Year : 2022 | Volume
: 12 | Issue : 3 | Page : 253--260
The usage of lasers in cleaning, shaping, and disinfection of root canal system
Taher Dr. Al Omari1, Hamza El-Farraj2, Hazem Mohammad Alzenate1, Nahed Al Charabi3, Rana Al Khatib4, Ayfer Atav Ateş5,
1 Department of Conservative Dentistry, Faculty of Dentistry, Jordan University of Science and Technology, Irbid, Jordan
2 Department of Operative, Preventive and Pediatric Dentistry, Charité - Universitätsmedizin Berlin, Berlin, Germany
3 Preventive Dentistry, Faculty of Dentistry, Jordan University of Science and Technology, Irbid, Jordan
4 Private Practice, Amman, Jordan
5 Department of Endodontics, Faculty of Dentistry, Istinye University, Istanbul, Turkey
Taher Dr. Al Omari
Department of Conservative Dentistry, Faculty of Dentistry, Jordan University of Science and Technology, P.O. Box: 3030, Irbid 22110
Since the laser was first used in endodontics in the 1970s, many studies have been conducted on this subject. This paper aims to summarize the studies about the effects of lasers in endodontics, which analyze the preparation and disinfection of the root canal system, postoperative pain, and the effect on the smear layer. The still-controversial question is; if lasers provide better results when used in tandem with conventional methods or alone. Another unknown factor is the side effects on teeth and surrounding tissues. With the increase in technology and knowledge in this field, developments are promising with different devices, laser tips, and wavelengths.
|How to cite this article:|
Al Omari TD, El-Farraj H, Alzenate HM, Al Charabi N, Al Khatib R, Ateş AA. The usage of lasers in cleaning, shaping, and disinfection of root canal system.Saudi Endod J 2022;12:253-260
|How to cite this URL:|
Al Omari TD, El-Farraj H, Alzenate HM, Al Charabi N, Al Khatib R, Ateş AA. The usage of lasers in cleaning, shaping, and disinfection of root canal system. Saudi Endod J [serial online] 2022 [cited 2022 Sep 24 ];12:253-260
Available from: https://www.saudiendodj.com/text.asp?2022/12/3/253/354826
Over the past few decades, new developments in the endodontics field have enabled endodontists to use innovative methods to save teeth and improve overall treatment outcomes. These developments include the introduction of new bio-materials, Ni-Ti rotary files, irrigation solutions, agitation techniques, and 3-D radiographs – such as cone-beam computed tomography (CT)–new obturation techniques, different types of lasers, and the improvement of visualization using operating microscopes.,
Lasers are regarded as fairly modern technology, which were introduced to overcome some of the shortcomings of conventional dentistry, for example, unpleasant noises and vibrations due to the use of conventional hand-pieces or fear of the anesthesia needle. Furthermore, lasers aim to facilitate complex dental procedures, save the time of both patients and dentists, and help enhance the overall treatment outcome.
Laser applications in dentistry started to emerge in the 1970s by Weichman and Johnson, who they tried to seal apical foramen in in vitro conditions with a high-powered Carbon dioxide laser. Currently, new lasers with different characteristics and applications look promising for use in different dental disciplines. Wavelengths that are produced in the ultraviolet region of the electromagnetic spectrum seem appealing in several endodontic procedures. For example, the Argon fluoride excimer laser (193 nm) has the ability to remove the necrotic tissues and debris slowly and selectively from the root canal, resulting in smooth and cracks free dentinal walls. Additionally, the xenon-chloride excimer laser (308 nm) can melt dentin and seal the dentinal tubules by closing their opening.,
This review article aims to describe and highlight the current and likely future applications of lasers in endodontics, involving the disinfection and shaping of the root canal system, the effect on smear layer removal, laser activated irrigation, the photon-induced photoacoustic streaming (PIPS), and shock wave-enhanced emission photoacoustic streaming (SWEEPS) techniques.
Application of Lasers in Cleaning, Shaping, and Disinfection of the Root Canal System
Preparation and shaping the root canal system
The main goal of endodontic treatment is to prevent and control pulpal and periradicular infections, and the microorganisms that are the primary etiological factor of apical inflammatory lesion. Various measures have been introduced to decrease and eliminate these microorganisms from the root canal system, including mechanical instrumentation techniques, irrigation regimes, and intracanal medicaments. Preparation of the root canal system is recognized as being one of the main stages of root canal treatment, because it facilitates the removal of tissues, debris, and microorganism by-products and creates space for the irrigation solutions and antibacterial medicaments to disinfect the root canal system. Preparation is important to facilitate the obturation of the root canal system.,
Various instruments have been introduced for cleaning and shaping the root canal system. Currently, a wide range of laser systems are used in the endodontic field, such as the Er: YAG laser, which has a stronger and more superficial effect on dental hard tissue., Studies have reported positive results about the efficacy of these systems in shaping and enlarging the root canal system.
A study by Kesler et al. assessed the efficacy of Er: YAG laser microprobes in disinfecting the straight root canals without mechanical instrumentation. According to their results, dentinal tubules were opened, the smear layer was removed, and there was no residual pulp tissue in the root canals. Thus, the authors concluded that using the Er: YAG laser was faster and more efficient compared to traditional methods.
An in vitro study used 940 nm diode laser along with 2.5% NaOCl and 17% ethylene diamine tetra-acetic acid (EDTA) irrigation assess the smear layer removal and conclude that using 940 nm diode laser enhances the removal of smear layer in the middle and apical areas without significant loss of mineral content.
Another study, conducted with scanning electron microscope (SEM) imaging, concluded that the cleaning efficacy of combined preparation techniques involving Ni-Ti rotary instrumentation, laser, and rotary-laser combined preparation techniques were better than that of the step-back technique. The combination of laser and rotary techniques was the most efficient method to disinfect the root canal system. In 2009, Inamoto et al. evaluated the cutting efficiency and changes in the morphological features of dentin, following the use of the ER: YAG laser. The authors concluded that the smear layer was completely removed after radiation and that the Er: YAG laser is an effective method for root canal preparation.
Shoji et al. designed a cone-shaped laser irradiation tip with a water nozzle to release 80% of a laser's energy laterally and 20% forward the outcome of using this tip to deliver Er: YAG irradiation on root canal preparation was investigated. The SEM images showed a cleaner dentinal surface when compared with the preparation of the canals using conventional endodontic instruments. Moreover, using this tip shortened the time needed to prepare the canals.
On the other hand, some studies showed several limitations of using these laser systems inside the root canal system. Other studies even reported negative effects. Altundasar et al. examined ultra-morphological features and changes in chemical compositions that happen in radicular dentin following exposure to Er, Cr: YSGG laser irradiation. They reported that Er, Cr: YSGG laser irradiation results in a partial or complete elimination of the smear layer, with few small areas of thermal injury. Minas et al. used endodontic tips to transmit the Er, Cr: YSGG laser beam to the root canals of posterior teeth. They found that it is possible to prepare the root canal space with lasers; however, the laser delivery system and energy levels need to be improved before lasers can be considered a possible substitute for conventional systems. Jahan et al. in an in vitro study, compared the effectiveness of the Er, Cr: YSGG laser with conventional methods of root canal preparation techniques and concluded that using a laser device to prepare curved root canals could lead to procedural errors, such as the formation of a ledge, zipping, perforation or over-instrumentation. All these studies show that there is a need for additional development in both laser devices and techniques to improve the outcomes of using lasers for root canal preparation, in particular for teeth with a curved root canal.
Disinfection of the root canal system
For the treatment to be successful, it is crucial to remove or reduce the number of microorganisms and their by-products in the root canal system. One of the reasons behind persistent and resistant periapical lesions and failure of treatment is inadequate disinfection of the root canal system. Therefore, effective mechanical and chemical disinfection of the root canal system is the essential key factor of endodontics.
The commonly used irrigation solution, sodium hypochlorite (NaOCl), and root canal disinfectant, and calcium hydroxide have the ability to penetrate inside the dentinal tubules, but the penetration is limited to about 130 μm only. As a result, there is a possibility of re-infection in endodontically-treated teeth.
These pools of infection remaining inside the root canal system can lead to a recurrence of infection after treatment. Due to the limitations of disinfecting the root canal system using conventional materials, new developments are being introduced to overcome these constraints and increase the efficiency of root canal disinfection. One of these new developments is the introduction of different laser devices to the endodontic field. Many studies have investigated the efficacy of using lasers for disinfection. Asnaashari et al. showed noticeable antibacterial effects on the Enterococcus faecalis biofilm in the root canal system when using photodynamic therapy (up to 98.8%) over the triple antibiotic paste and calcium hydroxide. Additionally, photodynamic therapy results in a reduction of overall treatment time, resulting in higher operational speed. Gutknecht, et al. concluded that the Holmium doped YAG laser (2100 nm) has a very efficient bactericidal effect on bacteria within root canals.
Macedo et al. reported that the bactericidal effect of NaOCl irrigation could be significantly improved by using Er: YAG laser irradiation. Another in vitro study used primary molars to evaluate Er: YAG laser irradiation in terms of antibacterial efficiency and the ability to remove the smear layer by PIPS, Nd: YAG, diode lasers, and conventional irrigation agents. The authors found that the Er: YAG laser with PIPS-activated irrigation is an effective agitation technique, which results in more dentinal tubules being opened, compared to the conventional NaOCl alone. The combination of the Er: YAG laser and NaOCl showed effective results against biofilms of E. faecalis, and also photoactivated disinfection using a 670 nm diode laser can reduce the bacterial load of E. faecalis by about 99.5% in 2 min and 98.89% in 4 min. Cheng et al. suggested a new option for effective disinfection of the root canal system by using Er: YAG laser irradiation at 0.5 W for 30 s combined with NaOCl irrigation. SEM results showed that the combination of the Er: YAG laser and NaOCl increases the effectiveness of disinfection and the penetration of the irrigation solution into dentinal tubules from 200 to over 500 μm. In addition, the depth increases with increasing irradiation power and time.
Multiple protocols were developed to understand and evaluate the way that laser energy provokes cavitation and acoustic streaming of intracanal irrigants. Laser-activated irrigation has been shown to rely primarily on the absorption of laser energy by water. The absorption of laser energy causes photoacoustic and photomechanical effects, as steam and air bubbles are formed within the irrigant solution inside the root canal system. These bubbles develop and then explode similar to those created using ultrasound devices. The only difference is that the laser tip location is stable. The irrigation solution will move rapidly due to shockwaves resulting from bubble collapse. Moreover, that process will create great shear stress on the walls of the root canal, which aids in removing the smear layer and debris, and also forces the irrigation solution to go deeper into the dentinal walls of the root canal, increasing the effectiveness of disinfection. From the earlier mentioned studies, it's clear that the volume of bacterial reductions within all experimental groups treated with lasers is greater than when using NaOCl alone, indicating that Er: YAG laser irradiation may improve the bactericidal effect of NaOCl by increasing its penetration deeper into dentinal walls.
Dickers et al. assessed the effect of an increased temperature during photo-activated disinfection of root canals on periodontal tissues. The increase in temperature was measured on the external root surface at working length. It was recorded that the average temperature increase was about 0.16°C ± 0.08°C after 150 s of photo-activated disinfection irradiation. According to these results, using photo-activated disinfection to disinfect the root canals is harmless for periodontal tissues in terms of temperature increases.
Yttrium Scandium Gallium Garnet (Er, Cr: YSGG) was assessed against 940 nm diode laser with radial firing tip at 0.51 W at 4 ms and 10 ms pulse durations. The increased outer surface temperature was significant with Yttrium Scandium Gallium Garnet Er, Cr: YSGG at 7.72°C compared to 5.07°C for the diode laser; however, both temperatures were below the critical threshold.
Holmium doped YAG laser was assessed to temperature increase with increased power setting and canal preparation size. The result showed a significant increase of temperature in the apical area as fiber size increased but not related to power settings. The temperature increase was ranged between 0°C and 10°C.
This was supported by the work of Al-Zand et al., where they assessed the 940 nm diode laser used for 50 s and reported increase in temperature range from 6.7°C to 8.5°C, which consider safe for the periodontal ligament.
In a more recent study, the Er: YAG laser and Nd: YAG were tested for increasing external root surface temperature and different power levels and found safe during irrigation with temperature range 6.3°C and 10.05°C.
On the other hand, it should be noted that using lasers in dentistry, in general and particularly during the canal disinfection process, has some disadvantages. Perin et al. showed that the effect of the Er: YAG laser cannot always reach the full working length with the delivery tip. According to Arslan and Kustarci, photo-initiated photoacoustic streaming “PIPS” activation in curved canals is associated with significantly higher extrusion debris compared to when there is no activation. In addition, another study using PIPS resulted in an increased volume of extruded irrigation solutions.
Effects on postoperative pain
Postoperative pain is affected by many procedural factors during endodontic treatment. For this reason, the effect of lasers on postoperative pain has been evaluated in different studies. Genc Sen and Kaya explored pain levels at 24, 48, and 72 h after retreatment and also recorded the number of analgesic pills used during this period. The findings suggested that using a diode laser is effective in reducing postoperative pain after endodontic retreatment, especially at the 24-and 48-h mark. Furthermore, the study found that diode lasers can reduce the amount of analgesic intake needed in the 3 days following the procedure, as well as the degree of pain from percussion on the 4th day. Another randomized clinical study demonstrated that using a 980 nm diode laser combined with conventional endodontic treatment methods to treat teeth with necrotic pulps results in lesser postoperative pain and a significant reduction in bacterial count for both aerobic and anaerobic bacteria.
Nd: YAG laser was assessed for postoperative pain in a randomized clinical trial. It was found that less postoperative pain was found with Nd: YAG laser compared to conventional treatment.
In a more recent study, both Nd: YAG and Diode lasers were compared to conventional treatment. No significant difference was found between groups in nonvital cases; however, Nd: Yag laser was better in vital cases.
In conclusion, the specific mechanism by which laser usage reduces postoperative pain is still unclear. While some researchers reported multiple mechanisms that alleviate pain by the diode laser, some authors reported that the diode laser has anti-inflammatory properties and reduces histamine, bradykinin, Prostaglandin E2, acetylcholine, serotonin, and substance p.
Effect on the smear layer
The smear layer is composed of organic and inorganic components and is normally produced by mechanical instrumentation of the root canal system. The layer consists of remnant of pulp tissue, microorganisms, blood cells, fluids, and particles of tooth structures. It has an amorphous and irregular appearance and consists of two separate layers. The first layer is superficial and loosely adheres to the underlying dentine, while the other is packed into dentinal tubules at distances up to 40 μm. Furthermore, the smear layer can be infected and act as a harbor for bacteria and bacterial products. The smear layer has also been shown to prohibit the penetration of intracanal disinfectants and sealers into dentinal tubules and can potentially compromise the seal of the root canal filling. This may be the main reason that most of the studies evaluated the smear layer. It is generally recommended to use NaOCl in combination with a chelating agent, such as EDTA for removing smear layer. Although these irrigation solutions are effective, they do not remove all of the smear layer. Thus, various methods have been suggested to enhance the efficiency of NaOCl and EDTA action. Recently, laser-activated irrigation methods were used for this purpose with conflicting results. Ozbay and Erdemir evaluated different lasers in terms of their PIPS mode for smear layer removal. Among the three laser systems tested, the Er: YAG laser, the Nd: YAG laser, and the Er, Cr: YSGG laser–the Er: YAG laser was the most efficient smear layer removal method, regardless of the solution used. And also, a previous study showed that all laser systems had considerable bacterial reduction, but the Er: YAG laser with PIPS-activated irrigation had the best results within the evaluated parameters. However, this result was not consistent with the reported result of Zhu et al. and Pedulla et al.
The Er: YAG laser-activated with PIPS was compared to the Erbium Chromium laser and to the Yttrium Scandium Gallium Garnet (Er, Cr: YSGG) laser with and without EDTA and NaOCl. Both systems were effective at smear layer removal. The effect of combining the activation and the use of EDTA and NaOCl had the best results.
The result was consistent with the findings of Sahar-Helft et al. Namely, that the Er: YAG laser-activated irrigation or PIPS was the most efficient at smear layer removal.
The XP-endo Finisher is one of the final irrigation activation files. In one study, this file was compared with a dual wavelength laser (Er, Cr: YSGG and diode 940 nm) in curved canals, and the overall removal of the smear layer was comparable in both systems, with predictable results of removing the smear layer in the apical part. The researcher recommended further studies to compare the disinfecting properties of the two systems.
Other types of laser-activated irrigation showed similar results as the Er: YAG laser. In a study of the Nd: YAG laser, the penetration of a fluorescent-labeled sealer was reported to be better; however, there was no statistically significant difference between procedures with and without activation of EDTA groups.
Laser-activated irrigation (photon-induced photoacoustic streaming and shock wave-enhanced emission photoacoustic streaming)
Modern endodontic irrigation activation techniques were analyzed in a recent Meta-analysis. There was improved cleanliness and smear layer removal, although the data did not allow for identifying the superiority of one technique over the others.
Laser-activated irrigation is a term similar to PIPS. It involves medium-infrared (2780 nm and 2940 nm) based lasers with laser tips that are placed inside the root canal space instead of the pulp camper used with PIPS.
The principles of PIPS and laser-activated irrigation techniques are based on the ability of the irrigation fluids to absorb the emitted laser. When this occurs, the irrigation fluid overheats above its boiling point, which subsequently causes a vapor bubble to start to develop at the fiber tip's end. The vapor bubble expands until it collapses, which activates the development of another bubble in a continuous manner. This eventually helps in moving the debris coronally, which causes it to reach the ramification and the untouched root canal surfaces.
De Moor et al. showed that laser activation irrigation and PIPS were greatly better and more efficient at removing compacted dentine debris from an artiﬁcial groove in a root canal than other techniques, like conventional sonic and ultrasonic irrigation.
Lloyd et al. also showed that laser-activated irrigation using PIPS tips eliminated organic debris from the canal isthmus at a signiﬁcantly greater level compared to standard needle irrigation.
A further study investigated the ability of different irrigation techniques using a laser scanning confocal microscope to examine the penetration of a final irrigation solution into dentinal tubules. The results showed that Er: YAG laser activation (Previso/PIPS) exhibited a deeper penetration area than passive ultrasonic irrigation, sonic irrigation, and continuous irrigation.
A recent study by Yang et al. reported that PIPS removed more accumulated hard tissue debris than ultrasonic-activated irrigation from mesial root canals of mandibular molars using micro-CT scan.
However, several studies reported that there was no difference between PIPS and ultrasonic-activated irrigation in debris and smear layer removal from the root canals.,
These conflicting results may be attributed to different reasons, such as design of the studies, canal preparation methods, irrigation during preparation, great variation in the preoperative debris, and activation time; in addition to differences in the shape, curvature, and the diameter between the root canals.
Nowadays, a novel mode for Er: YAG lasers, called SWEEPS, has been developed to enhance the cleaning and disinfecting efficacy of the PIPS procedure. The mechanism of action of SWEEPS differs slightly from PIPS in that SWEEPS delivers pulse pairs into the liquid with a proper temporal delay between the two laser pulses.
A recent micro-CT study compared the efficacy of three different irrigation activation techniques: Ultrasonic activated irrigation, PIPS, SWEEPS. The results showed that the SWEEPS mode was more effective in removing accumulated hard tissue debris from root canals (84.3% in mesial canal and 83.9% in distal canal) than PIPS or ultrasonic activated irrigation. Further studies should be conducted to investigate the new SWEEPS technique.
Comparing different type of laser
It is difficult to compare different lasers as there are many parameters and different power settings with different lasers. However, a summary of the different findings will be presented in this section.
The increased outer surface temperature was studied extensively. Diode laser was found to increase outer surface temperature by 5.07°C–8.5°C, however, when used with photo-activated disinfection, a minimal increase was noticed. Er, Cr: YSGG was noticed to increase temperature to 7.72°C. Holmium-doped YAG laser increases the temperature in a range of 0°C–10°C at different power settings and depth of insertion. Er: YAG and Nd: YAG lasers increase the temperature range 6.3°C and 10.05°C.
The Er: YAG laser, Diode laser, and Nd: YAG were found to be more efficient in the preparation of root canals.,,,, However, Er, Cr: YSGG laser irradiation has limited befits with some complications.,,
The disinfection of the root canal space was found to be good in most of the studies that evaluated different lasers. It enhances the smear layer removal and reduces the bacterial count rendering the canal space clean; however, it was noticed that the effect dose not reach the full working length.
Post-operative pain was less with diode laser and Nd: YAG laser, however, fewer clinical studies comparing the postoperative pain were found.,,
The Laser-activated irrigation was found to be more effective in removing the debris and smear layer; however, the heterogeneous study methods render identifying the superiority of an individual technique is difficult.
Studies have shown that the preparation and disinfection of root canals using lasers reduce the number of microorganisms and improve the irrigation solution's ability to penetrate the dentin and remove the smear layer. However, more studies are needed to explore the effects of lasers with different pulse modes, wavelengths, and thinner tips, in order to have better results. Meta-analysis and systematic review cannot be easily conducted to compare different lasers as a function of the heterogeneous in the methodology of different studies.
The authors would like to acknowledge the work of Miss Bonnie Sarigianis for English proofreading.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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