Diode Lasers and Root Canal Decontamination
   Roy Larick, PhD, Helios Laser

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. Recent peer reviewed articles confirm laser effectiveness when used in addition to standard procedures.¹ Following Olivi et al. (2011), four primary factors of root canal diode laser decontamination are summarized. Selected abstracts are presented below.

Root Canal Bacteria and Biofilm 
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.

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Near Infrared Absorption/Penetration
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 tradeoff with low absorption is increased penetration. In lieu 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.*

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Laser-Activated Irrigation
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. 

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Practical Tips
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.

A Root Canal Decontamination Primer
Condensed from Steven PA Parker (2011): Decontamination of the Root Canal, pp. 481-483. In Laser/light application in dental procedures, pp. 462-492. In Lasers in Dermatology and Medicine, Keyvan Nouri, editor. Springer-Verlag, London.

Conventional protocols should be followed to provide canal access, shaping and mechanical debridement and enlargement. The tooth should be isolated using rubber dam and X-Ray analysis and/or apex locator devices will allow the length of the canal to be determined. The quartz optic fiber can be used in 200 and 320up diameters … which relate to ISO #25-40 files. …

It is imperative that the laser energy is not allowed to pass through the root apex, as this may cause damage to the peri-radicular bone. To achieve this, the fiber or probe is measured to approximately 2mm short of the working length derived from the X-Ray or apex locator. The delivery tip is inserted to this depth and the laser operated as the tip is slowly rotated and removed through a 20-40 second cycle. This cycle may be repeated three to four times, with a short interval.

Within the confines of the root canal, the use of laser wavelengths without water cooling can lead to a potential high rise in temperature. Risks associated include melting/cracking of dentine walls and trans-apical irradiation of the tooth socket. With [near] infrared lasers … power levels of 0.75-1.5W should be considered maximal. 

Following laser use, the canal can be obturated according to personal choice of materials and technique. 

Summary
Diode lasers are effective in root canal decontamination. Near infrared emission effectively kills bacteria and removes the smear layer. Diode laser wavelengths balance between absorption and penetration to bring energy below dentinal surface without tending to damage it. Diode laser energy is able to activate chemical irrigants to increase their chelating capacity and bactericidal effects. 

* Medium Infrared Considerations 
Near infrared wavelengths work well for root canal decontamination even if they do not have optimal photonic properties. Water and dentine better absorb laser light in the medium infrared spectrum. Medium infrared wavelengths consequently have a superficial ablative and decontaminating effect on the root-canal surface. Within the medium infrared spectrum, Erbium lasers (2940nm), are significant if expensive dental instruments. Erbium laser emission heat root canal bacterial substrates more quickly. The downside of high absorption is, however, limited penetration. Bacteria deep below the dentin surface may escape erbium laser decontamination.

Erbium lasers may also use cone-shaped “side-emitting” fiber tips to irradiate root canal walls more efficiently. While side-emitting tips are an advantage, they impose treatment limits. In that emission is spread over a much larger surface area, therapeutic power densities are reduced. The side-emitting tip erbium laser must have sufficient power to overcome falling power densities. The power density issue makes side-emitting tips unpractical for diode lasers. 

Erbium lasers can also generate photo-acoustic to work in place of photo-thermal therapeutic effects. DiVito et al. (2010) and Peters et al. (2011) demonstrate the use of the Erbium laser at subablative energy density using a radial and stripped tip in combination with EDTA irrigation. The results indicate effective debris and smear layer removal without any thermal damage to the organic dentinal structure.

Note 1

Benedicenti, Stefano, C. Cassanelli, A. Signore, G. Ravera, and A. Francesca (2007). Decontamination of root canals with GaAlAs laser: an in vitro study. Photomedicine and Laser Surgery 11-Nov-2007.

Kreisler, M., W. Kohnen, Beck M, Al Haj H, Christoffers AB, Götz H, Duschner H, Jansen B, D’Hoedt B. (2003). Efficacy of NaOCl/H2O2 irrigation and GaAlAs laser in decontamination of root canals in vitro. Photomedicine and Laser Surgery 32(3):189-96.

Radaelli, C.A.R.M. (2002). Bacteria reduction in the infected root canal irradiated with diode laser. M.A. thesis, “Lasers in Dentistry.” Nuclear and Energy Research Institute, School of Dentistry. Advisors: Sheila C. Gouw-Soares, DDS, PhD; Denise Maria Zezell, DDS, PhD.

References
DiVito Enrico, Ove A. Peters and Giovanni Olivi (2010). Effectiveness of the erbium:YAG laser and new design radial and stripped tips in removing the smear layer after root canal instrumentation. Lasers Med Sci 2010 Dec 1.

Olivi, Giovanni, Rolando Crippa, Giuseppe Iaria, Vasilios Kaitsas, Enrico DiVito & Stefano Benedicenti (2011). Laser in endodontics, Part 1. Roots 7(1). Laser in endodontics, Part 2. Roots 7(2). 

Peters, Ove A., Sean Bardsley, Jennifer Fong, Goldie Pandher, and Enrico DiVito (2011). Disinfection of Root Canals with Photon-initiated Photoacoustic Streaming. Journal of Endodontics Volume 37, Number 7, July 2011.