Toothbrush

A tooth brush comprises a plurality of tufts each of which comprises a plurality of bristles embedded respectively in bored holes which are vertically and laterally formed in a head portion of the toothbrush. The tufts each comprises first and second bristles, such that in each of the tufts, the total of the first and second bristles is 50% or more, in number. The first bristles are tapered bristles having a factorial coefficient n=0.29 to 0.51 in the equation (I) r(x)=a{(L-x)/L}.sup.n. The distal ends of the second bristles are located in a lower position than the distal ends of the first bristles, vertical intervals between the bored holes are from 1.2 mm to 3.0 mm, and lateral intervals are from 0.75 mm to 1.5 mm. In formula (I), r(x): sectional radius, x: length from base of each bristle, L: length to distal end from base of each bristle, a: sectional radius in case x=O[=r(O)], n: factorial coefficient.

TECHNICAL FIELD 
The present invention relates to a toothbrush, and more particularly to a 
toothbrush which is excellent in performance with regard to the cleansing 
of surfaces of teeth and gums, the areas between adjoining teeth, and the 
marginal areas between the teeth and the gums. The toothbrush of the 
present invention is also excellent in performance with regard to the 
massaging of gums, is comfortable in the sense of feel, and is 
satisfactory in providing a long service life. 
BACKGROUND ART 
Ordinary toothbrushes are chiefly designed for the purpose of cleansing the 
surfaces of the teeth and gums, the areas between adjoining teeth (the 
areas between adjoining teeth are hereinafter referred to as 
"interproximal areas") and the marginal areas between the teeth and the 
gums (the marginal areas are hereinafter referred to as the "periodontal 
areas"), and removing dental plaque in the interproximal areas and the 
periodontal areas. This performance is hereinafter referred to as 
"cleansing performance". Also, the brushing with a toothbrush provides a 
massaging effect against the gums. Massaging the gums is known to be 
remarkably effective in preventing periodontitis or gumboil. This 
massaging effect is also one of the objects of toothbrush devices. In 
order to improve the cleansing performance, various types of toothbrushes 
have heretofore been proposed. 
One such example is disclosed in Japanese Utility Model Publication No. Sho 
61-10495 in which a toothbrush has tapered bristles and non-tapered 
bristles alternately embedded. The tapered bristles cleanse the 
interproximal areas and/or the periodontal areas, while the non-tapered 
bristles cleanse the surfaces of the teeth and gums. However, this 
toothbrush does not take into consideration a massaging effect against the 
gums. Therefore, the cleansing performance and massaging effect were left 
incompatible. 
Another Japanese Utility Model Publication No. Sho 63-31640 discloses a 
toothbrush in which non-tapered bristles having ball-like distal ends of 
different height are embedded such that the distal ends are steppingly 
arranged, so that the massaging effect will be enhanced. However, since 
this toothbrush has non-tapered bristles having ball-like distal ends, the 
distal end portions are difficult to flex. Moreover, it has room for 
improvement with respect to the removal of plaque and a massaging effect. 
Another Japanese Laid-Open Utility Model Application No. Hei 5-15834 
discloses a toothbrush having bristles which are all tapered. This 
toothbrush is not sufficient in stiffness as a whole and its bristles tend 
to overly flex. Accordingly, in spite of its comfortableness in sense of 
feel, it has deficiencies in cleansing performance and massaging effect. 
Furthermore, Japanese Laid-Open Patent Application No. Hei 7-284412 and 
U.S. Pat. No. 5,500,975 disclose a toothbrush in which two types of 
bristle end forms, one being of a ball-like shape and the other being of a 
tapered shape, are folded into two parts and embedded in bored holes 
respectively. This toothbrush has, indeed, the advantages that the 
ball-like end form of its bristles provides a good massaging effect to the 
gums and a good plaque scraping-off effect, and that the tapered end form 
provides a good plaque-removing effect from the periodontal pocket. 
However, in spite of those advantages, this toothbrush has the 
deficiencies that the bristles having the ball-like end form are more 
difficult to be flexed than the bristles having the tapered end form, and 
that the first-mentioned group of bristles having the ball-like end form 
are degraded in sense of feel and comfortableness. Moreover, this 
toothbrush is also not satisfactory with respect to long service life. 
The inventors of the present invention have studied very hard in order to 
overcome the above-mentioned deficiencies and finally succeeded in the 
development of a toothbrush capable of overcoming those deficiencies. It 
is, therefore, an object of the invention to provide a toothbrush which is 
excellent in performance with respect to the cleansing of surfaces of the 
teeth and gums, the areas between adjoining teeth, and the marginal areas 
between the teeth and the gums, and excellent in performance with respect 
to the massaging of gums, is comfortable in sense of feel, and is 
satisfactory in providing a long service life. 
DISCLOSURE OF INVENTION 
According to a feature of the present invention, there is provided a 
toothbrush comprising: a plurality of tufts each of which comprises a 
plurality of bristles embedded respectively in bored holes which are 
vertically and laterally formed in a head portion of the toothbrush; 
wherein: each of said tufts comprises first and second bristles, and in 
each of said tufts, a total of the first and second bristles is 50% or 
more. The first bristles are tapered bristles having a factorial 
coefficient n=0.29 to 0.51 in the following equation (1). Distal ends of 
the second bristles are located in a lower position than distal ends of 
the first bristles. Vertical intervals between each of said bored holes 
are from 1.2 mm to 3.0 mm, and lateral intervals between each of said 
bored holes are from 0.75 mm to 1.5 mm; 
EQU r(x)=a{(L-x)/L}.sup.n (I) 
where 
r(x): sectional radius 
x: length from base of each bristle 
L: length to distal end from base of each bristle 
a: sectional radius in case x=0[=r(0)] 
n: factorial coefficient 
According to a further feature of the present invention, the tufts each 
include from 10% to 90% of the first bristles and from 90% to 10% of the 
second bristles. 
According to a further feature of the present invention, a step d between 
the distal end of each of the first bristles and the distal end of each of 
the second bristles is from 0.5 mm to 4.0 mm. 
According to a further feature of the present invention, an outer diameter 
of the bases of each of the first bristles and each of the second bristles 
is from 0.15 mm to 0.30 mm, and an inside diameter of each of the bored 
holes is from 1.2 mm to 2.4 mm. 
According to a further feature of the present invention, the second 
bristles each have a ball-like portion formed on a distal end portion 
thereof. 
According to a further feature of the present invention, the second 
bristles are tapered towards the distal ends.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings, wherein like reference numerals designate 
identical or corresponding parts throughout the several views, one 
embodiment of a toothbrush according to the present invention will now be 
described. FIG. 1 is a side view of this embodiment, FIG. 2 is a 
perspective view showing a head portion in this embodiment, FIG. 3 is a 
side view showing bristles according to this embodiment, and FIG. 4 is a 
side view showing distal ends of the first and second bristles according 
to this embodiment when brushing. 
As shown in FIGS. 1 and 2, the toothbrush according to the present 
invention includes a plurality of tufts 1 each including a plurality of 
bristles, the tufts 1 being embedded respectively in bored holes 21, 21 . 
. . which are vertically and laterally formed in a head portion 2. The 
toothbrush of this embodiment is not different from the related 
toothbrushes in this respect. 
As shown in FIG. 2, the toothbrush of this embodiment has the features that 
the tufts 1 each comprise first and second bristles 11, 12, in each tuft 
1, the total of the first and second bristles 11,12 is 50% or more, in 
number. Each of the tufts 1 includes from 10% to 90% of the first bristles 
11, and from 90% to 10% of the second bristles 12. The first bristles 11 
are tapered bristles which have a factorial coefficient n=0.29 to 0.51 in 
the below-listed equation (I). The distal ends of the second bristles 12 
are located in a lower position than the distal ends of the first bristles 
11, vertical intervals P.sub.1 between the bored holes 21, 21 . . . are 
from 1.2 mm to 3.0 mm, and lateral intervals P.sub.2 are from 0.75 mm to 
1.5 mm. 
EQU r(x)=a{(L-x)/L}.sup.n (I) 
In the above equation (I), "r(x)" is a function of x and represents a 
radius of a circular cross-section of the bristle, "x" represents a length 
from the base of the bristle, "L" represents a length of the bristle from 
its base to its distal end, "a" represents a value of "r(0)" (sectional 
radius in case x=0), and "n" represents a factorial coefficient. In the 
case of the present invention, the factorial coefficient "n" is a value in 
a range from 0.29 to 0.51. 
It should be noted that although FIG. 2 shows only one each of the first 
bristle 11 and the second bristle 12 for the sake of clarity of the 
construction of the head portion 2, a plurality of the first bristles 11 
and a plurality of the second bristles 12 are, in actual practice, 
embedded respectively in the bored holes 21 as shown in FIG. 1. 
The toothbrush according to this embodiment will be described in more 
detail. As shown in FIG. 1, the toothbrush of this embodiment includes, as 
in the ordinary toothbrushes, the head portion 2 with a plurality of the 
tufts 1, 1 . . . embedded therein, a handle portion 4 to be gripped in 
use, and a neck portion 3 interposed therebetween for connecting the head 
portion 2 and the handle portion 4 together. 
The bristles 11, 12 embedded in the bored holes 21, 21 . . . are made of 
polybutylene terephthalate (PBT), nylon (6-12, 6-10, 6-6), polypropylene, 
or the like. Each bristle is folded generally at its center into two parts 
so that one of the two parts forms the first bristle 11 and the other part 
forms the second bristle 12, and is inserted and embedded in the 
corresponding bored hole 21 with its folded part supported by a flat plate 
22 as shown in FIG. 2. 
It should be noted that although FIG. 2 shows only one each of the first 
bristle 11 and second bristle 12 for the sake of clarity of the 
construction, a plurality of such first and second bristles 11, 12 are, in 
actual practice, embedded respectively in the bored holes 21. 
As shown in FIGS. 2 and 3, the first bristles 11 have a tapered form 
obtained by the aforementioned equation (I). The first bristles 11 are 
tapered by mechanical means such as a grinder or by chemical means through 
chemical treatment under usual practice. In this embodiment, the first 
bristles 11 and the second bristles 12 are tapered by mechanical means as 
later described in detail. 
The first bristles 11 are preferably from 9 mm to 13 mm in height h. If the 
height h of the first bristles 11 are less than 9 mm, the first bristles 
11 become extremely difficult to be flexed to thereby degrade massaging 
performance and cleansing performance. On the contrary, if the height h of 
the first bristles 11 are more than 13 mm, the bristles interfere when 
brushing and the stiffness of the bristles 11 is overly decreased to 
degrade massaging performance and cleansing performance. 
The thickness of the non-tapered portions of the first and second bristles 
11, 12 is preferably from 0.15 mm to 0.30 mm in diameter. If the thickness 
is less than 0.15 mm in diameter, the stiffness of the bristles 11, 12 is 
overly decreased to degrade massaging performance and cleansing 
performance, and the bristles are liable to be cut and badly worn to 
sacrifice the long service life. On the contrary, if the thickness is 
greater than 0.30 mm in diameter, the stiffness is overly increased to 
degrade massaging performance and cleansing performance. Viewing the 
massaging performance and cleansing performance, it is preferred that 
about from 9 to 25 pieces of the first and second bristles 11, 12 in 
combination are embedded in each bored hole 21 (although that is also 
under influence of the relation between the largeness of each bored hole 
21 and the thickness of the bristles 11, 12). 
The first bristles 11, as mentioned above, have a configuration as 
indicated by the above equation (I). In the equation (I), the closer "n" 
comes to 0, the more the configuration of each bristle resembles a 
circular column-like configuration, and the closer "n" comes to 1, the 
more each bristle resembles a cone-like configuration. In the case of this 
embodiment, "n" takes a value within the range of from 0.29 to 0.51 and 
the first bristles 11 each take a streamline-like distal end 
configuration. 
Since the first bristle 11 takes a tapered form as indicated by the above 
equation (I) in case the factorial coefficient "n" is from 0.29 to 0.51, 
the toothbrush according to this embodiment readily enters into the 
interproximal areas and the periodontal areas, not overly hard and 
therefore, is comfortable in sense of feel, has a stiffness which is 
suitable to massage the gums, and has a satisfactory long service life. 
That is, in order to satisfy all of those effects, the factorial 
coefficient "n" must be within the above-mentioned range. 
If the factorial coefficient "n" is less than 0.29, each of the first 
bristles 11 takes a form more resembling a circular column, and the 
stiffness of the first bristles 11 are overly increased to provide a hard 
sense of feel. Moreover, it causes the second bristles 12 to be somewhat 
raised from the surfaces of the teeth when brushing, instead of 
appropriately touching the surfaces. Accordingly, the first bristles 11 
are difficult to co-act with the second bristles 12, thereby degrading 
cleansing performance and massaging performance. On the contrary, if the 
factorial coefficient "n" is more than 0.51, each first bristle 11 takes a 
form more resembling a circular cone and the stiffness is overly 
decreased. As a consequence, the first bristle 11 is overly flexed to 
enter between the second bristles 12 and the teeth, and between the second 
bristles 12 and the gums when brushing. Accordingly, the first bristles 11 
are difficult to co-act with the second bristles 12, thereby degrading 
cleansing performance and massaging performance. It is preferable that the 
factorial coefficient "n" takes a value in a range from 0.33 to 0.40, 
because the service life is increased. 
Surface roughness Ra of each first bristle 11 at an area of from 30% to 80% 
of its overall length near its distal end is from 0.5 .mu.m to 1.5 .mu.m. 
In one example, this measurement of Ra is carried out with the use of a 
laser type surface configuration measuring microscope. Although FIG. 3 
shows one example of a bristle which is folded generally at its center 
into two parts so that one of the two parts forms the first bristle 11 and 
the other part forms the second bristle 12, the bristles of the toothbrush 
according to this embodiment are, in actual practice, ground into a 
tapered form after the bristles are embedded. 
Since each first bristle 11 takes a tapered form and the above-mentioned 
surface roughness within the aforementioned range, its distal end portion 
readily enters into the interproximal areas and the periodontal areas, and 
it is excellent in cleansing performance. Moreover, since the distal end 
is readily flexed, it is comfortable in sense of feel. In addition, 
although the distal end is readily flexed, dental plaque and dirt are 
efficiently scraped off with its side face. If the surface roughness Ra is 
less than 0.5 .mu.m, the side face of the first bristle 11 becomes too 
planar to offer the scraping off effect with its outer side face. As a 
consequence, plaque removing performance is decreased. On the contrary, if 
Ra is more than 1.5 .mu.m, not only will manufacturing become difficult, 
but also the service life of the first bristle 11 is decreased. Further, 
if the range of the surface roughness is less than 30% of its overall 
length near the distal end, the range of area, which is excellent in 
scraping off effect, is overly reduced and no sufficient scraping effect 
can be obtained. On the contrary, if the range of the surface roughness is 
more than 80%, the service life is decreased and in addition, manufacture 
is difficult. 
On the other hand, the second bristles 12 are formed at their distal ends 
with the ball-like portions 12a and tapered towards their distal ends as 
shown in FIGS. 2 and 3. In order to form a ball-like portion at the distal 
end of the tapered bristle, the distal end of the bristle is heated to 
form the ball-like portion after the bristle is preliminarily tapered, or 
the bristle is tapered by chemical treatment or mechanical means such as a 
grinder after the ball-like portion is formed on a circular column like 
bristle. The term "ball-like portion" used here refers to one in which the 
maximum lateral outer diameter of the ball-like portion is larger than the 
outer diameter of the base portion of the ball-like portion. 
The maximum lateral outer diameter of each ball-like portion 12a which is 
formed at the distal end of the second bristle 12, is preferably from 0.15 
mm to 0.38 mm. If it is less than 0.15 mm, a sufficient massaging effect 
is difficult to obtain and the effect for scraping off dirt and plaque on 
the surfaces of the teeth and gums is difficult to obtain. On the 
contrary, if it is more than 0.38 mm, manufacture becomes difficult and in 
addition, each tuft 1 of the bristles becomes difficult to flex, thus it 
becomes unpractical to use the toothbrush. 
The ball-like portions 12a formed at the distal ends of the second bristles 
12 may be formed into various forms as shown in FIGS. 6(a)-6(e). In an 
examples of FIGS. 6(a) through 6(c), a perfect ball-like portion varies in 
size. In a further example of FIG. 6(d), the ball-like portion 12a is 
vertically expanded. In a further example of FIG. 6(e), the ball-like 
portion 12a is horizontally expanded. In a further example of FIGS. 5(a)-5 
(e), the tapered form of the second bristles 12 is optional. However, it 
preferably takes one of the forms obtained by the aforementioned equation 
(I) as in the case with the first bristles 11. If the second bristles 12 
are designed to have the tapered form obtained by the equation (I), a 
longer service life can be obtained. 
Surface roughness Ra of each second bristle 12 at an area of from 30% to 
80% of its overall length near its distal end is also from 0.5 .mu.m to 
1.5 .mu.m. If the surface roughness Ra is less than 0.5 .mu.m, the side 
face of the first bristle 11 becomes too planar to obtain a satisfactory 
scraping effect by the outer side face. As a consequence, plaque 
removability is degraded. On the contrary, if Ra is more than 1.5 .mu.m, 
manufacture becomes difficult and in addition, the service life of the 
first bristle 11 is decreased. Further, if the range of the area having 
the surface roughness is less than 30% of its overall length near the 
distal end, the range which is good for the scraping off effect is too 
small to obtain a sufficient scraping off effect. On the contrary, if it 
is more than 80%, the service life is decreased and manufacture becomes 
difficult. 
The head portion 2 has a stepped configuration in which its central portion 
50 is recessed (FIG. 2). Two rows respectively of three pieces and four 
pieces of the bored holes 21, 21 . . . are formed in its forward area 51, 
three rows each of five pieces of the bored holes 21, 21 . . . are formed 
in its central area 50, and two rows respectively of five pieces and four 
pieces of the bored holes 21, 21 . . . are formed in its rearward area 52. 
Each bored hole 21 is designed to have a diameter from 1.2 mm to 2.4 mm, 
though a good range of the diameter depends on the thickness and hardness 
of the bristles 11, 12 to be embedded. If the diameter is less than 1.2 
mm, one such tuft 1 of the bristles is overly reduced in stiffness. 
Therefore, massaging performance and cleansing performance are degraded. 
On the contrary, if the diameter is more than 2.4 mm, one such tuft 1 of 
the bristles is overly increased in stiffness. Therefore massaging 
performance and cleansing performance are degraded. 
A step "D" formed on the central portion 50 of the head portion 2 is 
provided so that the tufts 1, 1 . . . of the bristles embedded in the 
higher stage (forward area 51 and rearward area 52) may have a greater 
grade of stiffness than that of the tufts 1, 1 . . . embedded in the lower 
stage (central portion 50). Accordingly, cleansing performance is enhanced 
by the tufts 1. Since the tufts 1 of the bristles embedded in the lower 
stage has a lower grade of stiffness than that of the tufts 1 embedded in 
the higher stage, the toothbrush as a whole is not overly increased in 
stiffness and therefore, massaging performance and the sense of feel are 
not degraded. 
The step D is preferably from 0.5 mm to 3.0 mm. If it is less than 0.5 mm, 
no difference in grade of stiffness is created between the tufts 1 
embedded in the higher stage (areas 51 and 52) and the tufts 1 embedded in 
the lower stage (portion 50). On the contrary, if it is more than 3.0 mm, 
since the difference in grade of stiffness between the tufts 1 embedded in 
the higher stage (areas 51 and 52) and the tufts 1 embedded in the lower 
stage (portion 50) is overly increased, it becomes difficult to enhance 
cleansing performance without degrading massaging performance and the 
sense of feel. 
The bored holes 21, 21 . . . are arranged preferably at vertical intervals 
of from (as indicated by P.sub.1 of FIG. 2) 1.2 mm to 3.0 mm, and at 
lateral intervals of from (as indicated by P.sub.2 of FIG. 2) 0.75 mm to 
1.5 mm. If the intervals PI and P.sub.2 are less than 1.2 mm and 0.75 mm, 
respectively, the adjoining tufts 1, 1 are too near to flex and the 
stiffness as a whole is overly increased to thereby degrade massaging 
performance and cleansing performance. On the contrary, if the intervals 
P.sub.1 and P.sub.2 are more than 3.0 mm and 1.5 mm, respectively, the 
adjoining tufts 1, 1 are so far that the tufts 1, 1 are readily flexed and 
as a result, the stiffness as a whole is overly decreased to thereby 
degrade massaging performance and cleansing performance. 
With respect to the ratio of area occupied by the bored holes 21, 21 . . . 
on the surface of the head portion 2, the ratio is preferably from 20% to 
35%. If the ratio is less than 20%, the tufts 1, 1 are too rare on the top 
of the head portion 2 and the stiffness as a whole is overly decreased to 
degrade massaging performance and cleansing performance. On the contrary, 
if the ratio is more than 35%, the tufts 1, 1 . . . are too dense on the 
top of the head portion 2 and the stiffness as a whole is overly increased 
to degrade massaging performance and cleansing performance. 
Though the length of the first bristles 11 at the forward area 51 and the 
rearward area 52 of the head portion 2 is different from that of the first 
bristles 11 at the central portion 50 of the head portion 2, the distal 
ends of all the first bristles 11 are generally on the same level of 
height. Similarly, though the length of the second bristles 12 at the 
forward area 51 and the rearward area 52 of the head portion 2 is 
different from that of the second bristles 12 at the central portion 50 of 
the head portion 2, the distal ends of all the second bristles 12 are 
generally on the same level of height. 
As previously mentioned, a step "d" is formed between the distal end of 
each first bristle 11 and the distal end of each second bristle 12. The 
step "d" is set to from 0.5 mm to 4.00 mm. The step "d" is provided to 
make it easy for the distal ends of the first bristles 11 to flex as shown 
in FIG. 4 during brushing. Also, owing to the provision of the step "d", a 
comfortable sense of feel is obtainable and the distal ends of the first 
bristles 11 can easily enter the interproximal areas and the periodontal 
areas in order to scrape off dirt and dental plaque therefrom. Further, 
the ball-like portions 12a of the second bristles 12 provide a favorable 
massaging effect to the gums, and dirt and dental plaque accumulated on 
the surfaces of the teeth and gums can be scraped off by the ball-like 
portions 12a. Furthermore, since the second bristles 12 are tapered, only 
the distal end portions of the second bristles 12 can easily be flexed 
without degrading cleansing performance and massaging performance, thereby 
providing a more comfortable sense of feel and a long service life of the 
bristles. 
If the step "d" is less than 0.5 mm, the distal ends of the first bristles 
11 are not flexed but merely allowed to contact the surfaces of the teeth 
and gums simultaneous with the ball-like portions 12a of the second 
bristles 12. Accordingly, the sense of feel is not enhanced. Further, 
since the distal ends of the first bristles 11 have difficulty in entering 
the interproximal areas and the periodontal areas, it is difficult to 
enhance the cleaning performance. On the contrary, if the step "d" is more 
than 4.0 mm, the second bristles 12 interfere with the distal ends of the 
first bristles 11 to thereby make it impossible to provide for a 
sufficient massaging effect. Moreover, since brushing is made only by the 
first bristles 11 having a smaller grade of stiffness, cleansing 
performance cannot be enhanced. 
In the case of this embodiment, since the bristles each having the first 
bristles 11 and the second bristles 12 formed on opposite ends of the 
bristle folded into two parts are used for forming each tuft 1, many first 
bristles 11 are located on one side of each tuft 1 and many second 
bristles 12 are located on the other side. Also, in all of the tufts 1, 
fit angles .alpha. (see FIG. 2) of the flat line 22 are evenly arranged 
with respect to a longitudinal axis L of the toothbrush. 
A device and procedures for forming the bristles in tapered form and 
finishing the side faces of the bristles to the above-mentioned surface 
roughness at one stage of manufacturing a toothbrush according to this 
embodiment will now be briefly described. The toothbrush according to this 
embodiment is manufactured from a toothbrush obtained by folding bristle 
members each of which has column-like ends both having ball-like portions 
at their foremost ends into two parts generally at the center, and 
embedding them respectively in the bored holes 21 with the use of the flat 
lines 22. Then, the bristles of this toothbrush are ground into a tapered 
form by a wire brush. Subsequently, they are ground by a nylon brush so 
that their side faces are caused to have the above-mentioned surface 
roughness. In this process, one of the ball-like potions formed at their 
both ends distinguishes by grinding. 
As shown in FIGS. 7 and 8, the abrasive device used for manufacturing a 
toothbrush according to this embodiment includes first abrasive means 103 
having a pair of cylindrical wire brushes 101, 102 which rotate in 
different directions, second and third abrasive means 104 and 105, and 
moving means 107 for causing a distal end of the fiber material to contact 
the rotating wire brushes 101 and 102, so that the toothbrush 106 is 
gradually moved in the longitudinal direction of the wire brushes 101, 102 
while planarly rotating the toothbrush 106 on the wire brushes 101, 102. 
Fourth abrasive means 122 having a pair of cylindrical nylon brushes 120, 
121, which rotate in different directions, is disposed at a forward 
location of the third abrasive means 105. 
The first abrasive means 103 through the third abrasive means 105 each have 
a pair of cylindrical wire brushes 101, 102 as shown in FIG. 8. The wire 
brushes 101, 102, in the form of one pair as one set, are rotatably 
mounted on a brush mounting base 108 and caused to rotate in different 
directions as indicated by arrows A and B of FIG. 8, by a brush rotation 
motor 109. 
That is, as shown in FIG. 8, the pair of wire brushes 101, 102 includes 
rotation transmitting gears 112, 113 engageable with a bevel gear 111 
disposed on a distal end of a drive shaft 110 of the brush rotating motor 
109. The arrangement being such that rotation of the brush rotating motor 
109 is transmitted to the wire brushes 101, 102 through the rotation 
transmitting gears 112, 113, so that the wire brushes 101, 102 will rotate 
in different directions. Accordingly, the wire brush 101 is rotated in the 
direction as indicated by an arrow A of FIG. 8, while the other wire brush 
102 is rotated in the opposite direction as indicated by an arrow B of 
FIG. 8. 
The wire brushes 101, 102 are swung generally in a perpendicular direction 
(direction as indicated by an arrow C of FIG. 7) to the direction of 
movement of the toothbrush 106 which moves in a way to draw a loop as 
indicated by an arrow W of FIG. 7. As shown in FIG. 9, the first abrasive 
means 103 through the third abrasive means 105 thus constructed are 
arranged in predetermined position along the direction of movement of the 
toothbrush 106 in order as shown in FIG. 7, so that the contacting height 
between the bristles of the toothbrush 106 and the wire brushes 101, 102 
is gradually increased. 
That is, the wire brushes 101, 102 in the first abrasive means 103 are 
located in the position indicated by a solid line H.sub.1 of FIG. 9, the 
wire brushes 101, 102 in the second abrasive means 104 are located in the 
position indicated by a one-dot chain line H.sub.2, and the wire brushes 
101, 102 in the third abrasive means 105 are located in the position 
indicated by a two-dot chain line H.sub.3, such that the height of the 
wire brushes 101, 102 are, either steppingly or steplessly, increased from 
the first abrasive means 103 to the second abrasive means 104 and then to 
the third abrasive means 105. 
As shown in FIG. 7, the abrasive means 103 through 105 are arranged in the 
direction of movement of the toothbrush 106 as follows. That is, the first 
abrasive means 103 is arranged at a rearward location of the supplying 
toothbrush 106 before the toothbrush 106 is ground, the second abrasive 
means 104 is arranged at a forward location of the first abrasive means 
103 at a predetermined space, and the third abrasive means 105 is arranged 
at a location which faces with the second abrasive means 104. 
The fourth abrasive means 122 is provided to make a smooth grinding surface 
because the grinding surface ground merely by the wire brushes 101, 102, 
is not smooth enough. 
The nylon brushes 120, 121 have abrasive grains kneaded to the surfaces. 
Since the fourth abrasive means 122 has the same construction as the first 
abrasive means 103 through the third abrasive means 105 except that the 
brushes are nylon brushes, description of the common parts is omitted. 
Next, the procedures for grinding the toothbrush 106 using the above device 
will be described briefly. When the toothbrush 106, which is not yet 
ground into the tapered form as mentioned above, is supplied to the 
device, the toothbrush 106 is pinched at its head portion by a toothbrush 
holder, not shown, with the bristles facing downward. The toothbrush 106 
is gradually and continuously moved, by the moving means 107, in the 
direction as indicated by an arrow W of FIG. 7. At that time, as shown in 
FIG. 8, the toothbrush 106 is rotated about the head portion in a 
horizontal plane. Then, as shown in FIG. 7, the toothbrush 106 contacts 
the wire brushes 101, 102 of the first abrasive means 103 rotating at a 
high speed but in opposite directions, and gradually moves in the 
longitudinal direction of the wire brushes 101, 102 while planarly 
rotating on the wire brushes 101, 102. 
In this first abrasive means 103, the toothbrush 106 contacts the wire 
brushes 101, 102 which are set to position as indicated by a solid line 
H.sub.1 of FIG. 9. That is, the foremost ends of the bristles of the 
toothbrush 106 contact the wire brushes 101, 102. Then, the toothbrush 106 
is ground by the wire brushes 101, 102 which swing in a generally 
perpendicular direction to the direction of movement of the toothbrush 106 
as indicated by the arrow C of FIG. 7, through interaction of rotation and 
swinging of the wire brushes 101, 102. 
During the time when the toothbrush 106 contacts the wire brushes 101, 102, 
cold water is introduced in order to reduce a possible deformation of the 
bristles and wash out the grinding powders. The cold water circulates 
after the grinding powers are recovered through a filter such as non-woven 
fabric and paper. When the grinding is finished in the first abrasive 
means 103, the toothbrush 106 is ground by the second abrasive means 104 
next arranged as shown in FIG. 7. In this second abrasive means 104, the 
toothbrush 106 contacts the wire brushes 101, 102 which are set to the 
position indicated by the one-dot chain line H.sub.2 of FIG. 9. That is, 
the toothbrush 106 contacts the wire brushes 101, 102 at its area 
extending slightly towards its base from its distal end. The toothbrush 
106 is ground likewise by the wire brushes 101, 102 through interaction of 
rotation and swinging of the wire brushes 101, 102. 
When the grinding is finished in the second abrasive means 104, the 
toothbrush 106 is ground by the third abrasive means 105 next arranged as 
shown in FIG. 7. In this third abrasive means 105, the toothbrush 106 
contacts the wire brushes 101, 102 which are set to the position indicated 
by the two-dot chain line H.sub.3 of FIG. 9. That is, the toothbrush 106 
contacts the wire brushes 101, 102 at its area extending slightly towards 
its base from its distal end. And the toothbrush 106 is ground likewise by 
the wire brushes 101, 102 through interaction of rotation and swinging of 
the wire brushes 101, 102. 
When the grinding is finished in the third abrasive means 105, the 
toothbrush 106 is ground by the fourth abrasive means 122 next arranged as 
shown in FIG. 7. In this fourth abrasive means 122, the toothbrush 106 
contacts the nylon brushes 120, 121 which are set to the same position 
where the wire brushes 101, 102 are set in the third grinding means 105, 
i.e., the position as indicated by the two-dot chain line H.sub.3 of FIG. 
9. The toothbrush 106 is ground likewise by the nylon brushes 120, 121 
through interaction of rotation and swinging of the nylon brushes 120, 
121. The toothbrush 106, for which the grinding is finished via the 
above-mentioned four grinding processes, is then released from its state 
held by the toothbrush holder in the moving means 107 and transferred to 
an outlet port not shown. 
According to the toothbrush of this embodiment thus constructed, the first 
bristles 11 each take a tapered form as indicated by the equation (I) in 
case the factorial coefficient n=0.29 to 0.51, and the distal ends of the 
first bristles 11 project further than the second bristles 12 with the 
step d formed on the distal end of each first bristle 11. Accordingly, the 
first bristles 11 are readily flexed only at the distal ends, without 
decreasing the stiffness of individual bristles. Further, the first 
bristles 11 can contact the teeth and the gums earlier than the second 
bristles 12 so that a comfortable sense of feel can be provided when 
brushing. Moreover, the distal ends of the first bristles 11 readily enter 
into the interproximal areas and the periodontal areas to thereby 
efficiently remove dirt and dental plaque from the teeth. In addition, the 
distal ends of the first bristles 11 can easily massage the gums near the 
interproximal areas and periodontal areas which were difficult to be 
massaged in the conventional manner. 
In case the factorial coefficient n is in the range of from 0.29 to 0.51, 
the following items are all satisfied: (1) the first bristles 11 are of a 
configuration which makes it easy to enter the interproximal areas and the 
periodontal areas, (2) the most appropriate stiffness for satisfying both 
the effects of cleansing performance and massaging performance is given; 
(3) the service life of the first bristles 11 is enhanced; and (4) the 
sense of feel is comfortable. Thus, the above range can be described as 
the best range for the factorial factor n. 
Further, according to the toothbrush of this embodiment, the distal ends of 
the second bristles 12 are located in a lower position than the distal 
ends of the first bristles 11. Accordingly, by co-acting with the first 
bristles 11 whose distal ends are readily flexed, there can be obtained, 
in addition to the above-mentioned effect, such an effect that dirt and 
dental plaque on the surfaces of the teeth and gums can be scraped off by 
the distal end portions. 
That is, the toothbrush according to this embodiment is comfortable in 
sense of feel rendered to the teeth and gums during brushing. It is 
excellent not only in cleansing performance of the surfaces of the teeth 
and gums but also in cleansing performance of the interproximal areas and 
the periodontal areas. Moreover, the toothbrush of this embodiment is 
excellent in massaging effect of the gums including those parts in the 
interproximal areas which would otherwise be difficult to be massaged. The 
toothbrush according to this embodiment includes all of those effects. 
The toothbrush according to the present invention is not limited to the 
above embodiment. For example, the tufts 1 may be constituted by folding 
two types of bristles into two parts, the first type of bristles having 
the first bristles 11 formed on opposite ends thereof, and the second type 
of bristles having the second bristles 12 formed on opposite ends thereof 
In the above embodiment, although the head portion 2 is of a stepped form 
having the step D, the head portion 2 may have a flat upper surface. 
In the above embodiment, the first bristles 11 are located on one side and 
the second bristles 12 are located on the other side with reference to the 
flat line 22, using the plurality of bristles of FIG. 3. In the 
alternative, the first bristles 11 and the second bristles 12 may be 
mixedly located on the same side, using the bristles of FIG. 3. Other 
parts of the toothbrush of this invention may also be modified according 
to necessity without departing from the gist of the invention. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein. 
Industrial Applicability 
The toothbrush according to the present invention is excellent with regard 
to the performance of cleansing the surfaces of teeth and gums, the areas 
between adjoining teeth, and the marginal areas between the teeth and the 
gums; and is excellent with regard to the performance of massaging the 
gums, is comfortable in sense of feel, and is satisfactory in providing a 
long service life of the bristles.