fig1 shows the external form of the rotative toothbrush of the present invention . an eccentric aperture p of a round brushhead 1 is connected with the end of a grip 2 by a shaft 4 . the eccentric aperture p is eccentrically and rotatively located at the center of the round brushhead 1 . the rotative toothbrush is well rotative and all the brushhairs 3 of the brushhead are contacted with the teeth . as long as the ratio of the eccentricity that is , the ratio of the short radius ( a ): the long radius ( b ) of the round brushhead is large , the round brushhead will be well rotative when the user uses the rotative toothbrush of the present invention . however , it is inconvenient for the user to use the toothbrush of which the ratio of the eccentricity is large . and as long as the ratio is small , it is convenient for the user to use it . however , the rotating forces will be weak . the preferable ratio of a : b is about 2 : 3 to about 1 : 3 . the brushhead 1 , the grip 2 , and brushhairs 3 can be made of the conventional plastic materials used in a conventional toothbrush . fig6 a shows an embodiment of the structure of the rotative parts of the toothbrush . the shaft 4 which has a rounded end 4 &# 39 ; and a seal 4 is loosely set in a hole 6 formed in the end of the grip 2 . the upper end 4 &# 39 ;&# 34 ; of the shaft 4 is covered with a cap 7 having a hole 6 &# 39 ; through the hole 6 &# 39 ; and then the upper end 4 &# 39 ;&# 34 ; is firmly fitted in a hole 8 of the brushhead 1 . the cap 7 is sealed with the end of the grip 2 by a conventional way , e . g . by a supersonic sealing or by adhesives which are not solved in water or by heat - sealing method . fig6 b shows another embodiment of the rotative parts of the toothbrush . a base plate 41 &# 39 ; of a shaft 41 is vertically molded into the upper end of the grip 2 . then , the shaft 41 is set into a housing 71 having a hole 71 &# 39 ; and a groove 71 &# 34 ; in a way that the shaft 41 having a projection 41 &# 34 ; is loosely fitted into the hole 71 &# 39 ; of the housing 71 having the groove 71 &# 34 ;. then , the housing 71 is fixed into a hole 81 of the brushhead 1 . the shaft 4 or 41 becomes freely rotative in the set state . there are other various conventional structures of the rotative parts which come under the scope of the present invention . as long as the thin shaft 4 is used , the thin shaft 4 becomes well rotative . however , it is desirable that the shaft 4 with a diameter from 0 . 5 mm to 2 . 0 mm is used . the shaft 4 can be made of metal or plastic . however , metal is more desirable than the plastic material because metal is usually more stronger than the plastic material . when the user moves the grip of the toothbrush right and left in a conventional way , the brushhead 1 is rotated by 180 degrees at its maximum owing to the difference of the friction between the brushhairs of short radius and the brushhairs of long radius contacting the teeth . therefore , the same effect of brushing the teeth vertically up and down is obtained when the toothbrush of the present invention is used in a conventional way . fig3 shows another embodiment of the rotative toothbrush of the present invention . in this case , one or more round projections 5 are formed on the back along the eccentric circle of the brushhead 1 ( see fig4 a and 4c . when the user uses the toothbrush having one or more round projections 5 on the back along the eccentric circle of the brushhead 1 , the round projections 5 contact the inside muscle of the user &# 39 ; s mouth and produce friction and contact a slot portion 2 &# 39 ; of an end portion of the grip 2 and adjacent to the shaft 4 so as to effectively rotate the round brushhead 1 ( fig6 a and 6b ); and therefore generate a kind of forces between the eccentric aperture p and the round projections 5 . so , the brushhead 1 rotates more effectively and efficiently . preferably , the round projection 5 numbers one , two , or three .
a rotary toothbrush comprises a round brushhead having at least one projection , bristles on the roundbrush head , a grip , a shaft extended from the grip and eccentrically , rotatably mounted to the round brushhead , whereby the toothbrush can perfectively clean the teeth .