Healthy Teeth Q & A

Here are a few questions Dr. Ellie answered in the last week. As always, if you have a healthy teeth question, feel free to comment below or email us at

Why is it that apple juice is acidic, yet apples are not? Are there guidelines, or do we need to test every food?

I assume that the acidity of apple juice may have something to do with apple fermentation ( sort of like wine / vinegar). I do not know for sure.
I invite anyone who may know, to explain.

It is often a surprise even to dentists that apple juice has a pH around 2.2 (Wow!)
I do not know how to provide guidelines that work for all foods even many “healthy” foods can be acidic.

The effect of eating acidic foods/drinks will be different in each mouth. The response will depend on the amount of saliva and the pH of this saliva. Those with dry mouth or acidic saliva will be most at risk from acidic foods, since acidity will be slowly washed away or never neutralized.

Those with plenty of alkaline saliva will be able to consume something acidic and their mineral-rich saliva will quickly wash away the acidic problem.

Mostly I work from the premise that eating a little xylitol at the end of each meal will limit propagation of dental disease bacteria and limit any acidic damage from the meal. Foods like cheese, milk, celery and nuts are tooth safe alternatives for those times when Zellies mints are not available!

You wrote that lactobacillis (or acidophilus) causes tooth decay. Is this not the bacteria I eat daily in my yogurt?

I do not think I mentioned this exactly, but a variety of bacteria are listed in text books and said to be involved in the process of dental disease (cavities and gum disease). The bacteria of most concern is Streptococcus Mutans. However only certain strains (types) of Strep. Mutans cause problems.

Some strains of Strep. Mutans appear to be harmless and even protective of teeth when they are in balance with the oral flora and proteins.

These harmless/healthy strains of Strep Mutans are non-sticky and do not produce acids. This kind of Strep Mutans appears to be “xylitol tolerant” in other words this kind will survive in a mouth where xylitol is consumed.

This is why in the presence of xylitol thick, sticky plaque does not form and plaque acid production is stopped.

On the other hand, acid-producing, sticky Strep. Mutans bacteria are found in acidic mouths.
This strain of Strep Mutans forms thick plaque. These bacteria absorb and utilize sugar and carbohydrates to fuel themselves, propagate and produce acids (that leach out of the plaque to destroy teeth).

As plaque layers thicken, some bacteria become oxygen deprived. In low-oxygen conditions the bacteria become anaerobic and the most dangerous bacteria for teeth and gums.

As much as your intestine requires the correct strain of bacteria to maintain health, so does the mouth. You could think of xylitol as antibacterial towards harmful mouth bacteria while behaving as a probiotic promoting the good and protective ones.

If I don’t have gum infections, do I need to keep using the Closys, or might salt water be enough for pH neutrality?

I would consider the salt water as a good alternative for someone with perfect gingival health.

Categories: Xylitol

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