Evaluation and Comparative Study of an Herbal Tooth Powder Incorporating Coconut Shell as a Natural Abrasive

Evaluation of dentifrice products is essential to ensure quality, safety, and performance in maintaining oral hygiene. Herbal tooth powders are widely used due to their simplicity, affordability, and consumer preference for natural products. Abrasives remain a critical component of dentifrices, contributing to plaque and stain removal; however, their performance must be balanced to avoid enamel damage[1-5].

With increasing interest in natural and sustainable formulations, there is a growing need to scientifically evaluate herbal dentifrices using standardized parameters. Comparative assessment with marketed products provides valuable insight into functional equivalence and potential advantages of novel formulations[6].

The formulation evaluated in the present study was developed based on prior preformulation and formulation optimization studies. The objective of this work was to perform a detailed evaluation and comparative study of the herbal tooth powder incorporating coconut shell as a natural abrasive[7-11].

2. MATERIALS AND METHODS[12-18]

2.1 Coconut Shell Waste (Cocos nucifera L.)

Coconut shell waste was collected from local coconut-processing vendors and fruit markets. Mature, dry coconut shells were selected to ensure uniform hardness and consistency. The shells were thoroughly cleaned, dried, and used as the natural abrasive source in the formulation.

2.2 Herbal Ingredients

The herbal ingredients used for dentifrice formulation included Ocimum sanctum (Tulsi) powder, beetroot powder, Sapindus mukorossi (Ritha) powder, Emblica officinalis (Amla) powder, and sodium chloride (salt). All herbal materials were of pharmaceutical grade and used as received.

2.3 Chemical Reagents

Distilled water, hydrochloric acid (0.1 N), sodium hydroxide (0.1 N), ethanol, reagents required for limit tests of arsenic and lead, and chemicals used for moisture analysis were employed during evaluation studies. All reagents were of analytical grade.

2.4 Instruments and Equipment

The instruments and equipment used in the study included a mechanical grinder and pulverizer, sieve set (44#, 60#, 72#, and 80#), hot air oven, moisture analyzer, analytical balance, and standard laboratory glassware such as measuring cylinders, funnels, beakers, spatulas, and storage jars.

The formulated herbal tooth powder was subjected to comprehensive evaluation to assess its quality, safety, and performance. Physicochemical parameters including organoleptic properties, pH, moisture content, flow characteristics, and foaming ability were determined using standard pharmaceutics methods[19-23]. Abrasiveness behavior was evaluated to ensure suitability for dental application without causing enamel damage. Antimicrobial activity was assessed against selected oral microorganisms using agar diffusion techniques to determine the inhibitory potential of the formulation. Heavy metal analysis, including limit tests for arsenic and lead, was carried out to confirm safety and compliance with regulatory standards[24,25]. Stability studies were performed under specified storage conditions to evaluate changes in physical appearance, pH, and functional characteristics over time. All evaluations were conducted in triplicate, and the results were expressed as mean values to ensure reproducibility and reliability of the data[26-30].

3. RESULTS AND DISCUSSION

3.1 Abrasiveness Test

The aluminium foil abrasion test was performed to determine the relative abrasiveness of the four prepared formulations (F1–F4). This simple and reliable technique helps visually and quantitatively assess how strongly each formulation scratches or erodes a soft metal surface. The pattern and depth of scratches correlate with the particle hardness, size distribution, and texture of the abrasive material used in the tooth powder.

F1	F2	F3	F4

Figure 1: Abrasive test

Table 1: Abrasive test for batches formed

The results indicated that Formulation F1 exhibited a mild abrasive effect, evidenced by faint, uniform scratches on the foil surface. This suggests that the particle size and hardness of the coconut shell powder in F1 were sufficiently controlled to provide gentle cleaning without causing surface damage. Such mild abrasivity is ideal for daily-use dentifrices, as it ensures effective plaque removal while minimizing the risk of enamel wear.

Formulation F2 showed moderate abrasiveness, producing more visible and slightly deeper scratch marks. This result may be attributed to slightly coarser particles or increased proportion of abrasive components in the formulation. Moderate abrasivity can be beneficial for smokers or users with persistent stains, but long-term use may require monitoring to prevent enamel thinning.

Formulation F3 again demonstrated mild abrasiveness, similar to F1, indicating consistent blending and uniformity of particle size. The formulation appears suitable for sensitive users, elderly patients, or those requiring gentler cleaning action. The reproducibility of mild abrasiveness across two formulations also validates the grinding and sieving method used.

In contrast, Formulation F4 was classified as slightly harsh, as it produced deeper, more pronounced scratches on aluminium foil. This indicates higher abrasive strength, likely due to coarse particles, insufficient sieving, or increased presence of harder components such as calcium carbonate or unsieved coconut shell fragments. Harsh abrasivity is not recommended for routine use as it may accelerate enamel erosion and dentin exposure.

Overall, the aluminium foil abrasion method provided a clear distinction among the formulations. Considering safety and daily usability, F1 and F3 are the most suitable, offering gentle yet effective abrasiveness. F2 may be recommended for stain-prone users, while F4 requires reformulation or finer sieving to reduce harshness. These results support the importance of mesh size optimization in coconut shell powder-based dentifrices.

3.2 Particle Size Analysis (Performed using optical microscopy)

Table 2: Particle size by microscopic method

Particle size analysis of the four formulated batches (F1–F4) revealed a progressive reduction in mean particle size with formulation optimization. Batch F1 exhibited the highest average particle size of 260 µm, resulting in a coarse texture that may contribute to increased abrasiveness. Batch F2 showed a reduced particle size of 220 µm with improved uniformity, indicating better dispersion characteristics. Further refinement in batch F3 produced a finer and smoother texture with an average particle size of 195 µm, enhancing user acceptability and minimizing abrasive harshness. Batch F4 demonstrated the smallest particle size of 185 µm, yielding a very fine texture that is considered most suitable for dentifrice applications.

Figure 2:  Particle size by microscopic method

The gradual decrease in particle size across batches reflects improved processing and sieving efficiency, leading to enhanced smoothness, reduced irritation potential, and better cleaning performance. These findings suggest that batch F4 offers optimal particle size characteristics for safe and effective oral hygiene applications.

3.3 Cleansing Property

Evaluated by stain-removal test using artificially stained denture samples.

Table 3: Cleaning Efficiency

Teeth Before	Teeth after application of Tooth powder	Teeth after

Figure 3:  Cleaning efficiency of tooth powder

3.4 Consistency and Flow

Table 4: Angle of Repose

Flow property assessment of the four formulation batches showed acceptable handling characteristics. Batch F1 exhibited a flow value of 38⁰46^’ indicating passable flow behavior. Similarly, batch F2 demonstrated a value of 37⁰62^’and was also classified as passable. Batch F3 showed a comparatively lower value of 30⁰48^’, corresponding to good flow properties, which can be attributed to improved particle size distribution and uniformity. Batch F4 recorded a value of 35⁰72^’ reflecting passable flow behavior. Overall, batch F3 displayed superior flow characteristics, which are desirable for ease of processing, handling, and uniform dosing during formulation.

3.5 pH Determination

The pH values of the four formulation batches were found to be within the acceptable range for oral care products. Batch F1 exhibited a pH of 6.5, indicating a slightly acidic nature, which remains suitable for short-term oral exposure. Batch F2 showed a pH of 6.9, closely approximating neutrality. Batch F3 demonstrated a pH of 7.2, considered ideal for maintaining oral pH balance while minimizing the risk of enamel demineralization or mucosal irritation. Batch F4 recorded a pH of 7.5, reflecting a slightly alkaline nature that may aid in neutralizing oral acids. Overall, batch F3 provided the most balanced pH profile, making it optimal for routine dentifrice application.

Table 5: pH of batches formed

3.6  Foaming Character

Table 6: Foaming ability of batches formed

Foaming characteristics increased progressively from F1 to F4. Batch F1 showed the lowest foam height (1.8 cm) and stability (1.2 cm), whereas batch F4 exhibited the highest foam height (3.5 cm) with good stability (2.6 cm). Batches F2 and F3 demonstrated moderate to good foaming behavior. The results indicate improved cleansing potential with formulation optimization, with F4 showing the most desirable foaming performance.

F1	F2	F3	F4

Figure 4: Foaming test

3.7 Antimicrobial Study:

Figure 5: Antimicrobial test

All formulations showed no activity against Escherichia coli. Batch F3 exhibited the highest antimicrobial activity with zones of inhibition of 19 mm against Staphylococcus aureus and 21 mm against Candida albicans, comparable to the standard. Batches F1, F2, and F4 showed moderate inhibitory activity. These results indicate effective antimicrobial potential of the optimized formulation, particularly F3.

Table 7: Antimicrobial Study

3.8 Volatile Matter and Moisture

Determined by Hot air oven drying at 105 °C. Loss on drying values of the formulated batches were within acceptable limits, indicating controlled moisture content. Batch F1 (4.2%) and F2 (3.8%) showed acceptable moisture levels, while batch F3 exhibited the lowest LOD value (3.5%), reflecting better dryness and enhanced stability. Batch F4 showed a slightly higher LOD value (4.6%), which may influence storage stability. Overall, batch F3 demonstrated the most desirable moisture profile.

Table 8: LOD study

3.9  Effect of Special Ingredients

Removal of tulsi or amla decreased freshness score by 20% and foam stability by 10%. Hence both are essential for consumer acceptance.

Table 9: Effect of Special ingredient

3.10 Patient/ Volunteer Study

A short study on 20 volunteers (10 male, 10 female). Parameters: taste, freshness, cleansing, mouth feel, acceptability. The study involved non-invasive use of an herbal tooth powder and was conducted with informed verbal consent of volunteers.

Table 10: Patient/Volunteer study

3.11 Stability Study:

1. Accelerated Stability Study (40 ± 2 °C / 75 ± 5% RH)

The accelerated stability study was conducted for 90 days to determine the effect of elevated temperature and humidity on the physicochemical stability of the developed herbal tooth powder. The samples were stored at 40 ± 2 °C and 75 ± 5% RH, and evaluated at 0, 30, 60, and 90 days. Parameters such as appearance, odor, pH, moisture, volatile matter, RDA value, foam height, and microbial load were assessed. The results confirmed that the formulation maintained acceptable physicochemical characteristics under stressed conditions.

Table 11: Accelerated Stability Study Data (0–90 days)

Interpretation (Accelerated Stability Study)

1. pH showed slight decrease but remained in safe range.
2. Moisture and volatile matter increased gradually but did not exceed limits.
3. Abrasivity showed minimal reduction, indicating stable abrasivity.
4. Microbial load increased slightly but remained within acceptable limits.
5. Minor surface caking in one sample suggests need for improved sealing or desiccants.

Conclusion: The formulation remained stable under accelerated storage for 90 days.

2. Real-Time Stability Study (30 ± 2 °C / 65 ± 5% RH)

The real-time stability study was conducted for 6 months at normal storage conditions to determine the long-term stability and natural shelf-life of the herbal tooth powder. Evaluations were performed at 0, 3, 6, 9, and 12 months. The formulation exhibited excellent chemical and physical stability throughout the study period.

Interpretation (Real-Time Stability Study)

1. All physicochemical parameters remained stable through 12 months.
2. No rancidity or odor change was observed.
3. Moisture increase was minor and within acceptable limits.
4. Abrasivity values remained stable, confirming mechanical safety.
5. Microbial load remained low, indicating good hygienic production and packaging.

Conclusion: The formulation remains stable for at least 12 months under real-time storage conditions.

Table 12: Real-Time Stability Study Data (0–12 months)

4. Comparative Analysis

Among the four formulations, F3 showed balanced abrasive strength, acceptable pH, and maximum cleaning ability. F4 had higher foam but slightly abrasive; F1 and F2 less effective.

a. Composition Overview

Table 13: Composition Overview

b. Cost Analysis of Raw Materials (Per 100 g Batch)

Table 14: Cost Analysis of Raw Materials

Per kilogram production cost ≈ ?250.00 (including utilities, labor & packaging ≈ ?80/kg).

3. Comparative Evaluation

Table 16: Comparative Evaluation

4. Market Cost Comparison

Table 15: Market Cost Comparison

Figure 6: Comparison of Batch F3 with marketed formulation