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Year : 2021  |  Volume : 12  |  Issue : 2  |  Page : 67-73

Assessing nonabrasive use of charcoal and its adsorptive microbial properties as a dentifrice

1 MSAE School, Fairfield, Iowa, USA
2 Foodchain ID, Fairfield, Iowa, USA

Date of Submission11-Dec-2020
Date of Decision05-Mar-2021
Date of Acceptance05-Mar-2021
Date of Web Publication30-Jun-2021

Correspondence Address:
Dr. Pradheep Chhalliyil
Ph.D, Sakthi Foundation, 129/1 Arcot Road, Virugambakkam, Chennai - 60092
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DOI: 10.4103/srmjrds.srmjrds_134_20

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Background: Root caries and teeth sensitivity are the two most common clinical conditions resulting from poor oral hygiene and incorrect use of dental cleaning aids and methodology. Aim: This study is to evaluate the safe nonabrasive use of charcoal as dentifrice along with its adsorptive properties on salivary bacteria, yeast, and polysaccharides in biofilm matrix. Materials and Methods: The Mohs Scale of Mineral Hardness was used to evaluate abrasiveness of charcoal by investigating the scratches it produces on rubbing steel, copper, and nickel plates. The adsorptive ability of charcoal to bind bacteria was measured using the quantitative polymerase chain reaction. Efficiency to bind polysaccharides by charcoal was performed by the spectrophotometric analysis. Results: The Mohs hardness test showed that charcoal caused less scratches on nickel plates. As nickel plates have a lower hardness index than enamel, this indicates that charcoal might not be significantly abrasive to enamel. Some toothpaste caused scratches on the nickel plates. The benefits of adsorptive nature of charcoal in normal oral hygiene procedure exceed possible side effects by far. Activated charcoal can be used as a safe dentifrice if used in nanometer sized powder form causing minimum abrasion and it can still disturb biofilm formation by adsorbing microbes, biomolecules, acids, and therefore, offer protection to enamel and helps in the prevention of caries. Conclusion: Using finely powdered charcoal with “Gum and teeth rubbing with Index Finger, followed by Tongue cleaning” (GIFT) method is nonabrasive and so safe like other commercial toothbrushes and toothpastes. Further studies investigating the safe use of charcoal are recommended.

Keywords: Abrasive, charcoal, GIFT, oral hygiene, safe dental cleaning, tooth brushing

How to cite this article:
Chhaliyil P, Schoel B, Chhalliyil P. Assessing nonabrasive use of charcoal and its adsorptive microbial properties as a dentifrice. SRM J Res Dent Sci 2021;12:67-73

How to cite this URL:
Chhaliyil P, Schoel B, Chhalliyil P. Assessing nonabrasive use of charcoal and its adsorptive microbial properties as a dentifrice. SRM J Res Dent Sci [serial online] 2021 [cited 2021 Jul 31];12:67-73. Available from:

  Introduction Top

Tooth brushing with fluoridated dentifrice for at least 2 min, twice daily, is approved as the best mechanical dental plaque control method since 1857.[1] However, tooth brushing can result in abrasion of tissues of the oral cavity if not done correctly.[2],[3]

Abrasion of teeth along with erosion and abfraction exposes the softer portions of the teeth, like dentin. This causes tooth sensitivity and mimics the symptoms of a cavity and is therefore termed as noncarious cervical lesions.[4] Root caries and teeth sensitivity are thus two most common clinical conditions resulting from poor oral hygiene and incorrect dental cleaning aids and methodology. Cleaning aids prevent caries by disrupting chondroitin-like sticky polysaccharides found in the matrix of dental biofilm. Charcoal effectively reduces caries by adsorbing to the sticky polysaccharide matrix in dental biofilm due to the strong Lifshitz-van der Waals forces between the microorganisms and activated carbon particles.[5]

Although charcoal has been known to effectively adsorb molecules for the industrial and clinical applications, it is still a taboo for dental cleaning due to its abrasiveness on dental enamel. The studies reporting the abrasive nature of charcoal could be due to the use of coarse charcoal husk.[6],[7]

However, charcoal-based products including charcoal toothbrushes are on the rise in several countries.[8] The newly introduced charcoal is in a finely powdered form at a nano size may reduce its abrasiveness but still retains or increases it absorptive nature.

Emerging new studies address the challenges of caries, teeth sensitivity and oral cleaning, including novel bedtime oral-cleaning technique, known as “Gum and teeth rubbing with Index Finger, followed by Tongue cleaning” (GIFT) method.[9] The GIFT method was initially designed as a control group, in which the participants were asked to use their flexible index finger to reach and rub all parts of their mouth, including their gums and teeth, without a toothbrush, toothpaste, or tooth powder. Interestingly, the authors found the group that used the GIFT method had significantly reduced bacterial counts as compared to other methods tested.[10] Using charcoal with the GIFT method improved its performance similar to tooth brushing with tongue cleaning[10] in reducing most of the harmful microbiota.

The aim of this study is to evaluate the safe nonabrasive use of charcoal as dentifrice along with its adsorptive properties on salivary bacteria, yeast, and polysaccharides in biofilm matrix.

To the best of our knowledge, there have been no such in vitro studies addressing this issue on the application of powdered charcoal using GIFT method for improving the oral hygiene.

  Materials and Methods Top

The study was designed in three levels

  1. Adsorption efficiency of activated charcoal and its ability to decrease bacteria and yeast counts was estimated using the real-time polymerase chain reaction (PCR) method.
  2. Molecular adsorption of biomolecules such as albumin and polysaccharides like chondroitin sulphate by activated charcoal followed by their decrease in levels was assessed using spectrophotometric analysis.
  3. Abrasive test using Mohs Scale of mineral hardiness principle was used to determine the abrasive nature of charcoal.

Charcoal preparation

100 g of rice husk was heated at 150°C–250°C in an iron vessel for 20–30 min until the color turned black. The surface area measurement of the charcoal was performed with TriStar II by micromeritics, based on the isothermal adsorption of nitrogen. A single-point or multipoint method was used to calculate the surface area using the Brunauer, Emmett, and Teller (BET) formula. The pore-size distribution was measured using nitrogen adsorption/desorption isotherms at liquid nitrogen temperature and relative pressures (P/Po) ranging from 0.05 to 1.0. The large uptake of nitrogen at low P/Po indicates filling of the micropores (<20 Angstrom). The surface area of charcoal particles was on an average 33 m2/g (BET) and pore size was 3.3 nM.

Commercial toothbrushes and toothpastes

Commercial toothpastes are recommended by dentists to be used as dentifrice with additional properties such as whiteners, reduce microbial counts, and prevent formation of biofilms. Therefore, these commercial toothpastes were compared with charcoal as positive controls in this study. Five different toothpastes including one charcoal toothpaste, one toothpowder were used in the study. These commercial toothpastes were used with charcoal because they had ingredients with antimicrobial activity such as stannous fluoride, glycerin, PEG, silica, pentasodium triphosphate, sodium lauryl sulfate, titanium dioxide, polyacrylic acid, cocamidopropyl betaine, and sodium saccharin. The ingredients of the tooth powder were calcium carbonate, sodium lauryl sulfate, flavor, sodium monoflurophosphate, and sodium saccharin. Preparations were done for this study for mimicking commercial charcoal tooth paste. 50%, 20%, and 5% of finely powdered charcoal powder were mixed with 20% glycerin and 2% xanthan gum. Three different commercial tooth brushes (soft, medium, and hard) were also used in this study as controls for comparing abrasiveness with charcoal used in GIFT method.

Bacteria and charcoal binding studies

0.5 ml human saliva was mixed 1:1 (vol/vol) with saline (0.9% NaCl) and then mixed it with 50 mg of either commercial fluorine containing tooth powder, untreated rice husk, rice-husk-activated charcoal, or left it untreated as a control. Then, the samples were allowed to rotate on a wheel for 60 min. The contents of the tubes were transferred into 2 ml vials containing 0.3 ml 60% sucrose solution and centrifuged for 2 min at 3000 rpm (method modified from Borkowski A, et al.).[11] This separates un-adsorbed bacteria (supernatant) from adsorbed bacteria (pelleted material). The supernatant and pelleted fractions were then subjected to DNA extraction (Magnetic Fast-ID DNA kit, Iowa, USA).[9],[10]

Yeast and charcoal binding studies

Bakers yeast at 10 mg per ml in phosphate-buffered saline (PBS) buffer was mixed with 50 mg of either commercial fluorine containing tooth powder, activated charcoal powder, or left it untreated as a control. Then, the samples were allowed to rotate on a wheel for 60 min. The contents of the tubes were transferred into 2 ml vials and centrifuged for 2 min at 3000 rpm (modified method from ref. Borkowski, Szala[11]). This separates un-adsorbed yeast (supernatant) from adsorbed yeast (pelleted material). The supernatant fractions were then subjected to DNA extraction (Magnetic Fast-ID DNA kit, Iowa, USA).

DNA extraction

The saliva tubes were homogenized with 0.1 mm zirconium beads (Research Products International Corp) using the BioSpec Mini-BeadBeater for 30 s at minimal 2500 rpm speed. DNA was extracted from the bacteria in the supernatant and pelleted fractions using the Magnetic Fast-ID DNA kit. 200 ng of pure DNA was used for Real Time PCR (qPCR) analysis.

Real-time polymerase chain reaction

For determination of the ratio of specific dental-damaging bacteria (DDB) quantitative real-time PCR (qPCR) was performed using Taqman universal bacterial primers and probes Nadkarni, Martin,[12] Aggregatibacter actinomycetemcomitans and Streptococcus mutans specific primers and probes Masunaga, Tsutae,[13] and TaqMan Universal PCR (Applied Biosystems) mastermix. The qPCR was performed using a BioRad CFX 96 with cycle conditions and primer-probe concentrations as previously described.[12],[13] The ratio of DDB to universal bacteria concentrations was calculated using BioRad CFX 96 software.

Molecular binding studies

PBS buffer containing Bovine Serum Albumin (BSA) or Chondroitin Sulfate (CS) at 1 mg/ml concentration were mixed with 50 mg of either commercial fluorine containing commercial tooth powder, activated charcoal powder, or left it untreated as a control. Then, the samples were allowed to rotate on a wheel for 60 min. The contents of the tubes were transferred into 2 ml vials and centrifuged for 2 min at 3000 rpm (modified method from ref. Borkowski, Szala[11]). This separates unadsorbed BSA and CS (supernatant) from the charcoal bound fraction. The concentration of the unadsorbed BSA and CS were measured using a spectrophotometer.

Abrasive test

The Mohs Scale of Mineral Hardness principle states that “hard object scratches soft object.” Using this principle, the ability of charcoal to scratch enamel was investigated by rubbing as comparison against steel, copper, and nickel plates 20 times Modified from Kodaka, Kobori.[14] Metal plates were purchased from Hongkong YEE Chen Tech and NapTags, MI, USA. Different brands of toothpastes were purchased from

  Results Top

Adsorption efficiency of activated charcoal

To evaluate the ability of the activated charcoal to bind and adsorb oral bacteria, saliva samples from subjects were mixed with either fluoride containing tooth powder, untreated rice husk, rice-husk activated charcoal, or left untreated as a control. After incubation with each of these materials, the amounts of total bacteria and DDB, such as A. actinomycetemcomitans that were bound (black) and unbound (white) to each of these agents were calculated.

The tooth powder adsorbed only a small amount of bacteria from the saliva (<20% of total bacteria and <5% of A. actinomycetemcomitans). The untreated rice husk bound a higher amount of bacteria (60% of total bacteria and 50% of A. actinomycetemcomitans). The highest amount of bacteria was significantly bound (P < 0.0005) by the activated charcoal (90% of total bacteria and 70% of A. actinomycetemcomitans).

Similarly, activated charcoal significantly adsorbed yeast (*P < 0.0001) compared to the tooth powder.

Molecular adsorption by activated charcoal

Biofilm matrix produced by bacteria consists of proteins and polysaccharides that help bacterial communities to adhere to each other (molecular glue) and provides protection and structure.[15] To examine the ability of nano charcoal to bind polysaccharides and protein, 10 mg/ml of nano charcoal or commercial tooth powder (T. PDR) were incubated with proteins such as BSA or CS at 1 mg/ml. Among these various agents, nano charcoal significantly adsorbed BSA and CS (P < 0.0005 and P < 0.001, respectively).

Abrasion test

Mohs Scale of Mineral Hardness principle states that “hard object scratches soft object.” Using this principle, the activated charcoal and other dentifrices were rubbed against steel, copper, and nickel plates for comparing their degree of abrasiveness. These metal plates were selected as having hardness properties higher or softer than dental enamel and dentin.[14] The dentin has roughly Mohs scale around 3.0 on the Mohs scale,[16] whereas enamel around 5.0.[17] Copper, nickel, and steel have a hardness on the Mohs scale around 2.5, 4.0, and 4.5, respectively.[18] Therefore, scratch resistance on copper may indicate that material is softer than dentin, while in steel may indicate softer than enamel.

The Mohs hardness test showed that the baby tooth has a hardness above 4.5 as it showed strong scratches (***) even on the steel plate. However, charcoal and toothbrushes were softer and caused less scratches on steel plates. On nickel plates, charcoal caused less scratches (**) indicating that it might be less abrasive to enamel. Some commercial toothpastes caused scratches on the nickel plates (*) indicating that it is mildly abrasive to dentin but safe on enamel [Table 1]. The charcoal in coarse form and finely powdered showed different levels of scratch resistance [Figure 1]. When finely powdered charcoal used in the study was mixed with glycerin and xanthan gum (mimick toothpaste) showed mild scratches on the metal plates.
Table 1: Abrasion testing-Mohs Scale of mineral hardness (scratch resistance)

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Figure 1: Illustrative photographs of the abrasive effects of different dentifrices and toothbrushes on metal plates. Activated charcoal and other dentifrices and toothbrushes were evaluated for their abrasive nature using the principle of the Mohs scale of mineral hardness for scratch resistance. Materials were rubbed against steel (1-4), and nickel plates (5-8) 20 times, and visible scratch evaluated

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Analysis of variance statistical analysis and Bonferroni adjustment for multiple comparisons was performed using Prism GraphPad (GraphPad Software, San Diego, California, USA). The error bars in the figures represent the standard error of the mean.

  Discussion Top

Charcoal's adsorptive properties are very popular both in the medical and industrial applications. However, in dentistry despite its high whitening action by removing stain on teeth and its adsorptive property in removing oral microbes, odor and acids, it is overlooked due to its abrasive nature. New studies on the metagenomic analysis of dental plaque and saliva samples of human subjects who used powdered charcoal show significant changes in the levels of damaging dental bacteria.[9],[10] The effectiveness of charcoal in oral hygiene led us to conduct this study to evaluate the abrasiveness of charcoal.

When powdered charcoal was mixed with human saliva that harbor millions of oral microbes, there was a significant decrease in the amount of bacteria in the saliva [Figure 2]. In other words, charcoal could adsorb significant amount of bacteria (P < 0.0005). However, this was not observed with the commercial tooth powder which had common ingredients such as calcium carbonate, synthetic flavors, sodium saccharin, and sodium lauryl sulfate that do not exhibit adsorptive properties. This trend was also seen in [Figure 3] in the ability of charcoal to significantly adsorb yeast which play a significant role in oral microbiota (P < 0.0001). Polysaccharides secreted by the dental biofilm allows other colonizing organisms to strongly adhere and interact with each other and mature into plaque.[15] Instead of using strong antimicrobials against biofilm and creating dysbiosis of healthy oral bacteria, a better approach would to adsorb these complex polysaccharides to prevent caries. Hence, we did a study to mimic the effect of charcoal in adsorbing BSA and complex carbohydrates like chondroitin sulphate. Charcoal showed a significant adsorption of these compounds [Figure 4].
Figure 2: Bacterial adsorption by activated charcoal. The percentage of total bacteria (a) and Aggregatibacter actinomycetemcomitans bacteria (b) bound, relative to the unbound bacteria remaining in the saliva. The error bars represent the standard error of mean values, and the P values were calculated using an Analysis of variance test (*P < 0.0005)

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Figure 3: Yeast adsorption by activated charcoal. The percentage of yeast remaining in the saliva and being adsorbed by tooth powder and activated charcoal powder. The error bars represent the standard error of mean values, and the P values were calculated using an Analysis of variance test (*P < 0.0001)

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Figure 4: Molecular adsorption by activated charcoal. The percentage of Bovine Serum Albumin (a) and Chondroitin Sulfate (b) at 1 mg/ml concentration bound to tooth powder (T. PDR) or charcoal, relative to the control. The error bars represent the standard error of mean values, and the P values were calculated using an analysis of variance test (*P < 0.0005, 0.001)

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The ability of charcoal to adsorb both microbial cells and their biomolecules used for interaction and communication might be one of the reasons of charcoal for long-term caries' prevention. This is very different from tooth brushing with toothpaste, where toothpaste does not have any adsorptive property like charcoal but only mechanically removes bacteria. Powell-Culling ford's survey found that participants using charcoal had less caries than those who used toothpaste and tooth brushing.[16] The activated charcoal has small, low-volume pores that increase the surface area available for adsorption,[17] and therefore, is used in many industrial applications to adsorb volatile and organic chemicals in filtration units.[18] It can adsorb chemical stains due to its efficient adsorbing properties.[19]

The nanopores in the charcoal also adsorb chemical compounds produced by microbes that cause malodor (halitosis). Charcoal can be used as a nontoxic alternative to chemical whiteners and fragrant compounds in toothpaste which may cause dysbiosis of healthy oral microbiota. The benefits of using charcoal with the GIFT method is because of its ability to adsorb stains, provide cosmetic benefits by whitening the teeth, as well as removing harmful oral bacteria.

S. mutans and other bacteria ferment carbohydrates into acids which drastically lower the pH. These acids de-mineralize and weaken the enamel structure of the teeth, ultimately leading to cavities.[20] Several studies have shown that charcoal is capable of adsorbing organic acids.[21],[22] Therefore, using charcoal in oral cleaning helps to protect the enamel by absorption of acids. All these results indicate the clinical significance of the adsorptive property of charcoal as a dentrifice.

Toothbrush is relatively ineffective at removing interproximal plaque which is important for gingival health and prevention of periodontal disease and caries. Not all the additional techniques such as floss, wood-sticks, rubber tips, and interdental brushes suit all to access the posterior dentition. Although flossing is the most widely used and American Dental Association approved method, its major drawback is the difficulty in ease of use and motivation.[23] Greater flexibility of a finger to reach all the areas of the teeth, gums, and inner cheeks that are not accessible to a toothbrush for disturbing the biofilm gives charcoal along with the GIFT method, additional benefits than the traditional tooth brushing. Since an undisturbed biofilm promotes plaque formation,[15] the use of charcoal with GIFT method is clinically important for oral health by disturbing biofilm formation and maturation.

Pathogenic bacteria, such as Streptococcus mitis, S. mutans, Streptococcus sanguis, and Streptococcus milleri,[24] and Candida adhere to plastic surfaces on the brush heads after short exposure times and a significant number of bacteria can be found in tooth brushes even after a day or week after brushing.[25],[26] A highly significant decrease in bacterial numbers was found after the use of a single-use and throw toothbrush[27]which is not economically feasible. Because contaminated toothbrushes can reintroduce microorganisms into the oral cavity and promote transmission of oral disease and oral infection,[26],[20] the charcoal used in GIFT method will help reduce these oral health challenges.

Charcoal used for tooth cleaning is commonly prepared by roasting rice husk until it turns black.[28] Most of the studies from rural villagers report the use of a coarse form of charcoal, which is very abrasive. The abrasive nature of charcoal could be due to the use of coarse charcoal husk.[7],[18] Many of the studies that report abrasiveness of charcoal also do not take into account how the individuals use it for cleaning teeth and how they rub and what force is used. The particle size, force applied on the charcoal, and the length of time used for rubbing on the teeth are factors that may not have been taken into account by the previous study groups.

However, several studies report that tooth brushing also causes abrasion if it is not done properly. Not only some commercial toothpastes containing abrasive chemicals that erode dental enamel[29],[30],[31],[32] but also the force and frequency of tooth brushing also causes wearing of tooth.[33],[34],[35] Apart from periodontal disease, gingival recession develops due to overzealous or improper tooth brushing. The cemento-enamel junction weakens the supporting periodontium leading to[36] and also abfraction, the loss of tooth substance in the cervical region.[37] Therefore, it cannot be concluded that activated charcoal when prepared and used in a proper manner is inferior to the use of certain commercial toothpastes and brushes.

Our study shows that the finely powdered form of charcoal is less abrasive or equivalent to the abrasive effect of some of the toothpastes and toothbrushes in the market. Using a powdered form of charcoal of nano size reduces its abrasiveness and increases its absorptive nature. This aspect is overlooked in studies involving charcoal being used as a dentifrice.

  Conclusion Top

This is the first study to show that powdered charcoal used with GIFT method is clinically important by effectively disturbing biofilm formation without being abrasive as a dentifrice. Further, the study highlights other added advantages of reaching to all the areas of the oral cavity without introducing carry over bacteria in cleaning aids and effectively reducing the microbial load through powdered charcoal's adsorptive properties. The only limitation of this study is the use of metal plates instead of tooth for checking abrasion, and therefore, future study is required to further confirm with patients.

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Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]


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