Regulate abrasiveness in solid dentifrices

Hi everyone.

This is my first question on the forum. I am currently interested in solid toothpastes (dental tablets), but would like to regulate the level of abrasiveness.

This is my starting formula:
51.00% Calcium carbonate
25.50% Kaolin
05.00% Stevia powder
05.00% Sodium cocoyl isethionate
01.50% Tincture of propolis
01.00% Peppermint essential oil
01.00% Ginger essential oil
10.00% Witch Hazel Hydrolate

I have thought about the following modifications:
a) replace part of the abrasives with non-colloidal microcrystalline cellulose
b) add 0.50% xanthan gum, so that it forms a paste on contact with saliva and creates a stable suspension of abrasives during use.

My main doubt is that microcrystalline cellulose is also used as an abrasive, but I can't find data about its degree of abrasiveness and if it would be too strong. I found a patent application for toothpastes with reduced abrasiveness where microcrystalline cellulose, colloidal and non-colloidal, are mentioned for this purpose, but the authors refer to pastes and, if I have understood correctly, they use mainly colloidal MCC.

Does anyone have any ideas about what approximate percentage I should substitute to get:
a) a toothpaste for regular use (given that in toothpastes the percentage of abrasives can be around 30%, I had thought 40-45% of non-colloidal MCC)
b) a toothpaste for sensitive teeth (I had thought 60% MCC)
or some other way to regulate the abrasiveness of the final product.

(I don't have access to colloidal MCC.)

Thank you very much for your attention and help.

Comments

  • HerbnerdHerbnerd Member
    Re calcium carbonate & kaolin - do you know the particle size of these two materials since these will be your two abrasives? 
    I currently use two different grades of calcium carbonate - one at 2 µm and another at 9 µm. The 2 µm is just a polishing grade, whereas the 9 µm is far more abrasive (currently out toothpastes are around the 120 RDA/90 PCR).

    Clays such as kaolin may not be as fine as you think - some have quite harsh particles in them - one of our toothpaste is around 150 RDA which is classified as harmful (some whitening toothpaste are as high as 250 RDA).

    Adding Xanthan gum and MCC will also help with tableting - I can't see MCC having much effect on the abrasivity though - and it might be hard finding any data to support the abrasivity of MCC.

    If you need to test your product, Indianan Dental School (Oral Health Research Institute) will be the way to go to test RDA/PCR.
  • Thanks a lot for your answer, Herbnerd. I really apreciate it  <3 .

    I asked this because, according to what I studied, the amount of abrasives (in addition to the particle size, of course) in a paste determines its level of abrasiveness, and depending on the orientation for the formulation that I had, these should be added in 15-50%, in depending on the degree of abrasiveness desired. In a solid toothpaste the proportion of abrasive is much higher, and I was looking for a way to reduce it...

    I feel a bit embarrassed now because I really don't know the particle size of these two abrasives :| . Here in Spain, I suppose it's the same in other countries, it is difficult for small formulators to access different qualities or granulometries of a material. It is sometimes difficult to get such accurate information from retailers.

    I made a 100g sample batch, using A.Vogel brand's kaolin, because it is the finest and purest I have been able to access, and calcium carbonate that the pharmacy on my street supplied me (they have been making pharmaceutical products since 1719 in their back room lab). I've just sent them an inquiry about the particle size of their carbonate, I hope they can answer me...

    In my sample I did not feel that the product was too abrasive, my teeth felt polished, and I felt a less gritty sensation than using, for example, Colgate Cavity Protection Caries (I can't find how it is valued by the RDA), although I know that is a subjective perception, and I's still concerned by the high amount of abrasives...

    Thanks again
  • chemicalmattchemicalmatt Member, Professional Chemist
    I cannot fathom how kaolin would be a better and less expensive abrasive than dicalcium phosphate, which was used traditionally in these dentrifices. Is there an issue using phosphates in E.U.? If you are to "put clay in the mouth" then try out the perlites from Imerys, a Spanish company. More abrasive than kaolin.
  • I cannot fathom how kaolin would be a better and less expensive abrasive than dicalcium phosphate, which was used traditionally in these dentrifices. Is there an issue using phosphates in E.U.? If you are to "put clay in the mouth" then try out the perlites from Imerys, a Spanish company. More abrasive than kaolin.
    I rely on this:

    "Products containing other abrasives (e.g., dicalcium phosphate, sodium bicarbonate, and calcium carbonate) generally had lower RDA values and usually lower PCR scores. There were exceptions (e.g., refined kaolin clay) that had high PCR scores and low RDA values, resulting in higher CEI values":

    Schemehorn BR, Moore MH, Putt MS. Abrasion, polishing, and stain removal characteristics of various commercial dentifrices in vitro. J Clin Dent. 2011;22(1):11-8. PMID: 21290981. 
     https://pubmed.ncbi.nlm.nih.gov/21290981/
  • HerbnerdHerbnerd Member
    Thanks a lot for your answer, Herbnerd. I really apreciate it  <3 .

    I asked this because, according to what I studied, the amount of abrasives (in addition to the particle size, of course) in a paste determines its level of abrasiveness, and depending on the orientation for the formulation that I had, these should be added in 15-50%, in depending on the degree of abrasiveness desired. In a solid toothpaste the proportion of abrasive is much higher, and I was looking for a way to reduce it...

    I feel a bit embarrassed now because I really don't know the particle size of these two abrasives :| . Here in Spain, I suppose it's the same in other countries, it is difficult for small formulators to access different qualities or granulometries of a material. It is sometimes difficult to get such accurate information from retailers.

    I made a 100g sample batch, using A.Vogel brand's kaolin, because it is the finest and purest I have been able to access, and calcium carbonate that the pharmacy on my street supplied me (they have been making pharmaceutical products since 1719 in their back room lab). I've just sent them an inquiry about the particle size of their carbonate, I hope they can answer me...

    In my sample I did not feel that the product was too abrasive, my teeth felt polished, and I felt a less gritty sensation than using, for example, Colgate Cavity Protection Caries (I can't find how it is valued by the RDA), although I know that is a subjective perception, and I's still concerned by the high amount of abrasives...

    Thanks again
    There are a number of different issues here. Proportion of abrasives does not necessarily mean something is more abrasive or less abrasive. I can use 25% of a certain grade of silicon dioxide and it will form a nice gel but will not clean teeth, I can use 6% of one silicon dioxide grade and get the same abrasivity as using 20% of another grade. But even within various grades of silicon dioxide, the amount you use can affect the abrasivity - the same grade could provide different RDA/PCR values depending on the quantity used.

    Even something like silica - you can have grades of silica that provide a sensory (gritty) aspect to the paste - and still have a low RDA.

    Abrasivity is governed by many aspects - the material you use, the particle size, the hardness of the material when compared against enamel. Even the time after eating when you brush.

    Talking with raw material suppliers and even testing laboratories, the tooth samples they use to test abrasivity can also affect results - certain cow breeds (they tend to use bovine teeth for testing unless your request human teeth), the area in which they were raised and even the year they were born can skew results.

    One of the tasks I have to do shortly is cost optomisation on the calcium carbonate - precipitated vs ground calcium carbonate. Even with precipitated calcium carbonate, there is no direct swap - crystal shape is also affecting not only abrasivity but also the viscosity and structure of the toothpaste (not necessarily and issue with a tooth powder). Most suppliers would not be able to tell you the aragonite to calcite ratio (in fact I have only found one supplier to states aragonite content.

    Personally, I wouldn't rely on a particular material until you have tested the finished product - especially if you intend to sell the finished product
  • HerbnerdHerbnerd Member
    I cannot fathom how kaolin would be a better and less expensive abrasive than dicalcium phosphate, which was used traditionally in these dentrifices. Is there an issue using phosphates in E.U.? If you are to "put clay in the mouth" then try out the perlites from Imerys, a Spanish company. More abrasive than kaolin.
     There were exceptions (e.g., refined kaolin clay) that had high PCR scores and low RDA values, resulting in higher CEI values":


    CEI is just a calculation based on PCR/RDA (CEI = (RDA + PCR – 50) ÷ RDA)

    - it gives and indication of cleaning efficiency. However talking with others in the industry, it seems there should be greater weight on the PCR rather than RDA - you want your teeth to be clean but not necessarily abraded away to the dentine.
  • I understand. But if all this is so vague, how do you formulate a prototype toothpaste for a specific purpose? I mean, you are looking for some characteristics and you need to have an idea about what ingredients to use and in what proportion to get closer to the result you are looking for, and then do the necessary tests to check if the product is correct and/or work on the corrections. There must be some general rules... Or is it just the supplier of each material who tells you the proper dosage?
  • HerbnerdHerbnerd Member
    edited May 17
    I understand. But if all this is so vague, how do you formulate a prototype toothpaste for a specific purpose? I mean, you are looking for some characteristics and you need to have an idea about what ingredients to use and in what proportion to get closer to the result you are looking for, and then do the necessary tests to check if the product is correct and/or work on the corrections. There must be some general rules... Or is it just the supplier of each material who tells you the proper dosage?
    Formulation to specific purposes is far easier with dental grade silicon dioxides, such as the zeodent range from Evonik.

    You can use the different grades for tooth whitening (High abrasives), to very gentle abrasion suitable for kids.

    Their website (although I have found it to be faulty and they are correcting this) allows you to target a specific RDA using specific grades of silicon dioxide; however, their mixing model  on the website doesn't allow you to mix different silicon dioxide. But if you deal with their innovation lab, they have different mixing modeling software that allows great targeted RDA.

    Other abrasives, such as calcium carbonate or calcium phosphate or even sodium bicarbonate, are much less flexible in formulating to a specific PCR/RDA - and there is a fair amount of trial and error.

    That said, Omya have a great range of dental grade calcium carbonates, also Specialty Minerals. Omya probably has better information sheets and grades.
  • Thanks a lot. As a student, all this is a valuable information, although it discourages me because I don't have access to that kind of ingredients, neither to the appropriate tests, so it seems quite useless to experiment with toothpastes at home  :(
  • HerbnerdHerbnerd Member
    Thanks a lot. As a student, all this is a valuable information, although it discourages me because I don't have access to that kind of ingredients, neither to the appropriate tests, so it seems quite useless to experiment with toothpastes at home  :(
    I don't mean to discourage you, just provide you with information. If you are manufacturing for home use, do carry on if that is what you want to do.

    If you want to develop for sale, there will be more work to do and providing safety trials will be part of that process.

    As for testing costs - when I started at the company I am with now, there was no budget set aside for trials and no consideration for testing costs. They were shocked when I put together scale-up trial and testing costs of around $250,000 - but this was for almost two dozen products and 500 kg scale up trials for each along with RDA/PCR, stability, PET, Fluoride stability, free & total fluoride assay, fluoride uptake etc etc etc and didn't include any re-trials because my manager insisted on running trials before we were ready.
  • I know, and I thank your honestity, that"s what I'm looking for🙏. Maybe I'll try at home again, but just for fun, I don't want to ruin my teeth 😉

    Thanks too for telling me about your experience, I like to know how work in the industry is, since I don't have thit experience by the moment (but I'd like It). I was used to participate in amateur forums but they are not reliable,  what a pleasure to have the opportunity to speak with professionals (Thanks, Perry, for this place)
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