Gradient hardness toothpaste based on oyster shell and calcined oyster shell and preparation method thereof

Abstract

The application discloses gradient hardness toothpaste based on oyster shell and calcined oyster shell compounding and a preparation method thereof, and belongs to the technical field of toothpaste preparation. Natural oyster shells are used as raw materials to prepare oyster shell powder with sharp micro cross sections and Mohs hardness of 4.0-4.5, and calcined oyster shell powder with obtuse micro cross sections and Mohs hardness of 2.5-3.0 prepared by calcining at 800-1000 DEG C. The two are compounded as a composite friction agent in different mass ratios to build gradient hardness toothpaste suitable for different groups of people. The gradient hardness toothpaste based on oyster shell and calcined oyster shell compounding and the preparation method thereof can accurately control the friction and wear properties of toothpaste, match the oral cleaning needs of all age groups, realize high-value utilization of oyster shell waste, and are simple and controllable in process and easy to industrialize.

Description

Technical Field

[0001] This invention relates to the field of toothpaste preparation technology, and in particular to a gradient hardness toothpaste based on a compound of oyster shell and calcined oyster shell, and its preparation method. Background Technology

[0002] Toothpaste is a core product in daily oral care for the general public. Its core cleaning function is mainly achieved through abrasives. Abrasives remove plaque, extrinsic stains, and food debris through mechanical friction with the tooth surface. They are the core components that determine the cleaning performance and safety of toothpaste. Currently, commercially available toothpastes generally use calcium carbonate, hydrated silica, and aluminum hydroxide as mainstream abrasives. While these materials can achieve basic cleaning functions, there are irreconcilable technical contradictions in practical applications: to improve the cleaning power against stubborn stains, the hardness or amount of abrasive needs to be increased, which can easily cause irreversible wear on tooth enamel. This is especially true for children whose enamel is not yet fully developed, the elderly with physiological wear of dentin, and people with sensitive gums. Long-term use of highly abrasive toothpaste can exacerbate enamel damage and lead to oral problems such as dentin hypersensitivity and pulpitis. On the other hand, reducing the hardness of the abrasive to reduce wear will significantly weaken the cleaning effect and fail to meet the cleaning needs of young adults for extrinsic stains such as tobacco stains and tea stains.

[0003] At the same time, existing abrasive products struggle to achieve precise, linear gradient control of cleaning power. Conventional calcium carbonate abrasives have a fixed hardness, making it impossible to continuously adjust abrasion performance through formulation adjustments. While hydrated silica can have its hardness adjusted through the manufacturing process, its production costs are high and the process is complex. Furthermore, it cannot achieve linear and controllable adjustment of abrasion performance through simple powder compounding, making it difficult to develop a series of toothpaste products with strong adaptability based on the oral physiological characteristics and cleaning needs of different populations.

[0004] Oysters are one of the core species in my country's marine aquaculture. The aquaculture process generates a large amount of solid waste from oyster shells, whose main component is calcium carbonate, accounting for over 90%, making it a natural calcium carbonate biomass resource. Currently, the resource utilization rate of oyster shells is extremely low. Large quantities of waste oyster shells are randomly dumped or landfilled, causing not only resource waste but also environmental problems such as soil and water pollution. While oyster shell powder is currently used as an abrasive in toothpaste, this is all direct application of a single powder: either uncalcined raw oyster shell powder is used, which has a high Mohs hardness and a sharp-angled microscopic cross-section, resulting in strong cleaning power but also significant abrasion, posing a risk of enamel damage with long-term use; or calcined oyster shell powder is used, which, while reducing hardness, has insufficient cleaning power to meet daily deep cleaning needs.

[0005] Therefore, there is an urgent need to provide a toothpaste and its preparation method that can achieve linear and gradient control of the tribological properties of toothpaste by constructing a composite abrasive system through precise compounding. Summary of the Invention

[0006] The purpose of this invention is to provide a graded hardness toothpaste based on a compound of oyster shell and calcined oyster shell, and a method for preparing the same, in order to solve the above-mentioned problems.

[0007] This invention provides a gradient hardness toothpaste based on a compound of oyster shell and calcined oyster shell, comprising a composite abrasive and excipients. The composite abrasive is composed of oyster shell powder and calcined oyster shell powder. The oyster shell powder is natural oyster shell powder obtained by washing, crushing, and grading without calcination, and its microscopic cross-section is acute-angled, with a Mohs hardness of 4.0 to 4.5. The calcined oyster shell powder is natural oyster shell powder obtained by calcining at 800℃ to 1000℃ for 1 to 3 hours, followed by cooling, crushing, and grading, and its microscopic cross-section is obtuse-angled, with a Mohs hardness of 2.5 to 3.0.

[0008] Preferably, the mass ratio of oyster shell powder to calcined oyster shell powder is (0-100):(100-0); wherein, a mass ratio of 0:100-30:70 yields a first-gradient hardness toothpaste, i.e., a mild toothpaste suitable for children and the elderly; a mass ratio of 50:50-80:20 yields a second-gradient hardness toothpaste, i.e., a daily cleaning toothpaste suitable for young adults; and a mass ratio of 90:10-100:0 yields a third-gradient hardness toothpaste, i.e., a deep-cleaning toothpaste.

[0009] Preferably, the particle size of both the oyster shell powder and the calcined oyster shell powder is 5μm to 20μm.

[0010] Preferably, the mass of the composite friction agent accounts for 20% to 40% of the total mass of the composite friction agent and auxiliary materials.

[0011] Preferably, the first gradient hardness toothpaste has a radioactive dentin abrasion RDA value of 45-55, the second gradient hardness toothpaste has a radioactive dentin abrasion RDA value of 85-95, and the third gradient hardness toothpaste has a radioactive dentin abrasion RDA value of 115-125.

[0012] Preferably, the excipients include a humectant, a thickener, a foaming agent, a sweetener, a flavoring, and deionized water; based on the total mass of the composite abrasive and the excipients, the mass percentages of each excipient are: humectant 20%–45%, thickener 0.5%–2%, foaming agent 1%–3%, sweetener 0.1%–0.3%, flavoring 0.5%–1.5%, with the remainder being deionized water. Among the excipients, the humectant can be one or more of the following commonly used in toothpaste: sorbitol, glycerin, propylene glycol, and polyethylene glycol; the thickener can be one or more of the following: sodium carboxymethyl cellulose, xanthan gum, hydroxyethyl cellulose, and carbomer; the foaming agent can be one or more of the following: sodium lauryl sulfate and sodium lauroyl sarcosinate; the sweetener can be one or more of the following: sodium saccharin, steviol glycosides, and xylitol; and the flavoring can be conventional oral care flavorings such as toothpaste-grade peppermint flavoring and fruit flavoring.

[0013] Preferably, the excipients further include sodium pyrophosphate at a mass ratio of 0.3% to 0.8%.

[0014] A method for preparing a graded hardness toothpaste based on a compound of oyster shell and calcined oyster shell, as described above, is provided, comprising the following steps: (1) Preparation of oyster shell powder: After cleaning, removing impurities and drying natural oyster shells, they are crushed and graded to obtain oyster shell powder with an acute-angled micro-section and a Mohs hardness of 4.0 to 4.5, which is used as a high-hardness cleaning functional unit. (2) Preparation of calcined oyster shell powder: After cleaning, removing impurities and drying natural oyster shells, they are calcined at 800℃~1000℃ for 1h~3h, and after natural cooling, they are crushed and graded to obtain calcined oyster shell powder with a blunt cross-section and a Mohs hardness of 2.5~3.0, which serves as a low hardness buffer protection unit. (3) Gradient paste preparation and filling: According to the preset mass ratio corresponding to the target gradient hardness, accurately weigh the oyster shell powder obtained in step (1) and the calcined oyster shell powder obtained in step (2), mix them evenly to obtain the target composite abrasive; mix the composite abrasive with the excipients and deionized water, and fill it after paste preparation, grinding, vacuum degassing to obtain the toothpaste with the corresponding gradient hardness.

[0015] Preferably, in step (2), the calcination temperature is 900℃ and the calcination time is 2h.

[0016] Preferably, in steps (1) and (2), the grading process is carried out by air jet milling; in step (3), when making the ointment, the composite abrasive agent, moisturizer, and deionized water are first mixed evenly, then the thickener is added and stirred until completely dispersed, and then the remaining excipients are added and stirred evenly.

[0017] Therefore, the present invention employs the above-mentioned gradient hardness toothpaste based on a compound of oyster shell and calcined oyster shell and its preparation method, which has the following beneficial effects: (1) Natural oyster shell powder and calcined oyster shell powder with different hardness and structural characteristics were prepared through a specific calcination process. The two powders were compounded as a composite abrasive to achieve a synergistic effect of cleaning and protection. The acute-angled structure of the natural oyster shell powder provides efficient cutting force, which can effectively remove dental plaque and stubborn extrinsic stains on the tooth surface and ensure cleaning effect. The obtuse-angled structure of the calcined oyster shell powder plays a buffering and polishing role during the friction process, which greatly reduces the scratches and wear on the enamel. By adjusting the compound mass ratio of the two powders, the linear and continuous control of the radioactive dentin abrasion (RDA) value of the toothpaste can be achieved, and a gradient product system from low abrasion to high cleaning can be constructed to accurately match the oral physiological characteristics and cleaning needs of different groups of people.

[0018] (2) Using waste oyster shells generated during aquaculture as the sole source of friction agent raw materials, it replaces traditional chemically synthesized friction agent products. This not only solves the environmental pollution problem caused by the random dumping and landfilling of waste oyster shells, but also realizes the reduction and resource utilization of solid waste. Furthermore, it significantly reduces the raw material cost of toothpaste friction agents, which is in line with the industrial concept of green environmental protection and sustainable development, and has significant environmental, economic and social benefits.

[0019] (3) Through the gradient formula design, it can cover the oral cleaning needs of all ages and all scenarios. From gentle cleaning for children and the elderly to daily care for healthy adults, and short-term deep cleaning for smokers and tea drinkers, it can be accurately adapted through simple ratio adjustment. There is no need to change the overall formula system. The product has strong extensibility and can meet the diversified needs of different consumer groups. It has strong market competitiveness and broad application prospects.

[0020] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0021] To better understand the above technical solutions, a detailed description of the specific implementation methods will be provided below. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0023] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0024] Example 1 This embodiment corresponds to the first-gradient hardness toothpaste. The mass ratio of oyster shell powder to calcined oyster shell powder is 0:100. The specific formula is as follows: 30 parts calcined oyster shell powder, 0 parts oyster shell powder, 20 parts sorbitol, 10 parts glycerin, 1 part sodium carboxymethyl cellulose, 2 parts sodium dodecyl sulfate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the balance of deionized water.

[0025] Preparation method: (1) Weigh calcined oyster shell powder, sorbitol, glycerin and deionized water according to the formula ratio, put them in the ointment making kettle and stir to mix evenly to obtain a premixed liquid; (2) Add sodium carboxymethyl cellulose to the premixed liquid and stir at high speed until completely dispersed and the system is uniform without lumps; (3) Continue to add sodium dodecyl sulfate, sodium saccharin and peppermint flavor to the system and stir to mix for 30 min until completely uniform; (4) After grinding the uniformly mixed ointment with a colloid mill, degas it under a vacuum of -0.09 MPa for 20 min, fill and seal to obtain the product.

[0026] Example 2 This embodiment corresponds to the first-gradient hardness toothpaste. The mass ratio of oyster shell powder to calcined oyster shell powder is 30:70. The specific formula is as follows: 21 parts calcined oyster shell powder, 9 parts oyster shell powder, 25 parts sorbitol, 10 parts glycerin, 1 part sodium carboxymethyl cellulose, 2 parts sodium dodecyl sulfate, 0.2 parts sodium saccharin, 1 part fruit flavoring, and the balance being deionized water.

[0027] The preparation method is completely consistent with that in Example 1.

[0028] Example 3 This embodiment corresponds to the second-gradient hardness toothpaste. The mass ratio of oyster shell powder to calcined oyster shell powder is 50:50. The specific formula is as follows: 15 parts calcined oyster shell powder, 15 parts oyster shell powder, 25 parts sorbitol, 10 parts glycerin, 1.2 parts sodium carboxymethyl cellulose, 2.2 parts sodium dodecyl sulfate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the balance being deionized water.

[0029] The preparation method is completely consistent with that in Example 1.

[0030] Example 4 This embodiment corresponds to the second-gradient hardness toothpaste. The mass ratio of oyster shell powder to calcined oyster shell powder is 80:20. The specific formula is as follows: 6 parts calcined oyster shell powder, 24 parts oyster shell powder, 25 parts sorbitol, 10 parts glycerin, 1.2 parts sodium carboxymethyl cellulose, 2.2 parts sodium dodecyl sulfate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the balance being deionized water.

[0031] The preparation method is completely consistent with that in Example 1.

[0032] Example 5 This embodiment corresponds to a toothpaste with a third-gradient hardness. The mass ratio of oyster shell powder to calcined oyster shell powder is 90:10. An auxiliary stain remover is also added. The specific formula is as follows: 3 parts calcined oyster shell powder, 27 parts oyster shell powder, 20 parts sorbitol, 10 parts glycerin, 1.2 parts sodium carboxymethyl cellulose, 2.5 parts sodium dodecyl sulfate, 0.5 parts sodium pyrophosphate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the balance being deionized water.

[0033] The only difference between the preparation method and Example 1 is that sodium pyrophosphate is added simultaneously in step (3), while the other steps are completely the same.

[0034] Example 6 This embodiment corresponds to a toothpaste with a third-gradient hardness. The mass ratio of oyster shell powder to calcined oyster shell powder is 100:0. The specific formula is as follows: 0 parts calcined oyster shell powder, 30 parts oyster shell powder, 20 parts sorbitol, 10 parts glycerin, 1.2 parts sodium carboxymethyl cellulose, 2.5 parts sodium dodecyl sulfate, 0.5 parts sodium pyrophosphate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the balance being deionized water.

[0035] The preparation method is completely consistent with that in Example 5.

[0036] Example 7 In this embodiment, the composite friction agent accounts for 20% of the total mass, and the mass ratio of oyster shell powder to calcined oyster shell powder is 50:50. The specific formula is as follows: 10 parts calcined oyster shell powder, 10 parts oyster shell powder, 28 parts sorbitol, 12 parts glycerin, 1.2 parts sodium carboxymethyl cellulose, 2.2 parts sodium dodecyl sulfate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the remainder deionized water.

[0037] The preparation method is completely consistent with that in Example 1.

[0038] Example 8 In this embodiment, the composite friction agent accounts for 40% of the total mass, and the mass ratio of oyster shell powder to calcined oyster shell powder is 50:50. The specific formula is as follows: 20 parts calcined oyster shell powder, 20 parts oyster shell powder, 22 parts sorbitol, 8 parts glycerin, 1.2 parts sodium carboxymethyl cellulose, 2.2 parts sodium dodecyl sulfate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the remainder deionized water.

[0039] The preparation method is completely consistent with that in Example 1.

[0040] In all the formulas in Examples 1-8, all "parts" refer to parts by weight, with the total weight calculated as 100 parts, and deionized water is used to make up the balance.

[0041] The general preparation method of the core powder used in Examples 1-8 is as follows: Oyster shell powder: Take natural seawater cultured oyster shells, rinse with clean water to remove mud, sand and meat residue, ultrasonically clean twice with deionized water, and dry with forced air at 60℃ to constant weight; after coarse crushing, use air jet mill for graded pulverization to control the powder particle size to 5μm~20μm, to obtain oyster shell powder with acute-angled micro-section and Mohs hardness of 4.0~4.5.

[0042] Calcined oyster shell powder: Take oyster shells from the same batch that have been cleaned and dried, place them in a muffle furnace at 800℃~1000℃ for 1h~3h, and after naturally cooling to room temperature, crush them by coarse crushing and air jet milling to control the particle size of the powder to 5μm~20μm, so as to obtain calcined oyster shell powder with a blunt-angled micro-section and a Mohs hardness of 2.5~3.0; the preferred calcination process is to keep it at 900℃ for 2h, which can stably prepare powder with uniform morphology and consistent properties.

[0043] Comparative Example 1 This comparative example uses a commonly used formula in mainstream commercial toothpastes, and the total amount of abrasive added is consistent with that in Example 3, except that the composite abrasive is replaced with commercially available ordinary light calcium carbonate. The specific formula is as follows: 30 parts light calcium carbonate, 25 parts sorbitol, 10 parts glycerin, 1.2 parts sodium carboxymethyl cellulose, 2.2 parts sodium dodecyl sulfate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the balance of deionized water.

[0044] The preparation method is completely consistent with that in Example 1.

[0045] Comparative Example 2 This comparative example only adjusts the particle size of the oyster shell powder; the rest of the formulation and preparation method are completely consistent with Example 6, as follows: Oyster shell powder preparation: Natural oyster shells from the same batch as in Example 6 were taken, and after the same washing, drying, and coarse crushing treatment, they were graded and pulverized using an air jet mill to control the powder particle size to 30μm~50μm, thus obtaining ultra-large particle size oyster shell powder. Formulation: 30 parts ultra-large particle size oyster shell powder, 20 parts sorbitol, 10 parts glycerin, 1.2 parts sodium carboxymethyl cellulose, 2.5 parts sodium dodecyl sulfate, 0.5 parts sodium pyrophosphate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the balance being deionized water.

[0046] The preparation method is completely consistent with that in Example 6.

[0047] Comparative Example 3 This comparative example only adjusts the calcination process of the calcined oyster shell powder; the rest of the formula and preparation method are completely consistent with Example 1, as follows: Preparation of calcined oyster shell powder: Take the same batch of natural oyster shells as in Example 1, and after the same cleaning and drying treatment, calcine them in a muffle furnace at 600℃ for 2 hours. After naturally cooling to room temperature, coarsely crush and graded by air jet milling to control the powder particle size to 5μm~20μm, thus obtaining non-standard calcined oyster shell powder (the powder has a Mohs hardness of 3.8 and an acute-angled microscopic cross-section). Formula: 30 parts non-standard calcined oyster shell powder, 20 parts sorbitol, 10 parts glycerin, 1 part sodium carboxymethyl cellulose, 2 parts sodium dodecyl sulfate, 0.2 parts sodium saccharin, 1 part peppermint flavoring, and the balance being deionized water.

[0048] The preparation method is completely consistent with that in Example 1.

[0049] Experimental Example 1 Tribological abrasion performance (RDA value) test of toothpaste with different formulation ratios: The experimental samples were the toothpaste samples prepared in Examples 1-6; Test method: The radioactive dentin abrasion test method was adopted. Under standardized brushing conditions, the abrasion amount of each toothpaste sample on human dentin blocks was measured using a brushing tester. The RDA value was calculated based on a standard reference toothpaste.

[0050] The test results are shown in Table 1.

[0051] Table 1. RDA value test results of toothpastes from different embodiments

[0052] Results analysis: As the proportion of oyster shell powder in the compound abrasive increases, the RDA value of the toothpaste shows a linear upward trend. The RDA value adjustment of the three graded toothpastes can achieve the goal of linear and gradient adjustment of the toothpaste's abrasive properties, precisely matching the oral cleaning and enamel protection needs of different groups of people.

[0053] Experiment Example 2 Cleaning effect versus enamel wear comparison test: Experimental samples: toothpaste samples prepared in Examples 1, 3, and 6, and Comparative Examples 1, 2, and 3; Test methods: (1) Cleaning effect test: Construct an in vitro artificial tooth stain model, record the initial color value L0 after artificial staining of standardized bovine tooth enamel blocks; use a tooth brushing tester, brush teeth for 10 minutes with each toothpaste sample suspension at a load of 200g and a frequency of 120 times / min, and record the final color value L1 after cleaning and drying, and calculate the color difference ΔL=L1-L0. The larger ΔL is, the better the stain removal and cleaning effect. (2) Enamel wear test: Use a three-dimensional surface profilometer to measure the change in surface roughness Ra value ΔRa of the tooth enamel block before and after brushing. The larger ΔRa is, the more serious the wear on the tooth enamel.

[0054] The test results are shown in Table 2.

[0055] Table 2 Cleaning effect and enamel wear test results of different samples

[0056] Results Analysis: The daily cleaning toothpaste of Example 3 showed significantly better cleaning performance than commercially available calcium carbonate toothpaste (Comparative Example 1), while reducing enamel abrasion by 24.6%. The mild toothpaste of Example 1 exhibited extremely low abrasion, making it suitable for children and the elderly with fragile enamel. The deep-cleaning toothpaste of Example 6 demonstrated outstanding cleaning performance, with abrasion significantly lower than that of Comparative Example 2, which had substandard particle size. Comparative Example 3, due to its calcination process, could not form a buffer structure with an obtuse-angle cross-section, resulting in both poor cleaning performance and a high risk of abrasion.

[0057] All performance tests in Experiment Examples 1-2 were conducted in accordance with the ISO 11609:2017 international standard "Dental Toothpaste". Each test was conducted in triplicate, and the average value of the results was taken.

[0058] Therefore, this invention employs the aforementioned gradient hardness toothpaste based on a blend of oyster shells and calcined oyster shells, and its preparation method. By adjusting the ratio of oyster shells to calcined oyster shells, the toothpaste's tribological properties can be linearly adjusted. Sharp-angled particles provide efficient cutting force to remove stubborn stains during brushing; obtuse-angled particles polish and protect the tooth enamel while cleaning, reducing scratches. For children and the elderly with thin enamel and sensitive gums, a high proportion of calcined oyster shells provides gentle cleaning; for young adults with heavier stains and higher cleaning needs, a high proportion of oyster shells ensures efficient stain removal. This fully utilizes marine shellfish waste, turning waste into treasure, and aligns with green environmental protection principles.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A graded-hardness toothpaste based on a compound of oyster shell and calcined oyster shell, comprising a composite abrasive and excipients, characterized in that, The composite friction agent is composed of oyster shell powder and calcined oyster shell powder. The oyster shell powder is natural oyster shell powder obtained by washing, crushing and grading without calcination. Its microscopic cross-section is acute-angled and its Mohs hardness is 4.0 to 4.

5. The calcined oyster shell powder is natural oyster shell powder obtained by calcining at 800℃ to 1000℃ for 1 to 3 hours, followed by cooling, crushing and grading. Its microscopic cross-section is obtuse-angled and its Mohs hardness is 2.5 to 3.

0.

2. The graded hardness toothpaste based on a compound of oyster shell and calcined oyster shell according to claim 1, characterized in that, The mass ratio of oyster shell powder to calcined oyster shell powder is (0-100):(100-0); wherein, a mass ratio of 0:100-30:70 yields a toothpaste with a first gradient hardness, a mass ratio of 50:50-80:20 yields a toothpaste with a second gradient hardness, and a mass ratio of 90:10-100:0 yields a toothpaste with a third gradient hardness.

3. The graded hardness toothpaste based on a compound of oyster shell and calcined oyster shell according to claim 2, characterized in that, The particle size of both the oyster shell powder and the calcined oyster shell powder is 5μm to 20μm.

4. The graded hardness toothpaste based on a compound of oyster shell and calcined oyster shell according to claim 2, characterized in that, The mass of the composite friction agent accounts for 20% to 40% of the total mass of the composite friction agent and auxiliary materials.

5. The graded hardness toothpaste based on a compound of oyster shell and calcined oyster shell according to claim 2, characterized in that, The first gradient hardness toothpaste has a radioactive dentin abrasion RDA value of 45-55, the second gradient hardness toothpaste has a radioactive dentin abrasion RDA value of 85-95, and the third gradient hardness toothpaste has a radioactive dentin abrasion RDA value of 115-125.

6. The graded hardness toothpaste based on a compound of oyster shell and calcined oyster shell according to claim 1, characterized in that, The excipients include humectants, thickeners, foaming agents, sweeteners, flavorings, and deionized water; based on the total mass of the compound friction agent and excipients, the mass percentage of each excipient is as follows: humectant 20%–45%, thickener 0.5%–2%, foaming agent 1%–3%, sweetener 0.1%–0.3%, flavoring 0.5%–1.5%, with the remainder being deionized water.

7. The graded hardness toothpaste based on a compound of oyster shell and calcined oyster shell according to claim 6, characterized in that, The auxiliary materials also include sodium pyrophosphate, which accounts for 0.3% to 0.8% of the total mass of the composite friction agent and auxiliary materials.

8. The method for preparing a graded hardness toothpaste based on a compound of oyster shell and calcined oyster shell as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) Preparation of oyster shell powder: After cleaning, removing impurities and drying natural oyster shells, they are crushed and graded to obtain oyster shell powder with an acute-angled micro-section and a Mohs hardness of 4.0 to 4.5, which is used as a high-hardness cleaning functional unit. (2) Preparation of calcined oyster shell powder: After cleaning, removing impurities and drying natural oyster shells, they are calcined at 800℃~1000℃ for 1h~3h, and after natural cooling, they are crushed and graded to obtain calcined oyster shell powder with a blunt cross-section and a Mohs hardness of 2.5~3.0, which serves as a low hardness buffer protection unit. (3) Gradient paste preparation and filling: According to the preset mass ratio corresponding to the target gradient hardness, accurately weigh the oyster shell powder obtained in step (1) and the calcined oyster shell powder obtained in step (2), mix them evenly to obtain the target composite abrasive; mix the composite abrasive with the excipients, and fill it after paste preparation, grinding, vacuum degassing to obtain the toothpaste with the corresponding gradient hardness.

9. The method for preparing a gradient hardness toothpaste based on a compound of oyster shell and calcined oyster shell according to claim 8, characterized in that, In step (2), the calcination temperature is 900℃ and the calcination time is 2h.

10. The method for preparing a gradient hardness toothpaste based on a compound of oyster shell and calcined oyster shell according to claim 8, characterized in that, In steps (1) and (2), the grading process is carried out by air jet milling; in step (3), when making the ointment, the composite abrasive agent, moisturizer, and deionized water are first mixed evenly, then the thickener is added and stirred until completely dispersed, and then the remaining excipients are added and stirred evenly.

Images