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Cosmet. Sd., 52, 163-167 (May/June 2001)
Abrasiveness evaluation of silica and calcium carbonate
used in the production of dentifrices
I. M. C. CAMARGO, M. SAIKI, M. B. A. VASCONCELLOS, and
D. M. ]tVILA, Instituto de Pesquisas Energdticas e Nucleares, Centro de
Qu/mica e Meio Ambiente, IPEN/CNEN-SP, Caixa Postal 11049, ZIP
05422-970, S•o Paulo, SP, Brazil.
Accepted for publication March 15, 2001.
Synopsis
Our purpose was to apply a radiometric method to an abrasivehess evaluation in samples of silica and
calcium carbonate used as an abrasive in a dentifrice, to help in a prudent selection of materials by dentifrice
producers. The results of RDA (radioactive dentin abrasion) abrasivehess indices obtained for these com-
pounds varied from 136 to 19. The relative standard deviations of these RDA results varied from 5.9% to
11.8%, showing a good precision in the method. Also, the results obtained indicated that the abrasivehess
indices increase with the particle size of the material. A comparison between different abrasives with similar
particle sizes showed that silica presents higher RDA values than calcium carbonate.
INTRODUCTION
Dentifrices are cosmetics used with toothbrushes to clean tooth surfaces to prevent the
accumulation of stains and plaques. Therefore, they should present an appropriate abra-
siveness to clean the teeth, but without causing wear. Consequently, knowledge of the
characteristics of the abrasive agents used for dentifrice manufacturing is of interest to
industries in order to obtain appropriate products for perfect oral hygiene without
causing wear to the teeth or restorative materials. The abrasives commonly utilized in
the dentifrices produced in Brazil are silica and calcium carbonate, and their quantities
in dentifrices vary from 30% to 48% in mass (1,2).
Among several articles related to the use of abrasives in the dentifrices, one by Boer et
al. (3) evaluated the wear caused by abrasives through the method of surface profilometry
and verified the correlation between abrasivehess and the particle size of abrasives. Also,
these authors obtained different abrasivehess values for distinct abrasives presenting
similar particle sizes, that is, the abrasive AI(OH) 3 of 7-1•m particle size showed greater
abrasivehess than that presented by CaCO 3 with 8-1•m particle size. This difference in
abrasivehess may be attributed to the distinct particle hardness of these two agents.
Address all correspondence to M. Saiki.
163
164 JOURNAL OF COSMETIC SCIENCE
Kinoshita et al. (4) examined several dentifrices by the methods of surface analyzer and
scanning electron microscopy. Among the several abrasives (CaHPO 4 ß 2H20, a mix of
CaHPO 4 ß 2H20 + CaHPO4, and CaSiO3) , CaSiO 3 appeared to be more abrasive than
the other two. Also, Panzeri et al., (5) examined by scanning electron microscopy the
particles of abrasives used in 17 dentifrices and concluded that the majority of their
particles present irregular forms and heterogeneous arrangements of the particles.
In this work, the abrasiveness of the samples of silica and calcium carbonate was
evaluated by radiometric method. This method consisted of brushing the irradiated teeth
(dentine) with an abrasive agent and reference material slurties, one at each time. The
beta radioactivity of 3•p transferred from the dentine to slurties was measured using a
plastic scintillatot detector. The abrasiveness index or RDA (radioactive dentine abra-
sion) is the ratio of 3•p counting rates obtained for abrasive and reference material
slurties (6).
MATERIALS AND METHODS
MATERIAL SAMPLE
The materials silica and calcium carbonate were provided from industries.
PROCEDURE
The radiometric method applied was based on a paper by Hefferren (6). The experi-
mental conditions were established in order to use the available facilities. This experi-
mental procedure consisted of the following steps:
Selection of the teeth. The substracts to be abraded were roots from extracted permanent
human teeth. After extraction, the teeth were stored in 4% formaldehyde solution. They
were cleaned by stirring in a domestic detergent solution and then were washed with
water and cut, separating the crown from the root.
Irradiation of roots of the teeth. The roots of the teeth immersed in formaldehyde solution
were irradiated in plastic vials during a one-hour period under a thermal neutron flux of
10 •2 n/cm-2/s -• at the IEA-R1 nuclear research reactor and in a position where the
temperature was lower than 40øC. After irradiation, the tooth samples were removed
from the core of the reactor to avoid damage from gamma radiation. During the
irradiation a part of 3•p present in the hydroxyapatite of teeth was converted to radio-
active 32p.
Brushing operation of the teeth. After about one week of decay time, these irradiated teeth
were fixed in a mold made by dental methacrylate resin that was fitted in a sample
holder (reservoir for slurry) of a brushing machine. The brushing machine was manu-
factured at IPEN/CNEN-SP and was equipped with two toothbrushes made of nylon
bristles of medium hardness and a stroke counter with 125 strokes/min. A pressure
corresponding to 150 g could be applied on each toothbrush. Before the first brushing,
the irradiated dentins were brushed with a slurry containing reference material of
calcium pyrophosphate for 6000 strokes in order to reduce irregular patterns of abrasion
on the surfaces of the newly mounted teeth. The number of strokes applied to each
toothbrushing operation was 1000.
EVALUATION OF DENTAL ABRASIVES 165
The slurries of reference material calcium pyrophosphate supplied by Monsanto Co. (St.
Louis, MO) or of abrasives were prepared using a mass of 10 g of the material and 50
ml of diluent. In the case of thickeners, the slurries were prepared using a mass of 5 g
of the material and 50 ml of diluent because of the large volume of the thickener. The
diluent was prepared by adding 5 g of carboxymethylcellulose in 50 ml of glycerin
heated to 60øC while stirring to obtain a homogenous mixture. Another 50 ml of heated
glycerin was added to the mixture, and then 900 ml of distilled water was added. The
stirring was continued at room temperature to obtain a clean solution of diluent.
Each radioactive slurry was stirred, and three aliquots of 3 ml were pipetted onto
separated planchets. These slurries were dried in an oven with air circulation, at 60øC,
carefully to avoid cracking in the dried samples. The beta radiation of 1.71 MeV 3•p
(with a half life of 14.3 days) of the dried samples was measured using a plastic
scintillator detector.
Calculation of abrasivehess indices. To calculate the abrasiveness indices, known as RDA,
the 32p counting rate obtained for abrasive material was compared to that obtained for
the reference material. A score of 100 for calcium pyrophosphate RDA was considered
according to an ADA (American Dental Association) committee (6). Correction factors
were also applied in this calculation because different abrasives may present distinct
self-absorption and backscatterring radiation characteristics.
Particle size and microscopy analysis of abrasives. The particle size of the silica and calcium
carbonate samples was determined by sedigraphic method and their particle forms were
examined using scanning electron microscopy at the Metallurgy Department of the
IPEN/CNEN-SP.
RESULTS AND DISCUSSION
Table I shows RDA values obtained for six samples of silica and three samples of calcium
carbonate, together with their particle sizes determined by sedigraphic method.
The RDA results for raw materials used as abrasive agents (silica 1 and calcium car-
bonate) presented in Table I varied from 136 to 19. The relative standard deviations of
these RDA results, in general, varied from 5.9% to 11.8%, showing a good precision in
Table I
RDA and Particle Size Obtained for Raw Materials, Silica and Calcium Carbonate
Silica 1 (abrasive)
Silica 2 (thickener)
Calcium carbonate
Samples A B C D E F G H I
RDA_+ s 136 + 8 94-+ 6 85 -+ 10 7 _+ 1 6.6_+ 1.0 5.5 -+ 2.1 54 + 4 24_+ 2 19-+ 2
s r (%) (5.9) (6.4) (11.8) (14.3) (15.2) (38.2) (7.4) (8.3) (10.5)
n 7 8 8 8 5 6 8 8 8
Mean diameter
(t•m) 4.26 3.21 2.54 1.20 0.31 0.32 3.13 1.77 1.49
RDA _+ s: RDA arithmetic mean values and standard deviation.
st: relative standard deviations of the RDA values.
n: number of determinations.
166 JOURNAL OF COSMETIC SCIENCE
the method. The silica 2 substances used as agent thickener presented less satisfactory
results, with relative standard deviations varying from 14.3% to 38.2% (Table I). The
precision of the thickener results was not so good, probably due to the difficulty in
obtaining a homogeneous slurry of thickener during the toothbrushing.
Table I indicates that there may be a relationship between the RDA results and particle
size of each type of raw material, that is, the abrasivity indices of CaCO_• and SiO 2 used
as abrasive agents increase with the particle size of the material. However, different types
of abrasives with similar particle size presented distinct RDA values. As can be seen in
the case of the sample, silica B with a particle size of 3.21 pm presented an RDA value
about two times higher than that presented by calcium carbonate G with a 3.13 ]am size.
This result is in agreement with those presented by Boer et al. (3).
Figure 1 shows the shapes of particles of silica and calcium carbonate obtained by
scanning electron microscopy. It can be observed that the particle shapes of the two
abrasives are not uniform and that the CaCO 3 appears to have more agglomerated
particles than SiO 2. According to Navarre (7), the materials constituted of particles with
heterogeneous arrangements and irregular forms are more abrasive than those formed
with homogeneous arrangements and regular forms.
RDA values for calcium carbonate were also evaluated using different masses of the
abrasives in the preparation of slurry with 50 ml of diluent. For 5, 10, 15 and 30 g of
CaCO3, the RDA values obtained were 52, 74, 71 and 73, respectively. This preliminary
study indicated the increase in RDA values with the mass of CaCO_• until about 10 g.
For quantities of CaCO3 higher than 10 g, the RDA values were very close.
According to Roa (1), the quantity of CaCO• generally used in dentifrice manufacturing
corresponds to about 20 g of CaCO3 in the slurry (50 ml) used in our RDA evaluation.
CONCLUSIONS
The determination of RDA values of the abrasives can be utilized for prudent selection
of raw materials by dentifrice producers. The radiometric method presented here is
simple and fast because it does not require long periods for toothbrushing. Also, the
RDA results obtained indicated that the abrasiveness of calcium carbonate and silica
compounds increased with the particle sizes of the materials. However, it is important
Figure 1. A: SiO 2 particles (502x magnification). B: CaCO• particles (447x magnification).
EVALUATION OF DENTAL ABRASIVES 167
to consider that others factors, such as particle hardness, shape, and distribution, can also
affect the abrasiveness of the raw materials.
ACKNOWLEDGMENTS
We acknowledge Colgate Palmolive Ltd. for supplying the raw materials; the Monsanto
Company for supplying calcium pyrophosphate reference material; the Dentistry School
and Faculty of Pharmaceutical Sciences of Ribeirgo Preto, University of Sgo Paulo, for
tooth samples; Dr. J.J. Hefferren from Kansas State University for advice; and CNPq
and FAPESP for financial support for this project.
REFERENCES
(1) W. E. P. Roa, Aplicagio e composigio de dentifrfcios, Aerosol Cosmet., 5, 5-14 (1983).
(2) H. Panzeri, Personal communication (Dentistry School of Ribeirio Preto, SP, Brazil, 2001).
(3) R. Boer, A. S. H. Duinkerke, and J. Arends, Influence of tooth paste particle size and tooth brush
stiffness on dentine abrasion in vitro, Caries Res., 19, 232-239 (1985).
(4) S. Kinoshita, T. Arai, and R. Uraguchi, Abrasive properties of commonly ua_d dentifrices, Bull. Tokyo
Med. Dent. Univ., 26, 225-242 (1979).
(5) H. Panzeri, E. H. G. Lara, F. Siessere, and R. M. Marchetti, Availagio de dentifrfcios. 2 a parte: Forma
a distribuigio de partfculas abrasivas, Odontd/ogo Moderno, VI, 13-25 (1979).
(6) J.j. Hefferren, A laboratory method for assessment of dentifrice abrasivity,J. Dent. Res., 55,563-573
(1976).
(7) M. G. Navarre, The Chemistry and Manuj•kcture of Cosmetics (Continental Press, Orlando, Florida, 1975),
Vol. III, pp. 445-470.
