In today's society cosmetic dentistry plays an important role in social relationships and in important aspects of life such as job applications and recruitment processes.

Currently, the only available treatment option for patients suffering from black dental pigmentation of bacterial origin is repetitive professional dental cleanings every two or three months, which involve a significant financial outlay, and have been found to be psychologically detrimental due to the lack of a perceived cure.

These pigmentations are of unknown etiology, although there has been reported the presence of black-pigment producing bacteria, such as Porphyromonas gingivalis, Tannerella forsythia and Aggregatibacter actinomycetemcomitans in such black plaque. These bacteria are found in a group known as periodontopathogens, bacteria responsible for the appearance of periodontitis, an oral chronic disease with high prevalence.

In this context, photodynamic therapy, which uses the application of diode light with a wavelength between 400-500 nm for the elimination of periodontal pathogenic bacteria, has demonstrated effectiveness and absence of adverse effects on the management of patients with periodontitis.

The proposed study seeks to evaluate the effect of photodynamic therapy on teeth with extrinsic black pigment, in order achieve an eradication of the stains. The investigators will also proceed to analyze in depth the bacterial composition of these stains before the application of photodynamic therapy, in order to stablish the aetiological agents of this black plaque.

One of the most common problems facing the dentist in daily practice is the treatment of the chromatic alterations of the teeth, both of extrinsic origin and of intrinsic origin. The former, caused by the incorporation of chromogenic materials into enamel and dentin, either before or after the tooth eruption, require more complex and usually more aggressive treatments in order to eliminate them. On the other hand, the latter, caused by the deposition of pigments or detritus on the tooth surface, are usually removed more easily, causing little or no damage to the enamel.

However, among the latter, black extrinsic dental stains caused by pigmented bacteria represent a clear exception to the rule. These deposits, which manifest in the form of points or lines of black color located parallel to the gingival margin of the teeth in the cervical third, are firmly attached to the enamel, making them very difficult to remove.

Although the exact etiology of the formation of dental black stain due to pigmented bacteria is not clear, it has been suggested that it arises due to the production of a pigment with characteristics similar to protohemin and protoporphyrin by black-pigmented bacteria. The application of light to inactivate and disinfect intraoral sites is gaining interest in the field of dentistry. Antimicrobial photodynamic therapy is defined as the inactivation of cells, microorganisms or molecules induced by light. The mechanism of action of photodynamic therapy is defined as the process by which a photosensitizer (photoactivable substance) is captured by microorganisms and, after exposure to light at an appropriate wavelength, remains in an excited state. The photosensitizer then transfers energy from light to oxygen molecules to generate singlet oxygen and free radicals that are cytotoxic to the cells.

Published studies suggest that antimicrobial photodynamic therapy can effectively reduce the population of microbial pathogens, also presenting the following advantages: absence of phototoxic effect for human cells, possible clinical, microbiological and immunological benefits, rapid and painless application of light, penetration of light into tissues and plaque and, thereby, elimination of bacteria present in gingival epithelial cells, and finally, selectivity towards pathogenic microorganisms.

The main objective of this research is the application of antimicrobial photodynamic therapy in the control of dental black stain caused by pigmented bacteria.

Inclusion Criteria:

• volunteers with dental black stain in at least two teeth (non-filled, with partner in the opposite arch)
• volunteers older than 12 years

Exclusion Criteria:

• volunteers receiving antibiotic treatment within the month prior to enrolment