The natural tooth color is determined by an inherent component associated with the enamel and dentin light absorption and diffusion optical properties and is influenced by the presence of surface or internal colour differences. Tooth bleaching is a highly conservative aesthetic treatment, with a favourable cost-advantage ratio, allowing the removal of all the organic components responsible of the pigmentations staining the teeth. It needs a preliminary clinical intraoral examination and a correct diagnosis and supervision by the dentist. Fundamental elements for the successful outcome of the treatment, patient related (personal needs, age, expectations, means) and operator related (product availability, knowledge of materials science), concur to the planning of a well suited therapeutic plan. Visible tooth pigmentations are not only an aesthetic problem but can also become a physical handicap and go further on and generate a self-image distortion with subsequent lack of confidence. Because of these reasons tooth bleaching has widely spread, becoming one of the most popular and successful aesthetic treatments. The growing public interest for smile beauty has been supported by a development and distribution of specialized and differentiated commercial products along with new application methodologies and dental bleaching procedure in the dentists’ clinical practice.
Intrinsic factors: they include irreversible dischromia depending on chromogenic molecule absorption by enamel and dentin, in the course of dental development or after tooth eruption. They depend on pulp chamber lesions (intrapulpal bleeding, necrosis, calcification with tertiary dentin deposit), endodontic therapy, congenital diseases (phenylketonuria, cystic fibrosis, congenital hyperbilirubinemia, amelogenesis and dentinogenesis imperfecta), medical drug use (tetracycline, fluorine).
Extrinsic factors: they include yellow-brown surface pigmentations affecting exclusively the enamel. They are connected to eating, drinking, smoking, poor dental hygiene, ageing (enamel thinning and dentin increase).
Active ingredient: Hydrogen peroxide, carbamide peroxide (organic molecule that releases hydrogen peroxide and urea; 10% is equivalent to 3.5% hydrogen peroxide), sodium perborate (monohydrate, trihydrate and tetrahydrate mixed with hydrogen peroxide) and calcium oxide.
Mechanism of action: oxidation of the double bonds of the chromophores conjugated chains (chemically stable long chain organic molecules) absorbed by the dental hard tissues (enamel and dentin) with subsequent brightness increase and chrome reduction. More specifically, hydrogen peroxide releases HO2— (peroxide anion) and free radicals, responsible for the chromogenic molecules destruction; carbamide peroxide in aqueous solution releases hydrogen peroxide and urea, able to denaturise dental tissues’ organic matrix proteins.
1. Temporary low/moderate increase in dental sensitivity found during and after the treatment in 2/3 of the patients who underwent vital teeth bleaching, due to a reversible pulpitis caused by the whitening agent and amplified by dental dehydration. It can be treated using topical fluoride prophylaxis (dentinal tubules occlusion and dentinal fluid reduction) or applying potassium nitrate that has an analgesic effect on the transmission of the nervous impulses.
2. Enamel microhardness reduction: the enamel exposed to the whitening agents presents a clinically non relevant reduction of its microhardness which spontaneously recovers after contact with saliva (saliva electrolytes). Studies on 10% carbamide peroxide have demonstrated that applying whitening agents on the enamel surface causes local microstructural modifications similar to those present in the initial stages of caries and that the amount of calcium ions lost by the enamel is around 1mcg/ mm2 – a neglectable amount from the clinical point of view.
3. Soft tissues irritation: concentration greater than or equal to 10% hydrogen peroxide can cause cellular damage, gingival ulceration and mucosa and skin burning. It is clinically possible to observe an initial reddish area leaving the place to a light coloured lesion that tends to heal rapidly without leaving any permanent harm. Soft tissues protection is thus mandatory.
4. Taste alteration. The patient may report the presence of a metallic taste after the whitening for several hours.
5. Intrapulpal temperature increase. A significant variation of the temperature, associated with a photothermal effect and possible pulp damage, is observed in the course of the bleaching treatment using hydrogen peroxide when activation sources (halogen lights, LED, laser) are used to speed up the process. Light sources increase hydrogen peroxide decomposition and thus the release of free radicals able to oxidise the dark pigments. Heat-producing activation sources may determine expansion of dentinal tubules fluid, causing pulp hyperemia and post-whitening hypersensitivity. Heat induces a more pronounced teeth dehydration and, subsequently, an increased post-whitening hypersensitivity. The free radicals chemical action, moreover, can make the pulp tissues damage worse.
6. Alteration of the composite fillings superficial texture and of the enamel-composite interface: a study on dental elements affected by Black class V carious lesions restored with composite and subsequently treated with 35% hydrogen peroxide (seven 30 min. treatments) proved that whitening determines alterations in the teeth surface topography with prevalence of depression areas that facilitate plaque build-up and increase the risk of caries and periodontal disease. The enamel-composite interface, analysed with the help of profilometric analysis and SEM, on the contrary, shows no alteration after the whitening treatment.
The whitening power of fluoride fortified products does not seem to be compromised in respect to traditional products, nor post-whitening fluoride prophylaxis is able to negate the treatment itself. Remineralisation of the enamel treated with whitening agents happens more rapidly and the loss of hard substance is inferior; therefore the teeth exposed to fluoride-based whitening show more resistance to acid dissolution (caries) than non-whitened teeth. The topic preliminary application of fluoride-based varnishes can, by itself, reduce dentin dehydration during the whitening process and the subsequent hypersensitivity.
The safety parameters of bleaching agents are defined according to the effects observed on the dental hard tissues, the pulpodentinal organ, oral soft tissues and in the case of swallowing the product in the course of a vital tooth extracoronal whitening. As far as soft tissues, the attention is mostly directed to the possible toxic effects of the free radicals released by the peroxides and able to react with proteins, lipids and nucleic acids, causing cellular damage. Hydrogen peroxide is thus a molecule that, at 10% concentration or more, may result cytotoxic ad be potentially harmful for the mucosa and the skin, causing a burning sensation. The risks connected with these lesions are mostly observable in the case of chairside professional treatment, usually performed with products releasing hydrogen peroxide at a concentration of 25% or more, when an adequate protection of the gingival tissues is not set up. On the other hand, no risk for oral and systemic health comes from professional home bleaching performed using ADA approved products made up of 10% carbamide peroxide (equivalent to 3.5% hydrogen peroxide). In the case of hard tissues, the risks include a temporary increase in dentinal sensitivity observable in the first phases of the bleaching, whose entity varies depending on peroxide concentration and duration of contact. It is worth remembering, that peroxide easily crosses both enamel and dentin after the first 5-15 minutes of application. Nonetheless, there is no evidence of long-term damage to the pulpodentinal organ (enzymatic inactivation) when the technique is performed correctly. The occurrences and the severity of the sensitivity seem to depend on product quality, chosen technique and on the individual response to the bleaching.
The length of the treatment and the expectations on the outcome depend on the aetiology of the stains (genetic defects or development problems, age-related changes, extrinsic pigmentations, intrinsic aspects) and on the diagnosis, as well as on the chosen product and how it is applied. In general, dark pigmentations respond well to whitening, while white spots are not affected, although they result less evident since there is less contrast with the adjacent teeth. Using the trays technique (individual trays), the teeth normally whiten up within 3 days to 6 weeks. Nicotine stains can take 1-3 months to disappear while tetracycline stains 2-6 months or even more of night use. The kind of stain and the initial tooth colour are to be taken in consideration; pigmentations localized on the neck of a tooth, dark grey or blue and important tetracycline-induced discromies are hard to treat.
-Preliminary investigations: an intraoral clinical examination along with all the necessary X-rays is the tool that lets us make a correct diagnosis and use whitening products in perfect safety: therefore, it must always come before the bleaching treatment. Collecting useful information (past or present dentinal hypersensitivity, presence of reconstructions, temporomandibular disorders, latex, silicone and whitening substances allergy) can help us choose the best methodology for each patient.
-Product choice: the ideal whitening agent should be designed with a neutral pH. Carbamide peroxide has proven more effective at night-time since urea induces the pH increase to the desired levels. Hydrogen peroxide has a low pH and is short-acting. For these reasons whitening formulations containing hydrogen peroxide require shorter contact but more applications while those containing carbamide peroxide take few days but require longer contact. Product choice, then, has to be compared to the patient’s habits and lifestyle, not to mention the possible dentinal hypersensitivity, the type of stains and the presence of carious lesions.
-Subsequent treatment: the need of a second treatment can greatly vary, ranging from 1-3 years to more than 10 years after the initial bleaching.
Vital teeth bleaching
External bleaching (extracoronal) is performed applying the active ingredient to the surface of the tooth to be treated, so that it can diffuse into the hard tissues without causing any enzymatic damage to the pulpodental organ. After a careful isolation of the soft tissues, the whitening agent can be fitted to the surface to be treated.
In the following pictures you can see a case of a maxillary-arch-only home whitening using 15% carbamide peroxide for 3 nights in order to highlight the chromatic improvement; afterwards the patients, happy with the achieved results, decided to have the same treatment performed on the mandibular arch.