18: Dental bleaching systems

Chapter 18 Dental bleaching systems

Introduction

Over the past 20 years, the general public and therefore dental patients have become much more conscious of the appearance of their teeth. Their awareness of the treatment options dentists can offer has also increased owing to the increased media attention to dental health and cosmetic dentistry: there are many television programmes showing patient transformations using cosmetic surgery including cosmetic dentistry; and the public is bombarded with photographs of models with very white teeth in advertisements and glossy magazines. Although these photographs are very often ‘adjusted’ with the use of digital software tools, the perception that white, straight, perfect teeth are the norm and therefore desirable, has in many countries, contributed to a cultural shift, particularly in the USA. The market for cosmetic products and treatments has greatly increased, and it is now very common for patients to enquire about whitening their teeth during their dental appointment. Tooth bleaching is now the most commonly requested cosmetic service. Frequently, this appears in the patients’ minds to be more important than the treatment of dental disease. Beauty salons and hairdressers are also offering tooth whitening treatments although there are legal issues (in the UK) concerning non-dental care professionals carrying out any form of dental treatment.

Successful tooth bleaching can greatly improve the patient’s self-image, self-confidence and physical attractiveness. This can then lead to improved employment prospects and increased social confidence. Many products which are designed to lighten teeth can now be bought over the counter (OTC) from pharmacies and chemists and sometimes even in supermarkets. Other products are available only to dentists. Treatments with these products need to be carried out under professional supervision either directly by the clinician or by the patient carrying out the treatment at home, and returning to the dental clinic from time to time to allow the dentist to monitor their progress. Some treatment regimes combine both processes.

Products and techniques are available to lighten both vital and non-vital teeth. This chapter discusses the materials which are used to bleach teeth and the issues which surround their use.

Chemical Reaction: An Oxidizing Process

The currently available products used to bleach teeth are based on hydrogen peroxide. This is a chemical which, on decomposition, produces species which can take part in an oxidizing reaction on tooth tissue, that is oxygen-free radicals and water. Many products also contain carbamide peroxide or sodium perborate, which both break down to release hydrogen peroxide.

Carbamide peroxide is a compound of hydrogen peroxide and urea. In the presence of water, carbamide peroxide breaks down into its two main constituents. Carbamide peroxide products have been shown to be active even after 10 hours of use so enhancing their efficacy. Carbamide peroxide is also referred to as urea peroxide, perhydrol urea and carbamyl peroxide.

Sodium perborate reacts with water to form sodium borate and hydrogen peroxide. The amount of hydrogen peroxide produced using sodium perborate is less than that from a similar amount of carbamide peroxide.

Mode of action

The free radical oxygen species produced by these compounds pass through the pores in the enamel and later the dentine by diffusion that is, moving from areas of high concentration to areas of low concentration until equilibrium is achieved or the source of the species is exhausted. This starts within a matter of 15 minutes of applying the product. It is possible that the active ingredient may eventually reach the pulp. To reduce this risk only a small quantity of the material should be used as the active species penetrates all coronal tissues. The diffusion process in the cervical region of the tooth is more rapid as dentine is more porous in this region. Penetration beneath restorations may occur and there is now some evidence of interactions between amalgam and the active species, leading to mercury release.

The free radical oxygen species break down the high molecular weight coloured complex organic molecules which cause staining. The smaller molecules so produced reflect less light from or they are lost from the tooth tissue with the result that the tooth tissue appears lighter in colour. Generally speaking, after an hour’s clinical use these breakdown products are rendered inactive (Figure 18.1).

The concentration of hydrogen peroxide in products varies, depending on whether the product is available to the public as an OTC product or is licensed for use under the direct supervision of a dentist. Concentrations range from 3% to 38%, respectively. The concentration of carbamide peroxide in any commercial product is three times the concentration of the hydrogen peroxide liberated, i.e. 10% carbamide peroxide will break down to release 3.3% hydrogen peroxide.

The degree of shade change depends on:

Common Ingredients in Tooth Whitening Products

Besides the active ingredients discussed previously, several other chemicals are included in bleaching products by the manufacturers. See Table 18.1.

Table 18.1 Common chemical ingredients in tooth whitening products

Chemical Reason for inclusion
Hydrogen peroxide Active ingredient
Carbamide peroxide Source of hydrogen peroxide
Sodium perborate Source of hydrogen peroxide
Urea Stabilizer, and increases the pH, which is less irritant to soft tissue
Increased antibacterial effect
Glycerine Increases viscosity, so that the product is retained in the bleaching tray
Carbopol (polyacrylic acid polymer) Increases viscosity, decreases breakdown in saliva and slows release of oxygen
Alcohol ethoxylates or sodium xylene sulphonate Surfactant – promotes wetting by lowering surface tension or to solubilize one of the ingredients, such as an insoluble fragrance
Amorphous calcium phosphate (ACP) Decreases sensitivity by occluding the dentinal tubules with calcium phosphate
Improves enamel smoothness and restores lustre
Potassium nitrate Decreases sensitivity by altering nerve conduction
Fluoride (e.g. sodium fluoride) Decreases sensitivity by occluding the dentinal tubules
Promotes remineralization
Provides caries resistance
Neutralizers Alkaline substances to create neutral pH
Flavourings Increases patient acceptability
Carotene Converts light energy to heat so increasing the activation of hydrogen peroxide by speeding up its dissolution into free radicals in products intended to be exposed to light energy

Side Effects, Risks and Hazards

No medical or dental treatments are without risk. Tooth bleaching is generally a safe treatment, but there are some associated side effects:

Thermal sensitivity

The most common side effect of bleaching treatments is sensitivity to thermal stimuli and occurs in between 25% and 50% of patients. As mentioned earlier, the oxygen species diffuse slowly through the hard dental tissues, eventually reaching the pulp. The volume reaching this site is dependent on the initial concentration and amount used. Many patients experience peak sensitivity on day 3 of treatment. The sensitivity tends to be transient and usually abates 2 days after discontinuation of treatment. Sensitivity has been reported more commonly in the lower than the upper arch, probably because of with relatively smaller size and volume of the tooth crowns. For this reason, many clinicians treat the upper arch before embarking on the lower. This also allows the clinician and patient to see what final result may be achieved (Figure 18.2). Long-term studies have shown no detrimental effects of this sensitivity after a period of 7 years.

Some products have desensitizing chemicals included in their formula. Some clinicians advocate the application of desensitizing agents (such as sensitive dentifrices or mouthwashes containing potassium nitrate or neutral sodium fluoride) alternately with the bleaching chemicals in an attempt to reduce sensitivity.

Jan 31, 2015 | Posted by in Dental Materials | Comments Off on 18: Dental bleaching systems
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