ROLE OF LASERS IN ENDODONTIC ROOT CANAL THERAPY !

Decontaminating a root canal consists of killing bacteria, vaporizing dead and diseased tissue, and cleansing the canal of the residue. 

Nearly 20 years ago, lasers were proposed as a decontamination aid. As a bactericidal agent, the near infrared wavelengths generate fatal structural modifications in bacteria cells. The primary damage takes place in the cell wall, causing an alteration of the osmotic gradient, leading to swelling and cellular death. The highest bactericidal effect is on E. coli (Gram-negative), and E. faecalis (Gram-positive). In addition to killing bacteria, the near infrared wavelengths can ablate the root canal biofilm, which comprises the primary bacterial substrate. Biofilm constituents include the smear layer, debris, residual pulp and collagen fibers.

The near infrared wavelengths are well suited for decontamination in that they balance absorption and penetration with respect to sensitive tissues. On one hand, hard dentinal tissues do not readily absorb the near infrared wavelengths; diode irradiation therefore has no ablative effect on dentinal surfaces. The risk of damaging root canal tissues is greatly diminished. The trade off with low absorption is increased penetration.

 In light of being absorbed, diode irradiation is able penetrate the dentinal walls at subablative levels. Light at the 810nm wavelength can penetrate up to 750µ; the 1064nm wavelength can penetrate up to 1mm. Penetration promotes decontamination on deeper dentine layers. Medium infrared lasers can also be used in root canal decontamination. There are advantages and disadvantages.*

Diode laser energy is able to activate chemical irrigants to increase their chelating capacity. This results in more complete removal of the smear layer. The most common irrigants are sodium hypoclorate (NaOCl) and calcium hydroxide (Ca(OH2)), the latter mixed with propylene glycol and camphorated paramonochlorophenol. For example, Benedicenti et al. (2007) show the efficiency of diode laser decontamination in combination with 17% EDTA, 10% citric acid and 5.25% sodium hypochlorite. Chelating helps laser light to penetrate into the dentinal walls promote decontamination (ibid). Laser-activated irrigation has been shown to be statistically more effective in removing debris and the smear layer in root canals compared with traditional techniques and ultrasound.

Diode laser root canal decontamination is usually done with the smallest available optical fiber diameter: 200µm. The endo fiber fits well in most prepared root canals; it is flexible enough to penetrate all but the most severe canal curvatures. The 200µm fiber usually allows insertion to within 1mm of the canal apex. As the fiber emits from its distal end, the target tissue lies directly in front of the tip. A fiber-delivered diode beam diverges 15-22° upon exiting the tip. The emission heats an area slightly larger than 200µm, but the beam does not fully irradiate all canal walls. In decontamination therapy it is therefore recommended to bring the tip into the apical area, begin emission, and then withdraw the tip with a circular motion. With this simple method, canal walls can be effectively irradiated.