ON A VISIT TO THE TOOTHPASTE aisle in the supermarket, you might be confused when you encounter row after row of products, each promising to make you happy and
attractive. As you stare at the seemingly endless array of choices, more and more questions pop into your head. Which toothpaste do
I need? How can I make sense of the ingredients listed on the tubes of toothpaste? Which
ingredients matter the most?
While cleaning your teeth is necessary to
preserve them and to enhance your overall
health, there are a few potential problems with
some toothpaste ingredients. When you are
shopping, it helps to know what they are and
what they do.
How bacteria attack
The main reason why we need to clean our
teeth is to fight harmful bacteria. The human
mouth contains certain bacteria that feed on
the sugars present in our mouths after we
eat—a big reason for these bacteria to hang
around and multiply. In the process, bacteria
produce acids that dissolve the outer layer
of our teeth, called the enamel. Chemically,
enamel is hydroxyapatite (Ca10(PO4) 6(OH) 2).
This process is known as demineralization.
Hydroxyapatite consists of positive calcium
ions (Ca2+) and negative phosphate (PO43–)
and hydroxide (OH–) ions that form an inter-
locked three-dimensional structure that is
insoluble if the surrounding pH is not too
acidic, that is, as long as the concentration of
hydrogen ions (H+) is not too high. But when
bacterial acids decrease the pH, the hydroxide
and phosphate ions bind with the hydrogen
ions, causing hydroxyapatite to dissolve.
Demineralization is always occurring. Under
normal conditions, there is a stable equilibrium between the calcium and phosphate ions
in saliva and the crystalline hydroxyapatite
(Fig. 1(a)), which can be described as follows:
Ca10(PO4) 6(OH) 2 ; 10 Ca2+
+ 6 PO4 3– + 2 OH–
When the bacterial acids decrease the pH,
the tooth surface becomes acidic, and phosphate in the saliva combines with hydrogen
ions (H+) to form three hydrogen phosphate
species: H3PO4, H2PO4–, and HPO42–.
In an effort to compensate for this decrease
in the amount of phosphate available in the
saliva, the rate of the demineralization reaction
(forward reaction in the equilibrium reaction shown above) will increase (Fig. 1(b)).
Under these conditions, phosphate is pulled
from tooth enamel, and the hydroxyapatite
dissolves. This begins the process known as
Preventing decay and gum
A clear way to get rid of bacteria on any
surface is simply to scrub it. This is a basic
physical process, called abrasion, that
removes the bacteria and keeps them from
To othp a ste!
By Valerie Brown
14 ChemMatters | FEBRUARY/MARCH 2017 www.acs.org/chemmatters
Modern toothpaste ingredients may not be perfect, but they
are a big improvement over the ingredients that our ancestors put on their woody or bristly brushes.
The Romans used powdered charcoal
to neutralize bad breath, along with
crab eyes and ground chalk, while
old Chinese toothpastes contained
ginseng. The oldest known recipe,
probably written by a Christian
monk in Egypt, dates back to 400
A.D.: Grind together rock salt,
dried iris flower, and pepper, and
rub on the teeth. Before the production of toothpaste in a tube, tooth powder was purchased in
cans, such as these vintage containers.