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Abrasion, polishing, and stain removal characteristics of various commercial dentifrices in vitro

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Abstract and Figures

To evaluate, using conventional in vitro procedures, the abrasivity, enamel polishing properties, and stain removal effectiveness of various commercial dentifrices that have a variety of compositions and are marketed for cleaning, whitening, and/or polishing capabilities, and to examine their relationships between stain removal and abrasivity. The Relative Dentin Abrasivity (RDA) method was used to measure abrasivity, and the Pellicle Cleaning Ratio (PCR) procedure was used to evaluate stain removal performance. A Cleaning Efficiency Index (CEI) was calculated using the RDA and PCR values. Enamel polish was determined on bovine enamel specimens using a reflectometer. All treatments were performed on a V-8 cross-brushing machine using aqueous dentifrice slurries and standard nylon-bristle toothbrushes. A total of 26 dentifrices, purchased at retail, were tested against the American Dental Association (ADA) calcium pyrophosphate reference standard. All dentifrices removed extrinsic stain and produced some dentin abrasion, but scores ranged widely between products (from 36 to 269 for RDA and from 25 to 138 for PCR). The majority of dentifrices contained hydrated silicas, and those with high PCR scores often, but not always, had higher RDA values. Products containing other abrasives (e.g., dicalcium phosphate, sodium bicarbonate, and calcium carbonate) generally had lower RDA values and usually lower PCR scores. There were exceptions (e.g., refined kaolin clay) that had high PCR scores and low RDA values, resulting in higher CEI values. Similarly, brushing with all dentifrices significantly increased reflectance readings of acid-dulled teeth, but polish scores also were highly variable among products (ranging from 38 to 97). The polish scores of dentifrices containing hydrated silica varied extensively (ranging from 38 to 80), and the scores of products containing other abrasives fell within this same range, except for dentifrices containing either Fuller's earth (86) or kaolin (97). With only a few exceptions, dentifrices marketed as "whitening" products were generally more abrasive to dentin, especially for those containing silicas. Similarly, aside from two non-silica products, those dentifrices advertised for polishing ability generally were no more effective than other products. The relationship between stain-removal ability and abrasivity of dentifrices was not necessarily direct.
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comprising silicas (e.g., hydrated silica), metal oxides (e.g., alu-
mina), phosphates (e.g., calcium pyrophosphate), carbonates
(e.g., calcium carbonate), and silicates (e.g., aluminum silicate).
Extensive research and development have been conducted
during the past half century in an effort to optimize the cleaning
efficiency of dentifrice abrasives, while minimizing any delete-
rious wear effects to the teeth. Although this might appear to be
easily accomplished, the practice of designing effective dentifrice
abrasive systems is actually quite complex,5and is dependent on
a variety of properties of the agent, including chemical compo-
sition, crystal structure, cleavage, friability, and hardness, as
well as concentration, shape, size distribution, and surface fea-
tures of the particles. In addition to balancing these characteris-
tics to optimize stain removal without causing harmful abrasion
to the teeth, abrasives must be compatible with other dentifrice
ingredients, particularly therapeutic agents (e.g., fluoride), and
must demonstrate acceptable formulation properties (e.g., vis-
cosity and flow) without compromising important consumer
attributes (e.g., taste and appearance).
Abrasion, Polishing, and Stain Removal Characteristics
of Various Commercial Dentifrices In Vitro
Bruce R. Schemehorn, MS
Dental Products Testing, Therametric Technologies, Inc.
Noblesville, IN, USA
Michael H. Moore, MS   Mark S. Putt, MSD, PhD
Health Science Research Center
Indiana University-Purdue University
Fort Wayne, IN, USA
Introduction
Historically, the need for abrasive agents in cleaning the teeth
has been recognized since ancient times, and various materials
(e.g., pumice, bone ash and powdered marble, shells and coral)
have been used for the mechanical removal of tooth debris and
stains.1In modern times, the application of dentifrices with a
toothbrush has been the primary method for cleaning the teeth.
A key function of dentifrices is to control stain accumulations,
which are attributable mainly to the chemical bonding of die-
tary chromagens with proteinaceous compounds in the salivary
pellicle that coat the tooth surfaces.2Extrinsic stain is tenacious,
and its prevention or removal requires dentifrices that contain
abrasive agents since tooth brushing without such is ineffec-
tive.3Traditionally, to achieve mechanical cleaning a dentifrice
needs three formulation components: 1) an abrasive agent; 2) a
thickening agent to hold the abrasive in suspension during brush-
ing; and 3) a surface-active agent to facilitate removal of oral
debris.4Abrasives, which are the principal component contribu -
ting to the physical removal of stains, are insoluble substances
11
Abstract
Objective: To evaluate, using conventional in vitro procedures, the abrasivity, enamel polishing properties, and stain removal
effectiveness of various commercial dentifrices that have a variety of compositions and are marketed for cleaning, whitening, and/or
polishing capabilities, and to examine their relationships between stain removal and abrasivity.
Methods: The Relative Dentin Abrasivity (RDA) method was used to measure abrasivity, and the Pellicle Cleaning Ratio (PCR)
procedure was used to evaluate stain removal performance. A Cleaning Efficiency Index (CEI) was calculated using the RDA and
PCR values. Enamel polish was determined on bovine enamel specimens using a reflectometer. All treatments were performed on
a V-8 cross-brushing machine using aqueous dentifrice slurries and standard nylon-bristle toothbrushes. A total of 26 dentifrices,
purchased at retail, were tested against the American Dental Association (ADA) calcium pyrophosphate reference standard.
Results: All dentifrices removed extrinsic stain and produced some dentin abrasion, but scores ranged widely between products
(from 36 to 269 for RDA and from 25 to 138 for PCR). The majority of dentifrices contained hydrated silicas, and those with high
PCR scores often, but not always, had higher RDA values. Products containing other abrasives (e.g., dicalcium phosphate, sodium
bicarbonate, and calcium carbonate) generally had lower RDA values and usually lower PCR scores. There were exceptions (e.g.,
refined kaolin clay) that had high PCR scores and low RDA values, resulting in higher CEI values. Similarly, brushing with all
dentifrices significantly increased reflectance readings of acid-dulled teeth, but polish scores also were highly variable among prod-
ucts (ranging from 38 to 97). The polish scores of dentifrices containing hydrated silica varied extensively (ranging from 38 to 80),
and the scores of products containing other abrasives fell within this same range, except for dentifrices containing either Fuller’s
earth (86) or kaolin (97).
Conclusion: With only a few exceptions, dentifrices marketed as “whitening” products were generally more abrasive to dentin,
especially for those containing silicas. Similarly, aside from two non-silica products, those dentifrices advertised for polishing ability
generally were no more effective than other products. The relationship between stain-removal ability and abrasivity of dentifrices
was not necessarily direct.
(J Clin Dent 2011;22:11–18)
12 The Journal of Clinical Dentistry Vol. XXII, No. 1
The objective of this investigation was to evaluate dentifrices
that are currently marketed for advanced cleaning, whitening, and
polishing properties in an effort to determine if these products re-
ally provide the benefits as advertized. Because there are a large
number of dentifrice products on the market and the formulations
undergo frequent modifications, the products selected for eval-
uation were not comprehensive, but rather representative of
those available mainly in the US.
Materials and Methods
Dentifrice Samples
A total of 26 commercial dentifrice products were purchased
in 2008 through local retail outlets or ordered online. Table I pro-
vides information obtained from the packaging labels, including
tradenames, manufacturers, putative abrasive systems, and other
ingredients that could possibly affect the test parameters. These
comprise, for example, minor insoluble ingredients and various
phosphates and other chemicals that may have surface condi-
tioning properties. Detergents and surfactants also could possibly
influence stain removal, but because all the dentifrices contained
these, they were not included. In addition, Table I has dentifrice
package label claims concerning stain removal, whitening, abra-
sion, and polishing that are relevant to this investigation.
Stain Removal Procedure
The Pellicle Cleaning Ratio (PCR) procedure was a modifi-
cation and improvement of the laboratory method described by
Stookey, et al.17 Squares (4 mm) of enamel were cut from bovine
permanent incisors, and were embedded in clear, self-curing
denture acrylic to provide square blocks (1.5 cm) with the labial
surface exposed. The labial surfaces of the enamel squares were
ground flat using a model trimmer to allow uniform instrumen-
tal color readings. The surface was smoothed on wet 400 grit
emery paper until all grinding marks were removed, and then the
flattened surface was highly polished with alumina. The fin-
ished specimens were examined under a dissecting microscope,
and discarded if surface imperfections were observed. Prior to
staining, the specimens were etched for 60 seconds in 0.2M
HCl, rinsed with water, and etched again for 60 seconds with 1%
phytic acid.
After a final water rinse, the specimens were attached to a
staining apparatus, constructed to provide alternate immersion
into a staining broth and air-drying of the specimens. The appa-
ratus consisted of an aluminum platform base which supported
a Teflon®rod (3/4 inch diameter) rotating at a constant rate (1.5
rpm). The tooth specimens, attached by plastic screws spaced at
regular intervals along the length of the rod, rotated through the
broth in a removable plastic trough (300 ml capacity).
The staining broth was prepared as described previously17 by
adding instant coffee, instant tea, red wine, and porcine gastric
mucin to sterilized trypticase soy broth, which was then inocu-
lated with a 24-hour Micrococcus luteus bacterial culture. The
apparatus, with the enamel specimens attached and the staining
broth in the trough, was incubated at 37°C with the specimens
rotating continuously through the staining broth and air. The
broth was replaced once daily for ten consecutive days. With
each broth change, the trough and specimens were rinsed and
Significant advances by dentifrice manufacturers during this
period have resulted in currently available multi-functional tooth-
pastes that deliver various therapeutic and cosmetic benefits,
including treatment of malodor, caries, gingivitis, dental plaque,
dental calculus, demineralization, and dentinal hypersensitiv-
ity.6,7 Nevertheless, in spite of this progress, the primary reason
people use toothpastes is to improve tooth appearance by clean-
ing the teeth and reducing unsightly stains.5
Moreover, in recent years there has been an increase in in-
terest by the general public in oral esthetics, which has stimu-
lated the development of new technologies for whitening teeth.
This has led to the widespread use of bleaching systems, such
as peroxide gels and strips, for treating intrinsic tooth discol-
oration and to whitening dentifrices for removing and/or pre-
venting extrinsic stain accumulations. In addition to abrasives,
two chemical approaches have been taken with dentifrice for-
mulations for the purpose of preventing and/or removing ex-
trinsic tooth stains: 1) surface-active agents that reduce stain
molecule adhesion or desorb already attached stain molecules
(e.g., surfactants, enzymes, chelators, and calcium phosphate
builders); and 2) bleaches/oxidizing agents that reduce stain by
oxidizing colored unsaturated compounds into uncolored car-
boxylic acids and alcohols (e.g., stabilized hydrogen peroxide
and carbamide peroxide).5-7 While all dentifrices contain com-
mon detergents (e.g., sodium lauryl sulfate or sodium N-lauroyl
sarcosinate), dentifrices have been introduced during the past
few years with other chemical agents that promote extrinsic
stain control (e.g., pyrophosphate and polyphosphates).8Den-
tifrices containing peroxide have utilized dual-phase systems
that combine paste and gel when extruded onto the toothbrush
immediately before use.9
Another characteristic of dentifrices that has not received as
much attention is polishing ability. Like stain removal and abra-
sivity, the polishing ability of a dentifrice is a physical phenom-
enon associated with the abrasive system. The concept of high
enamel luster is important for two reasons. First, from a cosmetic
viewpoint, an increase in luster contributes to the esthetics of the
dentition, and improved surface smoothness is conducive to a
feeling of oral cleanliness. Also, more highly polished enamel
appears whiter than duller enamel.10 Second, and more impor-
tantly, smooth highly polished tooth surfaces are less receptive
to the accumulation and retention of dental plaque, calculus,
and extrinsic stain, and the concomitant oral disease processes.
Many studies have demonstrated that rough, unpolished tooth
surfaces facilitate the formation and retention of dental plaque,
oral debris, calculus, and extrinsic stain.11-14 For example, initial
bacterial colonization of enamel surfaces starts in surface irreg-
ularities (e.g., pits, scratches, defects), and preferential retention
occurs on rough surfaces where bacteria are more protected
from shear forces.15,16
In summary, a dentifrice should have the ability to remove
extrinsic stains effectively without resulting in unnecessary de -
leterious abrasion to the teeth. Additionally, as a means of in-
hibiting dental accumulations (i.e., stains, plaque, and calculus),
a dentifrice should impart a smooth, highly polished surface to
the teeth, thereby contributing not only to oral esthetics, but
also to a concomitant improvement in oral health.
Vol. XXII, No. 1 The Journal of Clinical Dentistry 13
The specimens were stratified into groups of 16, with each
group having equivalent average baseline L*a*b* stain scores.
The specimens were positioned on a V-8 mechanical cross-
brushing machine19 equipped with soft, nylon-bristle toothbrushes
(Oral-B®35 Soft, Procter & Gamble, Cincinnati, OH, USA), ad-
justed to 150 g pressure on the enamel surfaces, and brushed with
the dentifrice slurries (25 g dentifrice, 40 g deionized water) for
800 reciprocating strokes. The control abrasive, American Den-
tal Association (ADA) reference material calcium pyro phosphate
(Monsanto, St. Louis, MO, USA) was mixed in a 1:5 ratio with
a 0.5% carboxymethylcellulose solution (CMC-7MF, Hercules,
Inc., Wilmington, DE, USA). Test products were randomly as-
signed to machine positions until all products were tested at all
positions twice. After the final color readings were made, the
specimens were pumiced to remove all residual stain from the
teeth, and color readings were repeated. This technique pro-
vided an inherent value for each specimen, representing the
brushed with water to remove any loose deposits. On the eleventh
day, the staining broth was modified by adding FeCl3
.6H2O, and
this was continued with daily broth changes until the stained pel-
licle film was sufficiently dark (L* score range 30–35). Then, the
specimens were removed, brushed thoroughly with water, and
refrigerated in a humidor until used.
The amount of stain on the teeth was measured by taking
color readings using a spectrophotometer with diffuse illumina-
tion/8° viewing angle and three mm aperture (Minolta CM-503i
Spectrophotometer, Minolta Camera Co., NJ, USA). Measure-
ments over the entire visible color spectrum were obtained be-
fore and after treatment using the CIELAB color scale.18 Stained
enamel specimens were air-dried at room temperature for 30
minutes, and color measurements were made by aligning the cen-
ter of the stained enamel square directly over the targeting aper-
ture of the spectrophotometer. Three color readings using the
L*a*b* scale were averaged for each specimen.
Table I
Dentifrice Product Information and Ingredients
No. Tradename Package Label Claims Manufacturer Abrasive System Other Relevant Ingredients
1 Aquafresh Extreme Clean Leaves teeth feeling clean, smooth and brighter GlaxoSmithKline Hydrated silica Iron oxide
2 Aquafresh White & Shine Cleans and polishes for whiter, shinier teeth GlaxoSmithKline Hydrated silica Disodium Phosphate, Mica
3 Arm & Hammer Dental Care Low abrasion formula/Helps remove Church & Dwight Sodium bicarbonate No other relevant ingredients
Advanced Cleaning surface stains
4 BlanX Non-abrasive Whitening Cleans, protects and whitens/In-depth Guaber, UK Silica Arctic lichen (Cetraria islandica)
cleaning without abrasive effects
5 Brite Smile Whiten teeth safely and effectively BriteSmile, Inc Hydrated silica Pentasodium triphosphate
6 Colgate Cavity Protection Cleans teeth thoroughly Colgate-Palmolive Dicalcium phosphate Tetrasodium pyrophosphate
7 Colgate Luminous For strong, shiny, whiter teeth Colgate-Palmolive Hydrated silica Tetrasodium pyrophosphate
8 Colgate Simply White Twice the whitening action of ordinary Colgate-Palmolive Hydrated silica Na phosphates, PVM/MA,
whitening toothpaste Na-Mg silicate,
Hydrogen peroxide
9 Colgate Total Whitening Whitens teeth Colgate-Palmolive Hydrated silica PVM/MA copolymer
10 Crest Cavity Protection No relevant claims Procter & Gamble Hydrated silica Sodium phosphates
11 Crest Extra Whitening Polishes for natural whiteness/Whitens Procter & Gamble Hydrated silica, Tetrasodium pyrophosphate,
teeth by gently polishing away surface stains Na bicarbonate Sodium carbonate
12 Crest Pro-Health Whitens teeth by removing surface stains Procter & Gamble Hydrated silica Na hexametaphosphate,
Trisodium phosphate
13 Crest Vivid White Whitens teeth by polishing away surface stains Procter & Gamble Hydrated silica Na hexametaphosphate
and acts to help prevent new surface stains
14 Dentisse Natural Reflection Premium polishing and whitening Dentisse, Inc Refined kaolin clay Bentonite clay
15 GoSmile AM Whitening Whiten naturally GoSmile, Inc Hydrated silica No other relevant ingredients
16 Jason’s Powersmile Exclusive natural whiteners Jason Natural Products Ca carbonate, Silica Na bicarbonate
17 Mentadent Advanced Whitening Noticeably whiter teeth Church & Dwight Hydrated silica, Hydrogen peroxide,
Na bicarbonate phosphoric acid
18 Pearl Drops Triple Action Gently cleans away surface stains/Safely Church & Dwight Na bicarbonate, Tetrasodium pyrophosphate
Whitening polishes for whiter & brighter teeth/ Hydrated silica
See the whiteness, feel the shine
19 Rembrandt Complete Whitens beyond surface stains/Low Johnson & Johnson Dicalcium phosphate Al hydroxide, Papain
abrasion formula won’t scratch enamel
20 Rembrandt Intense Stain Deep cleans and whitens gently Johnson & Johnson Hydrated silica, Al hydroxide, Papain
Dicalcium phosphate
21 Rembrandt Plus Whitens teeth beyond surface stains Johnson & Johnson Hydrated silica Urea peroxide, Al hydroxide,
without scratching enamel Silica, Papain
22 Sensodyne Extra Whitening No relevant claims GlaxoSmithKline Hydrated silica Na phosphate
23 Supersmile Removes stubborn stains without harmful Robell Research Dicalcium phosphate, Ca peroxide, Na perborate
bleaches or abrasives Na bicarbonate,
Ca carbonate
24 Tom’s of Maine Natural Contains calcium for clean teeth Tom’s of Maine Ca carbonate, No other relevant ingredients
Hydrated silica
25 UltraBrite Advanced Whitening Whitens teeth Colgate-Palmolive Hydrated silica, Tetrasodium pyrophosphate
Alumina
26 Umbrian Clay Whitening properties Fresh, Inc Fuller’s earth Sodium chloride
14 The Journal of Clinical Dentistry Vol. XXII, No. 1
maximum amount of stain that potentially could be removed by
the test dentifrice.
The difference between the pre-test and post-test readings for
each color factor (L* a* b*) represents the ability of the test prod-
ucts to remove stain and whiten teeth. The overall change in stain
was calculated using the following CIELAB equation:18
ΔE = [(ΔL*)2+ (Δa*)2+ (Δb*)2]1/2
The Pellicle Cleaning Ratio was calculated as follows:17
PCR = (Test sample ΔE ÷ ADA Reference sample ΔE) 100
Dentin Abrasion Procedure
The Relative Dentin Abrasion (RDA) procedure, which is
based on the Radioactive Dentin Abrasion method of Graben-
stetter, et al.,19was used for the determination of dentifrice abra-
sivity. Root dentin specimens from human permanent teeth were
irradiated in a neutron flux under controlled conditions outlined
by the ADA.20After mounting the specimens in dental acrylic
blocks, they were preconditioned by brushing on the V-8 cross-
brushing machine, equipped with ADA nylon-bristle tooth-
brushes, at 150 g pressure for 1500 strokes using a slurry con-
sisting of ADA reference material in a 1:5 ratio with 0.5% CMC
aqueous glycerin solution.
Following preconditioning, tests were performed using the
same parameters (150 g pressure and l500 strokes) in a sandwich
design, in which each test dentifrice slurry (25 g/40 ml water)
was flanked by the reference material slurries (10 g/50 ml 0.5%
CMC). Test products were randomly assigned to machine posi-
tions until all products were tested at all eight positions.
Aliquots (1 ml) were pipetted, weighed (± 0.01g) and added to
scintillation cocktail (4.5 ml). The samples were mixed well, and
immediately put on the scintillation counter for β-radiation de-
tection. Following measurement, the net counts per minute (cpm)
were divided by the weight of the sample to calculate a net cpm/g
of slurry. The net cpm/g of the pre- and post-sample ADA refer-
ence material for each test slurry was calculated and averaged to
use in the calculation of RDA (relative dentin abrasion) for the test
material. The reference material was assigned a value of 100 and
its ratio to the test material was calculated. As of 16 Aug 1999,
a new lot of the ADA reference material, which is less abrasive
than the original lots, has been used. This necessitates the addi-
tion of a 3.6% correction factor to the reference material cpm, per-
mitting direct comparisons to historical data for this procedure.
Cleaning Efficiency Index
The Cleaning Efficiency Index (CEI), which was introduced by
Schemehorn, et al.,21 was calculated according to the equation:
CEI = (RDA + PCR – 50) ÷ RDA
The CEI emphasizes the importance of good stain removal
properties and low dentin abrasivity. The equation was based on
clinical data that indicated a PCR value of at least 50 was needed
to provide acceptable cleaning power (extrinsic stain removal).21,22
Enamel Polish Procedure
The procedure for determining enamel polish was based on an
earlier methodology in which acid-dulled teeth were mechanically
brushed with dentifrice slurries, and the degree of polish quanti-
fied with a reflectometer that measured the intensity of specular
light reflected by the tooth specimens.23,24 The greater the inten-
sity of light reflected from a specimen, the higher was the luster
of the tooth, and hence the higher the numerical polish score.
All evaluations were made with bovine permanent incisors,
which are advantageous for testing due to their size and similar
polishing properties to human teeth.25 The teeth were trimmed
and mounted in self-curing dental acrylic blocks (2 cm) with the
labial surface exposed. In order to permit reflectance measure-
ments, a portion of the labial surface was ground using a water-
cooled surface grinder in such a way that a leveled area (approx -
imately 1 cm in diameter) was produced parallel to the base of
the mount.
Tooth specimens were dulled prior to treatment by individu-
ally etching them with agitation (0.2M HCl) for 30 seconds,
then thoroughly rinsing with distilled water, yielding a reflect -
ance score of 5 or less.
Polish measurements were made using a glossmeter with a
60° operating angle and 5 mm 10 mm aperture (Novo-
Curve™, Rhopoint Instrumentation Ltd., Bexhill-on-Sea, UK).
Each enamel specimen was inverted on the glossmeter platform
covering the opening, and read in Gloss Units (GU) as specified
in American Society for Testing and Materials (ASTM D523).
The glossmeter was calibrated to the manufacturer’s standard,
and data were presented as the percentage between 0 (no reflect -
ance) and 100 (white carrara glass standard).24
The specimens were positioned on a V-8 mechanical cross-
brushing machine equipped with soft, nylon-bristle toothbrushes
adjusted to 300 g pressure on the enamel surfaces, and brushed
with the dentifrice slurries (25 g/40 g water) for 2000 recip-
ro cat ing strokes. The control abrasive, ADA reference mater-
ial calcium pyrophosphate, was mixed in a 1:5 ratio with a
0.5% CMC-7MF solution. Test products were randomly assigned
to machine positions until all products were tested at all eight
positions.
Data Analysis
Data from the three test methods were averaged for each of
the 26 dentifrices tested for the following numbers of replicates:
PCR (N = 16); RDA (N = 8); and enamel polish (N = 8). Because
there were too many samples to perform meaningful multiple
comparison tests, repeated t-tests were carried out for each test
method in an effort to establish approximate differences in
mean values between dentifrices that were statistically significant
(p < 0.05).
Results
The data from each of the testing procedures (i.e., PCR, RDA,
and polish) are provided in Figures 1–3. In each figure, the data
bars are ranked in ascending or descending order according to the
mean values obtained for each product with the specific testing
procedure. Also, in each figure, the data for the calcium pyro -
phosphate reference standard is provided at the top as the first bar
above all the dentifrice products.
Figure 1 represents a composite summary of stain removal
data obtained using the PCR procedure for all 26 dentifrices. The
Vol. XXII, No. 1 The Journal of Clinical Dentistry 15
Figure 1. Pellicle Cleaning Ratio (PCR) data of commercial dentifrices ranked in order from lowest to highest stain removal. Dentifrices are labeled by tradename and
identification number from Table I. Lengths of bars represent means; error bars show standard errors (n = 16).
Figure 2. Relative Dentin Abrasion (RDA) data of commercial dentifrices ranked in order from highest to lowest abrasivity. Dentifrices are labeled by tradename and
identification number from Table I. Lengths of bars represent means; error bars show standard errors (n = 8).
16 The Journal of Clinical Dentistry Vol. XXII, No. 1
Figure 3. Enamel polish data of commercial dentifrices ranked in order from lowest to highest level of luster. Dentifrices are labeled by tradename and identification num-
ber from Table I. Lengths of bars represent means; error bars show standard errors (n = 8).
Figure 4. Cleaning Efficiency Index (CEI) data of commercial dentifrices ranked in order from lowest to highest values based on the equation in the text. Dentifrices are
labeled by tradename and identification number from Table I.
Vol. XXII, No. 1 The Journal of Clinical Dentistry 17
amount of stain removed varied extensively between dentifrices,
with PCR values ranging from a very low 25 for a silica-
containing dentifrice (Product 4) to a high of 138 for a hydrated
silica/alumina system (Product 25).
The relative dentin abrasion values for the various dentifrices
are summarized in Figure 2. Similar to the PCR data, a wide
range of dentin abrasion values was found during the evaluation
of the different products, with RDA values as low as 36 for
Product 4 to a high of 269 for a dentifrice with a hydrated silica
abrasive (Product 5). It is noteworthy that this variation existed
between dentifrices that contained different abrasive systems, but
it also occurred between dentifrices that contained the same type
of abrasive, namely hydrated silica.
The results of the testing of the same 26 dentifrices for enamel
polishing properties are assembled in Figure 3. All products
increased the luster of the acid-dulled teeth, but a wide range of
polishing abilities was observed from a relatively poor reflec tance
percentage of 38 for two hydrated silica-containing dentifrices
(Products 21 and 22) to a very high value of 97 for a denti frice
with a refined kaolin abrasive agent (Product 14). With values of
80, two dentifrices containing hydrated silica (Products 11 and 25)
polished moderately well, as did another containing Fuller’s earth
(Product 26) with an average value of 86.
The CEI values that were calculated from the PCR and RDA
data are presented in Figure 4, and range from just 0.31 for a silica-
containing dentifrice (Product 4) to a high of 1.78 for a refined
kaolin-containing dentifrice (Product 14). The four dentifrices
that were the most effective at removing stain were also among
the most abrasive (Products 2, 5, 7, and 25), which decreased
their CEI values. The products with the highest CEI values (e.g.,
Products 14, 19, and 20) had moderate to high PCR scores, but
relatively low RDA scores of less than 90.
Discussion
An ideal dentifrice should provide optimum cleaning (i.e.,
extrinsic stain removal) and polishing with minimum abrasion to
the dental hard tissues (viz. cementum, dentin, and enamel).
Maximum stain removal ability and low abrasivity are dia metric
opposites, as are high cleaning and high polishing. Thus, it is in-
evitable that some concessions must be made in order to achieve
a suitable compromise, a fact that accounts for the large differ-
ences in stain removal, polishing, and abrasion properties of the
various abrasive agents used in commercial dentifrices currently
available to the public.
The balance between extrinsic stain removal and abrasivity
properties of dentifrices has been investigated and debated for a
very long time, but there is general consensus with the statement
by Kitchin and Robinson26 more than 60 years ago that, “One
should use only as much abrasion as necessary to clean one’s
teeth.” The challenge, of course, is in defining what is necessary.
The results of this investigation are in agreement with earlier re-
ports17,27,28 that generally there is moderate correlation between
in vitro cleaning effectiveness and abrasiveness to dentin for var-
ious toothpastes, but RDA values are not always predictive of
clinical stain removal.29 Still, it is very relevant to this investiga-
tion that both the RDA test and the PCR method correlated lin-
early with cleaning power (i.e., stain removal) in a collaborative
clinical study using three different grading methods that evalu-
ated dentifrices with three different levels of abrasivity.21,22,30
The association between the RDA test and in vivo cervical/
dentinal abrasion is not well defined because of the large num-
ber of hard-to-determine variables and the near impossible dif-
ficulty conducting such clinical trials. In situ testing using tooth
sections mounted in dentures may provide useful information31
since it encompasses the contribution of the salivary pellicle,32
but the etiology of this condition is likely a combination of many
factors besides dentifrice abrasivity, including tooth brushing
techniques, toothbrush bristle stiffness, and dental erosion.29 Al-
though the RDA test can show substantial differences between
laboratories,29 the precision within the same laboratory can be ex-
cellent and distinguish a 10% difference between abrasives using
an eight-fold replication with an internal reference standard.20,30,33
With respect to the physical characteristics considered herein,
most commercially available dentifrices appear to have limita-
tions. For example, some products are unnecessarily abrasive to
dentin, many do not remove extrinsic stain efficiently, and the
majority are inadequate polishing agents. While it may not be
possible to determine the precise level of abrasivity that consti-
tutes irreversible damage to oral hard tissue by dentifrices, there
is general consensus that the RDA values should be below the
limit of 250 recommended by ISO standard 11609 and the ADA.6
Three of the dentifrices that were tested had RDA values greater
than 250 (Products 5, 7, and 25), but with the exception of Prod-
uct 13 the remainder of the dentifrices were below 200.
The difference in luster imparted by the various products was
visibly evident. An experienced observer can distinguish be-
tween teeth with mean polish scores differing by about 5 per-
centage units. Thus, the teeth polished by dentifrices in this
study can be visually ranked from low to high polish. The most
effective polishing was observed with dentifrices containing
clay minerals, namely kaolin and Fuller’s earth. It is reasonable
to recommend high-polishing dentifrices since their use can
inhibit the adherence of bacteria15,16 and contribute to decreased
formation and retention of pellicle, plaque, calculus, and extrin-
sic stains.11-14
It is interesting that in a study involving 43 dentifrices that was
published more than 40 years ago, similar wide ranges in clean-
ing, abrasion, and polishing properties were observed between
commercial products.27 The similarity is remarkable because
the types of abrasives were quite different from those of the
present investigation. At that time there were no silica- containing
dentifrices (hydrated silicas had not yet been developed for this
purpose), and nearly all products had calcium phosphate or cal-
cium carbonate abrasives. Silicas, which now are the most widely
used dentifrice abrasives in the US, are available in a variety of
grades that differ in manufacturing method and in particle size.
These differences result in a wide range of physical properties
that may account for the large differences observed in stain re-
moval, abrasivity, and polishing ability.
Conclusions
Stain-removal ability, abrasivity, and enamel polishing capa-
bilities of dentifrices, especially those containing silicas, were
highly variable, and there was no consistent relationship for
18 The Journal of Clinical Dentistry Vol. XXII, No. 1
these parameters that was associated with the abrasive systems
as listed on product labels. Dentifrices marketed as “whitening”
products generally were more abrasive than other products, al-
though there were some exceptions, and a direct relationship was
not always evident between dentifrice stain-removal ability and
abrasivity. Similarly, with one exception, dentifrices marketed for
their ability to polish or to impart luster to teeth were no more
effective than other products. When stain-removal and abrasiv-
ity parameters were incorporated into a CEI, several products
containing hydrated silica and/or dicalcium phosphate had rela-
tively high CEI values, but the most efficient dentifrice tested
contained refined kaolin clay as the abrasive.
Acknowledgment: No outside funding was provided for this investigation.
For correspondence with the authors of this paper, contact
Dr. Mark Putt—putt@ipfw.edu.
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