Does glycerine coat the teeth and inhibit remineralisation?

We have noticed through online threads that some natural health and ingredient-conscious consumers are concerned about the inclusion of glycerine in a toothpaste formulation. The main concern is that glycerine could coat your teeth and prevent remineralisation. We decided to investigate this claim and determine whether this is a fact or a myth.

What are the concerns, and where did they originate from?

There have been numerous online threads, propagated by influencers (often without any reference to the source), that glycerine coats the teeth and prevents remineralisation.

This idea originates from Dr Gerard Judd, a chemistry professor. In 1997, he wrote a self-published book called “Good Teeth Birth to Death”. Interestingly, the book itself only mentions “glycerol” twice. He writes that toothpastes with glycerol should be avoided but does not offer any explanation why. What is even more peculiar is that he reveals that he would use a bar of soap when brushing his teeth. Traditionally, most bars of soap are made using glycerine. Later, during 2001 and 2002, Dr Judd wrote letters to his followers and the government, where he briefly mentions that glycerine coats the teeth and creates a sticky barrier that takes 27 washes to remove.

Apart from his controversial claims about glycerine, Dr Judd also makes some unusual claims about the formation of cavities in his letters. He stated that the best way to prevent cavities from forming is to ensure that teeth are ‘clean’, hence the logic to brush with soap, and that consuming sugar, and an abundance of Streptococcus mutans, have no association with the development of cavities. The idea that sugar intake is associated with the progression of cavities is well-accepted and is supported by a recent updated systematic review that included 23 new studies published between 2011 and 2020. The review showed that previously published evidence reporting that greater sugar intake is associated with a greater risk of dental caries is well supported [1]. Furthermore, in a recent meta-analysis, 19 clinical studies measuring the oral microbiome and the abundance of S. mutans in caries-active and caries-free patients were assessed. The meta-analysis found that by looking at all the clinical trials, there is sufficient evidence to show that S. mutans is associated with the progression of caries [2].

Although Dr Judd was a chemistry professor, it does not mean that any statement that he makes can be cited as a scientific fact. Scientific claims and hypotheses need to be supported by appropriate empirical evidence and subjected to scientific scrutiny. When a claim concerns the clinical effects of an ingredient, well-designed controlled clinical trials, and ideally a consistent body of evidence from multiple studies, provide much stronger evidence than an individual’s professional opinion or theoretical reasoning alone. In addition to this, scientists usually publish their findings in scientific journals where an independent panel of reviewers can critique their work and identify bias in their study design or reporting of the results. A peer-reviewed scientific article has safeguards that a self-published book or letter does not have, and therefore a peer-reviewed article is far more reliable than a self-published book or letter.

Does glycerine interfere with remineralisation?

To date, there have been no published randomised controlled studies that specifically test whether glycerine inhibits remineralisation, and as a result, we could not find any reliable evidence in support of Dr Judd’s theory.

On the contrary, the results of randomised controlled trials testing the anti-caries effect of different toothpaste formulations with glycerine suggest that it is highly unlikely that glycerine does coat the teeth and prevent remineralisation. If remineralisation was impaired by the glycerine, then it would be expected that the toothpastes would not be able to prevent dental caries from forming.

Both hydroxyapatite and fluoride formulations were effective at preventing dental caries, even in caries-active orthodontic patients. Additionally, the hydroxyapatite formulations were not inferior to the 1400 and 1450ppm fluoride formulations [3,4]. Other randomised controlled clinical studies that have tested a hydroxyapatite toothpaste formulation with glycerine found that participants had reduced dentine hypersensitivity and they reported that their teeth felt whiter and smoother. This suggests that the hydroxyapatite was able to successfully perform its function as a remineralising and enamel repair agent without being impaired by the glycerine in the formulation [5].

Humectants in toothpaste

Glycerine is used in a toothpaste as a humectant to help retain water over time. It would be misleading to say that a humectant like glycerine should be removed simply because it is serving the stability and shelf life of the toothpaste, rather than offering a direct benefit for oral health. It is important to retain water in a toothpaste formulation because it helps effectively deliver and distribute the active ingredients in the formulation, and it prevents the toothpaste from drying out [6]. Additionally, glycerine helps reduce friction between the toothpaste and the oral surfaces, making the toothpaste feel smoother during brushing [7]. By improving the texture and mouthfeel of the toothpaste, it helps promote regular brushing, especially in children who are still learning to adopt the routine.

Something that we can agree on with Dr Judd is that conventional toothpaste can be made better, and it has been our goal from the start to offer toothpaste with better ingredients. However, we would argue that glycerine is not the problem. There are conventional (non-natural) toothpastes that use PEGs as humectants [6]. EvaGlo consciously chose to use glycerine as a more natural alternative to PEGs. EvaGlo is manufactured in a COSMOS-approved facility, and it is worth noting that PEGs are not approved for use in the COSMOS standard [8].

Conclusion

Due to the lack of scientific evidence supporting Dr Judd’s idea, the idea that glycerine coats the teeth and inhibits remineralisation cannot be cited as a fact. There are numerous randomised controlled studies that have tested hydroxyapatite and fluoride toothpaste formulations that include glycerine and have been found to successfully treat dental caries, even in high-risk caries patients.