Journal of Scientific & Industrial Research
Vol.64, February 2005, pp 101-107
Estimation of the essential inorganic constituents of commercial toothpastes
A O Oyewale*
Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria
Received 07 July 2004; accepted 02 December 2004
Commercial toothpastes, randomly sampled from the open market were analyzed for fluoride, phosphate, calcium,
sodium, potassium, magnesium, moisture content and pH. Colorimetry was used to determine the levels of fluoride using the
SPADNS-zirconyl chloride method and phosphate using the phosphovanadomolybdate method. Atomic Absorption
Spectrometer was used to determine the levels of calcium and magnesium, while Flame Photometry was used for sodium
and potassium determination. Moisture content was 20-39%, with 85% of the samples having water levels > 29 wt %. The
pH of the toothpastes ranged from 4-8, with 60% of them having a neutral pH. The levels of constituents depend on the
method of solubilization of toothpaste, with concentrated nitric acid digestion giving the best results. The concentrations
were: fluoride, 1.0-1.55; phosphate, 3-20; calcium, 0.04-1.26; sodium, 12-38; potassium, 0.01-0.99; and magnesium, 0.1-2.3
mg/g. The health implications for tooth care and of assimilation of the elements during the mouth cleansing process,
especially when present at unacceptable levels, was discussed.
Keywords: Fluoride, Phosphate, Mouth Cleaning, Toothpaste
Introduction
Toothpaste is a preparation for cleaning and
polishing the surfaces of teeth. Dentifrices
(toothpastes & toothpowders) usually contain mild
abrasives for polishing, binding agents, sudsier
(foaming agents), flavourings and humectants to
prevent hardening on exposure to air. Some
toothpastes, especially for children1,2,3, contain
fluorides to prevent dental decay. Principal
ingredients approved by Council of Dental
Therapeutics of American Dental Association, New
York, in toothpaste formulations are: polishing agents
(carbonates or phosphates of calcium and magnesium,
talc); detergents (soap anionic surface active agents);
binders (carrageen) and humectant (glycols, sorbitol,
mucilages or gums); sweeteners (saccharin, sabitrol);
preservatives (benzoic acid); flavours (spearmint,
wintergreen, peppermint); and water. Cellulose
derivatives (methyl cellulose) are sometimes used to
maintain satisfactory consistency and sodium fluoride
or monofluoro phosphate are added as anticaries
agents3,4,5. A prototype formula2 of toothpaste
contains: glycerol, 32.20; calcium phosphate, 27.00;
water, 36.675; sodium N-lauryl sarcosinate, 2.00;
caragreen TP-4, 1.00; flavouring, 0.500-1.000;
sodium monofluoro phosphate, 0.4; saccharine
________________
*Correspondance address
E-mail: [email protected]
sodium Vsp, 0.125; and sodium benzoate Usp, 0.100
wt %.
Dental decay (dental caries), a common human
disorder affecting more than 95 per cent population of
USA alone2, is caused by the formation of acid by
certain mouth bacteria. It is directly related to the
eating of sweet or starchy foods. Food articles that
remain in the mouth are acted on by bacteria to
produce acid, which dissolves the hard enamel
coating of teeth. Once enamel is penetrated, decay
process is speeded up because the bacteria then feed
on organic material (dentine) of inner portion of teeth.
Periodontal diseases result from chronic irritation of
the gums and periodontum, and its advanced form,
called pyorrhea, is caused by the accumulation of
dental plague on the teeth. Most dental plague can
easily be removed by adequate tooth brushing, but if
it becomes dental tartar, only dentist or dental
hygienist can remove it3,6.
Some constituents of toothpaste (fluoride, phosphate,
calcium, magnesium, sodium and potassium) are of
great importance in physiological functioning and
development of human body. Such constituents may
pass into the body system directly or indirectly during
mouth washing. Since toothpastes are household
essentials and many brands flood the market, their nature
and form of usage, especially for children, pregnant
women, the sick, is a subject of research interest.
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J SCI IND RES VOL 64 FEBRUARY 2005
Experimental Procedure
Analytical grade reagents were used. Distilled
deionized water was used for solution preparations.
All solutions were stored in polyethene bottles prior
to analysis.
PH
It was measured on 1 percent solution of the
sample in water using a Crison Micro pH 2000,
incorporating a glass cell and reference electrode.
Buffer tablets of pH 4, 7 and 9 were used to calibrate
the pH meter during measurements7.
Sample Preparation
Trademarked toothpastes (20) were randomly
sampled from the open market and labeled [A] to [T].
All samples were conventional toothpastes except for
samples [H] and [R] described as Smoker’s and [P]
as Herbal toothpastes by the manufacturers.
Sodium and Potassium
Drying
Concentrations for Ca and Mg were determined
using a Unicam 969 Atomic Absorption Spectrometer
at 422.7 and 285.2nm respectively8.
Weighed amounts of the samples were oven-dried
at 105oC until constant weight was obtained on
cooling in a desiccator.
Sample Dissolution
Method 1: Dried
toothpastes (1g each) were soaked
in Teflon crucible with 50 ml water for 24 h. The
mixture was filtered into 100ml volumetric flask, the
residue washed thoroughly and the filtrate made up to
volume with water.
Method 2: Dried toothpastes (1g each) was
transferred into Teflon crucible and digested with 5ml
concentrated HCl at moderate temperature on a hot
plate in a fume cupboard. After heating for 3-4 h,
another 5ml acid was added and heating continued
until fuming seized. The solution was cooled, filtered
into a 100ml volumetric flask and made up to volume
with water.
Method 3: Dried toothpastes (1g each) was
transferred into Teflon crucible and digested with 5ml
concentrated HNO3 at moderate temperature on a hot
plate in a fume cupboard. After heating for 3-4 h,
another 5ml acid and few drops of H2O2 were added.
The mixture was heated further, until the brownish
fumes of nitrous oxide ceased and clear solution was
obtained. The solution was cooled, filtered and filtrate
transferred into a 100ml volumetric flask and made up
to volume with water.
Standard Solution Preparation
Standard stock and working solutions of sodium,
potassium, calcium, magnesium, phosphorus and
fluoride were prepared using standard methods7.
Sample Analysis
Moisture Content
It was determined as percent weight loss between
wet toothpaste and dried toothpaste using oven drying
at 105 ± 3oC.
Concentrations for Na and K were determined
using a Gallenkamp Flame Photometer at 589 and
767nm respectively8.
Calcium and Magnesium
Phosphorus (as Phosphate)
Concentrations of phosphorus were determined
using the Phospho-vanadomolybdate method for
colour development and absorbance measured with a
HACH spectrophotometer DR/2000 using a 1 ml
glass cell at 470nm8,9.
Fluoride
Concentrations of fluoride were determined using
SPADNS method for colour development and
absorbance measured with a HACH spectrophotometer DR/2000 using a 1ml glass cell at
570nm9,10.
Results and Discussion
Moisture content of 20 toothpaste brands ranged
from 15.00 to 39.54 per cent; with 85 per cent
samples having water content > 29 wt per cent
(Table 1). Recommended moisture content for
dentifrices is about 39 wt per cent2. Most of the
toothpastes (60 %) have neutral pH in water while 35
per cent are acidic (pH 5-5.8). Only [P],
commercialized as herbal toothpaste, was alkaline
(pH 8.26). The pH value gives an indication of the
inorganic constituents in toothpastes. Acidic pH
encourages the growth of mouth bacteria that causes
dental carries3.
Aqueous and mild acidic medium for dissolution
were used to obtain optimum extractable constituents
akin to the mouth cleansing process. Nitric acid
dissolution gave the optimum extraction of all
constituents, followed by hydrochloric acid
dissolution and water extraction gave the least
extraction (Table 2). These constituents of toothpastes
are incorporated as calcium carbonate, magnesium
carbonate and phosphates, which generally have low
OYEWALE: ESTIMATION OF ESSENTIAL INORGANIC CONSTITUENTS OF COMMERCIAL TOOTHPASTES
103
Table 1  General characteristics, pH and percent weight loss of commercial toothpaste
Sample code
Country of manufacture
Colour
pH
Weight loss at 105 ± 3oC
%
A
Nigeria
Purple
5.34
33.75 ± 0.20
B
India
White
6.75
28.93 ± 0.22
C
India
White
7.72
31.22 ± 0.17
D
USA
White
7.64
35.48 ± 0.06
E
Nigeria
Red
5.12
15.90 ± 1.30*
F
India
White
7.64
33.68 ± 0.01
G
Korea
Light Green
5.08
34.81 ± 0.03
H
Indonesia
White
7.06
29.23 ± 0.05
I
Nigeria
Red
5.26
31.29 ± 0.08
J
Korea
White
6.10
30.91 ± 0.01
K
Nigeria
Green
5.30
23.60 ± 0.06
L
China
White
7.01
34.24 ± 0.08
M
Indonesia
White
6.76
36.25 ± 0.04
N
Germany
with Green stripe
7.10
33.64 ± 0.23
O
Indonesia
White
5.75
29.83 ± 0.22
P
India
Cream
8.12
26.44 ± 0.33
Q
Malaysia
White
7.10
39.59 ± 1.00
R
Britain
White
7.12
28.95 ± 0.52
S
Indonesia
Cream
7.35
38.17 ± 0.87
T
Nigeria
White
7.34
36.37 ± 0.98
*Sample swells and foams on heating
solubility in water. Acidic condition is often required
to release some of the constituents into water-soluble
form. This may partly account for the acidic nature of
some of the toothpaste samples. The fluoride content
is all essentially available even in aqueous medium
since they are often incorporated in toothpastes as
sodium salts, which are generally soluble in water.
The activity, potency and commercial acceptability
of toothpaste are often associated with the fluoride
and phosphate levels11,12. Fluoride is acclaimed to
prevent tooth decay and most of the dental diseases,
and phosphate believed to give strong teeth because
of its known association with bone formation and
sustenance13. The fluoride level in the toothpastes is
within 1.0-1.55 mg/g (1000-1550 ppm F) except for
sample [P] with fluoride concentration of 0.2 mg/g
(Fig. 1). A 1000 ppm F value is equivalent to approx
0.8 per cent sodium monofluoride phosphate that is
common inscribed on most toothpaste products to
indicate fluoride levels. The highest fluoride levels
were obtained in samples [H] and [R], the so-called
smokers toothpastes, and the least level was in sample
[P], the herbal toothpaste, whose acclaimed potency
in said to be herbal astringents and not fluoride. Since
mild exposure to fluoride (6-8 ppm in water) is known
to have adverse effect on human, especially children,
pregnant women and old people2,3, care must be taken
in the formulation and mode of usage of toothpastes,
which contain high levels of fluoride.
The phosphate levels in the toothpastes vary over a
wide range (3-20 mg/g), however, 70 per cent samples
contain phosphate level above 9 mg/g (Fig. 2).
Toothpastes [G], [J] and [O], which have the highest
phosphate levels of 18.0, 18.9 and 19.6 mg/g
respectively, also gave acidic pH solutions in water.
Similarly, the smoker’s toothpastes, [H] and [R], also
contain high phosphate levels of 16.7 and 16.6 mg/g
respectively; in addition to their high fluoride level. The
varied phosphate levels is not surprising as it is
incorporated in toothpastes in various forms, particularly
as the co-element for the alkali and alkali-earth metals.
The toothpastes with high phosphate level will be
beneficial to users who are deficient in phosphorus
especially at the early stages of bone development14.
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J SCI IND RES VOL 64 FEBRUARY 2005
OYEWALE: ESTIMATION OF ESSENTIAL INORGANIC CONSTITUENTS OF COMMERCIAL TOOTHPASTES
Fig.1-6Relative ratios of elements in toothpaste samples using the three dissolution methods
105
106
J SCI IND RES VOL 64 FEBRUARY 2005
Bone and teeth are made up essentially of calcium.
The main abrasion agent in most toothpastes is
calcium carbonate. The concentration of calcium
varies over a wide range (0.04-27mg/g); 65 per cent
samples with high calcium levels (>20 mg/g) while
remaining 35 per cent have low calcium levels (0.041.26 mg/g) (Fig. 5). Samples [G], [J], [O] and [R]
have high levels of phosphorus and calcium, a
combination that could be useful for people prone to
osteoporosis, a bone disorder associated with
deficiency in these elements3. The four samples also
contain significant amounts of fluoride. In addition,
several studies indicate that higher calcium reduces
fluoride toxicity because calcium precipitates fluoride
as calcium fluoride15,16.
The elements, sodium, potassium and magnesium,
with no significant role in toothpaste formulation and
tooth care, are introduced into toothpastes as vehicles
for incorporating fluoride, phosphates and other
additives. Presence of sodium (12-38 mg/g) in 70 per
cent samples is within 15-20mg/g (Fig. 3). Potassium
is present at 0.01-0.99 mg/g (Fig. 4), while
magnesium at 0.1-2.3 mg/g (Fig. 6). Sodium and
potassium are reported as associated elements because
their role in body metabolism tends to complement
each other. High sodium intake is associated with
hypertension and heart failure, while increased intake
of potassium can lower blood pressure and helps
prevent stroke2. People prone to heart complications
should avoid toothpastes with high sodium content
and derive the maximum possible benefit from
potassium. The sample [N], has unusually high
sodium level (38.5 mg/g) which is about 18 mg/g
higher than the nearest sodium level in the other
samples. Although specific significance of
magnesium in the cleansing progress and even in
body metabolism is limited, deficiency in this element
have been observed in diabetics, alcoholics and
individuals taking certain drugs, oral contraceptives
and cisplatin6; hence toothpastes rich in this element
could act as a source of supplement.
Conclusions
Because of water solubility of some of the
toothpaste constituents and that the tissues in the
mouth are soft and readily absorb, the probability of
these constituents finding their way into the body
during the mouth cleansing process is quite high. In
addition, some of these constituents can stick to the
teeth, tongue, gums during teeth cleaning, and be
wash down the throat by mouth salivation or during
the processes of eating and drinking. Similarly,
improper rinsing of mouth after washing and often
swallowing the paste during teeth cleaning by
children, will surely lead to the ingestion of these
elements into the body system.
Can toothpaste be used as a supplement for some
of the required daily elemental nutrients or
administered to correct deficiencies of certain
elements (e.g. fluoride, which is hard to come by in
the type of food eaten in the less privileged class) in
people with certain ailment; or in the prevention of
certain diseases? Caution must be exercised,
particularly by people who are vulnerable, children,
pregnant women, the elderly and sick, in the use of
some toothpastes until the health implication is
understood.
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