**6. Conclusions**

*Bacterial Biofilms*

added [71, 72].

singlet oxygen [69, 73, 74].

lene blue) [80, 81].

ness or other adverse effects [49, 65].

**5.1 Phototherapy and photodynamic therapy**

*P. gingivalis* can invade the tissue, so the persistence of these bacteria on the root surface can cause recolonization in sites that have already been treated [39].

In order to optimize the effects of SRP treatment, protocols have been proposed to associate systemic or local antibiotics to eliminate persistent bacteria after the SRP procedure. Studies have shown that this association provides improvement in the patient's clinical condition [63]. The main antibiotics commonly used in the treatment of periodontal disease are amoxicillin, metronidazole, clindamycin, azithromycin, ciprofloxacin, doxycycline, and minocycline [64]. However, the use of these drugs as an adjuvant to this disease has limitations, such as the emergence of bacteria resistant to these antibiotics as well as the side effects caused by these antimicrobial agents, such as diarrhea and vaginal candidiasis, which result from the commensal microbiota imbalance. In addition, drug interaction may occur between antibiotics and other drugs being used by patients, resulting in ineffective-

Thus, in recent years, in the area of dentistry, promising antimicrobial adjuvant therapies have been studied, such as phototherapy and photodynamic therapy [66, 67].

Studies have shown that some bacteria related to periodontal disease have the ability to produce a photosensitive substance intrinsically, such as protoporphyrin IX. Even without the addition of a photosensitizing drug, pigmented bacteria have been more susceptible when applied to phototherapy [66, 68]. Photosensitizers are molecules that when irradiated by a light source at a suitable wavelength undergo photochemical reactions to emit fluorescence. This process is used by photodynamic therapy to produce reactive oxygen species [69, 70]. Most bacteria do not have endogenous photosensitive compounds. Thus, cells lacking these compounds may become susceptible to light when an exogenous photosensitizing molecule is

The mechanism of action of photodynamic therapy happens when the photosensitive substance (intrinsic or extrinsic) is activated when irradiation is applied by a light source compatible with the length of the substance. This process will form reactive oxygen species, such as hydrogen peroxide, hydroxyl radical, and singlet oxygen, causing the death of the bacteria. This interaction of light and photosensitizer can occur through two types of reactions, called type I and II. In the type I reaction, charge transfer occurs between the photosensitizer and biomolecules, resulting in radicals and radical ions that react with molecular oxygen, forming reactive oxygen species. During the type II reaction, the excited triplet state photosensitizer transfers energy directly to the fundamental triplet state oxygen, forming

Studies involving photodynamic therapy and periodontal disease have investigated different light sources such as light-emitting diodes, low-power lasers, and conventional light [75–79]. As for photosensitizers, there are several molecules studied aiming at inactivation of periodontopathogens such as poly-L-lysine-chlorin-6 conjugate and phenothiazine dyes (toluidine blue and methy-

Photodynamic action is being increasingly studied to complement the microbial reduction achieved by conventional mechanical periodontal therapy. In vitro studies have shown that periodontopathogens have been suppressed in planktonic phase and biofilm, and after the application of photodynamic therapy, it has been verified that virulence factors of these bacteria have been decreased, such as lipopolysaccharides and proteases [82–84].Clinical trials have also shown that this therapy is effective as an adjuvant in the treatment of periodontal disease [85–87]. However,

**204**

The etiology of periodontal disease is multifactorial and directly associated with biofilm accumulation in the supra- and subgingival region, immune response and host susceptibility. In recent decades, several studies have sought to investigate the complex interactions of periodontopathogens in biofilm as well as adjuvant antimicrobial therapies that do not cause adverse effects in patients nor bacterial resistance. Phototherapy and photodynamic therapy are examples of treatments that have shown promising results in vitro and in clinical trials. Further investigations need to be done in order to establish parameters which allow the safe and efficient application of the therapy.
