Electric toothbrush

An electric motor-driven toothbrush comprising a holder having a motor device and a toothbrush member which has a lever releasably adapted to the holder in a cantilever configuration. The toothbrush member has a number of brushing hairs or `fillings` each of which is thin and resilient, implanted at a brush head portion and a transducer device which converts a rotational movement of a rotor of the motor to a reciprocal linear movement in the direction crossing at right angles to a rotational axis of the rotor. The transducer device is provided at and adjacent to the head portion. The head portion of the brush member is finely and linealy reciprocated at a high speed along the longitudinal direction of each filling.

BACKGROUND OF THE INVENTION 
The present invention relates to an electric toothbrush and this invention 
provides a new electric toothbrush which can remove dental, bacterial 
plaque and keep the oral cavity and teeth clean and healthy to prevent 
decayed tooth and pyrrhoea, or Rigg's disease, and other diseases of tooth 
and teethridge or gums. 
An electric toothbrush which moves a brush member or fillings i.e., 
bristles or filaments, back and forth at a high speed in a vertical 
(up-and-down) or lateral (side-to-side) direction relative to a denture, 
i.e., an arrangement of teeth, in an arc shape is known and available in 
the market. In the conventional electric toothbrush, the brush is moved 
along, and in parallel with, a surface of the tooth, in the same manner as 
manual toothbrushing. 
However, in the conventional manual and automatic toothbrushing operation, 
in which the brush is moved along, and in parallel with, a surface of the 
tooth, the brush fillings (i.e., natural or man-made hairs or filaments) 
are bent and, therefore, only a small force by a bending stress is 
delivered to a tip of each of the fillings of the brush. Accordingly, it 
is quite difficult to remove dental, bacterial plaque. Further, since the 
denture is formed with continuous, irregular undulations of tooth surface, 
a high speed or high stroke brushing fails to capture the important spots 
and places such as the portion between adjacent teeth, teethridge, and it 
is likely that the fillings of the brush jump over these important places 
to be cleaned where the bacterial plaque adheres. Further, the 
conventional electric toothbrush has the disadvantage that if it is 
operated at high speed, it is difficult to handle the toothbrush so that 
tips of the brush filling are focused on the brushing point. In addition, 
the conventional electric toothbrush has brush fillings which are stiff 
and have a stiffness as hard as that of manually operated toothbrushes. 
Thus, a rapid and/or large-length movement of the toothbrush causes 
excoriation of the teethridge and dental abrasion or abrasion of dental 
tissue. 
In general, dental plaque is not so hard, but rather soft, viscous and 
paste-like. In order to strip off such a dental plaque from the surface of 
teeth, the applicant has found that it is necessary to push the toothbrush 
softly in a vertical manner against the tooth surface with the fillings of 
the toothbrush being erected vertical to the tooth surface so that the 
fillings can be slightly curved and then moved along the tooth surface by 
a self-recovery force of the curved fillings of the brush. Thus, the 
fillings will not jump over the portion to be brushed, but catches the 
spot of dental plaque. In the present invention, each filling of the 
brush, which is made, for example, of nylon, is utilized as a `column` 
which receives a compression force which induces a bending stress as known 
in the technological field of material mechanics, and an alternating 
stress (i.e., alternating compression and tension) is added repeatedly and 
rapidly to the fillings (`columns`) so that stronger force is delivered to 
tips of the fillings even though each filling has a thickness smaller than 
the conventional ones. The tips of the brush fillings are rapidly and 
finely moved to efficiently remove the dental plaque without damage in 
teethridge. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an improved electric 
toothbrush. 
A further object of the present invention is to provide a new electric 
toothbrush which can efficiently remove dental plaque without odontic 
abrasion and excoriation. 
According to the present invention, there is provided an electric 
motor-driven toothbrush comprising a holder having a motor device and a 
toothbrush member which has a lever releasably adapted to the holder in a 
cantilever configuration. The toothbrush member has a number of brushing 
hairs or `fillings` each of which is thin and resilient, implanted at a 
brush head portion and a transducer means which converts a rotational 
movement of a rotor of the motor to a reciprocal linear movement in the 
direction crossing at right angles to a rotational axis of the rotor. The 
transducer means is provided at and adjacent to the head portion. The head 
portion of the brush member is finely and lineally reciprocated at a high 
speed along the longitudinal direction of each filling. 
In a preferred embodiment, the transducer means has an eccentric disc 
portion at an end of a rotational shaft connected to the rotor shaft of 
the electric motor, a guide groove formed in a front end of the arm of the 
holder, and a projection formed integral with the head portion and movable 
in the guide groove of the holder. 
When the electric motor mounted in the holder is driven, the head portion 
with the fillings is finely moved reciprocally at a high speed in the 
longitudinal direction of the fillings of the brush. By placing the 
toothbrush in position so that the filling abut vertically against the 
surface of the teeth, a larger compression stress is applied to the 
fillings of the brush in the forward stroke of the reciprocal, linear 
movement than in the conventional lateral toothbrushing in which the brush 
fillings are reciprocally moved but in the longitudinal direction of the 
toothbrush lever so that the fillings of the brush are bent and, 
accordingly, a resilient force is stored in each of the bent fillings of 
the brush. The filling ends are then moved along the tooth surface so as 
to release the stored energy of the resilient force. By this movement of 
the filling ends, the filling ends "peel off" a part of the dental, 
bacterial plaque. Thus, a continuous movement of the fillings in a 
vertical direction relative to a tooth surface can remove the dental 
plaque effectively, without providing excoriation and abrasion of dental 
tissue and can establish an effective toothbrushing.

PREFERRED EMBODIMENTS OF THE INVENTION 
With reference to FIGS. 1, 1A and 2 showing a first embodiment of the 
invention, the electric toothbrush has a toothbrush member 1 and a holder 
7 having a tubular casing 8 and a driving system in the tubular casing 8. 
The toothbrush member 1 is releasably coupled to a predetermined place of 
the holder 7 in a cantilever arrangement. The toothbrush member 1 has a 
lever 2 having a head portion 3 at one end, a neck portion 2a adjacent to 
the head portion 3, and a number of fillings 3a which are made of 
monofilaments or suitable synthetic resin such as nylon and implanted to a 
surface of the head portion in a manner similar to that of conventional 
toothbrushes. In the present invention, the toothbrush member 1 has, at 
its other end opposite to the head portion 3, a projection 4 on the upper 
surface of the head portion 3 which surface is opposite to the lower 
surface where the fillings are implanted and, at the other end, a fixing 
lug 5 on the lower surface and a recess 6 on the upper surface. In the 
present invention, the fillings 3a can be thinner and more flexible than 
the fillings of the conventional toothbrush. The neck portion can be 
formed thinner to provide a suitable flexibility thereto so as to 
facilitate a reciprocal movement of the head portion 3 by an electric 
micro-motor 10 which is known in the art. Reference character "S" 
represents a small gap between the neck portion 2a of the cantilevered 
brush member 1 and the arm 9 of the holder 7 for facilitating the 
reciprocal movement of the head portion 3. 
The holder 7 has a tubular body 8 at its rear-half portion and an arm 9 
extending from a front end of the tubular body 8. The tubular body 8 has 
an electric micro-motor 10, a dry cell 11 and an electric switching device 
12. The arm 9 has a hole 13 extending along the length of the arm 9 and a 
rotary shaft 16 extending through the hole 13 and coupled to a rotor shaft 
10a of the electric motor 10 through a suitable connector 15. The arm 9 of 
the holder 7 has, at its base or tail portion,, a groove 17 and a 
projection 19 on the groove surface for engagement with the recess 6 of 
the brush member 1. A threaded groove 18 is formed on the outer surface of 
the base portion of the arm 9 so that a fixing nut 20 is threadedly 
engaged therewith. In order to fit the toothbrush member 1 to the holder 7 
in position, the fixing nut 20 is moved toward the tubular body 8 and then 
the lever 2 of the toothbrush member 1 is inserted into the groove 17 of 
the arm 9 so that the projection 19 of the arm 9 is fitted to the recess 6 
of the toothbrush member 1. Then, the nut 20 is rotated to move toward the 
head portion 3 to firmly grasp the lug 5 of the toothbrush member 1 to 
thereby hold the toothbrush member 1 in position in a cantilever 
configuration. 
The arm 9 of the holder 7 has at its tip portion, where the head portion 3 
of the toothbrush member 1 is positioned when the toothbrush member 1 is 
fitted to the holder 7, a transducer 21 which functions to convert a 
rotational movement of the rotor shaft 10a of the electric motor 10 into a 
linear, reciprocal movement at right angles relative to the axis of the 
rotary shaft 16. 
The transducer 21 has an eccentric disc 22 which is formed by cutting 
eccentrically a tip of the rotary shaft 16, a guide hole 23 formed at the 
arm 9 adjacent to the eccentric disc 22, and the projection 4 of the 
toothbrush member 1 which is movably held in the guide hole 23. As shown 
in FIGS. 1 and 1A, the projection 4 of the toothbrush member 1 is 
contacted directly with the eccentric disc 22 of the rotary shaft 16. The 
eccentric disc 22 has an eccentricity so that a resultant stroke length of 
the reciprocal movement is as small as about 1.0 mm. In FIG. 1, reference 
numeral 32 represents an end cap releasably fitted to an end of the 
tubular body 8 so that the dry cell 11 is replaceably held in position by 
the aid of a spring 31. 
An operation of the electric toothbrush will be explained. After the 
toothbrush member 1 is adapted to the holder 7 as illustrated in FIG. 1, 
the electric motor 10 is driven to rotate the rotary shaft 16 through the 
connector 15. When the rotary shaft 16 is rotated, the head portion 3 of 
the toothbrush member 1 is moved reciprocally at a high speed for the 
small distance determined by the aforementioned transducer 21, as shown by 
bi-directional arrow (A) in FIG. 1. By the reciprocal, linear movement of 
the head portion 3, when the toothbrush is positioned in the oral cavity 
such that the fillings 3a contact the surface of the tooth substantially 
vertically, the fillings 3a are curved by a compression stress added 
thereto so that a resilient force is stored in the curved fillings, and 
the fillings 3a are moved along the tooth surface by a recovery force of 
the curved fillings 3a. Namely, the recovery force of the curved fillings 
forces each filling 3a to move along the tooth surface to peel off the 
dental plaque. This movement of the fillings is repeated at a high speed 
and accordingly an alternating impact load is produced to effectively 
brush the teeth. 
Referring to FIG. 3 showing a second embodiment of the invention, the 
projection 4 of the head portion 3 of the toothbrush member 1 has an 
aperture 24 for receiving the eccentric disc 22 of the rotary shaft 16 and 
the eccentric disc 22 is contacted directly to an inner top surface 4a so 
that a rotational movement of the eccentric disc 22 induces a reciprocal 
movement of the head portion 3 with the fillings 3a. In addition, as shown 
in FIG. 4, the lever 2 of the toothbrush member 1 has extended portions or 
wings 25 at its end portion, and the arm 9 has a guide groove 26 for 
receiving the lever 2 with the wings 25. In the embodiment of FIG. 3, a 
rotor shaft 10a of the electric motor 10 is coupled to the rotary shaft 16 
through a gear device 29 and a connector 15 which has a spiral spring 27 
which urges resiliently the rotary shaft 16 in the forward direction. 
After the tail portion of the lever 2 of the toothbrush member 1 is 
primarily fitted to the holder 7 as illustrated in FIG. 4, the toothbrush 
member 1 is pushed rearwardly toward the tubular body 8 so that the 
projection 4 pushes the tip end of the eccentric disc 22 against a 
resilient force of the spring 27, and thus the rotary shaft 16 is 
retracted so that an engagement is made between the recess 6 of the 
toothbrush member 1 and the projection 19 of the holder 7. Thus, the 
eccentric disc 22 is received in the aperture 24. In this state, the 
rotary shaft 16 is projected forwardly by the resilient force of the 
spring 27, and the toothbrush member 1 is fitted snugly to the holder 7. 
Thus, the toothbrush member 1 is held in position. If the toothbrush 
member 1 is to be released from the holder 7 for some reason such as 
replacing it with a new one, it is sufficient to pull the toothbrush 
member forwardly to release the engagement between the recess 6 of the 
lever 2 and the projection 19 of the arm 9 of the holder 7. The toothbrush 
member 1 can be fitted to the holder 7 much more easily in the embodiment 
of FIG. 3 than in the embodiment of FIG. 1 which uses the nut 20. 
In the embodiment of FIGS. 1 through 4, the eccentric disc 22 is rotated in 
one direction. This mode of operation can be modified to a rocking motion 
by using a suitable rocking mechanism (not shown). FIGS. 5 and 6 show a 
third embodiment of the invention. In this embodiment, the tubular body 8 
consists of two parts, that is, a front portion 8a and a rear portion 8b, 
which are connected together releasably by a snap-fit connection or the 
like, or otherwise unreleasably by a suitable adhesive agent. The arm 9 of 
the holder 7 is a hollow body as illustrated having a space 28 to seek 
reduction of weight without sacrifice of a suitable mechanical strength 
and rigidity so that the arm 9 does not deflect along with the reciprocal 
movement of the head portion 3 of the toothbrush 1. In the embodiment of 
FIG. 5, the ON-OFF switch 12 in the embodiment of FIG. 3 is positioned at 
a middle portion of the tubular body 8 whereas the switch 12 is positioned 
at a front end portion of the tubular body 8. Further, the connector 15 in 
this embodiment has no spiral spring as the spring 27 of FIG. 3, which, 
however, can be used if desired also in this embodiment. In FIG. 5, 
reference numeral 30 represents a connector for charging a rechargeable 
battery such as a Ni-Cd battery. Other structural and operational features 
are substantially similar to those of the previous embodiments and will be 
understood from the description of the previous embodiments. 
According to the present invention, a rotational movement of the rotary 
shaft 16 is converted to a reciprocal movement of the head portion 3 
having fillings 3a by the transducer 21, which is positioned above the 
head portion 3 of the toothbrush member 1 so that the rotational movement 
of the rotary shaft 16 is converted and directly transmitted to the head 
portion 3. Accordingly, the reciprocal movement having a very small stroke 
length of about 1.0 mm by the eccentric disc 22 can be fully transmitted 
to the fillings 3a. In this respect, if a vibration is added to the base, 
or tail portion, of the lever 2 of the toothbrush member 1 rather than to 
the head portion 3, the vibration will be absorbed in the length of the 
lever 2 and it will not be fully transmitted to the head portion 3 having 
the fillings 3a and, accordingly, a desired reciprocal movement of the 
head portion 3 will not be obtained. Further, the toothbrush member 1 is 
held by the motor device 7 in a cantilever configuration and accordingly, 
the toothbrush can be located accurately and easily at a predetermined 
position of the teeth while the head portion 3 is moved reciprocally, 
without rolling, pitching and other undesirable movement. Thus, a very 
delicate controlling of the toothbrush for positioning the fillings on the 
predetermined spot of the teeth can be realized easily. Further, it might 
be possible to produce a reciprocal movement to the head portion 3 without 
providing the lever 2 in the toothbrush member 1, but the applicant has 
found that some disadvantages such as rolling and pitching are produced 
during toothbrush operation if the tooth brush member 1 does not have a 
lever as the lever 2. In the present invention, the reciprocal movement of 
the head portion 3 permits the fillings to reach a thin and narrow spot 
and catch the dental plaque reliably without excoriation and abrasive 
damage in dental tissue.