Individuals with a history of extreme sensitivity to hot and cold food or drink, fracture lines in their teeth, large dental pulps, and severe loss of enamel. In such cases the procedure may precipitate sensitivity.

Decay and gum disease should be treated before any tooth whitening procedure is carried out. Tooth whitening should not be carried out on individuals with peroxide or a plastic allergy, or during pregnancy and breast feeding. Patients with severe tetracycline staining or severe fluorosis may need to consider veneers.

Safety studies have shown that whitening the teeth using the home whitening kit prescribed by the dentist is perfectly safe on the teeth, cheeks, gums and tissues of the mouth. Sometimes, if the gel touches the gum for a prolonged period of time, white areas may appear where the gum has dehydrated slightly. This will resolve within several days.

Tooth whitening will not damage teeth if the instructions given by the dentist are followed.

Several studies have been carried out to investigate the reaction of the pulp (contains the nerve and blood supply to the tooth) to the bleaching process. Evidence shows that bleaching may either have no effect or may cause an initial, mild, localised pulp reaction which is reversible several weeks post treatment.

There are no reports in the literature indicating that bleaching may exert a negative impact on existing restorations. Defective restorations should, however, be replaced before bleaching to minimise potential sensitivity.

Personal habits may need to be modified to achieve and maintain the desired goal of whiter teeth.
Teeth should be dry, and cleaned of debris before any bleaching agent is applied. During bleaching, teeth may be slightly dehydrated and consumption of food and drinks which can cause staining should be kept to a minimum. These foodstuffs should also be kept to a minimum for two weeks after tooth whitening. Avoiding smoking will also help prevent staining of he teeth.

If the teeth have white spots on them before whitening, these spots will appear whiter during the first few days, however, the contrast between the spots and the rest of the tooth will be less as the whitening progresses.

You may notice new white spots occurring on the teeth while you are undertaking the whitening treatment. These white spots were already present on the teeth before whitening. As the teeth become lighter, the white spots can become more visible.

Some teeth may appear banded with lighter/ whiter areas. This is because these bandings are originally present on the tooth but when the tooth was dark, these bandings were not obvious. As the tooth becomes lighter, the lighter parts of the tooth will lighten first followed by the darker banded area.

The necks of the teeth (near the gum) do not lighten as much as the rest of the tooth because the enamel is much thinner in this area, and the dentine will show through the teeth more than before they are whitened.

The most commonly observed side effects to Hydrogen Peroxide are tooth sensitivity to cold and occasional irritation of the soft tissues in the mouth, particularly the gums.

Tooth sensitivity often occurs in the early stages of bleaching treatment. About 67% of patients develop transient sensitivity during whitening, normally around the necks of the teeth where the gums have receded. If sensitivity occurs, stop the whitening process and use the trays with desensitising toothpaste (containing potassium nitrate) in them for an hour a day. Alternatively, you can rub the desensitising toothpaste into the gum margins with your finger, 5 times per day for a few days. This may take up to 2-4 days after which treatment can be continued. Usually, sensitivity will completely disappear once whitening stops.

In most cases, gum irritation is caused by an ill-fitting bleaching tray rather than the actual bleaching agent. Both of these conditions are usually temporary and disappear within a few days of the treatment finishing. If you encounter any of these side effects, you should consult your dentist.

Some individuals experience better effects from tooth whitening than others. Tooth whitening should last for 18-24 months. At this point you may choose to have a touch up treatment and the colour will usually change to the optimal shade readily. The effect is less likely to last as long if you smoke, or eat or drink products that can stain the teeth, for example, red wine, tea, coffee and berries.

The evidence on safety published to date tends to suggest that bleaching is a relatively safe procedure. Hydrogen peroxide breaks down into water and oxygen.

Cheaper, over the counter bleaching kits often contain an insufficient concentration of Hydrogen Peroxide to be effective. Some may contain acetic or citric acid as active ingredients. These acids have too low a pH (too acidic) and can cause significant structural damage to enamel when used for extended periods of time and worsen the discolouration through erosion. Bleaching trays provided are not made to fit your mouth and can therefore cause increased leakage and soft tissue irritation.

Whitening toothpastes do not affect the natural colour of teeth but may be effective at removing surface (extrinsic) staining because they contain abrasives. Before you use a tooth whitening product you should consult your dentist.

Tooth whitening only works on natural teeth and will have no effect on fillings crowns and veneers. If you have white fillings in your front teeth, these should be replaced approximately 4 weeks post- bleaching to ensure a good colour match and bond strength.

Very severe tetracycline stained teeth may not respond or have a limited response to tooth whitening. In these cases, porcelain veneers may be the treatment of choice. Mild to moderate tetracycline staining does, however, respond to extended bleaching regimes of 3-6 months. White fluorosis spots do not tend to bleach but will become less obvious as a result of lightening of the surrounding tooth area. It is very rare, but sometimes teeth do not lighten at all.

The effect of the bleaching gel on the foetus is unknown. You will swallow some of the gel while you are bleaching with home kits. It is now generally accepted to avoid unnecessary medical interventions during pregnancy in order to minimise any possible risks to the health of the foetus.