Tooth whitening
Tooth whitening or tooth bleaching is the process of lightening the color of
human teeth. Whitening is often desirable when teeth become yellowed over time
for a number of reasons, and can be achieved by changing the intrinsic or
extrinsic color of the tooth enamel.
The perception of tooth colour is multi-factorial. Reflection and absorption
of light by the tooth can be influenced by a number of factors including
specular transmission of light through the tooth; specular reflection at
the surface; diffuse light reflection at
the surface; absorption and scattering of light within the dental tissues;
enamel mineral content; enamel thickness; dentine colour, the human observer,
the fatigue of the eye, the type of incident light, and the presence of
extrinsic and intrinsic stains. Additionally, the perceived brightness of
the tooth can change depending on the brightness and colour of the background.
The combination of intrinsic colour and the presence of extrinsic stains
on the tooth surface influence the colour and thus the overall appearance of
teeth. The scattering of light and absorption within enamel and dentine determine
the intrinsic colour of teeth and because the enamel is relatively translucent,
the dentinal properties can play a major role in determining the overall tooth
colour. On the other hand, extrinsic stain and colour is the result of
coloured regions that have formed within the acquired pellicle on the enamel
surface and can be influenced by lifestyle behaviours or habits. For example,
dietary intake of tannin-rich foods, poor tooth
brushing technique, tobacco products,
and exposure to iron salts and chlorhexidine can
darken the colour of a tooth.
With increasing age, teeth tend to be darker in shade. This can be
attributed to secondary dentin formation and thinning of enamel due to tooth
wear which contributes to a significant decrease in lightness
and increase in yellowness. Tooth shade is not influenced by gender or race.
A healthy white smile is on just
about everybody’s wish list. There are many reasons why your teeth may darken.
Some we can’t control, such as age or accidents when we are young that may
disturb our tooth enamel’s development. That’s why it’s important to discuss
any plans you have for whitening your teeth with your dentist. He or she will
be able to tell you if your tooth discoloration is simply staining caused by
lifestyle factors (such as drinking too much coffee) or may be more a matter of
dental health. Although whitening is usually done for cosmetic reasons, your
dentist can guide you on what options you have for treating the type of
staining you have. The good news is that in many cases reversing teeth stains
is within our reach. That makes pursuing a healthy white smile worthwhile.
Tooth stains caused by lifestyle
habits:
Foods/drinks: Coffee,
tea, colas, wines, and some starchy foods such as pasta or potatoes, can create
conditions that cause staining.
Tobacco use: Smoking
or chewing tobacco can stain teeth.
Tooth stains caused by dental
health:
Poor dental hygiene: Forgetting
to brush and floss your teeth can cause plaque and food stains to build up.
Skipping professional dental cleanings can also allow stains to start.
Disease: Diseases
that prevent normal development of tooth enamel (the white exterior of your
teeth) and dentin (the more porous “yellower” core under enamel) can lead to
tooth discoloration. Certain medical treatments, such as head and neck radiation and chemotherapy can cause teeth to discolor. Some infections
in pregnant mothers can affect enamel development in your baby and discolor
their teeth.
Medications: It
has long been known that certain drugs discolor teeth in developing children.
The antibiotics tetracycline and doxycycline can affect enamel formation in
children under the age of 8. Mouth rinses and washes containing chlorhexidine
and cetylpyridinium chloride can also stain teeth. Antihistamines (like
Benadryl®), antipsychotic drugs and antihypertensive medications also can cause
teeth discoloration.
Dental materials: Some
amalgam restorations, especially silver sulfide-containing materials, can give a
gray-black cast to your teeth.
Aging: As
you age, the outer layer of enamel on your teeth gets worn away exposing the
yellow dentin. Your tooth dentin also grows as you age, which decreases the
size of the pulp. The translucency of the tooth reduces, making it look darker.
Genetics: Thicker
and whiter enamel runs in some families.
Environment: During
tooth formation, too much fluoride either from environmental sources (high fluoride
levels in water) or from excessive use of (fluoride applications, rinses,
toothpaste) can cause fluorosis, which look like white spots on teeth.
Trauma: During
sports, kids can get hit in the mouth. If they are younger than 8, the damage
can disturb enamel formation. Trauma can also discolor adult teeth when a
sports injury or other impact causes blood flow to decrease to the tooth or the
nerve to die.
The
chemical degradation of the chromogens within or on the tooth is termed as bleaching.
Hydrogen peroxide (H2O2) is the active ingredient most commonly used in whitening
products and is delivered as either hydrogen peroxide or carbamide peroxide. Hydrogen peroxide is analogous to
carbamide peroxide as it is released when the stable complex is in contact with
water. When it diffuses into the tooth, hydrogen peroxide acts as an oxidising agent that breaks down to produce unstable free radicals. In the spaces between the inorganic salts in tooth enamel, these unstable free radicals attach to organic pigment
molecules resulting in small, less heavily pigmented components. Reflecting
less light, these smaller molecules create a "whitening effect". There
are different products available on the market to remove stains. For
whitening treatment to be successful, dental professionals should correctly diagnose
the type, intensity and location of the tooth discolouration. Time exposure and the concentration
of the bleaching compound, determines the tooth whitening endpoint.
Prior
to proceeding to tooth whitening alternatives, it is advised that the patient
comes into the dental office to have a comprehensive oral examination that
consists of a full medical, dental, and social history. This will allow the
clinician to see if there is any treatment that needs to be done such as
restorations to remove caries, and to assess whether or not the patient will be
a good candidate to have the whitening done.
In dental office :
Before the treatment, the clinician should examine the patient: taking a
health and dental history (including allergies and
sensitivities), observe hard and soft tissues, placement and conditions of
restorations, and sometimes x-rays to determine the nature and depth of possible
irregularities. If this is not completed prior to the whitening agents being
applied to the tooth surface, excessive sensitivity and other complications may
occur.
The whitening shade guides are used to measure tooth colour. These
shades determine the effectiveness of the whitening procedure, which may vary
from two to seven shades. These shades may be reached after a single in office
appointment, or may take longer, depending on the individual. The effects of
bleaching can last for several months, but may vary depending on the lifestyle
of the patient. Consuming tooth staining foods or drinks that have a strong
colour may compromise effectiveness of the treatment. These include food and
drinks containing tannins such as; coffee, tea, red wines, and curry.
In-office bleaching procedures generally use a light-cured protective
layer that is carefully painted on the gums and papilla (the tips of
the gums between the teeth) to reduce the risk of chemical
burns to the soft
tissues. The bleaching agent is either carbamide peroxide, which
breaks down in the mouth to form hydrogen
peroxide, or hydrogen peroxide itself. The bleaching gel typically
contains between 10% and 44% carbamide peroxide, which is roughly equivalent to
a 3% to 16% hydrogen peroxide concentration. The legal percentage of hydrogen
peroxide allowed to be given is 0.1–6%. Bleaching agents are only allowed to be
given by dental practitioners, dental
therapists, and dental
hygienists.
Bleaching is least effective when the original tooth color is grayish
and may require custom bleaching trays. Bleaching is most effective with yellow
discolored teeth. If heavy staining or tetracycline damage
is present on a patient's teeth, and whitening is ineffective (tetracycline
staining may require prolonged bleaching, as it takes longer for the bleach to
reach the dentine layer), there are other methods of masking the stain.
Bonding, which also masks tooth stains, is when a thin coating of composite
material is applied to the front of a person's teeth and then cured with a blue
light. A veneer can also mask
tooth discoloration.
In-chair whitening is faster and more effective in comparison to the
take-home bleaching options. Some clinicians also make custom bleaching trays
for you, which can take up to a week to create, so that after the whitening
treatment is completed, you are able to use these trays in the future for
maintenance of your bleaching with at home kits or for the use of desensitising
products.
1-Light-accelerated
bleaching :
Power or light-accelerated bleaching uses light energy which is intended
to accelerate the process of bleaching in a dental office. Different types of
energy can be used in this procedure, with the most common being halogen, LED, or plasma arc. Use of light during bleaching increases the risk
of tooth sensitivity and may not be any more effective than bleaching without
light when high concentrations of hydrogen peroxide are used. The ideal source
of energy should be high energy to excite the peroxide molecules without
overheating the pulp of the tooth. Lights are typically within the blue light
spectrum as this has been found to contain the most effective wavelengths for
initiating the hydrogen peroxide reaction. A power bleaching treatment
typically involves isolation of soft tissue with a resin-based, light-curable
barrier, application of a professional dental-grade hydrogen peroxide whitening
gel (25–38% hydrogen peroxide), and exposure to the light source for 6–15 minutes.
Recent technical advances have minimized heat and UV emissions, allowing for a
shorter patient preparation procedure.
For any whitening treatments, it is recommended that a comprehensive
examination of the patient is done including the use of radiographs to aid in
the diagnosis of the current condition of the mouth, including any allergies
that may be present. The patient will need to have a healthy mouth and free of
periodontal disease or caries and to have had a debridement/clean done to
remove any tartar or plaque build up.
It is recommended to avoid smoking, drinking red wine, eating or
drinking any deeply coloured foods after this as the teeth may stain considerably
straight after treatment.
2- Nanoparticle catalysts for reduced hydrogen peroxide concentration :
A recent addition to the field is new light-accelerated bleaching agents
containing lower concentrations of hydrogen peroxide with a titanium
oxide nanoparticle-based catalyst. Reduced
concentrations of hydrogen peroxide cause lower incidences of tooth
hypersensitivity. The nanoparticles act as photocatalysts, and their size prevents them from diffusing
deeply into the tooth. When exposed to light, the catalysts produce a rapid,
localized breakdown of hydrogen peroxide into highly reactive radicals. Due to
the extremely short lifetimes of the free radicals, they are able to produce
bleaching effects similar to much higher concentration bleaching agents within
the outer layers of the teeth where the nanoparticle catalysts are located.
This provides effective tooth whitening while reducing the required
concentration of hydrogen peroxide and other reactive byproducts at the tooth
pulp.
3- Internal bleaching :
Internal bleaching is a process which occurs after a tooth has been
endodontically treated. This means that the tooth will have had the nerve of
the tooth extirpated or removed through a root canal treatment at the dentist
or by a specialist endodontist. Internal bleaching is often
sought after in teeth which have been endodontically treated as tooth
discolouration becomes a problem due to the lack of nerve supply to that tooth.
It is common to have this internal bleaching done on an anterior tooth (a front
tooth that you can see when smiling and talking). A way around this is by
sealing off the bleaching agent inside the tooth itself and replacing it every
few weeks until the desired shade has been achieved. The amount of time between
appointments varies from patient to patient and with operator preference until
the desired shade has been achieved. Even though this is a great option,
the disadvantage of this treatment is a risk of internal root resorption of the
tooth that is being internally bleached. This may not occur in every patient or
every tooth, and its occurrence is difficult to determine prior to completing
the treatment.
At home :
At home tooth whitening products are available from dentists or 'over the counter' (OTC). At home whitening methods include
over-the-counter strips and gels, whitening rinses, whitening toothpastes, and
tray-based tooth whiteners. OTC products can be used for milder cases of tooth
staining. Home-based bleaching (following manufacturer's instructions) results
in less tooth sensitivity than
in-office bleaching.
1-Strips and gels :
The plastic whitening strips contain a thin layer of peroxide gel and
are shaped to fit the buccal/labial surfaces of teeth. Many different
types of whitening strips are available on the market, after being introduced
in the late 1980s. Specific whitening strip products have their own set of
instructions however the strips are typically applied twice daily for 30
minutes for 14 days. In several days, tooth colour can lighten by 1 or 2 shades.
The tooth whitening endpoint does depend on the frequency of use and
ingredients of the product.
Whitening gels are applied onto the tooth surface with a small brush. The
gels contain peroxide and are recommended to be applied twice a day for 14 days. The
tooth whitening endpoint like that of the whitening strips.
2-Rinses :
Whitening rinses work by reaction of the oxygen sources such as hydrogen
peroxide within the rinse and the chromogens on or within the tooth. It is
recommended to use twice a day, rinsing for one minute. To see an improvement in shade colour, it can
take up to three months.
3-Toothpaste :
Whitening toothpastes differ from regular toothpastes in that they
contain higher amounts of abrasives and detergents to be more effective at
removing tougher stains.
Some whitening toothpastes contain
low concentrations of carbamide peroxide or hydrogen peroxide which help
lighten tooth colour however they do not contain bleach (sodium hypochlorite). With
continuity of use over time, tooth colour can lighten by one or two shades.
4-Tray-based :
Tray-based tooth whitening is achieved by wearing a fitted tray
containing carbamide peroxide bleaching gel overnight or for two to four hours
a day. If manufacturer's instructions are followed, tooth whitening can
occur within three days and lighten teeth by one or two shades. This type of
tooth whitening is available over-the-counter and professionally from an oral
health professional.
5-Baking soda :
Baking soda is a safe, low abrasive, and effective stain removal and
tooth whitening toothpaste. Tooth whitening toothpaste that have excessive
abrasivity are harmful to dental tissue, therefore baking soda is a desirable
alternative. To date, clinical studies on baking soda report that there
have been no reported adverse effects. It also contains acid-buffering
components that makes baking soda biologically antibacterial at high
concentrations and capable of preventing growth of Streptococcus mutans. Baking
soda might be useful for caries-prone patients as well as those who wish to
have whiter teeth.
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