been brushed. 
     Specifically, if the crown cap  2  and the grip handle  1  are assembled as shown in FIG. 1, then it is possible for the toothbrush to brush the outer surfaces of teeth on the lower jaw ranging from left back teeth to front teeth, and the inner surfaces of teeth on the lower jaw ranging from right back to front teeth, and also to brush the inner surfaces of teeth on the upper jaw ranging from left back to front teeth and the outer surfaces of teeth on the upper jaw ranging from right back to front teeth. 
     If the crown cap  2  is mounted in the opposite direction on the grip handle  1 , then it is possible for the toothbrush to brush the outer surfaces of teeth on the lower jaw ranging from right back teeth to front teeth, and the inner surfaces of teeth on the lower jaw ranging from left back to front teeth, and also to brush the inner surfaces of teeth on the upper jaw ranging from right back to front teeth and the outer surfaces of teeth on the upper jaw ranging from left back to front teeth. 
     FIG. 4 is an exploded perspective view of an electric toothbrush according to the present invention. 
     An electric toothbrush A 2  has a grip base  5  including a handle  1   a  on its distal end. The handle  1   a  can be actuated by a motor  51  housed as an electric actuator means in the grip base  5 , to angularly move back and forth about its own axis through a converter mechanism  53 . The converter mechanism  53  is of a known structure, and will not be described in detail. 
     In this embodiment, the handle  1   a  only moves angularly back and forth about its own axis. However, it is possible for the handle  1   a  to switch to back-and-forth sliding movement in the axial direction. A battery  52  is also housed in the grip base  5  and a switch  54  is mounted on the grip base  5 . 
     The structure of the distal end of the handle  1   a  and the structures of a crown cap  2  and bristle assemblies  3 ,  3   a  mounted on the handle  1   a  are the same as those of the toothbrush A 1  described above, and will not be described in detail. Those parts of the electric toothbrush A 2  which are identical or equivalent to those of the toothbrush A 1  are denoted by identical reference numerals. 
     A method of using the electric toothbrush A 2  and operation thereof are substantially the same as those of the toothbrush A 1  except that the bristle assemblies  3 ,  3   a  are angularly moved back and forth by electric energy for higher efficiency. 
     FIG. 5 is a perspective view of a toothbrush according to another embodiment of the present invention. 
     A toothbrush A 3  which is manually operable in use in the same manner as with the toothbrush A 1 . The toothbrush A 3  is structurally different from the toothbrush A 1  in that a grip handle  1  is fixed to an end of a crown cap  2   a , and a bristle assembly  3   a  is directly planted on a horizontal wing  22  without the brush base  30 , etc. used as adjusting means. 
     The structure of other portions of the toothbrush A 3  is the same as that of the toothbrush A 1 , and will not be described in detail. Those parts of the toothbrush A 3  which are identical or equivalent to those of the toothbrush A 1  are denoted by identical reference numerals. 
     A process of using the toothbrush A 3  and operation thereof are substantially the same as those of the toothbrush A 1 . However, the toothbrush A 3  has no adjusting means for bristle assemblies unlike the toothbrush A 1 , and the projection of the bristle assemblies cannot be adjusted. Since the wings of the crown cap  2   a  are structurally identical to each other, the toothbrush A 3  has no particular orientation, and can be used more conveniently as the crown cap  2   a  does not need to be changed in direction. 
     Fourth through seventh inventions will be described in detail below based on embodiments shown in the drawings. 
     FIG. 6 is a perspective view of a toothbrush according to an embodiment of the present invention. FIG. 7 is a view illustrative of the structure of bristle assemblies and the manner in which the bristle assemblies abut against tooth surfaces. FIG. 8 is an enlarged view of tip ends of bristles. 
     A toothbrush A 4  which is manually operable in use comprises a grip handle  1  and a crown cap  2 . The grip handle  1  is in the form of a rod of plastic and the crown cap  2  is fixed to a distal end of the grip handle  1 . 
     The crown cap  2  is molded of plastic and has a molar tooth fitting portion  90  having a substantially heart-shaped cross section and a front tooth fitting portion  91  having a substantially V-shaped cross section. The front tooth fitting portion  91  is of a curved shape such that its central region is slightly narrow as viewed in plan. The crown cap  2  has a round outer profile for protecting the inside of a mouth when in use. 
     A bristle assembly  3 ′ is planted on the inner surface of the molar tooth fitting portion  90  substantially in its entirety such that the bristle assembly  3 ′ is inclined at an angle of substantially 45° to surfaces of molar teeth to be fitted in the molar tooth fitting portion  90 . 
     Furthermore, a bristle assembly  3   a ′ is planted on the inner surface of the front tooth fitting portion  91  substantially in its entirety such that the bristle assembly  3   a ′ is inclined at an angle of substantially 45° to surfaces of front teeth to be fitted in the front tooth fitting portion  91 . 
     As shown in FIG. 8, the bristle assemblies  3 ′,  3   a ′ have bristles  41  whose tip ends are bent toward the bent corner of the crown cap  2  and are rounded. The bristles  41  thus shaped are sufficiently effective to remove plaque off teeth without damaging the gum when they brush the teeth. 
     A process of using the toothbrush according to this embodiment and operation thereof will be described below with reference to FIGS. 6 through 8. 
     (1) The molar tooth fitting portion  90  is fitted over a molar tooth T 1  and the bristle assembly  3 ′ are directed substantially at 45° with respect to surfaces of the molar tooth T 1 . Then, the grip handle  1  is manually angularly moved back and forth around its own axis or in the direction of the tooth axis or the direction normal thereto for thereby brushing the molar tooth T 1 . 
     Though the bristle assemblies  3 ′,  3   a ′ are angularly moved back and forth at this time, since the bristle assemblies  3 ′,  3   a ′ are inclined to the tooth surfaces, the frictional force is stronger upon movement toward the tip end of the tooth, and weaker upon movement in the opposite direction. Therefore, plaque, tartar, and calculus deposited on the occlusal tooth area, the tooth sides, and the tooth neck of the molar tooth T 1  are gathered toward the center of the molar tooth fitting portion  90 . For the same reason, the gum is not peeled off the tooth neck, and plaque, tartar, and calculus deposited on the tooth neck are removed without being pushed between the tooth and the gum. 
     (2) When the brushing of the molar tooth T 1  is finished, the front tooth fitting portion  91  is fitted over a front tooth T 2 . Upon brushing the front tooth T 2  in the same manner as with the molar tooth T 1 , plaque, tartar, and calculus are gathered toward the center of the front tooth fitting portion  91 , and removed without being pushed between the tooth and the gum. 
     FIG. 9 is a perspective view of an electric toothbrush according to the present invention. 
     An electric toothbrush A 5  has a grip base  5  including a handle  1   a  on its distal end. 
     The handle  1   a  can be actuated by a motor  51  housed as an electric actuator means in the grip base  5 , to angularly move back and forth about its own axis (as indicated by the arrows “a”) and in the direction of the tooth axis (as indicated by arrows “b”) through a converter mechanism  53 . The converter mechanism  53  is of a known structure, and will not be described in detail. 
     In this embodiment, it is possible for the handle  1   a  to switch in its movement between the direction around its own axis, the direction of the tooth axis, and the direction normal thereto with a selector switch (not shown). A battery  52  is also housed in the grip base  5  and a switch  54  is mounted on the grip base  5 . 
     The structures of a crown cap  2  and bristle assemblies  3 ′,  3   a ′ fixed to the distal end of the handle  1   a  are the same as those of the toothbrush A 4  described above, and will not be described in detail. Those parts of the electric toothbrush A 5  which are identical or equivalent to those of the toothbrush A 4  are denoted by identical reference numerals. 
     A method of using the electric toothbrush A 5  and operation thereof are substantially the same as those of the toothbrush A 4  except that the bristle assemblies  3 ′,  3   a ′ are angularly moved back and forth by electric energy for higher efficiency. 
     FIGS. 10 and 11 are front elevational views showing other structures of crown caps. 
     A crown cap  2   a  shown in FIG. 10 is of a structure having a molar tooth fitting portion  90  and bristle assembly  3 ′, only, and is used solely for brushing molar teeth. 
     A crown cap  2   b  shown in FIG. 11 is of a structure having a front tooth fitting portion  91  and bristle assembly  3   a ′ only, and is used solely for brushing front teeth. 
     Those parts of the crown caps  2   a ,  2   b  shown in FIGS. 10 and 11 which are identical or equivalent to those of the crown cap  2  are indicated by identical reference numerals. 
     While the crown caps  2   a ,  2   b  operate substantially in the same manner as the crown cap  2  according to the above embodiment, the crown caps  2   a ,  2   b  are simpler in structure and smaller in size, and hence can be moved easily in the mouth. 
     Eighteenth and nineteenth inventions will be described in detail below based on embodiments shown in the drawings. 
     FIG. 12 is an exploded perspective view of a toothbrush according to an embodiment of the present invention. FIG. 13 is a view illustrative of the structure of bristle assemblies and the manner in which the bristle assemblies abut against tooth surfaces. FIG. 14 is an enlarged view of tip ends of bristles. 
     A toothbrush A 6  which is manually operable in use comprises a grip handle  1  and three toothbrush bodies  92   a ,  92   b ,  92   c . The grip handle  1  is in the form of a rod of plastic and the toothbrush bodies  92   a ,  92   b ,  92   c  are detachably mounted on a distal end of the grip handle  1 . 
     Each of the toothbrush bodies  92   a ,  92   b ,  92   c  has a handle  93  with bristle assemblies  94  mounted on its distal end portion which have a round profile for protecting the inside the mouth from damage during use. 
     The structure by which the toothbrush bodies  92   a ,  92   b ,  92   c  are attached to the grip handle  1  will be described below. The distal end of the grip handle  1  has three fixing holes  95   a ,  95   b ,  95   c  defined therein and three threaded holes also defined therein between the fixing holes  95   a ,  95   b ,  95   c  and an outer surface of the grip handle  1 . Fastening screws  12  are threaded in the respective threaded holes. When the fastening screws  12  are tightened, the respective ends of the handles  93  of the toothbrush bodies  92   a ,  92   b ,  92   c  that are received in the fixing holes  95   a ,  95   b ,  95 C are secured therein. 
     The fixing holes  95   a ,  95   b ,  95   c  have a substantially elliptical cross section similar to that of the handles  93 , so that when the handles are inserted into the respective fixing holes  95   a ,  95   b ,  95   c , the angles of the toothbrush bodies  92   a ,  92   b ,  92   c  about their own axes are automatically set. 
     The angles to which the toothbrush bodies  92   a ,  92   b ,  92   c  are set will be described below with reference to FIG.  13 . 
     The toothbrush body  92   a  corresponds to the occlusal tooth area of a tooth, and its bristle assemblies  94  abut against the occlusal tooth area substantially perpendicularly thereto. The toothbrush bodies  92   b ,  92   c  correspond respectively to the opposite sides of the tooth. The bristle assemblies  94  of the toothbrush bodies  92   b ,  92   c  are inclined at an angle of substantially 45° to the tooth sides toward the tip end of the tooth which is to be fitted in a region surrounded by these bristle assemblies  94 . 
     As shown in FIG. 14, the bristle assemblies  94  have bristle fibers  210  whose tip ends are bent toward the tip end of a tooth and are rounded. The bristle fibers  210  thus shaped are sufficiently effective to remove plaque off teeth without damaging the gum when they brush the teeth. 
     A process of using the toothbrush according to this embodiment and operation thereof will be described below with reference to FIG. 12 through 14. 
     A tooth T is fitted into the space surrounded by the bristle assemblies  94 , and the bristle assemblies  94  corresponding to the sides of the tooth are directed substantially at 45° with respect to the tooth sides. Then, the grip handle  1  is manually vibrated around its own axis or in the direction of the tooth axis or the direction normal thereto for thereby brushing the tooth. 
     Though the bristle assemblies  94  are vibrated at this time, since the bristle assemblies  94  are inclined to the tooth sides, the frictional force is stronger upon movement toward the tip end of the tooth, and weaker upon movement toward the roots of the tooth. Therefore, plaque, tartar, and calculus deposited on the occlusal tooth area, the tooth sides, and the tooth neck of the tooth are gathered toward the center of the tip end of the tooth. For the same reason, even when rubbed by the bristle assemblies  94 , the gum is not peeled off the tooth neck, and plaque, tartar, and calculus deposited on the tooth neck are removed without being pushed between the tooth and the gum. 
     FIG. 15 is a perspective view of an electric toothbrush according to the present invention. 
     An electric toothbrush A 7  has a grip base  5  including an attachment  96  on its distal end. To the attachment  96 , there are attached three toothbrush bodies  92   a ,  92   b ,  92   c  as with the toothbrush A 6 . 
     The attachment  96  can be actuated by a motor  51  housed as an electric actuator means in the grip base  5 , to angularly move back and forth about its own axis (as indicated by the arrows “a”) and in the direction of the tooth axis (as indicated by arrows “b”) through a converter mechanism  53 . The converter mechanism  53  is of a known structure, and will not be described in detail. 
     In this embodiment, it is possible for the attachment  96  (handles  93 ) to switch in its movement between the direction around its own axis and the direction of the tooth axis with a selector switch  54 . In addition, the attachment  96  may be vibrated in the direction normal to the direction of the tooth axis (i.e., vibrated in the direction in which the attachment  96  moves into and out of the mouth). A battery  52  is housed in the grip base  5 . 
     Those parts of the electric toothbrush A 7  which are identical or equivalent to those of the toothbrush A 6  are denoted by identical reference numerals. 
     A method of using the electric toothbrush A 7  and operation thereof are substantially the same as those of the toothbrush A 6  except that the toothbrush bodies  92   a ,  92   b ,  92   c  (the bristle assemblies  94 ) are vibrated by electric energy for higher efficiency. 
     FIG. 16 is an exploded perspective view of an electric toothbrush according to another embodiment of the present invention. 
     An electric toothbrush A 8  has three handles  56   a ,  56   b ,  56   c  mounted on an attachment  96   a . The handles  56   a ,  56   b ,  56   c  can be vibrated about their own axes independently by a converter mechanism  53 . The handles  56   a ,  56   b ,  56   c  have respective fitting portions  57  of square-shaped cross section on their distal ends. 
     Toothbrush bodies  92   a   1 ,  92   b   1 ,  92   c   1  are detachably mounted on the respective fitting portions  57 . The toothbrush bodies  92   a   1 ,  92   b   1 ,  92   c   1  include respective handles  93  which have in their proximal ends respective fitting holes  201  that receive the respective fitting portions  57  fitted therein. The fitting portions  57  can detachably be fitted in the fitting holes  201  by known means in one operation. 
     The angles at which the toothbrush bodies  92   a   1 ,  92   b   1 ,  92   c   1  are attached around the axis of the toothbrush are set in the same manner as with the above embodiments. 
     Those parts of the electric toothbrush A 8  which are identical or equivalent to those of the electric toothbrush A 7  are indicated by identical reference numerals. 
     A method of using the electric toothbrush A 8  and operation thereof are essentially the same as with the electric toothbrush A 7  except that the toothbrush bodies  92   a   1 ,  92   b   1 ,  92   c   1  can be detached and attached with ease and the toothbrush bodies  92   a   1 ,  92   b   1 ,  92   c   1  (the bristle assemblies  94 ) can be vibrated about their respective axes by electric energy. 
     FIG. 17 is a fragmentary perspective view of toothbrush bodies according to a second embodiment: of the present invention. 
     In this embodiment, only a toothbrush body  92   a   2  has a handle  20 , and toothbrush bodies  92   b   2 ,  92   c   2  which are of substantially the same extent as bristle assemblies are attached to the toothbrush body  92   a   2  by curved arm pins  28  of stainless steel that are disposed on opposite sides of the toothbrush body  92   a   2 . The arm pins  28  are secured in position by nuts N that are tightened. When loosened, the nuts N allow only the toothbrush bodies  92   b   2 ,  92   c   2  to be replaced. 
     The angles at which the toothbrush bodies  92   a   2 ,  92   b   2 ,  92   c   2  are attached around the axis of the toothbrush are set in the same manner as with the above embodiments. 
     FIG. 18 is a fragmentary perspective view of toothbrush bodies according to a third embodiment of the present invention, and FIG. 19 is a cross-sectional view of one of the toothbrush bodies according to the third embodiment. 
     In this embodiment, toothbrush bodies  92   b    3 ,  92   c   3  are attached to a toothbrush body  92   a   3  by arm pins  29  extending from the neck of a handle  20  of the toothbrush body  92   a   3 . 
     As shown in FIG. 19, an adjustment screw  25   a  is undetachably rotatably mounted on an upper surface of the handle  93  near its distal end. The adjustment screw  25   a  has a threaded hole  31  defined in its lower portion. 
     The handle  93  has a recess  202  defined in a lower portion thereof near its distal end and housing a vertically movable body  203 . A screw  204  is vertically fixed to an upper surface of the vertically movable body  203 , and threaded in the threaded hole  31 . A bristle assembly  94   a  is mounted on a lower surface of the vertically movable body  203 . 
     When the adjustment screw  25   a  is turned, the vertically movable body  203  is vertically moved to adjust the height of the bristle assembly  94   a  of the toothbrush body  92   a   3  for use. 
     The angles at which the toothbrush bodies  92   a   3 ,  92   b   3 ,  92   c   3  are attached around the axis of the toothbrush are set in the same manner as with the above embodiments. 
     FIG. 20 is a fragmentary perspective view of toothbrush bodies according to a fourth embodiment of the present invention. 
     In this embodiment, toothbrush bodies  92   a   4 ,  92   b   4 ,  92   c   4  have fitting grooves  205  defined in their respective outer surfaces, and joints  33  of stainless steel having a channel shape in front elevation are fitted in the fitting grooves  205 . The joints  33  are secured in position to the toothbrush bodies  92   a   4 ,  92   b   4 ,  92   c   4 , thus integrally joining the toothbrush bodies  92   a   4 ,  92   b   4 ,  92   c   4  to each other. 
     The angles at which the toothbrush bodies  92   a   4 ,  92   b   4 ,  92   c   4  are attached around the axis of the toothbrush are set in the same manner as with the above embodiments. 
     FIG. 21 is a fragmentary perspective view of toothbrush bodies according to a fifth embodiment of the present invention. 
     In this embodiment, toothbrush bodies  92   a   5 ,  92   b   5 ,  92   c   5  are integrally joined to each other by a curved enclosing plate  35  of stainless steel which is fastened to them by screws  36 . A cushion  97  made of hard sponge, rather than bristle assembly, is attached to a lower surface of the toothbrush body  92   a   5 . 
     Those parts of the toothbrushes shown in FIGS. 17 through 21 which are identical or equivalent to those of the aforesaid embodiments are indicated by identical reference numerals. 
     Preferred embodiments of tenth through sixteenth inventions will be described below. 
     FIGS. 22,  23 , and  24  show an electric toothbrush  100  according to an embodiment of the present invention. 
     As shown in FIGS. 22,  23 , and  24 , the electric toothbrush  100  has a casing  114  with a handle  112  projecting from one end thereof. The casing  114  houses a bristle assembly  116  reciprocally angularly movable to swing upwardly along teeth sides while being held against the teeth sides or neighboring regions, and a reciprocally rocking mechanism  118  for reciprocally angularly moving the bristle assembly  116 . 
     As shown in FIGS. 22 and 23, the casing  114  comprises a vertical case  120  on one side and a horizontal case  122  on another side, the cases  120 ,  122  being joined in an inverted L shape as viewed in end elevation. The horizontal case  122  is joined to the vertical case  120  so as to project from an upper end of the vertical case  120 . 
     The vertical case  120  and the horizontal case  122  are made of a hard synthetic resin or the like. The vertical case  120  has a hole  124  defined in an inner side wall thereof for placing the bristle assembly  116  therein, and a drain hole  125  defined in a bottom wall thereof for draining water out of the casing  114 . 
     As shown in FIGS. 23 and 24, the reciprocally rocking mechanism  118  has a rotatable shaft  126  journaled in an upper position in the vertical case  120 , and a pair of swing shafts  128  disposed vertically in the vertical case  120  at respective positions near the ends of the vertical case  120 . 
     The rotatable shaft  126  is rotatably supported by a pair of bearings  130  disposed in the upper position in the vertical case  120 . A pair of plate cams  132  is fixedly mounted on the rotatable shaft  126  near its opposite ends and held in sliding contact with the respective upper ends of the swing shafts  128 . 
     The swing shafts  128  are journaled in shaft holes that are defined in two upper bearing plates  134  horizontally disposed in the upper position in the vertical case  120 , and shaft holes that are defined in a lower bearing plate  136  horizontally disposed in a lower position in the vertical case  120 . Coil springs  138  are mounted on the swing shafts  128 , respectively, between the upper bearing plates  134  for normally urging the swing shafts  128  to move upwardly. Pivot supports  140  by which the bristle assembly  116  are pivotally supported are fixedly mounted in upper and lower regions or the swing shafts  128  between the upper and lower bearing plates  134 ,  136 . 
     When the rotatable shaft  126  of the reciprocally rocking mechanism  118  is rotated, the swing shafts  128  are lowered against the bias of the coil springs  138  each time cam lobes of the plate cams  132  make one revolution, and hence are reciprocally moved in the vertical direction. The reciprocally rocking mechanism  118  is not limited to the rotating plate cams  132 , but crank mechanisms or the like may be combined with the rotatable shaft  126  for vertically moving the swing shafts  128  in interlinked relation thereto. 
     As shown in FIGS. 24,  25 , and  26 , the bristle assembly  116  have two or three bristle bases  142  positioned in upper and lower positions between the swing shafts  128  of the reciprocally rocking mechanism  118  and extending obliquely upwardly toward the hole  124  defined in the inner side wall of the vertical case  120 . Each of the bristle bases  142  is of a flat shape elongate in the horizontal direction and has a support shaft  144  extending longitudinally through and fixed to a lower end thereof. Bristles  146  are planted on an upper end of each of the bristle bases  142 . 
     The bristle bases  142  are pivotally supported by opposite ends of the support shafts  144  on the pivot supports  140  that are fitted over the swing shafts  128  in their upper and lower regions. Resilient members  148  such as coil springs are connected between the opposite ends of the bristle bases  142  and the swing shafts  128 . The bristle bases  142  project obliquely upwardly from within the vertical case  120  toward the hole  124  in the inner side wall thereof. 
     As shown in FIGS. 25 and 26, each of the bristle bases  142  is inclined upwardly at an angle of about 45° from its pivots on the swing shafts  128 . Upper and lower stoppers  150 ,  152  are horizontally mounted on the pivot supports  140  on the swing shafts  128  such that the bristle base  142  can swing vertically in an upward angle of about 15° from the inclined position and in a downward angle of about 15° from the inclined position. 
     When the bristles  146  on the bristle bases  142  abut against a tooth side and the swing shafts  128  are lowered, the bristle bases  142  are turned upwardly and hence closed until they are engaged by the upper stoppers  150  while being lowered. When the swing shaft  128  are lifted, the bristle bases  142  are spread and received by the lower stoppers  152  while being elevated. On their way upward, the bristle bases  142  are closed under the bias of the resilient members  148  and return to their original position. 
     At this time, the tip ends of the bristles  146  are reciprocally angularly moved upwardly in coaction with the swing shafts  128  along paths as shown in FIG. 27, i.e., a path a-b where the ends of the bristles  146  are lowered and substantially held against a tooth neck, a path b-c where the ends of the bristles  146  abut against the tooth neck and the bristles  146  are spread, a path c-d where the ends of the bristles  146  brush a tooth side upwardly in a scraping manner and move upwardly while being spread, and a path d-a where the ends of the bristles  146  are closed). 
     Since the bristles  146  are closed as they are lowered, they do not peel off the end of the gum. When the bristles  146  are elevated, they can scrape plaque deposited on the tooth neck and tooth side in the embodiment shown in FIGS. 23 and 24, the bristle bases  142  are disposed in upper, middle, and lower positions. The bristles  146  on the bristle bases  142  are longer, shorter, and medium successively from the lower position through the middle position to the upper position. With this arrangement, the bristles  146  of the bristle assembly  116  can be brought into abutment against a curved tooth surface extending from the tooth side along, the tooth neck for scraping off deposited plaque. 
     The bristle bases  142  may be located in upper and lower positions. In this case, the bristles  146  on the bristle base  142  in the lower position should preferably be longer than the bristles  146  on the bristle base  142  in the upper position for abutment against the curved tooth surface extending from the tooth side along the tooth neck for scraping off deposited plaque. 
     The bristles  146  may be planted through a coupling on the bristle bases  142  so that the bristles  146  can be replaced. 
     As shown in FIGS. 22 and 24, a temporary positioning member  154  for temporarily positioning the bristles  146  of the bristle assembly  116  for engagement with the tooth side and the tooth neck is mounted on the horizontal case  122  of the casing  114 . 
     The temporary positioning member  154  has a base plate  158  fitted in a recess  122  that is defined in a lower surface of the horizontal case  122 , and bristles  146  planted on a lower surface of the base plate  158 . Instead of the bristles  146 , a resilient member such as of sponge may be fixed in place to the base plate  158 . 
     An adjustment screw  162  threaded through a threaded hole  160  defined in the horizontal case  122  has a lower end loosely engaging the base plate  158  that is fitted in the recess  156 . When the adjustment screw  162  is turned in one direction or the other, the base plate  158  is vertically slid in the recess  156  for thereby adjusting the height of the bristles  146 . 
     When the bristles  146  of the temporary positioning member  154  is held in abutment against the occlusal area of the crown of a tooth, the bristles  146  of the bristle assembly  116  that project from the inner side wall of the vertical case  120  are accurately brought into abutment against the tooth side and the tooth neck, allowing the bristle assembly  116  to brush the tooth upon reciprocating angular movement. 
     As shown in FIGS. 22 and 23, the casing  114  has joint sleeves  164  extending from upper portions of its opposite ends for detachably joining handle  112 . In the joint sleeves  164 , there are disposed respective gears  166  fixed to respective opposite ends of the rotatable shaft  126  of the reciprocally rocking mechanism  118  which project into the joint sleeves  164 . 
     The handle  112  comprises a cylindrical body  170  detachably joined to one of the joint sleeves  164  and housing an actuator  168 , and a grip cylinder  174  detachably joined to the cylindrical body  170  and housing a battery  172  or a booster or the like for converting AC electric energy into DC electric energy. 
     The actuator  168  comprises a small motor  176  having a rotatable shaft to which a gear  178  is fixed, and a gear  166  fixed to the rotatable shaft  126  in the joint sleeve  164  is held in mesh with the gear  178 . When a switch  180  mounted on an upper surface of the cylindrical body  170  is turned on, the small motor  176  is energized to actuate the reciprocally rocking mechanism  118  in the casing  114 . The joined ends of the joint sleeve  164  and the cylindrical body  170  should preferably be reinforced by a reinforcing band  182  mounted thereon. 
     The electric toothbrush  100  according to the present invention is used as follows. While the user is gripping the handle  112 , the user holds the temporary positioning member  154  against the occlusal area of the crown  190  of a tooth T for thereby positioning the tip ends of the bristles  146  of the bristle assembly  116  in abutment against the tooth side to the tooth neck  192  of the tooth T, as shown in FIGS. 24 and 29. 
     Then, the user turns on the switch  180  on the handle  112  to cause the small motor  176  of the actuator  168  to rotate the rotatable shaft  126  in the casing  114 . The swing shafts  128  of the reciprocally rocking mechanism  118  are moved vertically, causing the bristle bases  142  of the bristle assembly  116  coupled to the swing shafts  128  to angularly move reciprocally. 
     The tip ends of the bristles  146  are angularly moved reciprocally in a manner to turn upwardly to scrape off plaque  194  deposited on the tooth side and the tooth neck without pushing the plaque into a gum groove  196 . The bristles  146  are also effective to massage the gum  198 . The temporary positioning member  154  of the casing  114  is moved along the occlusal areas of upper and lower teeth in abutment there against for thereby removing plaque deposited on the tooth side and the tooth neck of each tooth T. 
     When the electric toothbrush  100  is to be used on the back of teeth T or the opposite side of the teeth, the cylindrical member  170  of the handle  112  is fitted over the joint sleeve  164  on the other end of the casing  114 . 
     When the electric toothbrush  100  according to the present invention is used, therefore, the gum is prevented from being peeled off the tooth necks, and hence can be maintained in a healthy condition for protection against periodontites and dental caries. 
     As shown in FIG. 28, the lower end of each brush base  142  may be pivotally coupled to the swing shafts  128  in the vertical case  120  and the sides of each brush base  142  may be pivotally mounted in a lateral hole  184  defined in the inner side wall of the vertical case  120 . When the swing shafts  128  are moved vertically, the brush base  142  is angularly moved to cause the bristles  146  on the end of the brush base  142  to remove plaque and tartar deposited on the tooth side and the tooth neck of each tooth T. 
     With the electric toothbrush  100  according to the present invention, the casing  114  may not necessarily be limited to an inverted L shape, but may be of a shape spreading at an obtuse angle. Furthermore, only the vertical case  120  may serve as a casing with the bristle assembly  116  housed therein. Such an arrangement is easier to use. 
     The present invention with the above arrangement offers the following advantages: 
     (a) The bristle assemblies of a toothbrush are inclined at a certain angle with respect to the sides of teeth toward the tip ends of the teeth that are fitted between the bristle assemblies. Therefore, when the teeth are fitted in the tooth fitting portion to bring the tip ends of the bristle assemblies into abutment against the teeth surfaces, and the bristle assemblies are angularly moved reciprocally, the frictional force applied by the bristle assemblies is stronger upon angular movement toward the tip ends of the teeth, and weaker upon angular movement in the opposite direction. Therefore, plaque, tartar, and calculus deposited on the occlusal tooth areas, the tooth sides, and the tooth necks are gathered toward the center of the tooth fitting portion by the bristle assemblies, and efficiently removed. 
     (b) As described above, when the bristle assemblies are angularly moved reciprocally, the frictional force applied by the bristle assemblies is stronger upon angular movement toward the tip ends of the teeth, and weaker upon angular movement in the opposite direction. Therefore, even when the tooth necks are brushed, the gum is not peeled off the tooth necks, and plaque, tartar, and calculus deposited on the tooth necks are not pushed between the teeth and the gum, and do not cause periodontites. 
     (c) The electric toothbrush can brush teeth more efficiently than the manually operable toothbrush because the bristle assemblies can be angularly moved reciprocally at higher speeds. 
     (d) With the toothbrush including the adjusting means, the projection of the bristle assembly can be adjusted by the adjusting means such that the bristle assembly adjustable by the adjusting means will abut against the occlusal tooth areas of teeth and the other bristle assemblies will abut reliably against the boundaries (the tooth necks) between the tooth sides and the gum. The toothbrush can thus accommodate various lengths, which differ from individual to individual, of teeth projecting from the gum, and is capable of brushing teeth effectively in a manner to suit the user. 
     (e) The electric toothbrushes according to the tenth through sixteenth inventions have a bristle assembly reciprocally angularly movable to swing upwardly along teeth sides while being held against the teeth sides or neighboring regions, a reciprocally rocking mechanism for reciprocally angularly moving the bristle assembly, and an actuator coupled to the reciprocally rocking mechanism. When the bristle assembly held against the tooth sides and the tooth necks are repeatedly turned upwardly, the gum is prevented from being peeled off the tooth necks, and hence can be maintained in a healthy condition. The bristle assembly can efficiently scrape plaque off upwardly along the tooth sides and the tooth necks for protection against periodontites and dental caries.