Teeth whitening: What it is, methods and risks

Teeth whitening has become one of the most popular cosmetic dental procedures, offering quick and effective solutions to improve the appearance of one’s smile. As interest in cosmetic dentistry grows, many people are turning to teeth whitening treatments to restore the brightness of their teeth, which have been affected by factors such as food, drink, smoking or ageing.

Teeth whitening is a procedure that involves the use of special substances to remove stains and lighten the shade of the teeth. The most common substances used are hydrogen peroxide or carbamide peroxide, which work by oxidising stains on the surface of the teeth and in the deeper layers of the enamel.

Over time, teeth can lose their natural whiteness for a number of reasons:

• Food and drink: Coffee, red wine, tea and fizzy drinks are the most common causes of tooth discolouration.
• Smoking: The nicotine and tar in cigarettes stain the surface of the teeth and contribute to a yellowish or brownish tinge.
• Ageing: As we get older, tooth enamel thins, making the yellow dentine more visible.
• Trauma: Dental injuries can cause discolouration, particularly if the dental nerve is affected.
• Medicines: Antibiotics such as tetracycline can cause permanent discolouration if taken during childhood, when the teeth are still developing.
   

There are several options for teeth whitening, each with its own advantages and disadvantages. These fall into two main categories: professional whitening (carried out in a dentist’s surgery) and at-home whitening (using over-the-counter whitening products).

The effectiveness of whitening can be influenced by patient-related factors (for example, age, gender and the initial colour of the teeth), the whitening material used (e.g. the type of peroxide compound, peroxide concentration and other ingredients) and the method of application (e.g. contact time, frequency of application, and enamel protection prior to the whitening treatment). These factors contribute to the effectiveness of the whitening process and may affect the long-term stability of the whitening results achieved

Although teeth whitening is considered a safe procedure, there are certain risks associated with it, particularly if it is not carried out correctly or if unsuitable products are used:

• Tooth sensitivity: Some patients report sensitivity to extreme temperatures following teeth whitening. This is usually temporary and subsides after a few days. By following an appropriate protocol, the risks of tooth sensitivity can be significantly reduced.
  The mechanisms underlying tooth sensitivity are not fully understood; however, it is believed that the sensation is caused by the pulp’s response to H₂O₂ and free radicals. This assumption is largely based on in vitro studies showing that H₂O₂ from whitening gel applied to the enamel surface is capable of penetrating the enamel and dentine to reach the pulp chamber. In general, these studies show that <30 μg of H₂O₂ can reach the dental pulp following the application of gels containing up to 12% H₂O₂ to the enamel surface for up to 7 hours. The amount of H₂O₂ detected in the pulp chamber tends to increase with time and with the concentration of H₂O₂ in the gel, but not proportionally. It has been concluded that a quantity of 50,000 μg of H₂O₂ is required to inhibit pulp enzymes, so the amount of H₂O₂ detected as it penetrates the pulp chamber during tooth whitening does not cause damage to pulp tissues.
• Gum irritation: Whitening gels can cause irritation if they come into contact with the gums. During professional treatments, the dentist will protect the gums to minimise this risk.
  In-clinic whitening uses gels with high concentrations of H₂O₂, which can cause tissue burns on contact. Tissue ulceration is a chemical burn, sometimes referred to as ‘tissue bleaching’.
  The best treatment for this is to act immediately by applying water to the area to neutralise the damage. If caught early, the tissue turns red after about a minute, then returns to its pink colour. However, if strong whitening gel is left on the soft tissue and gums for too long, the ulceration takes much longer to heal and the patient may experience pain due to blisters.
• Uneven results: Teeth whitening can affect each tooth differently, particularly in cases where the patient has fillings or dental crowns, which do not change colour. It is important, before undertaking any type of teeth whitening, to seek advice from your dentist to determine whether old fillings or prosthetic work will need to be replaced following the treatment.

• Overuse of whitening products: Excessive use of whitening products can lead to damage to tooth enamel and the development of chronic sensitivity if they are not used in accordance with the dentist’s recommendations.

   

The effect of whitening on enamel has primarily been assessed in terms of three aspects: mineral loss, morphological changes to the surface, and alterations in surface microhardness. Most studies on the effect of whitening on enamel have been carried out using in vitro systems. The overall data indicate mineral loss during the whitening treatment; however, this does not appear to pose a significant risk due to the effective remineralisation mechanisms readily available in the oral cavity. Most scanning electron microscopy (SEM) studies and those examining surface microhardness have shown little or no change in the surface of bleached enamel.  Furthermore, studies have shown that certain soft drinks and fruit juices (e.g. orange, lemon and apple) can cause demineralisation and alterations to the morphology of the enamel surface comparable to, or greater than, those reported for whitening treatment. A six-month clinical study reported that daily use of a whitening gel containing 10% carbamide peroxide for six months did not adversely affect the surface morphology of human enamel.

After a teeth-whitening treatment, it is essential to follow a few preventive measures to maintain the results for as long as possible:

• Avoid foods and drinks that stain (such as coffee, red wine and tea) for at least the first few weeks after the treatment.
• Maintain good oral hygiene; brushing twice a day, flossing and using mouthwash help to remove plaque that can cause new stains.
• Use a straw when drinking coloured drinks.
• Avoid smoking.
• Visit your dentist regularly.

Teeth whitening can give you a brighter, more attractive smile, but to minimise potential risks and maximise the benefits, it is recommended that teeth whitening be carried out under the supervision of a dentist.
Therefore, when used correctly, teeth whitening is safe and effective.
Good oral hygiene and healthy eating habits can help you maintain a white, sparkling smile for longer.

“Teeth whitening is not just about the aesthetics of your smile, but about rediscovered confidence, increased self-esteem and a fresh new look.” – Dr Ionut Zaharii

References:

Safety issues of tooth whitening using peroxide-based materials