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Authors: Dr.Amarnath Shenoy, Dr. Deepak Nayak, Dr.Arjun Nayak.
Yenepoya Dental College, Deralakatte, Mangalore. 

The intraoral use of lasers has evolved over the last 4 decades as clinical experience along with scientific investigation, has increased the body of knowledge. The dental lasers of today have benefited from decades of laser research and have their basis in certain theories from the field of quantum mechanics, initially formulated during the early 1900s by Danish physicist Bohr, among others. In Endodontics lasers have a variety of applications. There are different types of lasers which have been developed for clinical use over the years.

A laser is a device is a device which transforms lights of various frequencies into a chromatic radiation in the visible, infrared and ultraviolet regions with all the waves in phase capable of mobilizing immense heat and power when focussed at close range. Early investigators like Stern and Sognnaes and Goldman et al studied the effect of lasers on dental hard tissues to reduce subsurface demineralisation.1 The credit for development of the theory of spontaneous and simulated emission of radiation is given to Albert Einstein. The first laser constructed by Maiman was a pulsed Ruby laser, which emitted light of 0.694µm wavelength .Second laser was a Neodymium laser. Nearly all researches in dentistry were done with ruby laser which may be the reason for delay of development of laser dentistry.1 The first laser in endodontics was reported by Weichman and Johnson who unsuccessfully attempted to seal the apical foramen in vitro by means of a high powered infrared laser.

Characteristics of a laser beam 3
Monochromatic: single wave length. The laser has one specific colour.
Collimated: having specific spatial boundaries and a very low divergence, ensuring constant size and shape of the beam
Coherency: light waves produced by a laser have specific form of electromagnetic energy which is in phase with one another.
Intense: light beam produced is intense in nature.

Lasers in Endodontics:
Laser Doppler flowmetry: (LDF) was developed to assess blood flow in micro vascular systems. This original technique utilised Helium-Neon laser.  Doppler principle is made use of here to measure the blood flow. Researchers found out that using forward scattered detection improved the results when compared to back scattered detections. Further studied showed that 633nm wavelength showed good specificity but poor sensitivity whereas 810 nm showed good sensitivity and poor specificity. Due to some inherent problems associated with this technology LDF has been considered limited in its usefulness for human pulp vitality testing.1 LDF is very technique sensitive and requires splints to hold sensors in place. Care has to be taken to see that there are no motion artifacts during procedure. This device at present has been developed for medical use and is expensive.3

Pulp capping and pulpectomy:
These two represent a more conservative form of pulp therapy compared to pulpectomy. Since laser has the ability to coagulate and seal small blood vessels the procedure is potentially bloodless. The wound will be sterile after interacting with laser and will have an improved prognosis. No damage in the underlying laser ablated tissues has been found in studies using Nd: YAG and CO2 lasers. There was presence of secondary dentin and the odontoblasts layer was regular and not disturbed.3

Hypersensitivity: 4
Dentinal hypersensitivity can be reduced using laser technology. The rationale is based on two possible mechanisms that differ greatly from each other. The first mechanism implies the direct effect of laser irradiation on the electric activity of nerve fibres within the dental pulp.  The second involves modification of the tubular structure of the dentin by melting and fusing of the hard tissue or smear layer and the subsequent sealing of dentinal tubules.

According to the hydrodynamic theory, rapid dentinal fluid flow serves as the stimulus in activating intradental nociceptors for many different types of stimuli.

For the exposed dentin to be sensitive the dentinal tubules have to be patent.4,5,6 SEM studies have shown that teeth with dentinal hypersensitivity have a significantly higher number of patent dentinal tubules per millimetre7 and a significantly greater mean diameter per tubule than control teeth.  Dentinal hypersensitivity management involves the application of therapies that reduce the flow of dentinal fluid or lower the activity of dentinal neurons.4

The lasers used for the treatment of dentinal hypersensitivity may be divided into two groups: 4

  1. low output power lasers (helium-neon and gallium/ aluminium/arsenide diode)
  2. Middle output power lasers (Nd: YAG and carbon dioxide.)
Helium-neon laser was used for the first time by Senda et al4 for treating dentinal hypersensitivity. The 6 mW laser which they used did not change the morphology of the teeth but a small fraction of energy reached the pulp, and effectiveness of this treatment ranged from 5.2 to 100 percent. It was observed that this laser irradiation affects electric activity (action potential) instead of Aδ or C-fibre nociceptors 4

Three gallium/aluminium/arsenide (diode) laser wavelengths (780, 830 and 900 nm) were used for the treatment of dentinal hypersensitivity. 7
Matsumoto et al4 used a diode laser which proved to be 85 to 100 percent effective when an output power of 30 mW was applied in a continuous wave irradiation for 0.5 to 3 minutes. The investigators considered that the analgesic effect was related to depressed nerve transmission caused by the diode laser irradiation blocking the depolarization of C-fibre afferents4

The CO2 laser with 0.5 W output used by Moritz et al with an irradiation time of 5 secs showed an effectiveness range from 59.8 to 100 percent. According to these investigators the CO2 laser reduced dentin hypersensitivity by occluding or narrowing the dentinal tubules.4 when moderate energy densities are used Sealing of dentinal tubules and reduction of permeability can be achieved with the CO2 laser.8 No nerve analgesia by CO2 laser irradiation has been reported.
Studies suggest that the Nd: YAG laser effect on dentin hypersensitivity is related to the laser-induced occlusion , narrowing of the dentinal tubules, direct nerve analgesia or a suppressive effect achieved by blocking the depolarization of A delta and C fibres.4,9

A low power erbium: yttriumaluminum-garnet (Er: YAG) laser irradiation (25 to 35 mJ per pulse) used showed the effectiveness ranged from 16% to 61 %. The investigators reported that the condition could recur and concluded that low-power irradiation by Er: YAG laser is effective for dentin hypersensitivity but has some limitations.4

Lasers have the ability to vaporize,melt,fuse or seal dentinal tubules by recrystallization of the mineral component of dentin and this has been reported with varying success.10 Stabholz et al 11,12 studied the effects of excimer lasers on exposed dentinal tubules of extracted human teeth and found melting of dentin and closure of exposed dentinal tubules. A dentin surface thus modified may prevent hypersensitivity and also prevent the bacterial penetration through dentinal tubules under the restorations   because melting and resolidification of the dentin and the closure of the tubules may be permanent. Advantage in using excimer lasers could be their relative safety as they don’t cause any thermal damage to the surrounding tissues. Further research is needed for these lasers if they are to be used in clinics.

A closer look at the melted areas through SEM frequently reveals that the dentin resembles glazed interconnected droplets. A solid uninterrupted melted and resolidified area can be less permeable and could more effectively prevent dentinal hypersensitivity and microorganism penetration into the dentinal tubules.

The 9.6µm CO2 laser on enamel and dentin show promising results regarding its ability to melt hard tissues of the tooth. [55]. This laser could serve as an important tool in the armamentarium of a modern dental office. Efforts should be focussed on the search for a laser wavelength with optimal irradiation parameters that will enable the clinician to produce ideal modification of dentin surface and other hard tissues of the tooth.

Sterilisation of the root canals:
Pulp space therapy will fail if pathogenic bacteria persist in the canals even after cleaning and shaping. Researchers have proved Nd: YAG and CO2 laser to disinfect the dentinal tubules and root canals. Lasers can be delivered into root canals using a hollow tube or thin fibre optics of 200µ.3All lasers have a bactericidal effect at high power that is dependent on each laser. There appears to exist a potential for spreading bacterial contamination from the root canal to the patient and the dental team via the smoke produced by the laser. This can cause bacterial dissemination. A strong vacuum pump can be used as a precaution.1Some limitations are that the laser beam is directed vertically downwards and not laterally into the dentinal tubules. It is not possible to irradiate all the dimensions of root canal. Inadvertent transmission of laser into the Periapical region can be dangerous. Er: YAG laser with a side firing tip has been developed to overcome this.3

Since clean and regular root canal walls can be achieved using Nd: YAG laser irradiation, root canal shaping using this has been suggested by Levy in 1992. Ar, CO2 and Nd: YAG lasers have been used to soften gutta- percha and results indicate Ar laser to produce a very good apical seal.1 softening of gutta percha has been attempted with CO2.Nd:YAG and Er:YAG lasers combined with the use of thermo plasticised gutta percha system.3

Apical surgery:
Laser has the ability to vaporize tissue and coagulate and seal small blood vessels and thus a bloodless field can be achieved. The cut surface if irradiated it is sterilised and sealed by the laser. Since no thermal and structural damage is caused by Er: YAG laser while properly cutting through dental hard tissues, the need for mechanical drill is eliminated.1Er: YAG laser gave smooth, clean resected surfaces in a study done by Paghdiwala. Clinically patients reported less discomfort and improved healing.3

Other applications for the endodontic treatment:
A pulsed dye laser emitted at 504 nm was used for the removal of a calcified attached denticle. SEM evaluation showed a sharp surface at the base of the pulp stone after the removal. CO2 and Nd: YAG lasers have been unsuccessfully used to approximate fractured roots.1 Ar, CO2, and Nd: YAG lasers have been successfully used in sterilisation of selected instruments. Argon laser was able to achieve this consistently at a low energy level.3

With the development of more advance mode of laser delivery the laser treatment will be more readily accepted. Numerous studies have proved the efficacy of laser in endodontic applications.  The acceptance of laser technology is less which may be due to the cost factor. The need for more than one laser frequency for many endodontic applications may be another factor .Once our knowledge of optimal laser parameters for each parameters is complete, lasers can be developed that will provide dentists with the ability to care for patients with improved techniques.


  1. Y.Kimura, P.Wilder-smith, K.Matsumoto. Lasers in Endodontics: a review: Int. Endod. J., 33:173-185, 2000.
  2. Leo.J.Miserendino. The history and development of laser dentistry: Lasers in dentistry.17-25.
  3. B.Suresh Chandra, V.Gopikrishna.Lasers in Endodontics: 12th edition, chapter 19: 460-468.
  4. Adam Stabholz, Sharonit Sahar-Helft, Joshua Moshonov: Lasers in Endodontics. Dent.Clin.North.Am, 48:809-832, 2004.
  5. Narhi.M,Konturri-NarhiV, Hirvonen.T,Ngasappa.D:Neurophysiological mechanism of Dentin hypersensitivity.,Proc Finn Dent Soc; 1992;88 (suppl 1):15-22.
  6. Absi EG, Addy M, Adams D. Dentin Hypersensitivity. A study of patency of dentinal tubules in sensitive and non sensitive cervical dentin. J Clin Periodontol 1987; 14:280-4.
  7. Kimura Y, Wilder-Smith P, Yonaga K, Matsumoto K. Treatment of dentinal hypersensitivity by lasers: a review. J Clin Periodontol. 2000; 27: 715-21.
  8. Bonin P, Boivin R, Poulard J. Dentinal permeability of the dog canine after exposure of a cervical cavity to the beam of CO2 laser. J.Endod.1991; 17:116-8.
  9. Lan W H, Liu H C. Treatment of hypersensitivity by Nd: YAG laser. J Clin Laser Med Surg.1996; 14:89-92.
  10. Stabholz A, Neev J, Liaw LL, Stabholz A Y,Khayat A, Torabinejad M. Effect of ArF-193nm excimer laser on human dentinal tubules. Oral Surg Oral Med Oral Pathol. 1993; 75:90-94.
  11. Stabholz A, Neev J, Liaw LL, Stabholz A Y,Khayat A, Torabinejad M. Sealing of human dentinal tubules by XeCl 308 nm excimer laser. J Endod 1993; 19:267-71.
  12. Stabholz A, Neev J, Liaw LL, Stabholz A Y,Khayat A, Torabinejad M. Efficacy of XeCl 308nm excimer laser in reducing dye penetration through coronal dentinal tubules. J Endod.1995;21:266-8.

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