The bactericidal effect of Nd:YAG, Ho:YAG, and Er:YAG laser irradiation in the root canal: an in vitro comparison

Principle and antimicrobial efficacy of laser-activated irrigation: A narrative review

In the last two decades, the activation of root canal irrigants with pulsed lasers as an adjunct in root canal treatment has become increasingly popular. This narrative review explains the physical basics and the working mechanism of laser-activated irrigation (LAI), explores the parameters influencing LAI efficacy, considers historical evolutions in the field and summarizes laboratory and clinical evidence with emphasis on the antimicrobial action of LAI. Cavitation is the driving force behind LAI, with growing and imploding vapour bubbles around the laser tip causing various secondary phenomena in the irrigant, leading to intense liquid dynamics throughout the underlying root canal. High-speed imaging research has shown that laser wavelength, pulse energy, pulse length and fibre tip geometry are parameters that influence this cavitation process. Nevertheless, this has not resulted in standardized settings for LAI. Consequently, there is significant variability in studies assessing LAI efficacy, complicating the synthesis of results. Laboratory studies in extracted teeth suggest that, with regard to canal disinfection, LAI is superior to conventional irrigation and there is a trend of higher antimicrobial efficacy of LAI compared to ultrasonic activation. Clinical evidence is limited to trials demonstrating similar postoperative pain levels after LAI versus no activation or ultrasonic activation. Clinical evidence concerning the effect of LAI on healing of apical periodontitis as yet is scarce.

Photobiomodulation Therapy and Pulp-Regenerative Endodontics: A Narrative Review

Regenerative endodontic procedures (REPs) were used to recover the dental pulp’s vitality in order to avoid the undesirable outcomes of conventional endodontic treatment and to promote dentinal formation, especially for immature permanent teeth. Photobiomodulation therapy (PBMT) exhibits photobiological and photochemical effects for improving the root canal’s environmental conditions by compensating for oxidative stress and increasing the blood supply to implanted stem cells and improving their survival. Basic research has revealed that PBMT can modulate human dental pulp stem cells’ (hDPSCs) differentiation, proliferation, and activity, and subsequent tissue activation. However, many unclear points still remain regarding the mechanisms of action induced by PBMT in REPs. Therefore, in this review, we present the applications of laser and PBMT irradiation to the procedures of REPs and in endodontics. In addition, the effects of PBMT on the regenerative processes of hDPSCs are reviewed from biochemical and cytological perspectives on the basis of the available literature. Furthermore, we consider the feasibility of treatment in which PBMT irradiation is applied to stem cells, including dental pulp stem cells, and we discuss research that has reported on its effect.

Push-out bond strength of two calcium silicate-based cements used for repair of artificial furcal perforation following different power outputs of Nd:YAG laser

Proper bond strength of endodontic materials is an essential factor in the final success of root canal treatments, including perforation repairs. This study was designed to evaluate the effect of two power outputs of Nd:YAG laser (1064 nm) on push-out bond strength (PBS) of ProRoot mineral trioxide aggregate (MTA) and calcium-enriched mixture cement (CEM Cement) in the repair of artificial furcal perforations. This ex vivo study enrolled 66 extracted human molars. After preparing the access cavity, perforations were created on the floor of the pulp chamber with a diameter of 1.4 mm. The teeth were randomly distributed into the following six groups according to the repair material (MTA and CEM) and power output of laser irradiation (1 W and 1.5 W); A: MTA (case), B: CEM (case), C: Nd:YAG (1 W)/MTA, D: Nd:YAG (1 W)/CEM, E: Nd:YAG (1.5 W)/MTA, and F: Nd:YAG (1.5 W)/CEM. Then, a universal testing machine was utilized to assess the PBS. Data analysis was performed using ANOVA and T tests. Significant level was considered at P < 0.05. The highest mean ± SD of PBS was noted in Group Nd:YAG (1 W)/MTA (58.92 ± 36.13), followed by Nd:YAG (1.5 W)/MTA > Nd:YAG (1.5 W)/CEM > Nd:YAG (1 W)/CEM > MTA > and CEM. A significant difference was noted between laser and non-laser applications (P < 0.05). However, the increase of power output from 1 to 1.5 W had no significant influence on PBS (P > 0.05). The PBS of MTA groups was always significantly greater than that of CEM groups (P < 0.05). Although Nd:YAG laser irradiation positively influenced on PBS values in both material studied, increasing power output was not effective.

Bactericidal effect of Er,Cr:YSGG laser irradiation on endodontic biofilm: An ex vivo study

AIM

This ex vivo study aimed to evaluate the of Er,Cr:YSGG laser effectiveness in the decontamination of an endodontic biofilm.

MATERIALS AND METHODS

Seventy-three single rooted human teeth, freshly were chosen. Each tooth was exposed to four associated species in an endodontic biofilm (Enterococcus faecalis, Streptococcus salivarius, Porphyromonas gingivalis, and Prevotella intermedia) and randomly allocated to one of the seven experimental groups. The group 1 (7 teeth) was used to finalize the reliable biofilm-forming technique. The groups 2 and 3 (15 teeth each group) were irradiated with two different Er;Cr:YSGG laser settings (0,75 W - 40 Hz and 4 W - 40 Hz, respectively). The groups 4 and 5 (15 teeth each group) were irrigated with two different solutions and laser irradiated with the same settings (1,5 W - 15 Hz). The group 6 (6 teeth) was the control group treated only with 4 ml 2,5% NaOCl irrigation during 60 s.

RESULTS

The observations of group 2 and 3 specimens showed the ripeness of the biofilm with the presence of Enterococcus faecalis and Streptococcus salivarius in chains but in group 3 thermal edge effects produced by the optic fiber in the canal walls were present. The group 4 specimens observation showed an average cleaning of the root canal walls while on the canal walls of group 5 samples the apical third presented several debris and smear layer and in the centre cracks and melting dentin of the radicular wall were observed.

CONCLUSION

In those experimental conditions, this study, demonstrated that Er,Cr:YSGG laser has a canals decontamination ability when associated to NaOCl irrigation.

A comparative evaluation of the efficacy of erbium: yttrium-aluminum-garnet and diode lasers in smear layer removal and dentin permeability of root canal after biomechanical preparation - A scanning electron microscopy study

The chemomechanical preparation of root canal dentin with hand or rotary instruments creates debris and a smear layer. Root canal preparation (RCP) along with irrigants is not effective in cleaning apical portions, and hence, different laser activation systems were used for better cleaning in the apical third. Aim: The aim of this study is to compare the efficacy of erbium: yttrium-aluminum-garnet (Er:YAG) and diode laser irradiation in smear layer removal and dentin permeability after biomechanical preparation using scanning electron microscopic investigation. Material and Methods: Thirty sound single-rooted human teeth were distributed randomly and equally into three groups (n = 10 each) based upon the type of laser irradiation after RCP: Group I (control group) - RCP with ProTaper rotary system using the standard irrigating protocol; Group II - RCP with ProTaper rotary system using the standard irrigating protocol followed by diode laser irradiation; and Group III - RCP with ProTaper rotary system using the standard irrigating protocol followed by Er:YAG laser irradiation. After root sectioning, specimens were dehydrated, then gold plated and observed using a scanning electron microscopy. Then, the smear layer scores were recorded and performed using the statistical analysis. Results: Smear layer removal efficacy of Er:YAG laser was more at coronal, middle, and apical third when compared to Group I and Group II. Debris removal score of Group III (Er:YAG) was better than Group I (17% ethylenediaminetetraacetic acid) and Group II (diode). Conclusion: Er:YAG laser-activated RCP was comparatively efficient in cleaning the smear layer and dentinal tubules opening.

Comparative evaluation of antibacterial effect of nanoparticles and lasers against Endodontic Microbiota: An in vitro study

Background

Present study was conducted with the aim of evaluating antimicrobial efficacy of silver (AgNP) and gold nanoparticles (AuNP) with and without Nd: YAG laser (L) irradiation against experimentally inoculated Enterococcus faecalis in infected human root dentin.

Material and Methods

120 extracted single rooted human teeth were prepared and inoculated with E. faecalis for 24 hrs. The teeth were then randomly divided into 4 experimental group: AgNPs group: irrigation for 3minutes with 50 μl of 100 ppm, the AuNPs group: irrigation with 50 μl of 100 ppm, the AgNPs & Nd: YAG lasers group: irrigation with 50 μl of 100 ppm + irradiation with 1.5W laser for 60 seconds, the AuNPs & Nd: YAG lasers group: irrigation with 50 μl of 100 ppm + irradiation with 1.5W laser for 60 seconds. One control group consisting of 2% CHX irrigation for 3 minutes was also there (n = 20). The specimens were collected from the canal before and after irrigation, and colony forming units were observed.

Results

Significant difference was found among all the groups in comparison to the control group (p<0.05). The greatest reduction in CFU's was observed with combination of AgNPs & Nd: YAG lasers group.

Conclusions

AgNPs in combination with Nd: YAG laser irradiation has the potential to be used as root canal disinfectant. Key words:Antibacterial efficacy, gold, silver, nanoparticles, lasers, solid-state.

The Effect of Er:YAG Laser on Entroccocus faecalis Bacterium in the Pulpectomy of Anterior Primary Teeth

Introduction: Successful root canal therapy depends on the complete elimination of microorganisms such as Entroccocus faecalis, which is impossible to achieve with the traditional methods. Lasers are recently introduced as a new method to solve the problem. The present study is planned and performed to examining the antibacterial effect of Er: YAG laser. Methods: Sixty extracted anterior primary teeth were prepared and sterilized. E. faecalis bacterium was cultured in canals. Samples were randomly divided into two groups. The first group was disinfected by NaOCl 5/25% and Er: YAG laser and the second group just by NaOCl 5/25%. Samples of canal contents were cultured and colony counts were calculated. The results were analyzed statistically by SPSS software and Mann Whitney test. Results: There was no significant difference between colony counts in both groups (P=0.142). But the number of colonies in the first group was lower than in the second group. Conclusion: Although, Er: YAG laser cannot completely eliminate E. faecalis bacterium, its simultaneous use with NaOCl decreases E. faecalis.

The Use of Lasers in Disinfection and Cleanliness of Root Canals: a Review

The outcome of root canal treatment is based on efficient disinfection of the root canal system and prevention of reinfection. Current chemomechanical cleaning methods do not always achieve these goals, and insufficient root canal disinfection is the main reason for endodontic failure. Due to high energy content and specific characteristics of laser light, laser treatment has been proposed for cleaning and disinfecting the root canal system. This paper reviews the literature covering the effect of Er:YAG, Er,Cr:YSGG, Nd:YAG and diode laser on the root canal wall in the removal of smear layer and against intracanal bacteria. Recently, the use of laser energy to induce cavitation and acoustic streaming of intracanal irrigants has been investigated. Based on recent literature, it can be concluded that lasers have bactericidal effects. However, they still cannot replace sodium hypochlorite and should be considered as an adjunct to the current chemical root canal disinfection protocols. Certain lasers can help in removing the smear layer and debris and can modify the morphology of the root canal wall. Unfortunately, there have not been enough randomized clinical studies evaluating endodontic treatment outcome following the use of laser.

Vitality of Enterococcus faecalis inside dentinal tubules after five root canal disinfection methods

Aim:

To compare the vitality of Enterococcus faecalis within dentinal tubules after subjected to five root canal disinfection methods.

Materials and Methods:

Dentin blocks (n = 60) were colonized with E. faecalis. After 4 weeks of incubation, the dentin blocks were divided into one control and five test groups (n = 10 each). The root canals of test groups were subjected to one of the disinfection methods, namely, normal saline (NS), sodium hypochlorite (NaOCl), chlorhexidine digluconate (CHX), neodymium-doped yttrium aluminum garnet (Nd: YAG) laser, and diode laser. The effect of disinfection methods was assessed by LIVE/DEAD BacLight stain under the confocal laser scanning microscopy to determine the “zone of dead bacteria” (ZDB). Mean values were calculated for ZDB and the difference between groups was established.

Results:

Penetration of E. faecalis was seen to a depth of >1000 μm. Viable bacteria were detected with NS irrigation. NaOCl and CHX showed partial ZDB. When the root canals were disinfected with Nd: YAG and diode lasers, no viable bacteria were found.

Conclusion:

E. faecalis has the ability to colonize inside dentinal tubules to a depth of >1000 μm. In contrast to conventional irrigants, both Nd: YAG and diode lasers were effective in eliminating the vitality of E. faecalis. NS, NaOCl, and CHX showed viable bacteria remaining in dentinal tubules.

Laser use in direct pulp capping: A meta-analysis

BACKGROUND

The authors of this study evaluated the effects of lasers on the outcome of direct pulp capping by means of a meta-analysis.

TYPES OF STUDIES REVIEWED

The authors completed a literature search on PubMed, Cochrane Library, Embase, and China National Knowledge Infrastructure, as well as a manual search of the reference lists of all identified articles since the introduction of lasers in endodontics in 1971 through May 30, 2016. The authors systematically evaluated the studies that met the inclusion criteria and performed a meta-analysis.

RESULTS

The authors selected 5 studies about 4 laser systems (carbon dioxide; diode; erbium,chromium:yttrium-selenium-gallium-garnet; and erbium:yttrium-aluminum-garnet) from the 510 articles to be included in this meta-analysis. Using a fixed-effects model, they found no significant heterogeneity between these studies (χ² = 0.83, P = .99, I² = 0%). Their results showed that the success rate (89.9%) of the laser groups was higher than that of 67.2% of the control groups, and the difference was statistically significant (risk ratio, 1.35; 95% confidence interval, 1.23-1.49; P < .00001).

CONCLUSIONS AND PRACTICAL IMPLICATIONS

On the basis of the limited evidence, the use of lasers effectively improved the prognosis of direct pulp capping treatment for permanent teeth.

Laser Application in Dentistry: Irradiation Effects of Nd:YAG 1064 nm and Diode 810 nm and 980 nm in Infected Root Canals-A Literature Overview

Objective. In endodontics, Nd:YAG laser (1064 nm) and diode laser (810 nm and 980 nm) devices are used to remove bacteria in infected teeth. A literature review was elaborated to compare and evaluate the advantages and disadvantages of using these lasers. Methods. Using combined search terms, eligible articles were retrieved from PubMed and printed journals. The initial search yielded 40 titles and 27 articles were assigned to full-text analysis. The studies were classified based upon laser source, laser energy level, duration/similarity of application, and initial and final bacterial count at a minimum of 20 prepared root canals. Part of the analysis was only reduced microorganisms and mechanically treated root canals upon preparation size of ISO 30. All studies were compared to evaluate the most favorable laser device for best results in endodontic therapy. Results. A total of 22 eligible studies were found regarding Nd:YAG laser 1064 nm. Four studies fulfilled all demanded criteria. 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, although only one study fulfilled all necessary criteria. Conclusions. Laser therapy is effective in endodontics, although a comparison of efficiency between the laser devices is not possible at present due to different study designs, materials, and equipment.

Safety Irradiation Parameters of Nd:YAP Laser Beam for Endodontic Treatments: An In Vitro Study

Objective. Nd:YAP laser has several potentialities of clinical applications in endodontics. The aim of our study is to determine the safety range of irradiation parameters during endodontic application of Nd:YAP laser that can be used without damaging and overheating the periodontal tissue. Material and Methods. Twenty-seven caries-free single-rooted extracted human teeth were used. Crowns were sectioned to obtain 11 mm root canal length. Temperature increases at root surfaces were measured by a thermocouple during Nd:YAP laser irradiation of root canals at different energy densities. Canal irradiation was accomplished with a circular and retrograde movement from the apex until the cervical part of the canal during 10 seconds with an axial speed of 1 mm/s. Each irradiation was done in a canal irrigated continuously with 2.25% NaOCl solution. Results. Periodontal temperature increase depends on the value of energy density. Means and standard deviations of temperature increases at root surfaces were below 10°C (safe threshold level) when the average energy densities delivered per second were equal to or below 4981 J/cm² and 9554 J/cm², respectively, for irradiations using a fiber diameter of 320 μm and 200 μm. Conclusions. Within the limitations of this study and under specific irradiation conditions, Nd:YAP laser beam may be considered harmless for periodontal tissues during endodontic applications.

An in-vitro evaluation of the effect of 980 nm diode laser irradiation on intra-canal dentin surface and dentinal tubule openings after biomechanical preparation: Scanning electron microscopic study

Context:

Very recently, diode laser has been used for disinfecting the root canals in endodontic treatment and increasing its success rate and longevity utilizing the thermal effect of laser on surrounding tissues.

Aims:

The aim of this study is to evaluate the effect of 980 nm laser irradiation on intra-canal dentin surface – scanning electron microscopic (SEM) - in-vitro study.

Methods:

A total of 40 single-rooted freshly extracted permanent teeth were collected. Teeth were sectioned at the cemento-enamel junction using diamond disc. Root canals of all samples were prepared using hand ProTaper, which were randomly assigned into two groups (n = 20 each). Group 1: Receiving no treatment after biomechanical preparation; Group 2: 980 nm diode laser-treated root canals. Teeth were prepared for SEM analysis to check the size of intra-canal dentinal tubule openings.

Statistical Analysis Used:

Data were analyzed using SPSS V.16 software and compared using Levene's and independent t-test.

Results:

On statistical analysis, width of intracanal dentinal tubule openings in Group 1 (control) was significantly higher than those observed in Group 2 (diode laser-treated) (P < 0.001).

Conclusion:

This study showed that the application of 980 nm diode laser on intra-radicular dentin resulted in ultrastructural alterations resulting in melting of dentin.

Human dental enamel and dentin structural effects after Er:YAG laser irradiation

Ideally projected to be applied on soft tissues, infrared lasers were improved by restorative dentistry to be used in hard dental tissues cavity preparations--namely enamel and dentin. This paper evidentiates the relevant aspects of infrared Erbium laser's action mechanism and its effects, and characterizes the different effects deriving from the laser's beams emission. The criteria for use and selection of optimal parameters for the correct application of laser systems and influence of supporting factors on the process, such as water amount and its presence in the ablation process, protection exerted by the plasma shielding and structural factors, which are indispensable in dental tissues cavity preparation related to restorative technique, are subordinated to optical modifications caused by the interaction of the energy dissipated by these laser light emission systems in the targeted tissue substrate.

CLINICAL RELEVANCE

Differences in the action of infrared Erbium laser system in regard to the nature of the ablation process and variations on the morphological aspects observed in the superficial structure of the target tissue irradiated, may be correlated to the structural optical modifications of the substrate produced by an interaction of the energy propagated by laser systems.

Antibacterial effects of two different types of laser and aqueous ozone against Enterococcus faecalis in root canals

OBJECTIVE

The purpose of this study was to investigate the antibacterial effects of two different types of laser and aqueous ozone in human root canals infected by Enterococcus faecalis.

BACKGROUND DATA

Many techniques have been developed to find an alternative to sodium hypochlorite as a disinfection agent for infected root canals. However, no study has evaluated the exactly the same antimicrobial agent with sodium hypochlorite (NaOCl).

METHODS

Eighty mandibular premolar teeth with single roots and canals were selected. Following root canal preparation and irrigation, sterilization was performed in an autoclave. E. faecalis was incubated in the root canals and kept at 37°C for 24 h. The teeth contaminated with E. faecalis were divided into one negative control group (NaOCl) and three experimental groups; (Er:YAG laser, KTP laser, and aqueous ozone groups)(n=20). A disinfection procedure was performed for 3 min in order to standardize all groups. After this procedure, the microbial colonies were counted.

RESULTS

The results indicated that whereas the NaOCl group exhibited the highest antibacterial effect among all groups, the aqueous ozone showed the highest antibacterial effect among the experimental groups. Whereas a statistically significant difference was noted between the aqueous ozone and laser groups (p<0.05), the difference between the Er:YAG and KTP lasers was not statistically significant (p>0.05).

CONCLUSIONS

The results showed that when aqueous ozone was applied with the aim of disinfecting the root canals, it exhibited a higher antibacterial effect than the KTP and Er:YAG lasers. However, the antibacterial effect of the aqueous ozone was insufficient when compared with NaOCl.

Bactericidal effects of Nd:YAG laser irradiation and sodium hypochlorite solution on Enterococcus faecalis biofilm

OBJECTIVE

The aim of this study was to evaluate the bactericidal effects of Nd:YAG laser on biofilm of Enterococcus faecalis.

BACKGROUND DATA

It is difficult to eliminate bacterial biofilms with routine endodontic preparation techniques. It might be possible to eliminate biofilms remaining in the root canals of teeth with lasers.

MATERIALS AND METHODS

The root canals of 60 extracted teeth were prepared and E. faecalis biofilms were formed within the root canals. Then the teeth were randomly divided into four groups of 15. Group 1 samples did not undergo any interventions, to serve as controls. Group 2 samples underwent a 3-W laser beam for 10 sec. The root canals in group 3 were irrigated with 1% sodium hypochlorite for 15 min and then irradiated with a 3-W laser beam for 10 sec. The root canals in group 4 were irrigated with 1% sodium hypochlorite for 15 min. Dentin chips were collected from the root canal walls and weighed. Then the chips were used to prepare a suspension. The classic colony-forming unit (CFU) counting technique was used to determine remaining bacterial counts.

RESULTS

The bacterial counts in groups 2 and 4 had decreased to 54% and 2.39% of the control group, respectively. In group 3 no bacterial growth was observed. There were no significant differences between groups 1 and 2 (p>0.05).

CONCLUSIONS

Based on the results of the present study, the effect of Nd:YAG laser beam on E. faecalis biofilm is less than that of sodium hypochlorite solution. A combination of laser and sodium hypochlorite results in complete elimination of E. faecalis biofilm.

Evaluation of Nd:YAG and Er:YAG irradiation, antibacterial photodynamic therapy and sodium hypochlorite treatment on Enterococcus faecalis biofilms

AIM

To compare the antimicrobial efficacy of two-high power lasers (Nd:YAG and Er:YAG) and two commercial antimicrobial photodynamic therapy (aPDT) systems with that of sodium hypochlorite (NaOCl) action on Enterococcus faecalis biofilms grown on dentine discs.

METHODOLOGY

Enterococcus faecalis biofilms were grown on dentine discs in a microtiter plate, incubated for 24 h and subjected to the following treatments: aPDT (Denfotex and Helbo system), Er:YAG laser irradiation (2940 nm, 50 mJ or 100 mJ, 15 Hz, 40 s), Nd:YAG laser irradiation (1064 nm, 2 W, 15 Hz, 40 s) and immersion in 2.5% (w/v) NaOCl for 1, 5, 10 and 30 min. Surviving bacteria were harvested, and the number of CFU per disc was determined by plate counting.

RESULTS

Significant reductions (anova, P ≤ 0.05) in viable counts were observed for aPDT (Helbo) (2 log(10) reduction), Er:YAG irradiation using 100 mJ pulses (4.3 log(10) reduction) and all NaOCl treatments (>6 log(10) reduction). NaOCl (2.5%) for 5 min effectively eliminated all bacteria. aPDT (Denfotex), Er:YAG irradiation using 50 mJ pulses and Nd:YAG treatment caused a reduction in the viable counts of <1 log(10) unit; these results were not significantly different from the untreated controls.

CONCLUSION

Within the limitations of this particular laboratory set-up, NaOCl was the most effective in E. faecalis biofilm elimination, while Er:YAG laser treatment (100 mJ pulses) also resulted in high reductions in viable counts. The use of both commercial aPDT systems resulted in a weak reduction in the number of E. faecalis cells. Nd:YAG irradiation was the least effective.

Bactericidal effects of 2.94 µm and 1.67 µm laser

The bactericidal effects of lasers with wavelengths of 1.67 and 2.94 µm on cariogenic Streptococcus mutans were investigated. Temperature during irradiation was also measured to determine the mechanism underlying the bactericidal effects of the lasers. An aliquot of 2 µl cell suspension of S. mutans JC-2 strain was placed on anhydrous quartz or dentin plate, covering an area of approximately 5.0 mm in diameter to a depth of approximately 0.1 mm. Cell suspension was then irradiated at a power of 0.8 W (3.1 J/cm²) at a rate of 40 pps for 30 sec. After irradiation, the plate was put into a bottle containing PBS and vigorously voltated. Solution was serially diluted and inoculated on MS agar. After incubation anaerobically for 72 hr, colony forming units on the agar were counted. The experimental group, the number of bacteria decreased significantly compared to the control group under all conditions. No significant differences were observed in effect of wavelength or plate on bactericidal activity. In conclusion, laser irradiation at a wavelength of 1.67 µm for 30 sec showed a bactericidal effect on S. mutans, suggesting that this wavelength is more useful than 2.94 µm due to greater tissue penetration.

High power-pulsed Nd:YAG laser as a new stimulus to induce BMP-2 expression in MC3T3-E1 osteoblasts

BACKGROUND AND OBJECTIVE

High-power laser has recently become a physical stimulus for bone regeneration. Little is known about how high-power laser irradiation affects osteoblast differentiation. This study investigated osteoblast responses to high-power laser and combined irradiation with BMP-2 treatment.

STUDY DESIGN/MATERIALS AND METHODS

MC3T3-E1 pre-osteoblasts were exposed to laser irradiation, 100 ng/ml BMP-2 or both. Cells were irradiated with a Q-switched, pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, with a 1,064 nm wavelength and 0.75 W output power under 1.5, 3, or 5 J/cm(2) energy densities. Cell proliferation was evaluated using tetrazolium salt, WST-8. To determine the effect of these treatments on in vitro osteogenesis, we examined alkaline phosphatase (ALP) activity, mineral deposition, and expression of genes associated with osteogenesis. Quantitative real time PCR or ELISA was used to examine cytokine expression. In each experiment, either non-irradiated or BMP-2 (100 ng/ml)-treated cells were used as controls.

RESULTS

High-power, low-level, Nd:YAG laser irradiation significantly increased ALP activity, when combined with BMP-2 or not. Cell proliferation declined in the irradiation and combined irradiation/BMP-2 groups. Interestingly, Nd:YAG laser stimulation resulted in significant induction of endogenous BMP-2 protein and gene expression. The increased expression of upstream regulators cbfa1 by Nd:YAG laser alone was comparable to exogenous BMP-2 treatment (100 ng/ml). Combined laser/BMP-2 treatment was synergistic in the expression of some genes (IGF-1, cbfa1) and ALP activity, compared to both BMP-2 treatment and laser irradiation alone. In vitro matrix mineralization was significantly accelerated by laser stimulation compared to that of the control, more so than with the combined laser/BMP-2 treatment.

CONCLUSIONS

The present in vitro findings demonstrate that high-power, low-level Nd:YAG laser increased osteoblast activity, very efficiently accelerating mineral deposition. Osteoinductive effect of laser is likely mediated by activation of BMP-2-related signaling pathway.

Bactericidal effect of a Nd:YAG laser on Enterococcus faecalis at pulse durations of 15 and 25 ms in dentine depths of 500 and 1,000 μm

The success of endodontic treatment depends on the effective elimination of microorganisms from the root canal, and lasers provide more effective disinfection than conventional treatment using rinsing solutions. The objective of this in vitro study was to determine the bactericidal effect of laser irradiation in dentine of various depths at a wavelength of 1,064 nm and pulse durations of 15 and 25 ms. A total of 90 dentine slices were cut from bovine incisors and divided into two groups (45 slices each) of thickness 500 and 1,000 μm. All were inoculated with a suspension of Enterococcus faecalis (5.07 × 10(9) bacteria/ml). Based on the clinically accepted dose (approximately 300 J/cm(2)), the following laser settings were chosen for this study: 1.75 W, 0.7 Hz for 4 s, three repetitions. The two groups were divided into two subgroups of 15 slices each to be irradiated with pulse durations of 15 and 25 ms. The remaining 15 slices per group were not irradiated to serve as a control. After irradiation, the colony-forming units (CFU) were counted and evaluated. To determine the bactericidal effect of irradiation with different pulse durations, the results in the different groups were compared statistically. For all irradiated subgroups a bactericidal effect was observed at pulse durations of 15 and 25 ms (p=0.0085 and p<0.0001). The corresponding average log kills were 0.29 (15 ms) and 0.52 (25 ms) for 500 μm and 0.15 and 0.3 for 1,000 μm, respectively. The results of this in vitro study showed that Nd:YAG laser irradiation with a pulse duration of 15 ms eliminated an average of 49% and 29% of E. faecalis at dentine depths of 500 μm and 1,000 μm, respectively, and irradiation with a pulse duration of 25 ms eliminated 70% (500 μm) and 50% (1,000 μm). However, these values are lower than those achieved with the established protocol using microsecond pulses.

Bactericidal effect of Nd:YAG and Er:YAG lasers in experimentally infected curved root canals

OBJECTIVE

The purpose of this study was to evaluate the bactericidal efficacy of Nd:YAG and Er:YAG laser in the experimentally infected curved root canals.

BACKGROUND DATA

Previous studies revealed that laser systems have a significant bactericidal effect in both human and bovine infected straight root canals.

MATERIALS AND METHODS

Sixty extracted single-rooted teeth with single root canals were selected and then instrumented with endodontic files to a size 60 (K-type file). The degree of root curvature was determined according to modified Schneider's method. Each of the specimens was incubated in a sterile centrifuge tube with 1 mL of the Enterococcus faecalis suspension at 37°C for 2 weeks under aerobic conditions. After laser irradiation at each of the two settings, 50 mJ, 10 pps (0.5 W) or 100 mJ, 10 pps (1.0 W), the number of E. faecalis in each root canal was examined.

RESULTS

In the straight root canals, the Er:YAG laser showed higher bactericidal effects by 6.4-10.8% than did the Nd:YAG laser. Conversely, the bactericidal effect of Er:YAG laser in the curved root canals was higher by 1.5-3.1% than was that with the Nd:YAG laser. The bactericidal effect of the Er:YAG laser in the curved root canal is significantly lower than that in the straight root canal (p < 0.05).

CONCLUSION

These results suggest that further development in the endodontic laser tip and technique is required to ensure its success in curved root canals sterilization.

In vitro studies of the ablation mechanism of periodontopathic bacteria and decontamination effect on periodontally diseased root surfaces by erbium:yttrium-aluminum-garnet laser

The erbium:yttrium-aluminum-garnet (Er:YAG) laser is now increasingly used in periodontal therapy. The purpose of this study was to investigate the effect of Er:YAG laser irradiation on the morphology of periodontopathic bacteria and to compare the bacterial elimination effect of the laser and the ultrasonic scaler on diseased root surfaces in vitro. Colonies of Porphyromonas gingivalis were exposed to a single-pulse Er:YAG laser at 40 mJ and were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Also, 20 pairs of periodontally diseased root surfaces with subgingival calculi of freshly extracted teeth were treated by Er:YAG laser scaling at 40 mJ/pulse (14.2 J/cm(2) per pulse) and 10 Hz with water spray or ultrasonic scaling, or were not treated. The efficiency of each treatment was determined as the area treated per second, and the treated surfaces were examined by SEM. The material scraped from the treated root surfaces was cultured in aerobic and anaerobic conditions, and the numbers of colony forming units (CFUs) were compared. SEM and TEM showed that the Er:YAG laser had easily ablated the bacterial colony, leaving an ablation spot with a crater and the surrounding affected area showing melted branch-like structures. The laser irradiation was as equally effective and efficient as the ultrasonic scaler in performing root surface debridement. The CFUs after laser treatment were significantly fewer than those after ultrasonic scaling in aerobic and anaerobic culture conditions. Er:YAG laser ablates periodontopathic bacteria with thermal vaporization, and its bacterial elimination effect on the diseased root surfaces appears to be superior to that of the ultrasonic scaler.

Temperature variation on the external root surface during intracanal Er:YAG laser irradiation

OBJECTIVE

To evaluate the temperature changes on the root's external surface during Er:YAG laser irradiation with different tips and pulse repetition rates.

BACKGROUND DATA

There have been limited reports that correlate temperature variations with Er:YAG laser irradiation using different tips and pulse repetition rates.

MATERIALS AND METHODS

Sixty roots of central incisors were sectioned 10 mm from the apex, biomechanically prepared, embedded in acrylic resin, and randomly distributed into six groups: the teeth in group I, group II, and group III were irradiated with an Opus 20 laser with a sapphire tip at 8, 10, and 15 Hz, respectively; the teeth in group IV, group V, and group VI were irradiated with the fiberoptic tip of a Kavo Key laser at 6, 10, and 15 Hz, respectively. Laser irradiation was applied for 20 sec to all teeth and temperature changes were recorded with thermocouples in the root surfaces.

RESULTS

There were significant differences (p < 0.05) among pulse repetition rates: 6 and 8 Hz (2.36 degrees +/- 0.91 degrees C), 10 Hz (4.92 degrees +/- 1.60 degrees C), and 15 Hz (8.23 degrees +/- 2.78 degrees C); and radicular thirds: apical (8.33 degrees +/- 2.69 degrees C), middle (4.70 degrees +/- 1.60 degrees C), and cervical (2.48 degrees +/- 0.83 degrees C). No significant differences were seen between the two types of laser tips used (p > 0.05).

CONCLUSION

The temperature changes on root external surfaces remained above the critical threshold (13 degrees C) during Er:YAG laser irradiation, except for irradiation with 15 Hz in the apical third. However, the type of Er:YAG laser tip used (sapphire or fiberoptic) did not affect the temperature variation.

Temperature rise during photo-activated disinfection of root canals

The aim of this study was to determine whether it is safe to use photo-activated disinfection (PAD) during root canal treatment without heating the periodontal tissues. Root canals of 30 freshly extracted single-rooted teeth were prepared using ProFiles up to size ISO 40 and then filled with photo-sensitiser: tolonium blue (1.2 mg/l). The 635 nm diode laser was used with the manufacturer's endo-tip. Samples were irradiated for 150 s (output power 100 mW, approximate energy density 106.16 J/cm(2)). Temperatures were recorded at working length on the external root surface. After 150 s of PAD irradiation, the average temperature rise was 0.16 +/- 0.08 degrees C. All values were lower than the 7 degrees C safety level for periodontal injury. It was concluded that, regarding the temperature increase, the use of PAD in root canals could be considered harmless for periodontal tissues.

Bactericidal efficacy of Er,Cr:YSGG laser irradiation against Enterococcus faecalis compared with NaOCl irrigation: an ex vivo pilot study

AIM

To compare the efficacy of a standard NaOCl irrigation procedure with that of Er,Cr:YSGG laser irradiation in contaminated root canals having small and large apical foramina.

METHODOLOGY

Forty root canals of extracted central incisor teeth with straight roots were chosen so that their apical foramina just permitted the tip of a size 20-K file to pass through. The canals were then enlarged with files to size 60 and randomly divided into four groups of 10 teeth each. The apical foramina of one group were widened further so that the tip of a size 45-K file could just pass through. After sterilization, all roots were inoculated with Enterococcus faecalis for 48 h at 37 degrees C. The first group was used as a control, the second group was irrigated with 3% NaOCl solution for 15 min, and the last two groups having different sizes of apical foramina were irradiated with the Er,Cr:YSGG laser at output power from 0.5 W, with 20% air and water levels. The disinfecting efficacy of the groups was tested by collecting dentine chips from the inner canal walls of the specimens and counting viable E. faecalis on Mueller-Hinton agar plates.

RESULTS

The differences in the mean number of viable colonies between the control and laser groups were statistically significant (P < 0.05). The control specimens had the highest number of microorganisms (153 x 10(3) +/- 39 x 10(3)). Complete sterilization was achieved in the 3% NaOCl group. The mean colony forming units (CFU) values obtained after Er,Cr:YSGG laser irradiation were 6.6 x 10(3) CFU and 6.5 x 10(3) CFU in root canals having large and small apical foramina respectively.

CONCLUSION

In teeth with straight roots the Er,Cr:YSGG laser reduced the viable microbial population in root canals with small and large apical foramina but did not eradicate all bacteria. Three percent NaOCl inhibited the growth of E. faecalis and effectively sterilized all root canals.

Bactericidal effect of Nd:YAG laser irradiation on some endodontic pathogens ex vivo

AIM

To define the role of neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers in root canal disinfection along with a minimally invasive treatment concept.

METHODOLOGY

The hypothesis was tested ex vivo that Nd:YAG laser irradiation has a bactericidal effect on endodontic pathogens inoculated in root canals. Resultant colony-forming unit counts were associated with observations of bacterial cell structural changes using conventional scanning electron microscopy (CSEM) and environmental scanning electron microscopy (ESEM) on inoculated dentine surfaces, following indirect and direct Nd:YAG laser irradiation, respectively.

RESULTS

The Nd:YAG laser irradiation (1.5 W, 15 Hz, four times for 5 s) of Enterococcus faecalis inoculated canals resulted in a significant reduction (P < 0.05, Wilcoxon signed rank test) of the bacterial load, meaning a 99.7% kill, but no sterilization. The CSEM procedure verified that the extent of radiation damage was in line with the total amount of laser energy applied. After 2 h of incubation and three cycles of indirect laser treatment (i.e. through a 1-mm-thick dentine disc), no morphologically intact bacteria of Actinomyces naeslundii or Streptococcus anginosus were discernible. However, when micro-colonies of S. anginosus and specially biofilms of E. faecalis were present after 2 days, the in situ experiment using ESEM and direct laser treatment showed that bacterial eradication was reduced in deep layers.

CONCLUSIONS

The Nd:YAG laser irradiation is not an alternative but a possible supplement to existing protocols for canal disinfection as the properties of laser light may allow a bactericidal effect beyond 1 mm of dentine. Endodontic pathogens that grow as biofilms, however, are difficult to eradicate even upon direct laser exposure.

Disinfection of Root Canals Using Er:YAG Laser at Different Frequencies

OBJECTIVE

This study evaluated, in vitro, the degree of disinfection of the Er:YAG laser in root canals contaminated with Bacillus subtilis, Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans, for 28 days.

METHODS

Forty-six single-rooted human teeth were divided into five groups of eight teeth each; three teeth were used as negative controls and three as positive controls. After contamination, the root canals were prepared mechanically. Three groups were irradiated with Er:YAG laser at 100 mJ, varying the frequency (7, 10, and 16 Hz). Two groups were irrigated with 1.0% and 2.5% NaOCl solution. After treatment, two sterilized paper cones were placed in the root canals for 5 min. One cone was transferred to 2.0 mL of Letheen broth culture medium, incubated at 37 degrees C for 48 h, and then 0.1 mL of that solution was placed in 2.0 mL of brain heart infusion for 48 h to determine microbial growth. The other cone was transferred to a test pipette with peptone and water for serial dilution and spread in Müeller Hinton medium. After 24 h of incubation, the colony-forming units (CFUs) were counted.

RESULTS

There was a microbial reduction of 85.33% for the group irradiated with Er:YAG laser at 100 mJ/7 Hz, 74.58% at 100 mJ/10 Hz, and 89.50% at 100 mJ/16 Hz. For the groups irrigated with 1.0% and 2.5% NaOCl solution, 83.15% and 84.46% values of microbial reduction were obtained respectively.

CONCLUSION

All the groups showed statistically similar results (p > 0.05%). No method totally eliminated microorganisms.