Creative Developments
(Cosmetics) Limited
Cosmetic
care of the oral cavity is concerned with the removal of calculus and plaque
and prevention of dental caries. It also entails cleaning and brightening the
teeth, refreshing the mouth and preventing bad breath. All these conditions are
related.
The
most common product forms are tooth powders, toothpaste and mouthwashes and
examples of each of these may be found in cosmetic textbooks published nearly a
century ago. Also, many of the ingredients look familiar. Askinson [REF 1]
describes toothpaste containing clove and peppermint oil, the use of calcium
carbonate (chalk) and of talc as abrasives and of starch flour or orrisroot as
a thickener. Less likely now is the use of substantial quantities of sugar
syrup. Tooth powders were based on chalk but sodium borate (borax), ground
cuttlefish bone and ammonium carbonate were also suggested although one based
on powdered charcoal was probably not a commercial success. It is still
possible to find porcelain pots from the late nineteenth century that were used
for toothpowder. Mouthwash formulae described by Askinson are interesting
because they contained citrus oils and essential oils of lavender, cinnamon,
myrrh and rose. While these were for perfuming the breath, chloral hydrate,
salicylic acid and potassium permanganate were recommended for destroying bad
breath caused by bacterial decay.
Some
ten years later Poucher [Ref 2] discussed the germicidal value of mouthwash
preparations and concluded that thymol and most other germicides in use at that
time were ineffective on the bacteria to be found in the oral cavity. He also
reported that peppermint oil was the most popular flavour in Europe and methyl
salicylate (oil of wintergreen) the most popular in North America. Toothpaste
was beginning to displace toothpowder in popularity and glycerine had replaced
sugar syrup as the excipient. Soap was used to help disperse the paste in the
mouth and by the middle of the century sodium ricinoleate (SR) and sodium
lauryl sulfate had replaced soap in popular brands.
Early
product improvements had mostly been concerned with presenting a more pleasing
product to use and by 1950 the importance of rheological properties and the
dangers of products being too abrasive were known. Further improvements were
based on a better understanding of the causes of dental decay and oral
diseases. Major changes since then have been the addition of red stripes
although they no longer contain hexachlorophene, the addition of fluorides and
the launch of clear gel dentifrice. Mouthwashes were improved by the addition
of cetylpyridinium chloride (CPC) but the basic formulations in all three
product categories have remained virtually unchanged for fifty years. The main
differences are in the additives and actives although many of these may also be
traced back to the early years. Thus Askinson, Poucher and others suggested
liquorice as a flavour; now it is known to have an anti-inflammatory and
bacteriastatic action. Paroxite market Liquiritina, a liquorice (glycyrrhiza
glabra) extract recommended for toothpaste and mouthwash and because it also
has surfactant properties, it is able to penetrate between the teeth.
Ground
chalk is now rarely used as the principal abrasive but precipitated calcium
carbonate is available in three carefully controlled grades from WCD
International. Calcium carbonate cannot be used with fluorides. Other popular
abrasives include phosphates and polyphosphates, hydrated aluminium oxide,
sodium bicarbonate and silicas, which are also used for transparent toothpaste.
The use of sodium bicarbonate is relatively new and can lead to product
instability. This may be improved by the addition of sodium carbonate to
provide a buffered system. Ground cuttlefish bones and charcoal seem to have
disappeared from today’s ingredient listings but no doubt they will return.
Carrageenan
was one of the first rheology modifiers to gain acceptance in toothpaste and
partly because it does not suffer enzymatic degradation, its popularity remains
undiminished. Hygel TP-1, Hydralco GmbH, is a cold-soluble grade said to have
an excellent rheology profile and good flavour release characteristics. Its gel
is transparent so it may be used in clear silica-based products and its strong
interaction with glycerine or sorbitol make it possible to reduce their dosage
level. It is stable in the pH range 7.0 – 10.0. Cellulose derivatives are
probably the most common thickening aids. They are stable over a wide pH range
and are cost effective. However they are susceptible to enzyme degradation and
being thixotropic, the extruded ribbon takes time to regain viscosity and so
may sag on the toothbrush. The non-ionic hydroxyethyl cellulose is particularly
useful if a cationic antimicrobial material is to be incorporated. Xanthan gum
(Kelco, Rhodia and others) may be used as the sole thickener or in combination
with Veegum. Xanthan gum is very stable over a wide pH range and forms
pseodoplastic structures. Thus the paste is easy to extrude as a ribbon and it
holds its shape. Veegum (R.T Vanderbilt), Laponite (Laporte Industries) and
bentonite are three clay-like materials that may also be used to impart the
desired rheological attributes to the product.
When
glycerin replaced sugar syrup as the excipient ways had to be found to sweeten the
product. Sodium saccharin and aspartame have long been the sweeteners of choice
but are unsuitable for natural based products. Talin, Hays Ingredients, is a
natural flavour enhancer obtained from the fruit of the Katemfe plant of West
Africa. It is available in its pure form as a powder, blended with gum arabic
(Acacia Catechu) for toothpaste and blended with glycerin for mouthwash
applications. Although its principal use is as a sweetener it is said to
enhance the flavour of peppermint, spearmint, wintergreen and cherry products
giving them more roundness and longevity. It also prolongs the fresh, cooling
effect of mint flavours and may be used in synergy with sodium saccharin to
mask the metallic note associated with the latter. Typical use levels are 5 -
20 ppm. and it has worldwide approval as a food additive.
A
surfactant is added to toothpaste to assist its break-up in the mouth and to
disperse the flavour and abrasive during the brushing action. A glance at
ingredient listings shows that sodium lauryl sulfate is the most used but
others are available. Betafin BP20 from Cornelius Produce Company is derived
from sugar beet. Chemically it is trimethylglycine, INCI name Betaine, and
clinical trials [Ref 3] show that it is effective against Xerostamia or Dry
Mouth Feel. A toothpaste was made containing 4.0% Betafin BP20 and administered
to patients suffering from Xerostamia. Although there were no statistically
significant changes in the amount of saliva produced by the patients nor in the
flora of the oral cavity there was a significant improvement in mouth-feel by
subjective assessment. Another surfactant of interest for toothpaste use is
Olivem 400, INCI name Sodium PEG-7 carboxylated olive oil, from B&T Srl.
This has been used in conjunction with dental silicas from Huber Chemicals to
good effect; details are available through the Cornelius Produce Company.
Mouth-care
products are usually designed to reduce the number of bacteria that lead to the
formation of dental plaque in the oral cavity. Plaque may develop into calculus
and can result in serious teeth problems like caries and gingivitis. Despite
Poucher’s misgivings over the effectiveness of the germicides then found in
oral hygiene products the introduction of new antimicrobials has been relatively
slow. Triclosan (Ciba Specialty Chemicals) has been the most commonly used one
for the last twenty-five years, recent studies show that it is effective as an
inhibitor of arachonidonic acid metabolism, resulting in a reduced formation of
pro-inflammatory metabolites [Ref 4]. A patent, [Ref 5] claims that bovine
colostrum, when incorporated in a mouth-care product, strengthens the natural
defence system and results in improved healing of gums. It is used in
mouth-care compositions either as itself or in a dry form or as an extract in
combination with sodium fluoride. The optimum pH range is 5.5 – 8.0 and the
level found to be effective varies from 0.5% in a mouth rinse to 15% in a tooth
powder.
A
patent filed by Quest [Ref 6] claims that antimicrobially active proteins,
adsorbed onto a positively charged inorganic porous carrier particle, can be
efficiently delivered to a target site with high affinity and specificity.
Suitable proteins include glucose oxidase and galactose oxidase that can
generate hydrogen peroxide and peroxidases that use the hydrogen peroxide to
form hypohalite, both of which rapidly decompose in-vivo. Invertase is included
to convert sucrose to glucose that then acts as a substrate for the glucose
oxidase to form hydrogen peroxide. This is effective against Streptococcus
mutans and S sanguis that are to be found in dental plaque. Urease may be
included to convert ureum to carbon dioxide and ammonia that raises the pH of
the dental plaque to a level that inhibits growth of micro-organisms. A
different but not unrelated mechanism is described in patent US 698474 (1999)
that claims a peroxidase-activating oral care composition. A non-enzymatic,
water-soluble hydrogen peroxide precursor is encapsulated in a non-hygroscopic
material and this, in association with a pH-adjusting agent is included in the
final product. The composition facilitates the rapid release of hydrogen
peroxide and results in the activation of a peroxidase enzyme in an oral
cavity.
Incompatibility
problems abound in oral care compositions, but whether it is a problem between
cationic antimicrobial and anionic foaming agents, between calcium ions and
fluoride ions, between enzymes and thickening aids, all involve water. A novel
way round this is claimed in US Patent 599364 (1996) for an anhydrous dental
bleaching gel. It comprises propylene glycol, polyethylene glycol, glycerin,
neutralised carboxypolymethylene, hydroxypropylcellulose and carbamide
peroxide. When applied it releases oxygen. Patent EP 0 845 258 (1997) describes
a method of manufacture that combines peroxide and fluoride together in a
dentifrice and which may also contain sodium bicarbonate. The peroxide is added
as calcium peroxide and an essential part of the composition is tetrasodium
pyrophosphate. The optimum pH lies between 9.5 and 10.0. The water content is
relatively low at about 10% and there is a similar concentration of xylitol
that acts as both sweetener and humectant. The method of mixing is critical and
despite the obvious difficulties inherent in the formulation it is claimed to
be stable, effective and aesthetically pleasing.
Zinc
ions are currently in vogue for all types of preparations involving
antiperspirant, antimicrobial or enzyme activity. Patent US5897891 describes compositions for
oral use containing zinc and copper compounds and an amino acid. Zinc ions are
slowly released in the mouth with beneficial effect, the amino acid provides
the composition with a palatable taste and the copper compound provides copper
ions which serve to counterbalance a large intake of zinc upon prolonged oral
use of the composition. Patent EP 0 845 217 (1997) describes a method of
preventing undesireable taste in oral compositions by inhibiting the production
of intracellular phosphatase enzymes of taste cells.
After
nearly a century the flavours to be found in toothpaste have hardly changed
with peppermint still the predominant one in Europe. Mouthwashes have been a
little more adventurous and fruit and citrus flavours have been used besides
mint. Mouthwashes are responsible for the majority of cases of child poising in
Britain and some countries refuse a licence for those containing alcohol on
religious grounds. Worth consideration, especially if formulating an alcohol-free
composition, are the water-soluble Hydroessentials from Vevy Europe. Sambucus,
matricaria, mellisa and citrus aurantium are suggested for their refreshing
notes.
1.
Perfumes and Cosmetics; G W Askinson, Norman
Henley Publishing Co. New York (1915)
2.
Perfumes, Cosmetics and Soaps, Vol II; W A
Poucher, Chapman & Hall (1926)
3.
Betaine containing toothpaste relieves
subjective symptoms of dry mouth; E Soderling et al, Acta Odontal Scand 56 pps
65-69 (1998)
4.
Triclosan, an antimicrobially active ingredient
with anti-inflammatory action, Ciba Specialty Chemicals (1998).
5.
EP 0 743 060 A1; Sara Lee (1995)
6.
PCT/EP96/05601 Quest International (1996)