Formulating Toothpaste
Author: Hani Fares, Ph. D.
Most personal care formulators are familiar with skin, hair and make-up formulations. Oral care formulation has always been a distant cousin. The ingredient listing on the back of the carton seems very familiar, but the technology is quite distinct. In this article, I will try to explain certain elements to simplify the development process of toothpaste formulations.
In the United States, toothpaste is considered an over-the counter dosage form that falls under the anticaries drug products monographs. In fact, the monograph defines dentifrices as “an abrasive-containing dosage form for delivering anticaries drug to the teeth”1. Interestingly enough, there are two key messages in this definition: the first one is that dentifrices must contain abrasives, and the second is that they should deliver actives to teeth. As such, dentifrices do not have to be gels or pastes, they could be powders. In fact, tablets were introduced recently as alternatives to traditional paste. However, pastes and gels are the most common forms used by consumers.
There are three anticaries actives approved for use in dentifrices, namely sodium fluoride, sodium monofluorophosphate (naMFP), and stannous fluoride. One thing to note is that the source of fluoride used must be paired with the recommended abrasive. For example, sodium fluoride and stannous fluoride toothpastes are typically paired with silica abrasives and naMFP is typically paired with calcium carbonate or dicalcium phosphate. The idea of pairing actives with abrasives is based on relating these dentifrices to the original clinical studies conducted on such combinations.
In addition to pairing abrasives and actives, several tests must be performed on any newly launched toothpaste. The first test is a biological animal caries reduction test. This test must be paired with either Enamel Solubility Reduction (ESR) or Fluoride Enamel Uptake (FU). However, since there has been a lot of pressure on reducing animal testing, companies have been using other methodologies2 that showed equivalence to animal testing. Manufacturers are also required to generate data on free fluoride in the dentifrice. Such data is typically generated based on accelerated stability protocols before launch and can be substituted with real-time data once the product is launched.
Dentifrice manufacturers have been quite active in going beyond just the anticaries and antiplaque claims that they can achieve with a traditional fluoride toothpaste. Generating additional claims and benefits to consumers has led to formulating new premium toothpastes. One area of premiumization was to launch antigingivitis toothpastes. Such toothpaste will fall under the antigingivitis/antiplaque monograph3. These dentifrices are formulated with stannous fluoride as the active ingredient and silica as the abrasive. In addition to all the tests described in the fluoride monograph, these must be tested in vitro for their antimicrobial activity against plaque organisms commonly associated with gingivitis. These tests must include MIC assays, 30-second kill-time studies and plaque biofilm assays . In addition, these products must demonstrate activity ex-vivo using a Plaque Glycolysis and Regrowth Model (PGRM)4. Companies seeking the antigingivitis claim outside of the monograph must go through the New Drug Application (NDA) process. One well-known example is “Colgate Total,” which used Triclosan as the antimicrobial and PVM/MA Copolymer (commercially known as Gantrez™) as the polymeric delivery system for the oral cavity. The NDA process is quite long and expensive but typically allows certain exclusivities to the marketing company.
Another area that has gained a lot of popularity in dentifrices is whitening. Claiming to whiten teeth is generally a cosmetic claim, though many companies conduct consumer studies to measure the whitening effect of their toothpaste on panelists. Whitening teeth involves removing extrinsic stains or bleaching extrinsic/intrinsic stains. Removing extrinsic stains has been achieved by using sodium hexametaphosphate. Other types of phosphates have been used as well but are not as efficacious. Hydrogen peroxide is the most widely used form of peroxide used in toothpaste to bleach intrinsic and extrinsic stains. That is due to its acceptable taste and its availability in a complex form with PVP which makes it quite stable for a longer time. Other forms of peroxide like urea peroxide are used as well but are not very popular. Whitening toothpastes are typically anhydrous formulations due to the instabilities of sodium hexametaphosphate and hydrogen peroxide in the presence of water. These formulations require a special type of thickener and do have a unique mouthfeel.
Another area of interest to consumers is treating sensitive teeth with toothpaste. This area is covered by a monograph as well and the two actives allowed are potassium nitrate and stannous fluoride. Potassium nitrate is typically formulated in silica/sodium fluoride base.
As you can see, there are some intricacies in formulating toothpaste but at the end of the day, it all comes down to consumer experiences and product performance. A skilled formulator is always capable of marrying all the ingredients in a formulation to deliver a delightful experience and a great mouthfeel. Formulation has always been a blend of science and art, and many dentifrices are able to provide this great consumer experience. I hope I have shed some light onto the world of formulating formulation-let’s go create new formulations!
References
- Federal register, Vol 60, No 194, 21CFR 310.
- Featherstone, J., Stookey, G., Kaminski. M., and Faller, R. Recommendation for non-animal alternative to rat carries testing, Am J. Dent., 5 (2011) 289-294.
- Federal register, Vol 68, No 103, 21CFR356
- White, D., Cox, E., Liang, N., Macksood, D., and Bacca, L., A new Plaque Glycolysis and regrowth Method (PGRM) for the in vivo determination of antimicrobial dentifrice/rinse efficacy towards the inhibition of plaque growth and metabolism – method development, validation and initial activity screens., J. Clin. Dent. 6 (1995) 59-70.
Dr. Fares started his career in personal care studying the effect of solvents on sunscreen chemicals. His interest in skin drug delivery especially from polymeric matrices grew during his graduate work at Rutgers, where he received his Ph. D.
Dr. Fares worked at Block Drug and GlaxoSmithKline where he held positions in research and development in the areas of skincare and oral care. After that, he joined L’Oréal where he held several positions of increasing responsibility leading to AVP of skincare. He is currently the Global Lead of skincare and oral care at Ashland Specialty Ingredients. Dr. Fares is the author of many publications, and patents and made many presentations in national and international meetings in the areas of suncare, skincare, and oral care. Dr Fares chairs the NYSCC scientific committee and has won multiple awards in the areas of sun care and polymer chemistry.