White & Shine
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White & Shine

Teeth tend to lose their whiteness with age, so it’s crucial to understand teeth whitening options on the market.

Why do teeth lose their whiteness? For one, as we grow older, the outer layer of the teeth’s enamel gets worn away, revealing the underlying material known as dentin, which is naturally yellow. But tooth discolouration can also happen because of the following reasons.

Causes of Discolouration

Food and drinks

One common culprit is what we ingest. Coffee, tea, cola and wine are notorious for staining teeth. The acidity of these beverages erodes the enamel, the hard surface of the teeth. Smoking and chewing tobacco also stain teeth because of the nicotine and tar in them (nicotine is colourless, but turns yellow when oxidised). To what extent the discolouration occurs also depends on how well we brush, floss and use mouthwash to remove plaque and offending stain-producers.

Diseases that affect enamel and tooth colour

The development of enamel in infants can be affected by infections when the mother is pregnant. Irradiation of the head and neck and chemotherapy can also cause teeth to discolour.


Antibiotics such as tetracycline and doxycycline can discolour teeth that are still developing, such as those in children aged eight and below. Antihistamines such as Benadryl, antipsychotic drugs, and medication for high blood pressure can also discolour teeth. Ironically, mouthwash containing chlorhexidine and cetylpyridinium chloride have been known to stain teeth!

Dental materials

Dental amalgams, especially those containing silver sulfide, can turn teeth greyish.


In another irony, fluoride, which is often associated with dental health, can cause teeth to discolour. It can be present in high amounts in water or after excessive use of fluoride toothpaste and oral fluoride supplements.


Physical distress caused to teeth, such as damage by a fall, can disrupt proper enamel formation in children, whose teeth are still developing. Physical trauma can also cause internal discoloration to adult teeth, turning them blue or grey due to internal bleeding, as the blood leaks in through the dental nerves.

Whitening Options

If you’re thinking of whitening your teeth, know that options fall into two categories:

  • Category 1
    peroxide-containing bleaching agents
  • Category 2
    whitening toothpastes

Extrinsic stains - those caused by food and drinks, smoking and poor dental hygiene - are best removed through routine scaling and polishing. Intrinsic discolourations - those caused by medication, fluoride and ageing - can be treated with professionally prescribed teeth whitening procedures. Some options for you to consider:

Category 1: in-office teeth whitening by your dentist

This provides immediate results, with whiter teeth after just one session. Depending on the discolouration, multiple sessions may be necessary. To maximise contact between teeth and the whitening gel, routine scaling and polishing will first be done. Then the dentist applies a whitening gel to the teeth, and activates it with a light source.

Category 1: take-home teeth whitening kit from your dentist

Results are slower compared to in-office teeth whitening; they usually can only be seen after a few weeks.

During your first visit, your dentist will create dental impressions to make customised trays for your teeth. On your second visit, you will receive the trays and syringes of bleaching gels. Scaling and polishing are done at this point to ensure maximum contact between the gel and the teeth.

Depending on your teeth’s condition and the bleaching gel’s concentration, bleaching duration lasts between 20 minutes and two hours daily.

Extrinsic stains are best removed through routine scaling and polishing. Intrinsic discolourations can be treated with professionally prescribed teeth whitening procedures.

Category 1: over-the-counter teeth whitening kits

Common forms are trays and strips you paste on your teeth. These aren’t prescribed by a dental professional so it would be wise to exercise caution. Using products with excessive hydrogen peroxide (H2O2) can damage teeth and gums, and cause sensitivity. See sidebar.

Category 2: whitening toothpastes

These contain polishing or chemical agents that remove surface stains through non-bleaching actions. Whitening toothpastes available at retail outlets do not require a prescription; however, they cannot remove discolouration from intrinsic stains.


If you’re taking the plunge into DIY whitening, be sure the hydrogen peroxide levels in the products you choose are well within the Singapore Dental Association’s guidelines.

It recommends a comprehensive oral examination by a dental professional to determine the most appropriate whitening treatment. It also suggests the following regarding the sale and prescription of tooth whitening or bleaching products:

  • Tooth whitening products with concentrations of up to 0.1% hydrogen peroxide (equivalent to 0.3% carbamide peroxide) are allowed in consumer oral hygiene products. These include tooth whitening toothpastes.
  • Tooth whitening products with up to 6% hydrogen peroxide (equivalent to 18% carbamide peroxide) can only be prescribed for a patient’s home use by a registered dental practitioner, and only after consultation. Such products are not for direct sale to the public.
  • Tooth whitening products with over 6% hydrogen peroxide and up to 35% carbamide peroxide can be legally accessed only by a registered dental practitioner. These products should only be applied to patients in dental clinics under the supervision of a registered dental practitioner.