A review on natural teeth whitening

Abstract

Background: Discoloration of teeth occurs for various reasons. Common ingredients like substances from tea and coffee, as well as antibiotics like tetracycline, or food dyes, can percolate into the teeth, and, as such, these stains may persist in the porous structure of the enamel. Smoking is also contributory to dental discoloration, with toxins of tobacco smoke accumulating in a similar way. With aging, teeth tend to be discolored with accumulation of various stains in addition to the enamel gradually eroding to expose the yellow dentin.
Highlight: This review focused on the effect of several natural ingredients with teeth-whitening properties and their daily clinical application. Metabolic dental bleaching mechanisms, as well as tooth discoloration and decay, were also reviewed. The current scientific literature (mostly from 2000 to 2020) was consolidated from manuscripts retrieved from Scopus, PubMed, ResearchGate, and Google Scholar.
Conclusion: Natural teeth whitening effectively lightens the natural color of teeth without eroding dental surfaces. On the other hand, commercially available whiteners containing hydrogen peroxide and carbamide peroxide, in high concentrations, can lead to deproteinization and demineralization of teeth through oxidation processes. If used extensively, these compounds may cause a number of adverse effects. Alternative natural teeth-whiteners include ingredients like lemons, strawberries, oranges, papaya, and other fruits. Such natural ingredients offer a milder and safer way of whitening teeth than whiteners containing hydrogen peroxide or carbamide peroxide.

Full text

Review
A review on natural teeth whitening
Asma Gasmi Benahmed
a
, Amin Gasmi
b
, Alain Menzel
c
, Ihor Hrynovets
d
,
e
,
Salvatore Chirumbolo
f
,
g
, Mariia Shanaida
h
, Roman Lysiuk
d
,
e
, Yurii Shanaida
h
,
Maryam Dadar
i
, Geir Bjørklund
j
,
*
a
Acad
emie Internationale de M
edecine Dentaire Int
egrative, Paris, France
b
Soci
et
e Francophone de Nutrith
erapie et de Nutrig
en
etique Appliqu
ee, Villeurbanne, France
c
Laboratoires R
eunis, Junglinster, Luxembourg
d
Danylo Halytsky Lviv National Medical University, Lviv, Ukraine
e
CONEM Ukraine Life Science Research Group, Danylo Halytsky Lviv National Medical University, Lviv, Ukraine
f
Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
g
CONEM Scientific Secretary, Verona, Italy
h
I. Horbachevsky Ternopil National Medical University, Ternopil, Ukraine
i
Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
j
Council for Nutritional and Environmental Medicine (CONEM), Mo I Rana, Norway
article info
Article history:
Received 19 April 2021
Received in revised form
2 December 2021
Accepted 7 December 2021
Available online xxx
Keywords:
Teeth
Toothpaste
Tooth bleaching
abstract
Background: Discoloration of teeth occurs for various reasons. Common ingredients like substances from
tea and coffee, as well as antibiotics like tetracycline, or food dyes, can percolate into the teeth, and, as
such, these stains may persist in the porous structure of the enamel. Smoking is also contributory to
dental discoloration, with toxins of tobacco smoke accumulating in a similar way. With aging, teeth tend
to be discolored with accumulation of various stains in addition to the enamel gradually eroding to
expose the yellow dentin.
Highlight: This review focused on the effect of several natural ingredients with teeth-whitening prop-
erties and their daily clinical application. Metabolic dental bleaching mechanisms, as well as tooth
discoloration and decay, were also reviewed. The current scientific literature (mostly from 2000 to 2020)
was consolidated from manuscripts retrieved from Scopus, PubMed, ResearchGate, and Google Scholar.
Conclusion: Natural teeth whitening effectively lightens the natural color of teeth without eroding dental
surfaces. On the other hand, commercially available whiteners containing hydrogen peroxide and
carbamide peroxide, in high concentrations, can lead to deproteinization and demineralization of teeth
through oxidation processes. If used extensively, these compounds may cause a number of adverse
effects. Alternative natural teeth-whiteners include ingredients like lemons, strawberries, oranges,
papaya, and other fruits. Such natural ingredients offer a milder and safer way of whitening teeth than
whiteners containing hydrogen peroxide or carbamide peroxide.
©2021 Japanese Association for Oral Biology. Published by Elsevier B.V. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................. 00
2. Insights on the loss of white color from bacteria colonization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................. 00
3. Enamel structure: how is enamel when targeted by tooth whitening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................ ............. 00
4. The biological activity of modern and straightforward teeth whiteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................. 00
5. Teeth whitening metabolism . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...................... ....... 00
6. Industrial pharmacy of whitening agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..... ........................ 00
7. Natural ingredients in teeth whitening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . ............................. 00
*Corresponding author. Council for Nutritional and Environmental Medicine
Toften 24, 8610 Mo i Rana, Norway.
E-mail address: bjorklund@conem.org (G. Bjørklund).
Contents lists available at ScienceDirect
Journal of Oral Biosciences
journal homepage: www.elsevier.com/locate/job
https://doi.org/10.1016/j.job.2021.12.002
1349-0079/©2021 Japanese Association for Oral Biology. Published by Elsevier B.V. All rights reserved.
Journal of Oral Biosciences xxx (xxxx) xxx
Please cite this article as: A. Gasmi Benahmed, A. Gasmi, A. Menzel et al., A review on natural teeth whitening, Journal of Oral Biosciences,
https://doi.org/10.1016/j.job.2021.12.002

8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................. 00
Ethical approval . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................. 00
CRediT authorship contribution statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . ............................. 00
Conflicts of interest . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................................................... 00
References ................................................................. .. ..................................................... 00
1. Introduction
People can have a number of reasons as to why they need to
make their teeth white, with the most popular reason being for
cosmetic purposes where just as individuals want a lighter skin
tone, people also do want to have a bright smile to flaunt so that
they can stand out from the rest. Desperately wanting to whiten
teeth in a short period, perhaps before a wedding or for some
occasion, people resort to shortcuts by using commercially avail-
able whiteners, which contain hydrogen peroxide and carbamide
peroxide in high concentrations [1].
In particular, vital tooth bleaching for whitening teeth, such as
carbamide peroxide penetration in the dental pulp, was very
popular several years ago [2]. Yet raised questions about the more
proper approach to whiten teeth without affecting their functional
integrity and mouth health [3e6]. Anyway, teeth whitening is a
process that is requested because of the continuous deleterious
action on the tooth component and vitality by residents and oral
bacteria.
So, many existing commercial teeth whiteners contain the
synthetic chemical compound hydrogen peroxide or hydroxyl
carbamide. Although only a small quantity is being used in
whitening strips and mouthwashes, prolonged usage might have
more adverse effects as a gradual erosion of the enamel happens to
expose the dentine [19].
As we talk about the oral cavity, the major concern of these
compounds is their chemical biosafety. Bacteria present in the oral
activity can always chemically modify and interact with chemical
whiteners, causing possible toxicity from these substances [20].
Nevertheless, it seems that carbamide peroxide has an antibacterial
activity [21].
Criticisms were raised on some approaches to whiten teeth
[23,22], and new straightforward proposals to address correct teeth
whitening with high safety protocols became crucial [24]. For
example, a new technique allows whiten teeth safely without
damaging enamel via an approach using a modified titanium
dioxide nanoparticles activated with blue light [25].
Once the dentine is damaged, it can enter the pulp of the living
tooth, causing a fastened tooth decay with the bacteria building
plaques, resulting in the loss of a tooth. Natural tooth whitening
ingredients benefit oral health and reduce enamel erosion while
giving a bleaching effect.
The acidic pH of saliva and plaque, in particular, are important
factors in dental caries development (Fig. 2). Studies have found
that the pH of saliva in the oral cavity under normal conditions is in
the range of 6.2e7.6, with an average value of 6.7 [26]. The con-
centration of Н
þ
ions in the oral cavity affects the activity of saliva
enzymes, the processes of enamel mineralization and reminerali-
zation, microcirculation, microflora activity, specific and nonspe-
cific resistance of oral tissues [27]. The pH of the oral fluid (saliva) is
constantly changing [28], e.g., at intervals after meal consumption,
the value is close to neutral (6.5e6.8). After ingestion (saturated
saliva), the pH changes mainly in the acidic direction and is
sometimes lower than 4.0, which is considered the reason for
remineralization and the formation of tooth decay. It is believed
that in teeth whitening processes, the pH should be in the range of
6.8e7.4, which prevents demineralization due to dental caries or
tooth decay. In this perspective, new formulations to whiten teeth
safely should be promoted [29,30].
The purpose of this review is to outline how to use natural
compounds to replace tooth whiteners even if without peroxide-
derived compounds. Nature-derived compounds may be
endowed with higher safety, respect other approaches, so they
should be further investigated.
2. Insights on the loss of white color from bacteria
colonization
Dental caries or tooth decay is a condition brought about by
acids produced by bacteria resulting in the erosion of teeth, leading
to the breakdown of teeth. These acids can dissolve the enamel,
dentin, and cementum [7]. The cavities can take a number of
different colors ranging from yellow to black. Bacteria produce acid
when food debris such as sugars found on the tooth surface
breakdown, as sugars are a source of energy for bacteria. When the
mineral breakdown is higher than the build-up from sources like
saliva, it results in caries and associated gum disease, exposing the
root of teeth (Fig. 1). Complications can occur, too, including
inflammation of the tissue surrounding teeth, leading to loss of
teeth and infection or abscess formation. Brushing and flossing
teeth helps to prevent decay.
The factors that initiate caries formation include bacteria, decay,
carbohydrates such as sucrose, and long exposure time on the
enamel or dentin. Tooth decay involves the formation of dental
plaque formed due to adherence of sugars to teeth and acid
creation due to bacterial metabolism [8,9]. Moreover, dental plaque
is a complex biofilm found in the oral cavity when the biofilm ac-
cumulates on the hard surface of the teeth [10]. There are nearly
500 bacterial species that can form the plaque, and this plaque
formation occurs as a regimented pattern where initial colonizers
in the enamel salivary pellicle, followed by interbacterial adhesion
due to secondary colonization. Molecular interactions and adhe-
sions contribute to plaque formation and development, leading to
periodontal disease and caries [11].
An effort has been made to find the mechanism involved in
microbial adhesion to the surface of teeth with the presence of both
specific and nonspecific forms of adhesion. The pioneer colonizers
form a selected part of the microflora in the mouth, and the spec-
ificity has been attained by the adhesion receptor interaction
between the pellicle and the microbial surface [12]. This microbial
adhesion to the surface of teeth is a prerequisite for theinitiation of
plaque formation. The build-up of dental plaque is mainly due to
the multiplication of microbes. The local environmental factors
such as pH of the mouth, presence of food are also equally impor-
tant than the initial adhesion per se for dental plaque build-up.
Site-related characteristics and highly individual characteristics of
the flora present in plaque show the environment's selective power
[13]. As the oral environment is not uniform, it forms a very distinct
A. Gasmi Benahmed, A. Gasmi, A. Menzel et al. Journal of Oral Biosciences xxx (xxxx) xxx
2

ecosystem, and the microbes at the site are dependent on
interactions between host and microbes and microbeemicrobe
interactions. The in vivo interactions are rather difficult to assess.
Thus, it is seen that bacterial plaque and calculus are the
cause of progressive periodontal disease and are facilitated by a
roughened root surface [14]. This calculus can induce inflam-
mation in the adjacent periodontal tissue serving as a suitable
substrate for subgingival microbial colonization [15]. The com-
mon colonizers causing tooth decay and dental caries are Strep-
tococcus mutans, Streptococcus sobrinus, lactobacilli, and Candida
ssp [16,17]. In low numbers of cariogenic bacteria and fungi, their
influence gets aggravated with the shift in the balance of the
local environment, such as infrequent biofilm removal and high
sugar intake. If this state remains untreated, it can lead to
infection or loss of teeth. The S. mutans forms the biofilm on the
surface of teeth, and these bacteria carry out fermentation of
sugars producing high levels of lactic acid, which reduces the pH
producing suitable conditions for the cariogenic bacteria to
multiply. The cementum of the root surface gets easily
demineralized compared to the enamel, which causes root caries.
When representatives of Actinomyces, Candida, Streptococcus,
Nocadia, Lactobacillus acidophilus ssp. gather around the gums
and collect in the grooves it can lead to subgingival plaque
formation and when left untreated, it causes tooth decay.
The microbial biofilm and calcified deposits are eliminated
through root surface debridement as part of anti-infective therapy.
Due to its porous nature, the calculus can absorb much toxic matter
and retain these endotoxins to substantial levels, damaging peri-
odontal tissues [18]. The toxins are found on the exterior but not
within the diseased tooth surfaces. Thus, the surfaces are treated
carefully without damaging the cementum.
3. Enamel structure: how is enamel when targeted by tooth
whitening
Enamel covers the crown and partially the neck of the tooth and
is located on top of the dentin. Physiologically the tooth enamel is
so hard because it is composed primarily of inorganic materials:
Fig. 1. The process of formation of soft/hard plaque, of bacterial plaque, and as a consequence of the development of gum disease and tooth decay.
A. Gasmi Benahmed, A. Gasmi, A. Menzel et al. Journal of Oral Biosciences xxx (xxxx) xxx
3

95% comprises calcium and phosphate ions that compose a strong
substance - hydroxyapatite crystals (Fig. 3)[31].
The molecular structure of apatites emineralized tissues of
the tooth, as in the conditions of the physiological norm and in
pathological conditions, can differ sharply. The optimal composi-
tion of the hydroxyapatite (HA) corresponds to the formula Ca10
(PO4)6 (OH)2 with a molecular ratio of ions Ca2þor P3- corre-
sponding to 1,67 [32,33].
Occasionally there is HA with the ratio index from 1,33 to 2,0,
which is due to the presence of vacant clusters in the structure of
HA and the ability to substitute atoms and ions in the crystal. The
abovementioned items determine the variability of the crystalline
structure of HA. The trigger mechanism for forming a degradation
site of enamel with caries is the demineralization process, which is
characterized by changes in the structure of HA. Apatite enamels
include carbonate groups and a number of chemical elements in
residual (trace amounts) (including Na, Mg, K, Zn, Co, Sr, Pb, Al, Cu,
and Mn). Besides, free crystal lattices are often stored in the crys-
talline vacancies that affect the crystalline density of biological
apatite and its solubility. The release of ions from apatite into the
environment begins with a decrease in a certain number of free
ions that form this apatite. First, dissolved apatites contain
carbonates, magnesium, sodium, citrates, and apatite with fluo-
rides. The cationic composition of the enamel matrix varies due to
the tooth's activity due to the ability of HA crystals to isomorphic
and hetero morphological rearrangements.
It should be noted that according to scientific data concerning
the specifics of the chemical structure of the crystal HA, the anions
determine the shape, charge, crystalline polarity that affects its
structure and functions. Therefore, for the early detection of
pathological changes in the structure of enamel, the ratio of the
concentrations of anions and the determination of their quantita-
tive and qualitative characteristics should be monitored [34,35].
It is established that the nature of chemical bonds in the
structure of enamel allows determining the initial changes that
lead to a violation of the stoichiometry of HA crystals and their
demineralization and recrystallization [36].
However, almost all professional teeth whitening methods in
dental clinics can be called chemical ones since most of these
procedures involve using a special gel that affects dentin and not
tooth enamel. The main components of such gels are hydrogen and
carbohydrates.
4. The biological activity of modern and straightforward
teeth whiteners
A tooth-whitening formulation containing bromelain, ficin, and
papain showed a good safety level, as the peroxide-free formula-
tion was reported as strengthening enamel and did not affect cell
viability [30]. Another approach uses piezoelectric technology. This
allows the possible organic dyes to be disrupted using a piezo-
catalysis of BaTiO
3
(BTO) nanoparticles, usually performed under
ultrasonic vibration to simulate daily tooth brushing. In this
circumstance, teeth stained with blueberry juice, black tea, wine, or
any other colorful natural dye can be notably whitened by the poled
BTO turbid liquid after vibration for 3 h [29]. Da Costa et al. eval-
uated two similar methods in homes and dental offices, reporting
that no difference can be found [37], confirming previous similar
studies [37,38]. Ntovas et al. evaluated mouthrinses containing
non-hydrogen peroxide tooth whiteners and reported that they
only slightly improved tooth whiteness [39].
Home-made tooth whiteness usually accounts for herbal
components.
Anyway, other technologies, such as blue light, are entering the
scene. For example, blue light can accelerate whitening via direct
Fig. 2. Scale pH and dependence on it the color of teeth and formation of tooth decay. (For interpretation of the references to color in this figure legend, the reader is referred to the
Web version of this article.)
A. Gasmi Benahmed, A. Gasmi, A. Menzel et al. Journal of Oral Biosciences xxx (xxxx) xxx
4

photobleaching or photon-assisted oxidation using sequential
longitudinal bleaching [40].
5. Teeth whitening metabolism
To understand the factors behind teeth taking a discoloration, it
is also important to understand the physiology and metabolism of
teeth. The dentin is the structure, which forms the bulk of the
tooth's crown and root. The interior of the crown and tooth is
nourished by the dental pulp supplied through blood vessels [41].
The root dentin is covered by the cementum helping the root to
attach to the bone. The enamel protects the crown dentin, and the
thickness can vary depending on age and food habits. The enamel
covering the tooth's outer exposed region helps prevent destruc-
tion from outside. Thus, the resistance of teeth, mainly in young
people, is primarily dependent on the ability of the enamel to
withstand the attack from acids, which is a main cause of dental
caries [42]. It is observed that when the pH drops to become acidic,
either due to harsh teeth whitening products or organic acids of
foods coupled with the action of bacteria, it leads to the progression
of periodontal disease leading to the yellowing of teeth, dental
caries, and finally a loss in the tooth [43]. When the enamel erodes,
the yellow dentin shows up.
The resistance of the enamel against various external envi-
ronmental factors in systematic conditions determines the dental
caries of teeth and the health of dental tissue. The enamel
growth of teeth starts at the dentino-enamel junction, and it
progresses outwardly, with the last formed appearing on the
surface of the teeth [44]. The enamel cuticle is cut off from all
blood supply, and systemic disturbances of a person's body do
not impact the enamel and are only affected by factors such as
the amount of saliva, bacteria present, and the amount of food
retained [45].
Enamel is a protein matrix, and it is more abundant among
youth than in older generations. Scientific evidence shows that
enamel is permeated by lymph, increasing its hardness, which
protects against destructive products of decomposed food and
bacteria, but when the external atmosphere becomes too acidic,
resistance to attacks decreases. When acidity in the oral cavity is
high, the enamel tends to be more permeable to dyes and other
food stains. This gives a discoloring to teeth, such as tea or coffee
stains, chewing of beetle leaves, smoking, or long-term antibiotic
usage like tetracycline. The discoloring of the enamel is due to the
fact that it may include several channels to transport lymph. The
fermentation of food debris and other pathogenic bacteria present
on the exterior of teeth progress for dental caries. The food debris
and the bacteria surrounding the teeth form the dental plaque that
progressively leads to periodontal disease.
Metabolically it is seen that the right nutrition is essential to
prevent dental caries. A lack of vitamins C, B or D and the proper
minerals in the diet can lead to weak teeth [46]. A disturbance in
the calcium-phosphorus balance, including vitamin D, is respon-
sible for the high activity of dental caries. By including fresh fruit
and vegetables in the diet, these mineral and vitamin deficiencies
can be overcome. A calcium-phosphorous balance helps in the
resistance of teeth to decay. Diets rich in refined sugar increased
dental plaque and caries from observations seen in 323 children
over two years [47].
Dental plaque is formed as a natural biofilm and plays a lead role
in caries and periodontal disease. The acid production by plaque-
producing bacteria helps in the erosion of teeth minerals, and the
carcinogenicity of the plaque would depend on the presence of
mutant Streptococci, which are acid-tolerant bacteria [48]. How-
ever, the plaque character depends on diverse flora that includes
less acid-tolerant mutants where some produce ammonia from
urea to arginine to counter acidification. However, some bacteria
enhance the acidification process leading to erosion of the enamel
to show the yellow dentine. With age, the enamel is said to wear
out too. There is evidence that subgingival plaque is also associated
with periodontitis that metabolizes low oxygen levels through
NADH oxidase through anaerobes like Treponema denticola. Thus,
the biofilm character of plaque bacteria produces protective en-
zymes and the coexistence of aerobes, anaerobes, and micro-
aerophiles [49]. When this balance is disturbed, more acidification
in the oral cavity can lead to dental caries. The pH of plaque and the
concentration of volatile acids and lactic acid present before and
after exposure to sugars have been studied. It was seen that after a
period of 30 min with sugar, the concentration of
L
-lactate had
increased the pH recovery from acidity was lower. The same effect
can be seen when commercial teeth whitening agents are used as
the peroxides can induce high acidity levels in a short period of
time. However, organic acids from fruits do not cause the enamel to
erode at the same rate as the level of acidity is low [50,8].
6. Industrial pharmacy of whitening agents
The desire to gain whiter teeth has made tooth bleaching the
most sought-after treatment [51,52]. Tooth whitening is a process,
Fig. 3. A scheme of the structure of tooth enamel.
A. Gasmi Benahmed, A. Gasmi, A. Menzel et al. Journal of Oral Biosciences xxx (xxxx) xxx
5

which lightens the color of teeth. This whitening can be achieved by
changing the intrinsic color or removing or controlling the extrinsic
stains (Fig. 4). In 1989 with the introduction of tray bleaching,
dentistry has increased tooth whitening, and individuals have been
looking for bleaching techniques, which work the best [53].
Teeth whitening isone of the most requestedcosmetic services at
the office of a dentist. Whether one uses a 10% carbamide peroxide
with 3% hydrogen peroxide or OTC whitening strips with 6% peroxide
or in-office bleach with about 25e35% hydrogen peroxide, the result
is generally the same as there is the oxidation of organic pigments or
chromogens found in the tooth [54]. The cost of the product is
determined by the differences in concentration and exposure time.
These common commercial synthetic agents like hydrogen
peroxide and carbamide peroxide [55,56] can penetrate the enamel
and dentine, causing faster erosion of teeth, and it has been proved
in clinical trials that the overall safety of peroxides is in question
and can lead to potential complications such as teeth deproteini-
zation and demineralization. Although many over the counter teeth
whitening products are available for at-home and in-office whit-
ening with these above compounds, many people are now looking
for safer options to bleach and perform whitening of teeth, with
natural ingredients such as limes, lemons, strawberries, apples, and
other fruits, which contain organic acids helping to whiten the
enamel safely [57]. Valid concerns have occurred using chemical
bleaching products for months and years with long-term adverse
effects on the soft and hard tissues, which cannot be ruled out
when these products are overused. Clinical experience and clinical
trials; however, it has proved that if the products are used correctly,
it is quite safe to use [53].
Tooth discoloration can be due to many factors. Extrinsic
staining can be attributed to environmental factors, including
pigments in food and beverages and antibiotics like tetracycline or
smoking [58]. Intrinsic staining occurs in early childhood or at
birth and cannot be removed through prophylactic stain removal.
As people age, the teeth can appear yellower over time. Thus, it is
needed to brush and floss regularly to prevent the build-up of
tartar and plaque on the tooth's surface. This form of yellow
discoloration can be treated through bleaching. An individual's
enamel can wear out with time, revealing the dentine found in-
side, yellow in color. The thinner the enamel, the more likely the
dentine will show. However, for this instance, bleaching products
will be of little use [59].
Vital tooth bleaching with natural ingredients would be a safe
and effective aesthetic procedure to treat subjects with discolored
teeth.
7. Natural ingredients in teeth whitening
The enamel, which is the tooth's outer covering, is generally
white, and the dentine below is yellow or yellow-brown. When the
enamel wears out, it begins to show the dentine below. Commercial
whitening agents on long exposure over a period can wear out the
enamel and is bad for the teeth. High acidic and sweet food, gum
disease, aging, and neglect of hygienic standards are known factors
to bring about tooth enamel decay.
The natural ingredients listed are known to help whiten teeth
more safely than hydrogen peroxide or hydroxyl carbamide alone.
Herbal medicines are finding their more and more usefulness in the
arena of dentistry [60].
Limonene, a predominant component of citrus fruit peels
essential oil, has shown great promise in teeth whitening. This
ingredient can easily be used in homes to whiten teeth [61].
Commercial products incorporate limonene in their mouthwashes
with citric-based ingredients, helping to whiten teeth and prevent
plaque formation.
Another compound, which is found in citrus fruits, is
L
-ascorbic acid (vitamin C). As a popular antioxidant, it helps to
prevent gum disease and improves the gingival index. It helps in
preventing caries and tooth loss. Ascorbic acid from natural fruits
and vegetables can be considered a good alternative to hydrogen
peroxide or carbamide peroxide for teeth whitening [51]. Citric
acid is another predominant compound of citrus fruits. It is a
weak organic acid with mild bleach properties. This compound is
a popular ingredient in toothpaste and mouthwashes, helping to
whiten the teeth [62]. Malic acid is another weak acid in fruits,
including apples, grapes, and cherries which helps whiten the
teeth in a nondestructive way [62]. Being weak acids, these
components help to bring about a mild whitening effect to the
teeth. Thus, it can be seen that the abovementioned fruits can
help to provide a polishing effect on the superficial layer of the
enamel.
Phthalimido peroxy caproic acid found in Vanilla fruits has
shown to be an ingredient that can whiten teeth. The product
iWhite Instant has caproic acid incorporated, and this can be
bought over the counter and is an effective whitening agent
[63]. Lactic acid, which is found in dairy milk products, helps
prevent periodontitis by hampering the growth of bacteria,
which is involved in gingivitis. Lactic acid is a bio-protective
agent, and it helps control oral infections and keep the mouth
healthy.
There are naturally occurring enzymes to help in bringing about
the whitening of teeth. Lactoperoxidase is an enzyme, which is
found in saliva, and it is an antibacterial agent. Its oxidized product
is a potent bactericidal compound. This compound is enough to
prevent plaque formation and supplement it as an intake helping
inhibit the homologous plaque formation [64]. Bromelain and
papain are also enzymes that are found in fruits of pineapple and
papaya, respectively. These protease enzymes are incorporated
commercially in toothpaste and mouthwashes to reduce plaque
formation. These two enzymes are antiplaque, anti-gingivitis and
help maintain good dental health by reducing the stains in the
teeth [65,66]. Actinidain is also like papain found mostly in Kivi
fruits, and it also helps to remove the teeth' biofilms. The accu-
mulation of calculus and tartar brings about discoloration of teeth,
and this component helps remove the biofilm to whiten teeth.
Actinidain is a non-peroxidase-based compound that does not
bring about the erosion of teeth used for whitening [67]. Activated
charcoal, a processed form of porous carbon, adsorbs chemicals and
protects the teeth from being stained. Thus, the high adsorption
properties of charcoal make it a very good agent for teeth
whitening and is currently very popular in commercial use to
whiten teeth [68].
Commonly found, banana peel is a good whitening agent and a
great source of minerals for the teeth used at home. A quick brush
with the peel helps replenish potassium and prosperity, helping to
re-mineralize and strengthen the teeth.
The re-whitening effect of strawberry juice on stained coffee
teeth was also proved experimentally [69]. Strawberry juice pro-
vides a bleaching effect due to its acidic properties, working as a
strong oxidizing agent on the tooth's enamel surface. There were
differences in the tooth whitening level between immersion in
strawberry juice, apple juice, and mineral water, with the most
effective tooth whitening level found in the strawberry juice im-
mersion [70].
Polyherbal toothpaste uses these agents and Himalayan rock
salt, which has a certain percentage of fluoride to strengthen teeth
[25,71,27]. Products of herbal origin such as chamomile, eucalyptus,
fennel, echinacea, ginger, tincture of myrrh, tea tree oil, and clove
oil are applied in oral hygiene maintenance [72]. The anti-
inflammatory effect of Aloe vera juice has a positive impact on
A. Gasmi Benahmed, A. Gasmi, A. Menzel et al. Journal of Oral Biosciences xxx (xxxx) xxx
6

patients with sore ridges and ill-fitting dentures and partials due to
a decrease of irritation caused by fungi and bacteria [73], and it
leads to healthier oral cavity and teeth whitening by the natural
way. However, very important for oral hygiene is the careful and
regular brushing of teeth using polyherbal pastes.
The cortex of Salvadora persica, namely miswak, demonstrates
the whitening effects on extracted stained teeth [74,75]. Miswak
has a long history of oral hygiene and tooth whitening in Asian
countries [76e78]. Traditional use of S. persica as an antimicrobial
toothbrush stick for oral hygiene and to treat gum inflammation is a
part of the Greeko-Arab medical system and is a centuries-old
practice [79]. Eucalyptus globulus,Rosmarinus officinalis, and
Monarda fistulosa essential oils can also enhance oral health by
acting as an antimicrobial agent, helping to reduce the microbial
load and keeping the mouth fresh [80,81]. Tea tree (Melaleuca
alternifolia) essential oil with terpenes-4-ol (30%e40%) as a main
active principle responsible for its antibacterial and antifungal
properties [60] is a very effective antiseptic agent [72].
It is important to remember that applying the extracts and
essential oils of plants with high antioxidant properties [81,82] can
strengthen the previously bleached teeth' enamel [83].
Nicotine gum is a motivation for tobacco smokers who reduce
the stain caused by smoking and is a good nicotine replacement
therapy. For instance, 2e4 mg nicotine gum helps to reduce the
discoloration of teeth [84]. Sodium bicarbonate is a very common
ingredient at home with slight abrasive effects that help remove
plaque and whiten teeth.
A summary of the main natural components commonly used in
the teeth whitening process is given in Table 1.
Hydrogen peroxide and hydroxyl carbamide are powerful com-
mercial synthetic agents, which bring about a bleaching effect on teeth.
However, using these compounds combined with natural organic acids
can act as an effective and not harmful whitening agent [85].
To minimize the risks of bleaching on teeth, resin composite,
and bonding to patients by synthetic agents, clinicians should
inform them about the possible changes [86].
Fig. 4. Different techniques for bleaching of tooth enamel.
A. Gasmi Benahmed, A. Gasmi, A. Menzel et al. Journal of Oral Biosciences xxx (xxxx) xxx
7

8. Conclusion
Teeth whitening is an effective way of lightening the natural
color of one's teeth without removing any of the tooth surface.
Hydrogen peroxide and carbamide peroxide as components of
the most popular commercially available whiteners cause tooth
deproteinization and demineralization through oxidation pro-
cesses. However, at the same time, theylead to the lightening of the
demineralized teeth by breaking the organic structure. It can have
negative adverse effects on long-term use as the enamel gets
eroded fast to expose the dentine, which can affect the strength of
the tooth and ultimately result in being an easy target for dental
caries and the loss of a tooth. Alternative to harsh chemicals
available as teeth whiteners in the form of gels, strips, and paste
now organic components, found in natural ingredients like lemons,
strawberries, oranges, and other fruits like papaya or activated
charcoal help in bringing about progressive whitening of teeth
which is safer for the teeth as it is mild and the same effect can be
achieved.
When studying the metabolism and physiology of teeth, it was
shown that there are many reasons, which lead to discoloration of
teeth. The enamel of teeth is a porous structure, and due to this, it
leads to the percolation of dyes and stains. Common ingredients
like tea and coffee and antibiotics like tetracycline and food dyes
can percolate into the teeth, and thus, the stain can remain.
Smoking is also a factor, which causes discoloration of the teeth. In
addition, with aging, the teeth tend to discolor with the accumu-
lation of stains and the enamel wearing out to expose the dentin,
which is yellow in color. Calculus and tartar formation can also
affect the color of teeth leading to discoloration. As discussed
before, dental plaque, which is formed naturally as a biofilm,
consists of aerobic and anaerobic bacteria, forming as a coating on
the teeth. The dental plaque can lead to dental caries when cario-
genic bacteria multiply in a conducive atmosphere, which is acidic,
leading to finally losing a tooth.
It cannot be underestimated the periodic examination of the
teeth condition by dentists and their professional advice. Thus, as
preventive measures, it is important to be careful in adopting the
right whitening methods, which would give teeth their aesthetic
beauty and help to protect them.
Ethical approval
This article does not contain any studies with human partici-
pants or animals performed by any of the authors.
CRediT authorship contribution statement
Asma Gasmi Benahmed: Conceptualization, Literature search,
Writing eoriginal draft. Amin Gasmi: Conceptualization, Literature
search, Writing eoriginal draft. Alain Menzel: Conceptualization,
Literature search, Writing eoriginal draft. Ihor Hrynovets: Writing
ereview &editing. Salvatore Chirumbolo: Writing ereview &
editing. Mariia Shanaida: Writing ereview &editing. Roman
Lysiuk: Writing ereview &editing. Yurii Shanaida: Writing e
review &editing. Maryam Dadar: Writing ereview &editing. Geir
Bjørklund: Writing eoriginal draft, Writing ereview &editing.
Conflicts of interest
The authors declare that they have no conflict of interest.
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D
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