Preformulation Studies and Development of a Herbal Tooth Powder Using Coconut Shell as a Natural Abrasive

Dentifrices are widely used oral-care preparations designed to clean teeth, remove dental plaque, and maintain oral hygiene. Tooth powders remain popular in several regions due to their simplicity, cost-effectiveness, and ease of formulation. Abrasives constitute a key component of dentifrices, as they assist in mechanical removal of stains and debris; however, excessive abrasivity may result in enamel damage, emphasizing the need for controlled and standardized abrasive materials [1,2]. Growing interest in herbal and natural oral-care products has encouraged the exploration of plant-based and naturally derived excipients. Herbal dentifrices are preferred due to their perceived safety, biocompatibility, and reduced side effects compared to synthetic formulations [3]. Concurrently, pharmaceutical research is increasingly focused on sustainable development through utilization of agricultural waste as functional excipients. Coconut shell is a lignocellulosic agricultural by-product generated in large quantities during coconut processing. Traditionally considered waste, coconut shell possesses hardness and structural properties that make it suitable for conversion into fine abrasive powder [4]. The present study aims to conduct systematic preformulation studies and develop a herbal tooth powder formulation using coconut shell powder as a natural abrasive [5,6,7].

MATERIALS AND METHODS

MATERIALS

1. Coconut Shell Waste (Cocos nucifera L.)

– Collected from local coconut-processing vendors and fruit markets.

– Mature, dry shells selected for uniform hardness.

2. Herbal Ingredients (for dentifrice formulation)

Tulsi powder, Beetroot Powder, Ritha powder, Amla powder, Salt

3. Chemical Reagents

Distilled water, Hydrochloric acid (0.1 N), Sodium hydroxide (0.1 N), Ethanol, Reagents for limit test of arsenic & lead, Chemicals for moisture analysis

1. 2. Instruments and Equipment

Mechanical grinder & pulverizer, Sieve set (44#, 60#, 72#, 80#), Hot air oven, Moisture analyser, Analytical balance, Glassware: measuring cylinders, funnels, beakers, spatulas, jars will be required for this project.

METHODOLOGY OVERVIEW

2.3.1 Procurement of Coconut Shell Waste

• Coconut shell waste was collected from local fruit markets.
• Defective, fungal-infected, or immature shells were discarded.
• Shells were washed with water to remove dust and sun dried.

2.3.2 Reduction of Particle Size [8,9]

• Dried shells were crushed to coarse powder.
• Coarse pieces were ground using a mechanical grinder.
• Powder was sieved using mesh numbers #44, #60, #72, and #80.
• Four batches were prepared based on mesh size.

2.3.3 Pre-Formulation Studies

2.3.1 General Appearance: Physical examination like colour, odour, taste was done by organoleptic inspection.

2.3.2. Angle of Repose: Angle of repose was measured by fixed funnel method. The fixed funnel method uses a funnel being secured with its tip at a given height h above the graph paper which was placed on a flat horizontal surface, granules were carefully transferred through the funnel until the apex of the conical pile touching the tip of the funnel10,11].

???????????? ?=?????

Where ? = angle of repose

r = radius of the base of conical pile and

h= height of pile

Observation: Batch C (#72/#80 range) exhibited balanced flow and abrasivity, selected for formulation.

Figure 1: Angle of Repose

2.3.3 Bulk density: The bulk density is defined as the ratio of bulk mass of the granule to the bulk volume and it is denoted by Vb [12].

Bulk density=MVb

Where M = mass of the sample, Vb = bulk volume

2.3.4 Tapped Density: The tapped density is defined as the ratio of the weight of powder to the minimum volume occupied into the measuring cylinder. It is determined by placing a graduated cylinder containing a known mass of drug or formulation on a mechanical tapper apparatus which is being operated at fixed no. of taps until the powder bed reached to a minimum volume.

Tapped density=MVt

Where, M= weight of powder blend, Vt= tapped volume

2.3.5 Carr’s Index: Based upon the apparent bulk density and tapped density, the percent compressibility of the powder mixture was determined by the given formula [13-16].

Carr's index=Tapped density-Bulk densityTapped density X 100

2.3.6 Hausner’s ratio: It is and indirect index of ease of measuring of powder flow with lower Hausner’s ratio (≤ 1.25) indicating better flow properties than higher ones (≥ 1.25)

Hausner's ratio=Tapped densityBulk density

1. 1. 7. Solubility: Solubility of the powder was determined in distilled water and ethanol using the shake flask method. An accurately weighed quantity of the powder was mixed with a fixed volume of solvent and agitated continuously for 24 h at room temperature (25 ± 2°C) to attain equilibrium. The dispersion was allowed to stand, followed by filtration to remove undissolved particles. A measured volume of the clear filtrate was evaporated to dryness and the residue was weighed to determine the amount of dissolved material. Solubility was expressed in terms of weight per volume and classified according to standard pharmacopeial solubility descriptors [17-20].

3. Formulation of Tooth Powder

3.1 Selection of Optimized Batch

• Based on flow property, abrasivity, compatibility.
• Generally, 60# or 72# mesh provided best balance.

3.2 Tooth Powder Formulation Steps [21-25]

1. Weighing of ingredients accurately.
2. Coconut shell powder mixed with calcium carbonate.
3. Addition of clove, salt, charcoal, mentha extract.
4. Uniform mixing using geometric dilution.
5. Sieving to ensure uniform texture.
6. Packing in airtight containers.

RESULT & DISCUSSION

4.1 Procurement & Authentication

The Coconut shell waste was collected from local market; cleaned and dried. Other chemicals & excipients like tulsi, amla, beetroot, ritha, common salt procured from reputed local suppliers. The Authentication of Coconut shell was done by Dr. Vishal R. Marathe, Science College Nanded.

4.2 Reduction of Particle Size and Batch Preparation

The dried shell was pulverized using a high-speed grinder and passed through sieves #44, #60, #72, #80 and four batches (A–D) were labeled accordingly.

Table 1 – Particle Size Distribution

1. 3. Preformulation study:

The pre-formulation evaluation of the four coconut shell powder batches (A, B, C, and D) demonstrated that all samples possessed a uniform clear light-brown appearance, indicating consistency in drying, carbonization stability, and grinding conditions. This uniformity confirms that the raw material quality remained constant across batches and that no visible contamination, charring, or moisture-induced discoloration had occurred during processing. Bulk density and tapped density values showed noticeable variation among the batches. Batch C exhibited the highest bulk density (0.85 g/ml) and tapped density (1.09 g/ml), which reflects tighter packing characteristics and heavier particle compaction. This suggests that Batch C contains more uniformly ground, relatively finer particles that settle more densely. In contrast, Batch D showed the lowest bulk density (0.55 g/ml), indicating lighter, more porous particles. These differences illustrate the influence of mesh size on powder packing behavior.

Table 2 – Pre-formulation Results

Figure 2: Solubility in ethanol & water

The compressibility index (Carr’s Index) further supported these observations. Batch A showed a value of 7.24%, signifying excellent flow, while Batch B (13.33%) also exhibited acceptable flow behavior. However, Batch C (22.01%) and Batch D (25.67%) displayed moderate flow properties, consistent with their higher packing density and increased cohesiveness. Since Carr’s Index between 20–25% is considered a borderline range, Batch C stands out as having a balanced flow suitable for formulation after minor flow enhancers or optimized mixing. The Hausner’s ratio values also correspond with flow characteristics. Batch A (1.07) and Batch B (1.15) fall well within the ideal range (<1.25), while Batch C (1.228) remains acceptable. Batch D (1.34), however, exceeds the optimum threshold, indicating higher interparticle friction and poorer flow. This suggests that mesh size and moisture levels contributed to varied flow properties among batches and highlights Batch C as the most practically workable material among the higher-density powders. Angle of repose values showed the same trend. Batches A (28°48′) and B (24°00′) demonstrated good natural flow, whereas Batches C (35°12′) and D (38°46′) reflected reduced flowability, aligning with their compressibility and density behavior. Considering that a repose angle below 35° indicates acceptable flow, Batch C meets the requirement, while Batch D shows comparatively poorer flowability. Specific gravity results were proportional to density trends, with Batch C again showing the highest value (1.09), confirming that its particles are heavier and more compact. The ash values (9–12%) were within acceptable limits for plant-derived materials, confirming organic purity and minimal inorganic contamination. Moisture content across all batches remained below 25%, which is within acceptable stability limits, although Batch C and D showed slightly higher moisture (21–19%), possibly due to finer particle size retaining humidity. Solubility testing indicated that all batches were insoluble in water but slightly soluble in ethanol, which is expected for lignocellulosic materials. Insolubility in water supports stability and non-swelling behavior, desirable for abrasive dentifrice applications, while mild ethanol solubility suggests the presence of extractable organic components such as phenolics or lignin derivatives. Overall, the pre-formulation discussion identifies Batch C as the most suitable optimized batch, offering balanced density, acceptable flow, correct moisture level, and favorable physicochemical properties for the preparation of herbal tooth powder formulations.

4.4 Formulation of Tooth Powder

Four formulations (F1–F4) prepared using optimized batch C powder.

Figure 3: Formulation flowchart

Table 3 – Composition of Formulations (100 g Batch)

Mixing is done by geometric dilution; sieved #60 to ensure uniformity. Stored inside airtight containers.

Figure 4: Medicinal tooth powder batches formed