One possible application of laser systems in medicine is photoactivated chemotherapy (PACT) (synonyms: antimicrobial photodynamic therapy, aPDT, PACT, photodynamic therapy, photoactivated therapy), which takes advantage of the photochemical interactions between low-intensity laser light and a photosensitizer with the goal of inactivating germs. Laser systems are used in a variety of ways in medicine today. Photodynamic therapy plays an important role in cancer treatment. Photoactivated chemotherapy requires diode soft lasers with low energy and power at a long wavelength (635-810 nm) and a so-called photosensitizer, as well as the presence of oxygen. A laser emits coherent monochromatic light, which means that all laser beams have the same frequency and wavelength. The power of soft lasers is usually only 30 to 100 mW. The wavelength depends on the semiconductor material of the emitting light emitting diode. The PACT 200 laser is a soft laser with a wavelength of 635 nm, which is tuned to the photosensitizer toluidine blue. The device is offered in a convenient handpiece form. Photosensitizers are dyes that are transformed by laser light into energetically higher states, which are the prerequisite for the further course of chemical reactions. In endotherapy (root canal treatment), they are introduced into the root canal system in liquid form (e.g. PACT Fluid Endo), while a gel-like consistency is suitable for other applications (e.g. PACT Gel). Photosensitizers do not exhibit antimicrobial or fungicidal activity without exposure to light. Commonly used phenothiazine derivatives are as follows:
- Toluidine blue (tolonium chloride, TBO) – such as in the PACT laser.
- Methylene blue
Mode of action
The photosensitizer first acts on the infected tissue. In doing so, it chemically binds to surface structures of the target cells. After the exposure time, the molecules of the photosensitizer by low-intensity laser light into the more energetic excited singlet state and thereby activated. Highly reactive oxygen (singlet oxygen) is formed. Oxidation (oxygen binding) of microbial cell components such as cell walls and membranes, proteins, lipids, nucleic acids, and others irreversibly damages the germs. Different bacterial strains have different affinities for the various photosensitizers due to their different surface structures. In particular, pathogenic anaerobes (disease-causing germs that thrive in oxygen deficiency) are very well inactivated by the highly reactive singlet oxygen. In healthy body tissue, on the other hand, the toxic effect is not developed, so that the body’s own cells are spared. Photoactivated chemotherapy is considered to be:
- Universally applicable
- Painless in the application
- Safe
- Free from side effects
- Free from impairment of hard and soft tissues adjacent to the infected area.
The following pathogenic (disease-causing) bacteria of the oral cavity can be eliminated using PACT therapy:
- Streptococcus mutans
- Total streptococcus
- Streptococcus sobrinus
- Streptococcus intermedius
- Actinomyces
- Lactobacillus
- Prevotella intermedia
- Peptostreptococcus micros
- Fusobacterium nucleatum
- Enterococcus faecalis
Indications (areas of application)
Antimicrobial photodynamic therapy is used for broad-spectrum disinfection by inactivating a wide variety of pathogens (disease-causing germs) that form biofilms on tooth surfaces, in gingival pockets, on implant surfaces, or on wound surfaces:
- Periodontitis (inflammatory disease of the periodontium/dental periodontium): therapy in the periodontal pocket of the periodontally damaged tooth (with periodontal inflammation) in support of mechanical cleaning (tartar and calculus removal, Vector method).
- Peri-implantitis (periodontal disease in the area of implants): for closed application and in support of open surgical sanitation of implant bed inflammation.
- Soft tissue infections: support of wound healing by photodynamic therapy, e.g., in postoperative inflammation-related wound healing disorders.
- Herpes: photodynamic therapy promotes faster healing of oral soft tissue infections with herpes simplex (viral disease with typical vesicle formation, e.g., in the lip area).
- Endotherapy: the root canals of a tooth with the dentinal tubules originating from them (in the dentin) are a very complex system that is difficult to access for disinfection measures. Here, photodynamic therapy supports the mechanical preparation and chemical disinfection by means of rinsing solutions or medicinal inserts.
- Alternative to antibiotics: The increase in resistance to antibiotics forces medicine to rethink and exploit other antimicrobial (acting against germs) therapy options. Thus, photoactivated therapy is particularly indicated in treatment-resistant infections.
- Cavity disinfection: instead of disinfecting a tooth prepared for a filling, e.g., with chlorhexidine, disinfection can be performed with PACT.
- Caries: Photodynamic disinfection of carious dentin (tooth decay affected tooth bone) offers the possibility of a substance gentler excavation (removal of carious substance by drilling) especially in caries profunda (deep caries near the pulp).
- Candidiasis: infection with the fungus Candida albicans, for example, on the soft tissues covered by dentures in the form of denture stomatitis.
- Oral stomatitis: Therapy of soft tissue infections of the oral cavity with a wide variety of pathogens as the cause of disease.
Contraindications
There are no known contraindications.
Before the procedure
- For periodontitis or peri-implantitis therapy, tooth or implant surfaces are cleaned mechanically, e.g., with ultrasonic instruments or subgingival (below the gum line in the gingival pocket) glycine-based powder jet cleaning.
- For caries therapy, caries-affected enamel and softened dentin (dental bone) are first gently removed.
- For endotherapy, the root canals are mechanically prepared and rinsed with disinfecting solutions, e.g. sodium hypochlorite. Afterwards, the canals are conditioned and dried with paper tips.
- Soft tissue infections are cleaned mechanically, e.g., using swabs.
The procedure
- First, the photosensitizer – toluidine blue in the PACT system – is applied to the area to be treated and worked in (e.g., with the help of a mini brush in caries therapy).
- Within an indication-dependent defined exposure time (60-120 seconds), the photosensitizer accumulates in the tissue and enters into a chemical bond with the surfaces of the germs.
- Before laser application, suitable protective goggles are put on.
- After that, irradiation with the soft laser takes place over a period of time that is again defined according to the indication (usually 30 seconds, in the case of endotherapy also significantly longer) and with a light guide suitable for the area of application (e.g., PACT Universal, Endo, XL). In endotherapy, it should be noted that the channels must be irradiated over their entire length.
- In endotherapy, the photosensitizer solution is removed again by rinsing with e.g. sodium hypochlorite or distilled water before the final root canal filling.
