We know that long periods of low pH select for acid producing bacteria. Thus, the makeup of the biofilm (thin layer of bacteria we all have on our teeth) can shift as a result of the pH of the oral cavity. Additionally, ‘good’ bacteria, if given the right environment (low pH) start behaving like ‘bad’ acid producing bacteria. pH is important because not only does low pH select for acid producing bacteria, it can transform good bacteria to bad bacteria. On the other hand, elevating the pH has shown to de-selct for the acid producers in favor of the ‘good’ bacteria in the biofilm.
We know that the critical pH of enamel is 5.5, which is true in the larger sense, however, you need to know how much saliva and calcium and phosphate and nano particles of nano hydroxyapetite and fluorapetite they have in their saliva, or the more mineral they have in the saliva, the lower the critical pH becomes. On the other end of the spectrum, having less saliva and less mineral created an environment where the critical pH for the enamel may be higher.
“Thus the critical pH is not a constant, because the levels of calcium and phosphate in plaque fluid vary among individuals. The more calcium and phosphate that are present in a solution, the lower the critical pH.” (Dawes C. What is the critical pH and why does a tooth dissolve in acid? JCDA December 2003. 69(11):722-24)
It is important to use products to elevate the pH, in order to try and mimic saliva and select for healthy bacteria.
“Therefore, the suppression of sugar catabolism and acid production by the use of metabolic inhibitors in oral care products, the consumption of nonfermentable sweeteners in snacks, the stimulation of saliva flow, and/or other strategies that maintain supragingival plaque at a pH around neutrality will assist in the maintenance of microbial homeostasis in plaque.” (Marsh PD. Dental plaque as a biofilm: the significance of pH in health and caries. Compend Contin Educ Dent March 2009; 30(2):76-90)
The image to the right shows the black spots are acid producing bacteria. The difference between the top panel and the bottom panel, is they controlled for pH. The bottom panel shows the bacteria in an elevated pH environment periodically over a period of days–ridding some of the acid producing bacteria.
“In silico modelling studies have been performed which support the concept that either reducing the frequency of acid challenge and/or the terminal pH, or by merely slowing bacterial growth, results in maintaining a community of beneficial bacteria under conditions that might otherwise lead to disease (control without killing).” (Marsh PD, Head DA, Devine DA. Ecological Approaches to Oral Biofilms: Control without Killing. Caries Res. 2015;49 Suppl 1:46-54)
“No current oral products can easily change or modify xerostomia as a caries risk. However, there are some products available that contain calcium, phosphate, and pH buffering ingredients that may play a role in the reduction of caries risk.” (Chapman RJ, Roberts DR, Kugel G. Caries and Periodontal Risk Assessment and Management)
We also know that within the biofilm there is a gradient and clustering of bacteria. This shows that the way the bacteria grow are not random. There are certain bacteria always found together.
“We demonstrated that some bacterial species implicated in caries progression show selective clustering with respect to pH gradient, providing a basis for specific therapeutic strategies.” (Kianoush N, Adler CJ, Nguyen KA, Browne GV, et al. Bacterial profile of dentine caries and the impact of pH on bacterial population diversity. PLoS One. 2014 Mar 27;9(3):e92940)
pH is, therefore an important therapeutic strategy for the management of the biofilm.
When looking at both the pH and the demineralizing effect of certain products on patients with dry mouth, researchers found the CTx2 Spray had the highest pH and the same demineralization effect of tap water 0.0%.
“The average pH values are as follows: Oasis, 6.3, Bioténe Moisturizing Mouth Spray, 6.1, CTx2 Spray, 9.1, Mouth Kote, 3.0, Thayer’s, 6.3, Bioténe Oral Balance, 6.6, Rain, 7.1, tap water 6.99, and citric acid 1.33. The results (% of tooth structure lost) of the gravimetric analysis were as follows: Mouth Kote, 9.6%, Bioténe Moisturizing Mouth Spray, 4.6%, Oasis, 3.2%, Thayer’s, 2.0%, Bioténe Oral Balance, 0.0%, Rain, 0.0%, CTx2 Spray, 0.0%, tap water 0.0%, and citric acid 18.8%. There was a significant negative correlation between the pH values and the erosive potential.” (Delgado AJ, Olafsson VG, Donovan T. pH and Erosive Potential of Commonly Used Oral Moisturizers. J Prosthodont. 2015 Jul 27. doi: )