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Toothpastes can be formulated with different abrasive systems, depending on their intended clinical application. This formulation potentially affects their effectiveness and safety and, therefore, requires proper understanding. In this article, the authors focused on abrasive aspects of toothpastes containing sodium bicarbonate (baking soda), which have gained considerable attention because of their low abrasivity and good compatibility, while providing clinical effectiveness (further detailed in the other articles of this special issue). The authors first appraised the role of toothpaste abrasivity on tooth wear, exploring some underlying processes and the existing methods to determine toothpaste abrasivity.
Types of Studies Reviewed
The authors reviewed the available data on the abrasivity of toothpastes containing baking soda and reported a summary of findings highlighting the clinical implications.
Conclusions
On the basis of the collected evidence, baking soda has an intrinsic low-abrasive nature because of its comparatively lower hardness in relation to enamel and dentin. Baking soda toothpastes also may contain other ingredients, which can increase their stain removal effectiveness and, consequently, abrasivity.
Practical Implications
Even those formulations have abrasivity well within the safety limit regulatory agencies have established and, therefore, can be considered safe.
The success of an oral hygiene regimen depends primarily on its ability to properly remove food debris and biofilm formed on dental surfaces without disrupting the physical and chemical integrity of these surfaces. Many factors contribute to achieving this goal, including brushing technique and behavior, as well as specific toothpaste-related aspects. Toothpastes function as vehicles for active ingredients with therapeutic and cosmetic functions and inactive ones such as detergents, humectants, and flavors.
Among therapeutic agents, fluoride is probably the most important, with strong evidence on dental caries and dental erosion prevention; fluoride not only shifts the mineral equilibrium between the tooth and the surrounding environment toward the remineralization phase but also makes the tooth more resistant to demineralization. Other relevant constituents include antimicrobials to inhibit biofilm growth, tartar control compounds to inhibit calculus formation, and antisensitivity agents. Abrasive components are fundamental to removing dental surface stains, but they also improve toothbrushing efficiency. Historically, abrasives in the form of tooth powders or toothpastes have been used for dental cleaning purposes since ancient times. As previously reported,
ancient Egyptians scrubbed their teeth with a mixture of ox hoof ashes, burned eggshells, and pumice; later, their medical Ebers Papyrus reported a toothpaste made of ground pebbles, honey, verdigris, incense, and pulverized fruits. Ancient Greeks used a mixture of burned shells, coral, talc, salt, and honey, and ancient Romans used a blend of crushed bones and oyster shells plus powdered charcoal and bark. More recently, in the 18th century, reports indicated that the British included brick dust and crushed china in their tooth powder.
Over time, the selection and incorporation of abrasives in toothpastes have been optimized, and attention has been given to some specific abrasive systems. However, despite the considerable historical background, the large variety of toothpastes available with different abrasive properties requires a proper understanding of their clinical applications, as well as of potential effectiveness and safety concerns. In particular, the use of sodium bicarbonate (baking soda) has attracted attention because it has relatively low abrasivity. In this article, we review the effect of toothpaste abrasivity on tooth wear, evidencing some mechanisms of abrasive action; the existing evaluation methods used to determine toothpaste abrasivity; and the literature on the abrasive level of toothpastes containing baking soda, highlighting some of the clinical implications.
Dental Abrasives and Toothpaste Formulation
From a safety standpoint, toothpaste abrasives often are investigated for the potential deleterious effects they cause during toothbrushing. The ideal toothpaste should have enough abrasiveness to remove surface stains properly without damaging the tooth. Therefore, excessively abrasive materials can abrade the tooth surface away, resulting in undesirable tooth wear. Many factors define the degree of abrasivity of a given compound, including its hydration level; the size, hardness, shape, and concentration of its particles; source; purity; and how it has been treated physically and chemically.
and enamel and dentin mineralization level. Some of the dental abrasives currently used include hydrated silica, hydrated alumina, calcium carbonate, dicalcium phosphate dihydrate, calcium pyrophosphate, sodium metaphosphate, perlite, nanohydroxyapatite, diamond powder, and baking soda.
Ideally, abrasives should not interact chemically with the active ingredients in the toothpaste. For instance, a calcium carbonate–based toothpaste should not be formulated in conjunction with sodium fluoride because chemical binding may occur between the 2 components reducing the amount of available fluoride.
In that case, a more chemically stable fluoride compound such as sodium monofluorophosphate is preferable. From this perspective, hydrated silica abrasive and baking soda systems are advantageous because they are compatible with most active ingredients.
Because of the different properties of each of these abrasives and the intended clinical application of the toothpaste, the amount added in each formulation varies.
For instance, the most common abrasives, hydrated silica and calcium carbonate, may be used in the range of 8% to 20% weight per weight; alumina and perlite, however, are added in lower concentrations of 1% to 2% weight per weight, given their higher abrasivity in relation to enamel. In ideal circumstances, the toothpaste formulation should be abrasive enough only to aid properly in the removal of dental plaque and stains from dental surfaces.
This makes baking soda a particularly interesting option because it long has been regarded as 1 of the least, if not the least, abrasive material, allowing it to be added in much higher concentrations, often exceeding 50% weight per weight.
Tooth Wear and Toothpaste Abrasivity
Wear can be defined as the progressive loss of material because of relative motion between surfaces and contacting substances. Four main types of wear are relevant to dental surfaces; namely, abrasive, corrosive (caused by chemical agents), fatigue, and adhesive wear.
In abrasive wear, material is removed or displaced from a surface by the action of hard particles either moving between surfaces in relative movement or embedded in 1 of the surfaces in relative movement.
The latter arrangement describes 2-body abrasion, exemplified by bruxism, also called dental attrition. The former mechanism describes 3-body wear, when particles are interposed between the surfaces. Examples are wear resulting from toothbrushing and mastication. Corrosive wear occurs in situations in which the environment surrounding a sliding surface interacts chemically with it and reaction products are worn off from the surface.
In the oral cavity, corrosion best describes dental erosion or erosive tooth wear, which results from the tooth’s exposure to nonbacterial acids of intrinsic or extrinsic origin. Fatigue wear occurs by means of intermittent loading, resulting in repeated stressing and unstressing, which in time may lead to the formation and eventual break off of microcracks at or below the surface.
Fatigue has been the primary mechanism behind dental abfraction lesions. Adhesive wear refers to the process in which 2 surfaces contact each other under load, leading to the local welding at the tips of the major asperities of the surfaces.
Mechanical behavior and failure analysis of prosthetic retaining screws after long-term use in vivo, part 1: characterization of adhesive wear and structure of retaining screws.
Dental abrasive wear is of particular importance because it may result from toothbrushing, the main intervention universally performed to remove dental plaque and control caries and periodontal disease.
Lippert F, Arrageg MA, Eckert GJ, Hara AT. Interaction between toothpaste abrasivity and toothbrush filament stiffness on the development of erosive/abrasive lesions in vitro [published online ahead of print June 2, 2017]. Int Dent J. http://dx.doi.org/10.1111/idj.12305.
Lippert F, Arrageg MA, Eckert GJ, Hara AT. Interaction between toothpaste abrasivity and toothbrush filament stiffness on the development of erosive/abrasive lesions in vitro [published online ahead of print June 2, 2017]. Int Dent J. http://dx.doi.org/10.1111/idj.12305.
Mechanical tooth wear: the role of individual toothbrushing variables and toothpaste abrasivity.
in: Addy M. Embery G. Edgar W.M. Orchardson R. Tooth Wear and Sensitivity: Clinical Advances in Restorative Dentistry. Martin-Dunitz,
London, UK2000: 161-170
Simulation studies on lifetime enamel toothbrushing wear showed it to be minimal or clinically irrelevant, even if one considers enamel at its thinnest anatomic area (near the cervical area).
because of the frictional forces caused by abrasive particles. In 2-body abrasion, abrasive particles constitute an integral part of 1 surface that slides against the other. This sliding takes place during toothbrushing because part of the abrasive particles of the toothpaste are trapped under the toothbrush filament tips and scratch the surface.
In 3-body abrasion wear, abrasive particles are interposed between 2 surfaces in contact but are free to roll as well as to slide. Consequently, abrasive particles in the toothpaste constitute the third party interposed between the toothbrush and the tooth surface.
However, the dental wear magnitude may vary according to the pressure, duration, and frequency of brushing, as well as to the toothbrush bristle stiffness and tip geometry of the filaments.
Despite the functional importance of abrasives, there are few reports in which the investigators have compared the various abrasives that may be contained in toothpastes. In such studies, calcium carbonate has shown lower abrasivity than has hydrated silica,
Limited knowledge exists with regard to the influence of the abrasive particle size on tooth wear. Toothpastes with larger particles cause higher abrasion rates than those with small ones, on both sound
Investigators have hypothesized that there exists a threshold above which the wear rate changes in different ways (that is, increases at lower rates, becomes constant, or decreases), but it is likely that wear also depends on the type of abrasive used in the toothpaste formulation.
At least when hydrated silica is used, the content of the abrasives plays a role in the tissue loss of softened enamel.
Absence or high concentrations of hydrated silica particles produced less tissue loss than did formulations containing approximately 15% of such abrasives. These results may be because in high concentration, abrasive particles tend to agglomerate, preventing their rolling and therefore causing less abrasion. Investigators have found such nonproportional association between particle content and abrasivity in a study with results showing that increasing the level of particle concentration had only a minor effect on the friction coefficient when brushing was performed in the presence of diamond particles.
Mechanical tooth wear: the role of individual toothbrushing variables and toothpaste abrasivity.
in: Addy M. Embery G. Edgar W.M. Orchardson R. Tooth Wear and Sensitivity: Clinical Advances in Restorative Dentistry. Martin-Dunitz,
London, UK2000: 161-170
However, although there is evidence that brushing load influences abrasion of acid-softened enamel, investigators have speculated that it might be of minor importance for sound enamel.
Results of simulations in our laboratory (Sabrah and colleagues, unpublished data, September 2013) have shown that, depending on the toothpaste abrasivity, tooth wear may be maintained or increased because of brushing duration. When a low-abrasive toothpaste is used, increasing brushing duration does not play a role in the volume loss of teeth. In contrast, for high-abrasive toothpaste, tooth wear increases exponentially with the duration of brushing.
Although there are equivocal findings on how toothbrush stiffness affects abrasion,
Lippert F, Arrageg MA, Eckert GJ, Hara AT. Interaction between toothpaste abrasivity and toothbrush filament stiffness on the development of erosive/abrasive lesions in vitro [published online ahead of print June 2, 2017]. Int Dent J. http://dx.doi.org/10.1111/idj.12305.
In another laboratory simulation (Binsaleh and colleagues, unpublished data, November 2015), we observed that toothbrush bristle stiffness seems irrelevant when brushing with low-abrasive toothpaste. In addition, the choice of a soft, medium, or hard toothbrush is of lesser relevance to enamel than to dentin abrasion.
Lippert F, Arrageg MA, Eckert GJ, Hara AT. Interaction between toothpaste abrasivity and toothbrush filament stiffness on the development of erosive/abrasive lesions in vitro [published online ahead of print June 2, 2017]. Int Dent J. http://dx.doi.org/10.1111/idj.12305.
However, one should bear in mind that filament stiffness is likely to follow toothpaste abrasivity in terms of relevance in the abrasion process, even for dentin substrates.
Lippert F, Arrageg MA, Eckert GJ, Hara AT. Interaction between toothpaste abrasivity and toothbrush filament stiffness on the development of erosive/abrasive lesions in vitro [published online ahead of print June 2, 2017]. Int Dent J. http://dx.doi.org/10.1111/idj.12305.
In a laboratory simulation, however, flat-ended filaments entrain and trap fewer particles at the filament tip region than do filaments with rounded tips,
From the clinical perspective, the importance of dental wear diseases has increased considerably, especially with the increase in lifespan and tooth retention rates. Because teeth are kept for longer in the mouth, they become more susceptible to the development of dental wear. The abrasive level of toothpastes can affect this process and, despite the lack of clinical data in this area, should not be underestimated. Highly abrasive toothpastes can accelerate the progression rate of dental abrasion,
especially in the cervical area, where dentin root surfaces may be exposed owing to trauma or periodontal disease.
Therefore, there is great interest from clinicians and especially oral care product manufacturers in testing the abrasive levels of toothpastes. Although clinical evaluation of all the commercially available toothpastes is not feasible, laboratory tests may provide a good indication of their abrasive potential in relation to enamel and dentin. A radiation-based method developed more than 50 years ago
and known as radioactive (or relative) dentin abrasivity (RDA) and radioactive (or relative) enamel abrasivity (REA) remains the standard test adopted by the International Organization for Standardization ([ISO] standard 11609).
International Organization for Standardization. ISO 11609:2017—dentistry–dentifrices–requirements, test methods and marking. Available at: https://www.iso.org/standard/70956.html. Accessed September 11, 2017.
Briefly, this test measures the abrasivity level of dentifrices (RDA-REA value) in relation to a standard abrasive material, which is given an arbitrary value of 100 for RDA or 10 for REA. To obtain comparable RDA-REA data from different dentifrices, this test relies on the use of a specific reference material (a specially manufactured lot of either calcium pyrophosphate or hydrated silica materials) described in ISO 11609. The test simulates toothbrushing conditions by brushing dental specimens created from extracted human teeth (root dentin for RDA and enamel for REA), previously irradiated with a neutron flux sufficient to produce approximately 1 millicurie of phosphorus 32 beta radiation, in an automated toothbrushing machine. Slurries of test toothpastes or dental abrasives are prepared to mimic their mixture ratio with saliva in the mouth and are used for the brushing procedure. Depending on the abrasivity of the test toothpaste, more or less irradiated dental substrate is abraded away from the tooth and released into the test slurry. The radiation level of the slurry is measured with a standard method such as a scintillation counter and is used to calculate the abrasivity of the toothpaste, in relation to the standard abrasive material, tested in the exact same conditions.
The RDA-REA tests were developed with the aim of reducing and controlling for the variables and relevant behavioral, chemical, mechanical, and biological aspects, which invariably limits its clinical application.
As an example, brushing dental surfaces for 1,500 to 2,000 strokes continuously, as recommended by the ISO standard guideline to allow for proper sensitivity of the test, has limited clinical application. Similarly, the lack of saliva in the testing system affects the characteristics of the slurry, most importantly its acidity and viscosity control
However, the use of pooled fresh human saliva in this type of laboratory study is not practical, and the use of artificial saliva without all the components of natural saliva would have a substantially reduced effect. To address these and other clinical aspects, we recommend more elaborate in vitro and in situ models. Although there are several limitations that might affect clinical abrasive wear, RDA can be considered a useful tool for determining the relative abrasive level of dentifrices and abrasive powders.
The ISO 11609 also describes an alternative method for assessing abrasivity, which measures toothbrushing and toothpaste abrasive effects directly on the dental substrate by means of profilometry. It has the advantage of not using irradiated specimens, therefore not requiring access to a research reactor and regulatory clearance for isotope use. Results of studies in which the investigators compared the profilometry- and radiation-based methods
have shown that these methods have potential as alternatives, although further verification seems to be needed. Because of its historical seniority and the large body of research data, the RDA radiotracer method should take precedence over the profilometry-based method when a discrepancy between them arises.
Given the limitations imposed by the laboratory nature of the RDA-REA tests, one should use caution when extrapolating these results to the clinical situation. The oral care industry and some researchers arbitrarily have proposed a rank based on the toothpaste RDA values, suggesting that a high-abrasive toothpaste would be in the range of approximately 151 to 250, a moderate-abrasive toothpaste would be in the range of 70 to 150, and a low-abrasive toothpaste would be below 70.
Although this classification seems reasonable from a purely abrasive property perspective, there are myriad clinical factors that directly or indirectly can affect the clinical dental abrasive wear caused by the toothpaste. Additional modulating factors should be considered, such as the behavioral (frequency, pressure, length, and so on), chemical and physical (fluoride, detergents, pH, temperature, and so on), mechanical (abrasive, toothbrush), and biological (type and condition of the substrate, saliva, and dental pellicle), as well as any particular interaction among them.
Therefore, clinical validation still is needed. Nonetheless, it is important to pay attention to the fact that the ISO guideline previously mentioned sets the upper acceptable abrasivity limit of the toothpaste to be 250 (2.5 × the reference material) and 40 (4 × the reference material) for the RDA and REA values, respectively. Therefore, for safety reasons, investigators must consider these limits.
International Organization for Standardization. ISO 11609:2017—dentistry–dentifrices–requirements, test methods and marking. Available at: https://www.iso.org/standard/70956.html. Accessed September 11, 2017.
show that toothpastes containing baking soda, even when associated with cleaning and whitening claims, showed RDA ranging between 35 and 134 (for those for which data were available), which is well within the safety limit of 250 proposed by the ISO. Such RDA values may be ascribed to the fact that baking soda is 1 of the softest abrasives present in the most toothpastes.
The intrinsic hardness of baking soda is of the same magnitude as that of dentin and is less than that of enamel or of other commonly used dentifrice abrasives, such as calcium carbonate, anhydrous dicalcium phosphate, and calcium pyrophosphate.
Although studies still are needed, baking soda toothpastes may be appropriate for patients at high risk of developing dental erosion because these toothpastes have lower abrasive levels and can minimize abrasive wear on softened or eroded dental surfaces. The same applies for exposed root surfaces with dentin hypersensitivity symptoms. Baking soda is a low-abrasive substance and appropriate for dental resin composites and acrylic resin denture teeth because their hardness values are equivalent to or higher than that of dentin.
which one mistakenly could assume to be more abrasive than toothpastes containing this ingredient at lower concentrations (10%-20%, 35%-45%, or 50%-65%), despite an inverse relationship that seems to exist between baking soda content and toothpaste abrasivity.
However, baking soda toothpastes also may contain other abrasives to improve dental cleaning and whitening effectiveness, including hydrated silica, which invariably increases their abrasivity level. In this respect, 5 of 11 (Table)
formulations with no baking soda had RDA values that hypothetically would characterize higher-abrasive toothpastes (RDA, 181-245). In general, the increase in abrasive level of toothpastes resulted in improvement of stain removal effectiveness in a laboratory model (Table).
However, not enough data were available for better understanding of the effect of baking soda content and concentration on the cleaning ability of the toothpaste. The figure illustrates the lower abrasivity of a high-content (50%-65%) baking soda toothpaste (RDA, 35), after a laboratory toothbrushing simulation of 35,000 brushing strokes. No tooth wear was visible in the brushed cervical area, similar to findings in the teeth brushed with only water. In contrast, deep notched lesions were visible in the cervical area of teeth brushed with the higher abrasive toothpaste (RDA, 245), whereas less pronounced lesions were visible with brushing with the medium abrasive toothpaste (RDA, 132).
FigurePhotos of toothbrushing wear on cervical area with toothpastes of different abrasivity levels. Lower abrasivity: PeroxiCare (Arm & Hammer; radioactive [or relative] dentin abrasivity [RDA]: 35; 50%-65% baking soda). Medium abrasivity: Truly Radiant Clean & Fresh (Arm & Hammer; RDA: 132; 10%-20% baking soda). Higher abrasivity: Pro Health Advanced Whitening Power (Crest; RDA: 245; no baking soda). ∗After horizontal toothbrushing laboratory simulation of 35,000 double brushing strokes at 200-gram loading.
Besides its low-abrasive nature, baking soda has biological compatibility, acts as an acid-buffering agent, and possesses antibacterial activity in high concentrations.
Baking soda has a long history of safe use and is considered generally recognized as safe by the US Food and Drug Administration. The amounts of baking soda in toothpastes bear no clinical concern related to toxicity.
Baking soda is a safe toothpaste ingredient and has a low abrasive potential in relation to dental surfaces. The addition of other abrasives to toothpastes containing baking soda, mostly hydrated silica, seems to improve the toothpastes’ cleaning effectiveness and abrasive levels. Nonetheless, even these more abrasive formulations are well within the safety limit defined by regulatory agencies and, therefore, can be considered safe.
Mechanical behavior and failure analysis of prosthetic retaining screws after long-term use in vivo, part 1: characterization of adhesive wear and structure of retaining screws.
Lippert F, Arrageg MA, Eckert GJ, Hara AT. Interaction between toothpaste abrasivity and toothbrush filament stiffness on the development of erosive/abrasive lesions in vitro [published online ahead of print June 2, 2017]. Int Dent J. http://dx.doi.org/10.1111/idj.12305.
Mechanical tooth wear: the role of individual toothbrushing variables and toothpaste abrasivity.
in: Addy M. Embery G. Edgar W.M. Orchardson R. Tooth Wear and Sensitivity: Clinical Advances in Restorative Dentistry. Martin-Dunitz,
London, UK2000: 161-170
International Organization for Standardization. ISO 11609:2017—dentistry–dentifrices–requirements, test methods and marking. Available at: https://www.iso.org/standard/70956.html. Accessed September 11, 2017.
Dr. Hara is an associate professor, Department of Cariology, Operative Dentistry and Dental Public Health, Indiana University School of Dentistry, 415 Lansing St., Indianapolis, IN.
Dr. Turssi is an assistant professor, Division of Cariology and Restorative Dentistry, São Leopoldo Mandic Institute and Dental Research Center, Campinas, São Paulo, Brazil.
Article Info
Publication History
Publication of this article was sponsored by Church & Dwight Co., Inc. The articles in this issue have an accompanying online continuing education activity available at http://www.ADA.org/bakingsoda.
Footnotes
Disclosure. Drs. Hara and Turssi each received an honorarium from the American Dental Association.
We were surprised and disappointed that none of the articles in the November 2017 JADA supplement titled “Baking Soda Dentifrices and Oral Health” (Ciancio SG, ed. JADA. 2017;148[11 suppl]:S1-S34.) mentioned the 2- and 4-year results1-4 of the award-winning5 National Institutes of Health–funded randomized clinical trial of baking soda and sodium peroxide that were reported 30 years ago.
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