The bacterial contamination of the root canal system in a tooth is the main factor of pulpal and periapical lesions [
In the past, the removal of an infected tooth was the only method of therapy success. In the 1940s, penicillin was used to treat infected teeth and periodontal tissues [
For decontamination, the infected teeth were treated by chemical-mechanical preparation to achieve a complete removal of the entire pulp tissue [
None of the known chemical agents are currently able to satisfy all demanded requirements of root canal rinsing solutions [
A lege artis primary root canal treatment lies—according to the published success—between 70 and 85% [
Schematic representation of the canal ramifications of teeth 13 and 24 by Blechschmidt and Meyer. A portion leads to the periodontal ligament, while another ends blindly in the dentin [
If certain sections of a tooth are insufficiently prepared, infected tissue remains, which can lead to an exacerbation of the inflammatory process. Moreover, an effective antiseptic rinsing is not possible if the preparation size is too low [
The limited penetration depth (approx. 100
To remove the smear layer formed by the mechanical preparation to prevent a recolonization of the root canal system [
In addition, adverse effects like toxicity, bad taste, and unpleasant odor of irrigation solutions have been shown in several clinical trials [
Spratt et al. proved in 2001 that the rinsing solution is only able to have an adequate bactericidal effect in reducing the biofilm through long exposure time [
Another important factor is that root canals are noncircularly sectioned yet have an oval cross section, which restricts a mechanical treatment with round instruments. A disinfecting rinsing solution combined with a laser could also provide valuable assistance to effectively remove any remaining tissue and bacteria.
Samiei et al. showed statistical differences in their in vitro study about mechanical stepback technique and laser cleaning of the root canals in teeth. The cleaning efficacy of combined laser and rotary was better than the single stepback technique [
Calcium hydroxide has also been proven particularly effective in root canals. This antibacterial product should remain in the root canal for at least seven days to achieve the best effect. In this context, Archilla et al. demonstrated that only a single Nd:YAG laser session is necessary to eliminate the same amount of endotoxin as calcium hydroxide is able to achieve in seven days [
The laser development occurred in the 1950s, shortly after which it was used in medicine and primarily in the field of ophthalmology and dermatology. In 1971, the first CO2 laser was used in endodontics to seal the apical foramen [
The term laser (English for light amplification by stimulated emission of radiation) is an acronym describing its operating principle indeed. It acts as a light amplifier and promotes the exponential reproduction of photons due to induced emission. Each laser has various purposes in dentistry, depending upon different wavelengths.
The effects of laser irradiation in biological tissue depend on various factors [
wavelength and absorption in tissue, mode of operation CW (clocked, pulsed, and Q-switched), energy or power output (single-pulse energy/power Watt per cm2), active time (e.g., pulse duration), repetition rate (Hz), application method of the laser (contact/noncontact, focused/defocused, and rapid movements/at one point), time of application.
air, water, blood.
absorption coefficient corresponding to laser wavelength, thermal conduction coefficient.
The laser light can be reflected on the surface
The higher the absorption, the lesser the penetration depth and thermal side effects, since the energy is absorbed by the tissue absorption and its associated processes.
Laser energy can be delivered in various forms, whereby the operating mode depends on the kind of power output: continuous power output = continuous wave = CW, chopped mode, free running pulse, Q-switch mode. direct heat absorption through the bacterium itself, heating by absorption of the substrate in which the bacterium is located, photodamage effect.
Three possible theories exist for bactericidal effects of NIR laser light in the literature [
The commonly used lasers in dentistry are the neodymium:YAG laser with 1064 nm, the diode laser with 810–980 nm, erbium lasers with 2940 nm/2780 nm, and the CO2 laser with 10600 nm. Table
Lasers in dentistry.
Laser device | Use in dentistry | Wavelength |
---|---|---|
Neodymium:YAG laser (Nd:YAG laser) | Surgery, endodontics, and periodontics | 1064 nm |
Erbium:YAG laser (Er:YAG laser), erbium, and chromium:YSGG laser (Er, CR:YSGG laser) | Surgery, endodontics, and cavity preparation | 2940 nm, 2780 nm |
Diode laser | Surgery, endodontics, and periodontics | 810–980 nm |
CO2 laser | Surgery | 10600 nm |
Many attempts have been made to investigate the antimicrobial potential of lasers, with numerous studies showing that the emission of laser light has a bactericidal effect in a root canal [
This literature overview provides the current state of science about Nd:YAG and diode lasers (1064 nm, 810 nm, and 980 nm) in endodontics and their action spectra in periodontal tissue with determined power settings. A comparison of these effects should evaluate a preferable laser device as support for the best results in endodontic treatments.
The Department of Restorative Dentistry at RWTH Aachen University in Germany—headed by Professor Dr. Gutknecht—has already developed a treatment protocol that could support the classic endodontic therapy concept due to the laser-specific bactericidal effect.
The proper use of the laser as an adjunct in endodontic therapy with known standards is recommended for the best clinical benefits for the patient.
To compare the variety of studies, the following criteria were selected for an adequate comparison: comparable operational settings of the laser device (200/300/400 microns fiber, 1.5 W, 15 pps/cw), similar experimental design, at least 20 treated root canals, prepared root canals to minimum ISO 30.
These parameters were chosen on account of the ability for reproduction and the actual state of knowledge by research results of the Conservative Dentistry Department, RWTH Aachen. The operational setting of 1.5 W and 15 pps showed acceptable clinical results. In these studies, the risk of possible damaging side effects was also clarified.
Some studies did not operate with contaminated teeth but rather with dentin cuts, inoculated agar plates, or animal teeth. Since these studies used at least similar parameters compared to what is mentioned above, they were also included in the general evaluation owing to the impact of the laser light on different microorganisms.
Furthermore, different variables such as the effect of the laser with respect to apical reinfection after successful root filling are listed separately or edited in Section
First, a PubMed online search was performed using specific keywords, which are listed in Table
Keywords used to research and their number of results on the website
Search keyword | Results |
---|---|
Laser in dentistry | 6688 |
Laser, endodontics | 795 |
Diode laser, in dentistry | 614 |
Nd:YAG-laser, in dentistry | 532 |
Nd:YAG-laser, root canal | 160 |
Nd:YAG-laser, endodontics | 143 |
Diode laser, root canal | 100 |
Diode laser, endodontics | 98 |
Laser, root canal | 37 |
A manual search in the library of Conservative Dentistry of the RWTH Aachen was progressed, whereby the listed magazines were evaluated.
Journal of Clinical Laser Medicine & Surgery, Photomedicine and Laser Surgery, The Journal of Oral Laser Applications, Lasers in Medical Science.
Zeitschrift für Laserzahnheilkunde, Laserzahnmedizin Jahrbuch ’11.
Most of the studies encountered in print media were also available online. The search was conducted from April 2011 until April 2016.
For Nd:YAG laser, a total of 22 studies fulfilled the inclusion criteria for the most part and researched with rateable scientific evidence plotted in Figure
Presentation of search strategy for Nd:YAG laser 1064 nm.
Figure
Presentation of search strategy for diode laser 980 nm.
Proceeding strictly according to the required laser settings, only one study was found for diode laser 810 nm that fully complies with the requirements detailed in Figure
Presentation of search strategy for diode laser 810 nm.
For the Nd:YAG laser, a total of four comparable studies were found, as shown in Table
Overview of comparable studies for Nd:YAG 1064 nm.
Year of publication | First author | Study design | Title |
---|---|---|---|
1999 | Moritz [ | In vitro | The bactericidal effect of Nd:YAG, Ho:YAG, and Er:YAG laser irradiation in the root canal: an in vitro comparison |
1997 | Moritz [ | In vivo | Nd:YAG laser irradiation of infected root canals in combination with microbiological examinations |
1996 | Gutknecht [ | In vivo | Long-term clinical evaluation of endodontically treated teeth by Nd:YAG lasers |
1996 | Gutknecht [ | In vitro | Bactericidal effect of the Nd:YAG laser in in vitro root canals |
Moritz et al. showed that a setting of 1.5 W for Nd:YAG laser has the best results in terms of bactericidity with less risk of thermal damage to tissue [
Moritz et al. achieved an almost complete elimination of bacteria in their in vivo study in 1997 with the Nd:YAG laser after two radiation treatments. In 50% of cases, they reached this result after the first radiation. The maximum log kill amounted to 4.22 for
Gutknecht et al. showed a success rate in their longitudinal study of 82% and reached a germ reduction of 84% with Nd:YAG laser up to a depth of 1000
For each diode laser device (810 nm and 980 nm), only one study fulfilled the demanded parameters, as shown in Tables
One study for the diode laser 810 nm matches all demanded criteria.
Year of publication | First author | Study design | Title |
---|---|---|---|
2012 | Beer [ | Extracted teeth | Comparison of two diode lasers on bactericidity in root canals—an in vitro study |
One study for the diode laser 980 nm matches all demanded criteria.
Year of publication | First author | Study design | Title |
---|---|---|---|
2006 | Schoop [ | Dentin cuts | Innovative wavelengths in endodontic treatment |
Beer et al. could achieve a bacterial reduction of 98.8% with the 810 nm diode laser in 2012, describing “the laser as modern state-of-the-art instrument for endodontics” [
In their study published in 2006, Schoop et al. also observed that above a setting of 1.5 W there are signs of changes in the surface and increased bactericidal effect with diode laser. The desired efficiency increases with the intensity of the laser [
The comparison of the three laser systems showed that the applied formulas for calculating the actual bactericidal effect widely differ. Most studies choose different parameters of the laser device such as the intensity of radiation, exposure time, and the laser fiber used or they differ in purely practical approaches.
To investigate the actual effect of the laser on the respective microorganisms, laser fibers with a greater diameter were also used in the studies and are mentioned. In this context, clinical restrictions like heavy accessibility, strong curved root canals, or poor visibility should be eliminated. Thus, a lighter ability for reproduction could be guaranteed. These studies allow partial statements about a possible target of the selected settings to achieve the best possible bactericidal effect and are listed in Table
Listing of additional mentioned studies with different parameters as they occur in the text.
Year of publication | First author | Title |
---|---|---|
1983 | Eriksson [ | Innovative wavelengths in endodontic treatment |
1998 | Farge [ | In vitro study of a Nd:YAP laser in endodontic retreatment |
1999 | Lan [ | Temperature elevation on the root surface during Nd:YAG laser irradiation in the root canal |
1997 | Ramsköld [ | Thermal effects and antibacterial properties of energy levels required to sterilize stained root canals with an Nd:YAG laser |
1995 | Weller [ | In vitro radicular temperatures produced by injectable thermoplasticized gutta-percha |
2001 | Mazaheri [ | Temperaturentwicklung auf der wurzeloberfläche bei einer endodontischen behandlung mit einem diodenlaser |
2000 | Gutknecht [ | Diode laser radiation and its bactericidal effect in root canal wall dentin |
1993 | Behrens [ | Die transmission und absorption der temperatur und energie des Nd-YAG-lasers im dentin |
2013 | Sadik [ | Effects of laser treatment on endodontic pathogen |
2004 | Gutknecht [ | Irradiation of infected root canals with Nd:YAG lasers. A review |
1997 | Klinke [ | Antibacterial effects of Nd:YAG laser irradiation within root canal dentin |
2011 | Pirnat [ | Study of the direct bactericidal effect of Nd:YAG and diode laser parameters used in endodontics on pigmented and nonpigmented bacteria |
1999 | Neuman [ | Characterization of photodamage to |
2008 | Mirsaidov [ | Optimal optical trap for bacterial viability |
2012 | Meire [ | In vitro inactivation of endodontic pathogens with Nd:YAG and Er:YAG lasers |
2007 | de Paz [ | Redefining the persistent infection in root canals: possible role of biofilm communities |
1985 | Nair [ | Root canal and periapical flora: a light and electron microscopy study |
1997 | Klinke [ | Antibacterial effects of Nd:YAG laser irradiation within root canal dentin |
1996 | Odor [ | Pattern of transmission of laser light in teeth |
1995 | Vaarkamp [ | Propagation of light through human dental enamel and dentine |
1997 | Jalil [ | Surface topography of enamel and dentine from primary teeth following infrared Nd-YAG laser irradiation: an in vitro study |
1994 | Hardee [ | Evaluation of the antibacterial effects of intracanal Nd:YAG laser irradiation |
1997 | Moritz [ | Irradiation of infected root canals with a diode laser in vivo: results of microbiological examinations |
1993 | Kales [ | Review and forecast of laser markets |
2014 | Kanumuru [ | Efficacy of Ca(oH)2 against |
Across existing literature, there are relatively few studies dealing with periodontal tissue damage by overheating. In 1983, Eriksson and Albrektsson defined a heating of 47°C as critical limit for the survival of bone in rabbits [
In this research, a value of 1.5 W for the diode and Nd:YAG laser has been set as an inclusion criterion. With this setting, a thermal damage is excluded within recommended handling for both laser devices and the bactericidal effects are acceptable [
In a systematic review of the current literature about the effectiveness of Nd:YAG laser on the pathogenic gram-positive bacteria
Gutknecht described that an application of the laser below 1 W is less important in endodontics because neither is the smear layer completely removed nor are the dentinal tubules sealed. With settings of 1.25 W–1.5 W significant changes on the root canal surface were determined. The organic material was completely removed and the surface of the inorganic substance was merged, resulting in a partial or complete occlusion of dentinal tubules [
In 2008, Klinke et al. discussed the angle between the optical fiber of the laser and the dentinal wall [
Beer et al. investigated irradiating the opening cavity of a tooth before irradiating the root canal itself, resulting in a significant higher bactericidal effect [
Pirnat et al. examined the direct effect of Nd:YAG (1064 nm) and diode laser (810 nm) on
The gram-positive bacterium
The agar plates and the bacterial suspensions used in this study absorbed the laser light to a small extent. Furthermore, nonpigmented bacteria were used, which could explain the lesser effect of the Nd:YAG laser in this experiment. The different absorption of wavelengths in dentin has an effect on the depth of penetration. The Er:YAG laser had a lesser effect on the bacteria found in deeper dentinal tubules, whereas the Nd:YAG laser was significantly superior.
Meire et al. supported the statement made by Pirnat et al. that the Nd:YAG laser kills the bacteria probably by heating their environment. A comparison of studies covering the antimicrobial effect of laser light is not easy to realize because the statements about energy density or experimental conditions are often lacking. In a natural environment such as root canal wall dentin bacteria occur in a biofilm [
Meire et al. suppose that blood or blood products in a natural environment could lead to a raised number of
Hardee et al. achieved a bacterial reduction of 99% of the test bacterium
The Department of Restorative Dentistry, RWTH Aachen, currently deals with the effect of ring-firing laser fibers in the root canals, which allows the laser light to not only emit in vertical direction. New possibilities concerning the bactericidal depth effect of diode lasers and Nd:YAG lasers could be achieved.
A direct comparison of the selected devices is currently not feasible in relation to exact similar demanded experimental setups.
In 1997, Moritz et al. described the diode laser (810 nm) and the Nd:YAG laser (1064 nm) in endodontic treatment as equally effective and they recommended further studies to evaluate the anaerobic bacteria [
In a study by Kanumuru and Subbaiah in 2014, the Nd:YAG laser was most effective in the elimination of
Due to the accumulation of different aggressive and resistant bacteria in an infected root canal, the additional use of Nd:YAG and diode lasers in combination with conventional methods such as mechanical conditioning or rinsing fluids seems to hold a positive value, as can be demonstrated by this literature review.
Furthermore, it removes the smear layer in a root canal, which interferes with adequate disinfection using additional rinsing fluids. It also has a simultaneous additional bactericidal effect.
Comparing the 810 nm with the 980 nm diode laser, both are equally favorable. Both are adequate funds in endodontic therapy and should be investigated in further detail. For 810 nm diode lasers, the majority of studies can be found in the literature, although the parameters are not exactly comparable.
According to a study of Kales in 1993, the diode laser determines 99% of the turnover on the whole market and is estimated at 25% by the buyers in comparison to all other laser devices [
Sadik et al. postulated that the various investigated laser systems of the past 30 years could not be compared with a meta-analysis since the results of the studies were not presented in a standardized manner. From this perspective, it would be desirable if future studies use a solid study design with the same basic parameters, such as the diameter of laser fiber, the same practical approach to the irradiation of the teeth (number of repetitions, pauses), pulse frequency (pps), and power (W) [
This statement is the final testimony and prime cause because this present literature review also does not lead to any clear result in terms of effectiveness brought against the bacteria in an infected root canal compared to the three lasers. There are too many different variable facts in the studies to make a statement about the more effective wavelength or the preferable device and the data situation is contradictory. The Nd:YAG laser is more frequently evaluated, although the comparability of the different study designs is also lacking. The various studies are difficult to measure, given that different parameters, fiber strengths, or handling methods are used.
At present, a statement based upon recommended guidelines is not really possible. When properly used, it emerges that disinfection by laser can increase the endodontic success with a very low risk of damaging side effects and with acceptable durability.
A recommended standardized procedure for the individual wavelengths is suggested, although further scientific studies would be desirable. Additional in vivo studies with Nd:YAG and diode lasers in endodontics are necessary. It should be considered internationally with the same procedure including a clear treatment outline. Generally established criteria such as the same fibers (diameter), the same settings of the laser parameters (power, pulse frequency), the same trace of radiation in practical implementation, and duration are essential to conduct a comparison about the antibacterial effects of endodontic treatment between the three laser devices. This would be desirable to define an evidence-based “gold standard.”
In endodontics, Nd:YAG laser (1064 nm) and diode laser (810 nm and 980 nm) devices are used to remove bacteria in infected teeth. This literature overview aimed to compare and evaluate the advantages and disadvantages in using these laser devices with standardized settings.
The PubMed database was searched using precise keywords between April 2011 and April 2016. Likewise, print media from the Library of RWTH Aachen University were examined.
A total of 22 eligible studies were found regarding Nd:YAG laser 1064 nm. Four studies fulfilled all demanded criteria in this review for this laser device. Seven studies referring to the diode laser 980 nm were examined, although only one fulfilled all criteria. Eleven studies were found regarding the diode laser 810 nm, but also only one study could fulfill all necessary criteria.
The analysis of the selected studies showed that all three laser systems are able to successfully decimate bacteria that are present in infected teeth. Pigmented bacteria are efficiently better removed by the Nd:YAG laser. Moreover, in deeper dentin layers, Nd:YAG laser showed better results. Concerning handiness, size, and purchase price, the diode laser is preferable.
In summary, a direct comparison cannot be made between the selected laser devices due to different study designs, materials, and equipment. Prospective randomized trials are needed to further verify which laser system is to be preferred for the best results in endodontic therapy and evaluate an evidence-based and international guideline.
The authors declare that they have no conflict of interests.