Method of cleaning teeth and compositions for use in such method

The invention relates to a method of cleaning teeth by applying thereto one or more elements selected from yttrium, scandium and lanthanum and the lanthanides, and to compositions, such as mouthwashes, toothpastes and dental gels, for use in such a method.

This invention relates to dental hygiene, and more particularly it relates 
to a method of cleaning teeth. 
It is known that a wide variety of elemental cations, including those 
derived from gallium, yttrium, lead, indium, beryllium, cerium, 
dysprosium, iron, arsenic, thorium, iridium, rubidium, vanadium, 
zirconium, titanium, tin, thallium, aluminum, copper, ruthenium, gold, 
samarium, rhodium, mercury, lithium, cobalt, lanthanum, uranium, zinc, 
barium, caesium, strontium, calcium, cadmium and chromium, reduce the acid 
solubility of tooth enamel in an in vitro test system (R. S. Manly and B. 
G. Bibby, J.Dent.Res., 1949, 28, 160-171). It is also known that tooth 
enamel may be remineralised by sequential application to the teeth of a 
cationic and an anionic component which react below the tooth surface to 
form an insoluble salt. Examples of the cationic component are ions 
derived from barium, lanthanum, manganese, lead, tin, zinc, indium, 
zirconium, iron, titanium, vanadium and cadmium (UK Patent specification 
No. 1,452,125). 
It has been found that administration of yttrium nitrate to rats, either by 
intraperitoneal injection or via the drinking water, reduces the incidence 
of caries and this effect has been attributed to the incorporation of 
yttrium into the dental enamel, thus reducing its acid solubility. (R. 
Castillo Mercado and T. G. Ludwig, Archs.oral Biol., 1973, 18, 637-640). 
It has also been found that mouthrinsing with a stannous fluoride solution 
reduces plaque formation on tooth enamel (N. Tinanoff, J. M. Brady, and A. 
Gross, Caries Res., 1976, 10, 415-426; N. Tinanoff, J.Dent.Res., 1977, 56, 
Spec. Issue A, A138). 
It has now been discovered, and herein lies our invention, that deposits 
such as dental plaque may be removed from the surface of teeth, or may be 
prevented from adhering thereto, by application of a cation of a selected 
group of elements. 
According to the invention there is provided a method of cleaning teeth by 
applying thereto a cation of one or more elements selected from yttrium, 
scandium and lanthanum and the lanthanides. The lanthanides include 
cerium, praseodymium, neodymium, promethium, samarium, europium, 
gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and 
lutetium. These elements are very closely related chemically since they 
all fall within Group IIIb of the Periodic Table. Lanthanum and the 
lanthanides form the first group of Inner Transition Elements within Group 
IIIb. 
The method of the invention is particularly useful for cleaning teeth in 
human beings. The efficent cleaning of teeth is, of course, of immense 
cosmetic value. One of the substances routinely found on the surface of 
teeth is bacterial plaque and the method of this invention is particularly 
useful in removing plaque from teeth or in preventing its adhering 
thereto. The method of the invention is also useful in removing various 
types of stain from teeth, for example the stain produced by smoking 
tobacco. In addition, bacterial plaque is generally regarded as a dominant 
etiological factor in caries and periodontal disease and removal of plaque 
from teeth or prevention of its accumulation is known to have a beneficial 
effect in those conditions. 
Only a very small proportion of the population of an industrialised country 
is free from caries or periodontal disease, and it is to be expected 
therefore that, for the majority of that population, application of the 
method of the invention will result in the additional benefit of a 
reduction in the incidence of caries and/or periodontal disease. 
The preferred cations for use in the method of the invention are those 
derived from lanthanum and the lanthanides, and a particularly preferred 
cation is the lanthanum cation. 
When used in the method of the invention, the cation may be in the form of 
a salt, and preferably in the form of a water-soluble salt. Examples of 
such water soluble salts are the chloride, bromide, iodide, nitrate, 
acetate or sulphate. The cation may also be used in the form of a salt 
with an antibacterial anion. 
The preferred compound for use in the method of the invention is lanthanum 
chloride, LaCl.sub.3. 
The amount of cation used in the method of the invention may vary from 0.01 
m.moles to 1 m.moles of cation and preferably from 0.1 m.moles to 0.5 
m.moles of cation, and it may be applied from once a week to 1 to 10 times 
per day. A preferred regime is three times per day, after meals, or 
failing this, twice per day, night and morning. 
The method of the invention achieves a satisfactory result simply by 
application of the cation to the teeth, for example in the form of a 
simple aqueous solution. However, an improved degree of cleansing can be 
achieved if the method of the invention is combined with one or more of 
the normal mechanical methods of cleaning teeth, for example if combined 
with the use of a toothbrush, toothpick, dental floss, dental probe or 
rotary dental brush. A particularly preferred adjunct to the method of the 
invention is the use of a toothbrush. 
The cation for use in the method of the invention may be presented in the 
form of a composition such as a simple aqueous solution or suspension or 
in the form of a more sophisticated composition such as a mouthwash, 
toothpaste, prophylaxis paste, toothpowder, pastille, chewing gum or oral 
spray, or it may be incorporated into a beverage, nutritional substance or 
confection. It may also be incorporated into the public water supply. 
The compositions described above are those which are well known to those 
skilled in this art. They may incorporate any of the ingredients normally 
used in such compositions, with the addition of the cation in the form of 
a salt. In the case of a mouthwash or oral spray the cation is 
incorporated at the desired user concentration. In the case of a 
toothpaste, prophylactic paste, toothpowder, lozenge or chewing gum, it 
may be necessary, depending on the nature of the ingredients in the 
composition, to increase the concentration of the cation to above the 
level of the desired user concentration, for example by up to five times 
the desired user concentration, in order to allow for incomplete 
availability of the cation in use as a result of specific binding of the 
cation to one or more of the ingredients. In these formulations it is 
preferable to use ingredients which avoid precipitation of the cation in 
the form of an insoluble salt. 
A typical mouthwash has an aqueous base and generally incorporates a 
thickener and a flavour. 
A gel has an aqueous base and generally incorporates a gelling agent, a 
surfactant, a flavour and a preservative. 
A toothpaste has an aqueous base and generally contains an abrasive, a 
binder, a thickener, a surfactant, a humectant, a flavouring agent and a 
sweetening agent. 
Specific compositions are described, by way of example only, in Examples 6 
to 9. 
According to a further feature of the invention there is provided a 
composition for use in the method of cleaning teeth described above which 
is in a form for use in a non-sequential manner. By the words "in a form 
for use in a non-sequential manner" we mean, for example, that the 
composition is presented as a single pack which is intended to be used on 
its own, and is not intended to be used immediately before or immediately 
after a second different composition in a sequential manner. It is not, 
for example, part of a two-component pack, and it is not a single 
composition which is designed to release separately two components in a 
sequential manner. On the contrary the composition of the invention is, 
for example, a simple aqueous solution or suspension, or a more 
sophisticated composition such as a mouthwash, toothpaste, prophylaxis 
paste, toothpowder, lozenge, chewing gum or oral spray which is presented 
in a single pack for use on its own. The pack may optionally carry 
instructions on how the composition should be used for cleaning teeth 
according to the method of the invention, and such instructions may 
indicate that the composition should be used in a non-sequential manner. 
The instructions will be appropriate to the nature of the composition. 
Thus, for example, if the composition is a toothpaste the instructions may 
indicate that the user should use the paste as the sole agent for brushing 
his or her teeth. 
The invention is illustrated, but not limited, by the following Examples:

EXAMPLE 1 
Sixty dental students, average age 19 years, volunteered for the 
experiment. After having had a thorough prophylaxis, all the students were 
instructed to suspend oral hygiene for 3 days. To provoke plaque formation 
the students rinsed with 10 ml. of 15% w/v aqueous sucrose solution for 1 
minute every second hour between 8 a.m. and 10 p.m. At the end of this 
period the amount of plaque which had accumulated on the teeth was 
estimated by use of a Plaque Index, as follows: 
0--No firmly attached plaque 
1--No firmly attached plaque visible, but some collected with a dental 
probe 
2--Slight amount of firmly attached plaque visible 
3--Extensive amount of firmly attached plaque visible. 
The 16 individuals showing the highest Plaque Index values were selected 
for further study over a period of 4 days. At the start of this period, 
the participants were brought to Plaque Index=0. During the test, no oral 
hygiene was allowed, and in addition to the sucrose rinses, 2 daily rinses 
with 10 ml. of 20 m.molar aqueous lanthanum chloride solution were 
instituted in a group of 8 individuals, the remaining 8 acting as 
controls. At the end of the 4 day period, plaque estimations were made by 
one person, the results being statistically averaged. The whole experiment 
was carried out under double blind conditions. 
The control group had a mean Plaque Index of 1.0 whereas the treated group 
had a mean Plaque Index of zero. The very small amount of deposit which 
was present in the treated group was very loosely attached to the tooth 
surface and could be blown off with an air jet. 
In a parallel experiment, individuals who rinsed with a 20 m.molar solution 
of aqueous stannous fluoride had a mean Plaque Index of 0.3. 
EXAMPLE 2 
A test panel of ten volunteers had a thorough prophylaxis to remove plaque 
from their teeth so that the Plaque Index measured according to Loe, 
J.Periodontol., 1967, 38, 610-616, was zero at the start of the 
experiment. The panel was provided with new toothbrushes and instructed to 
brush their teeth each morning and evening for 30 seconds over a period of 
four days, according to each individual's own habits, with a 10 ml. test 
solution, and then to rinse the teeth with the remainder of the test 
solution. The test solutions were 20 mM aqueous NaCl, 10 mM aqueous 
LaCl.sub.3, 20 mM aqueous LaCl.sub.3 and 20 mM aqueous YCl.sub.3. The 
whole experiment was carried out under double blind conditions, each 
person using one of the test solutions in turn. Each person's Plaque Index 
was brought to zero before using a new test solution. The results obtained 
were as follows: 
______________________________________ 
Plaque Index 
Volunteer 20 mM 10 mM 20 mM 20 mM 
Number NaCl LaCl.sub.3 
LaCl.sub.3 
YCl.sub.3 
______________________________________ 
1 0.88 0.43 0.30 0.41 
2 1.12 0.63 0.44 0.54 
3 0.68 0.48 0.31 0.30 
4 1.09 0.63 0.45 0.59 
5 1.02 0.83 0.52 0.50 
6 0.62 0.60 0.48 0.60 
7 0.88 0.62 0.32 0.48 
8 0.55 0.42 0.34 0.42 
9 0.90 0.66 0.46 0.60 
10 0.84 0.88 0.62 0.60 
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EXAMPLE 3 
In a parallel experiment solutions of 20 mM aqueous GdCl.sub.3 and aqueous 
YbCl.sub.3 were tested in groups of four people according to the protocol 
described in Example 2. The results obtained were comparable with those 
obtained for YCl.sub.3 in Example 2. 
A similar result was obtained using 20 mM La.sub.2 (SO.sub.4).sub.3 though 
a complete solution at this concentration was not achieved. 
EXAMPLE 4 
A test panel of 10 volunteers all of whom had intact buccal surfaces on 
their upper and lower teeth, first molar to first molar inclusive, were 
separated into two groups (A and B) having five persons in each. 
On Day 0 each person's mouth and teeth was stained with a plaque disclosing 
agent, erythrosine and then each person had a thorough prophylaxis in 
order to reduce to zero the Gingival margin Plaque Index measured 
according to Harrap, J.Clin.Periodontol., 1974, 1, 166-174. 
On Days 1 and 2 each person was instructed to brush their teeth as normal 
with their own toothbrush and toothpaste. They were then re-examined to 
ensure the presence of healthy gingiva, and their Gingival margin Plaque 
Index was again reduced to zero. 
On Day 3, at 7 a.m., each group brushed their teeth with 20 ml. of either a 
20 mM aqueous lanthanum acetate solution or water respectively with a new 
soft toothbrush dipped in the respective test solution. Rinsing for 1 
minute was then carried out with the remainder of the test solution. No 
after-rinses with water were permitted. 
On Day 4, at 1 pm., each person's teeth was stained with disclosing agent 
and the Gingival margin Plaque Index scored, the scoring being performed 
blindly. 
Days 1 to 4 of the test period were repeated, groups A and B interchanging 
test solutions. 
The results obtained were as follows, the figures in the second and third 
column being a summation of the percentage score for each of the 24 teeth. 
______________________________________ 
Gingival margin Plaque Index 
Volunteer 20 mM lanthanum 
Number acetate Water Difference 
______________________________________ 
1 140 140 0 
2 390 470 - 80 
3 110 770 -660 
4 530 1610 -1080 
5 1930 2130 -200 
6 1170 1760 -590 
7 240 370 -130 
8 1300 1300 0 
9 520 490 + 30 
10 750 280 +470 
______________________________________ 
EXAMPLE 5 
A subject rinsed his mouth and teeth with 10 ml. of 20 mM aqueous 
LaCl.sub.3 solution for 1 minute. The solution tasted salty but was not 
unpleasant--there was no metallic taste. After rinsing the subject spat 
out pieces of organic debris. His mouth and teeth felt much cleaner and in 
particular his teeth felt dry and clean. 
On a separate occasion the same subject rinsed with 10 ml. of 20 mM aqueous 
stannous fluoride. The solution tasted acid and metallic. The cleansing 
effect experienced with stannous fluoride was not as great as that with 
LaCl.sub.3. 
A different subject found that rinsing with 20 mM aqueous LaCl.sub.3 
solution significantly reduced the amount of tooth stain caused by smoking 
tobacco. 
EXAMPLE 6 
______________________________________ 
Mouthwash % w/v unless otherwise stated 
______________________________________ 
LaCl.sub.3 . 7H.sub.2 O 
0.74 
Sorbitol Solution 
30.0 
Ethyl Alcohol 95% v/v 
7.0% v/v 
Peppermint Flavour 
0.1 
Ponceau 4R 0.001 
Purified Water to 
100 
______________________________________ 
EXAMPLE 7 
______________________________________ 
Dental Gel % w/v 
______________________________________ 
LaCl.sub.3 . 7H.sub.2 O 1.0 
Hydroxyethylmethyl Cellulose 
3.0 
Isopropanol 4.0 
Spearmint Oil 0.05 
Polysorbate 80 0.5 
Purified Water to 100 
______________________________________ 
EXAMPLE 8 
______________________________________ 
Toothpaste % w/v 
______________________________________ 
LaCl.sub.3 . 7H.sub.2 O 
1.5 
Alumina 33.0 
Sorbitol Solution 30.0 
Colloidal Silicon Dioxide 
1.5 
Hydroxyethylcellulose 
0.5 
Isopropanol 4.0 
Polyoxyethylene 50 Stearate 
2.0 
Spearmint Oil 0.1 
Sodium Saccharin 0.05 
Water to 100 
______________________________________ 
EXAMPLE 9 
______________________________________ 
Pastille Base % w/w 
______________________________________ 
LaCl.sub.3 . 7H.sub.2 O 
0.1 
Gelatin 35.0 
Glycerol 25.0 
Citric Acid 2.0 
Sodium Benzoate 0.2 
Lemon Oil 0.1 
Menthol 0.05 
Water to 100 
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