Performance assessment of novel side firing flexible optical fibers for dental applications

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.

Water-soluble vitamin-E for enhancing fluorescence diagnosis in infected human dentine treated with NaOCl

INTRODUCTION

Bacterial fluorescence methods are of interest in endodontics for informing endpoints for debridement. This study explored potential fluorescence quenching reversal effects of a water-soluble vitamin E conjugate (d-α-Tocopherol polyethylene glycol 1000 succinate, TPGS) when applied to polymicrobial biofilms grown on dentine that had been exposed to sodium hypochlorite (NaOCl) to cause quenching.

METHOD

Extracted human teeth were debrided, embedded in transparent acrylic resin and sectioned. After smear layer removal, tooth dentine sections were inoculated with a polymicrobial inoculum, and cultured for 7 days to create biofilms. Samples (n = 8 per group) were exposed to 1 % or 4 % NaOCl for 2 or 4 min, and then treated with TPGS. Bacterial fluorescence readings under laser excitation at 655 nm were assessed over 10 min using a calibrated DIAGNOdent device. All data were assessed for normality (Kolmogorov-Smirnov test) and analysed with ANOVA followed by Bonferroni post-hoc tests.

RESULTS

NaOCl at both concentrations quenched fluorescence readings of biofilms grown on dentine samples, with a maximal reduction of 40.4 % at 5 min after 4 % NaOCl. Treatment with TPGS gave faster recovery of fluorescence readings compared to the control at 5 and 10 min.

CONCLUSION

The water-soluble antioxidant TPGS partially reversed fluorescence quenching caused by NaOCl. This agent may have value clinically for reducing the time needed for fluorescence readings to recover when NaOCl is used as an irrigant. This will facilitate more accurate assessment of endpoints for canal debridement.

Photodynamic therapy adjuvant to non-surgical periodontal therapy: Systematic review of randomized clinical trials

OBJECTIVES

To systematically evaluate randomised controlled trials (RCTs) on whether adjuvant application of antimicrobial photodynamic therapy (aPDT) through the technique of irradiation in the external region of the periodontal pocket with optic-fibre tip offers benefits to scaling and root planning (SRP).

METHODS

Five databases were searched by two independent reviewers according to pre-specified eligibility criteria up to April 2023. No restrictions regarding date of publication, language and minimum follow-up period were imposed. The Cochrane Collaboration's Risk of Bias tool (RoB 2.0) was used for quality appraisal and Grading of Recommendations, Assessment, Development and Evaluation for assessing the certainty of evidence.

RESULTS

A total of 1388 publications were identified and reviewed for eligibility. Four of them fulfilled the inclusion criteria. The sample consisted of a total of 83 patients with periodontitis. In these, 330 periodontal sites were evaluated. The clinical findings of the majority of the included studies demonstrated that patients who received the association of aPDT + RAR with the protocol evaluated here, obtained clinical results similar to patients who received only the SRP alone. In none of the evaluated RCTs, clinical advantages were observed that would categorise this aPDT protocol as superior to conventional treatment.

CONCLUSION

Applying aPDT after SRP with external irradiation of the periodontal pocket does not seem to result in any clinical benefit compared to the use of SRP alone in patients with periodontitis.

Evaluation of Er:YAG and Er,Cr:YSGG lasers on intraradicular bonding using modified glass fiber tips

The aim of this study was to determine whether erbium laser irradiation emitted by modified glass-fiber tips would improve the intraradicular bonding of fiber posts. Forty human canines were endodontically treated and prepared for fiber-post placement. Roots were divided into five groups (n=8); according to the laser-tip combinations (2,940 nm Er:YAG and 2,780 nm Er,Cr:YSGG). Non-irradiated root canals served as control. Posts were cemented with self-adhesive resin cement and subjected to push-out test. Failure modes were characterized, and intraradicular bonded interfaces were analyzed by SEM and submitted to nanoleakage evaluation. Data were analyzed by two-way ANOVA and Tukey test (α=0.05). No significant differences were observed in cervical and middle sections (p>0.05), while significantly higher bond strengths were observed in apical sections (p<0.05). Laser irradiation reduced adhesive failures, cement-dentin gap formation, and nanoleakage apically. Laser-irradiation protocols employing end- or radial-firing tips improved bonding to apical intraradicular dentin contributing to more uniform bonded interfaces.

Laser-fluorescence assessment of sodium hypochlorite quenching reversal agents on human dentine

BACKGROUND

Laser-fluorescence diagnostic technology for real-time clinical assessment of residual bacteria could help assist in determining the endpoints for root canal debridement. Sodium hypochlorite (NaOCl) can however quench fluorescence and lead to false low reading. This study aims to evaluate various antioxidant for their ability to recover quenched fluorescence in dentine treated with NaOCl.

METHODS

Human dentine fluorescence was measured using 655 nm laser at baseline and again after a 2 min application of 4% NaOCl. The putative recovery agents were then applied, and the fluorescence measured after 5, 10, 20, 30 and 60 min. Recovery from quenching was also assessed using laser confocal scanning microscopy (CLSM) with a bound tetracycline fluorophore using 488 nm excitation.

RESULTS

A 5 min application of vitamin E oil or buffered 2% lignocaine solution (1:80,000 adrenaline) was effective in regaining quenched fluorescence within the following 5 mins. Distilled water, sodium thiosulfate, unbuffered 2% lignocaine with 1:80000 adrenaline and phosphate buffered saline were less effective, and of equal performance. Ascorbic acid and butylated hydroxyanisole were not effective and had deleterious effects on the levels of dentine fluorescence. CLSM provided confirmation of recovery from quenched fluorescence using vitamin E oil.

CONCLUSION

Based on these findings, reversal agents should be employed when assessing the fluorescence of dentine that has been exposed to NaOCl or other quenching agents.

Quick identification of prostate cancer by wavelet transform-based photoacoustic power spectrum analysis

Pathology is currently the gold standard for grading prostate cancer (PCa). However, pathology takes considerable time to provide a final result and is significantly dependent on subjective judgment. In this study, wavelet transform-based photoacoustic power spectrum analysis (WT-PASA) was used for grading PCa with different Gleason scores (GSs). The tumor region was accurately identified via wavelet transform time-frequency analysis. Then, a linear fitting was conducted on the photoacoustic power spectrum curve of the tumor region to obtain the quantified spectral parameter slope. The results showed that high GSs have small glandular cavity structures and higher heterogeneity, and consequently, the slopes at both 1210 nm and 1310 nm were high (p < 0.01). The classification accuracy of the PA time frequency spectrum (PA-TFS) of tumor region using ResNet-18 was 89% at 1210 nm and 92.7% at 1310 nm. Further, the testing time was less than 7 mins. The results demonstrated that identification of PCa can be rapidly and objectively realized using WT-PASA.

Evaluation of the effect of various endodontic irrigants and medicaments on dentine fluorescence

This study examined the effect of various root canal irrigants and medicaments on dentin fluorescence elicited by 655 nm visible red laser light. To replicate clinical use, irrigants were applied onto dentin samples for 2 min, while medicaments were applied for 2 weeks. Fluorescence values tracked from baseline across the following to 24 h, starting 5 min after exposure. Sodium hypochlorite, hydrogen peroxide, and articaine local anaesthetic (4% articaine with 1:1000,000 adrenaline) all significantly quenched fluorescence (p < 0.0001), which then returned to baseline levels after 20 min. Conversely, elevated fluorescence readings were recorded after 3% mepivacaine (p < 0.05), 0.2% chlorhexidine (p < 0.01) and chloroform (p <0.05). A 2 week application of Ledermix™ paste containing 3% demeclocycline caused an irreversible increase in fluorescence (p < 0.0001). Other tested endodontic materials (15% EDTA, eucalyptus oil, calcium hydroxide, Odontopaste™ clindamycin paste, and distilled water) had no impact on dentine fluorescence. The influences of endodontic materials on dentin fluorescence need to considered when using fluorescence endpoints to guide the progress of root canal treatment.

Evaluation of Surface Roughness of a Ni-Cr Alloy Treated With the Nd/YAG Laser and the Sandblast Technique

Introduction: This study was to assess the effect of various output parameters of laser treatment on roughening the surface of a commercial nickel-chromium (Ni-Cr) alloy as compared to the sandblasting technique. Materials and Methods: Ninety-six disk-shaped (5 mm diameter and 2 mm thickness) specimens in total were made of a nickel-chromium alloy by using the lost-wax technique. Air-abrasion surface treatment was used for sixteen specimens. Specimens were divided into six groups; one of them was sandblasted and the rest were irradiated by different Nd:YAG laser output parameters as follows: Group A: energy: 122 mJ, frequency: 20 Hz, irradiation duration: 20 seconds, spot size: 1.5 mm; Group B: energy: 122 mJ, frequency: 20 Hz, irradiation duration: 20 seconds, spot size: 3.5 mm; Group C: energy: 122 mJ, frequency: 10 Hz, irradiation duration: 20 seconds, spot size: 3.5 mm; Group D: energy: 102 mJ, frequency: 10 Hz, irradiation duration: 20 seconds, spot size: 3 mm; Group E: energy: 102 mJ, frequency: 20 Hz, irradiation duration: 20 seconds, spot size: 3 mm. The surface roughness of all surface-treated specimens was evaluated by using a profilometer, and their average roughness (Ra) was calculated. The average value of each group was analyzed by t test and one-way ANOVA (SPSS 17). Results: Significant differences (P<0.05) were observed between the study groups. The highest Ra was achieved for the sandblasted group. The Ra value in group C was the highest value among the laser-etched groups. Conclusion: Based on the results, Nd:YAG laser irradiation increases surface roughness, but it is not as efficient as the sandblasting method as a gold standard.

Ultrafast laser ablation of a multicore polymer optical fiber for multipoint light emission

We demonstrate the use of ultrafast laser pulses to precisely ablate the side of polymer multicore optical fibres (MCF) in such a way that light is efficiently coupled out of a set of MCF cores to free space. By individually exciting sets of MCF cores, this flexible "micro-window" technology allows the controllable generation of light sources at multiple independently selectable locations along the MCF. We found that the maximum fraction of light that could be side coupled from the MCF varied between 55% and 73%.

Fluorescence characteristics of E. faecalis in dentine following treatment with oxidizing endodontic irrigants

INTRODUCTION

This study aimed to assess changes in the fluorescence characteristics of Enterococcus faecalis in human dentine over a period of 24 h following treatment with endodontic irrigants.

METHOD

Sterilised, non-functional extracted third molars were embedded in acrylic resin and uniformly sectioned into 2 mm thick dentine sections. After the removal of smear layer, the dentine sections were inoculated with E. faecalis and cultured for 7 days. The infected dentine sections were subsequently treated with different concentrations of sodium hypochlorite (NaOCl) and hydrogen peroxide (H₂O₂). Bacterial fluorescence readings were assessed at different time points using a calibrated laser device. All data were assessed for normality (Kolmogorov Smirnoff test) and analysed using ANOVA with Bonferroni post-hoc tests.

RESULTS

Fluorescence readings were quenched when E. faecalis infected human dentine sections were treated with oxidizing irrigants in vitro. Throughout a 24-hour period, fluorescence recovered in part but did not return to baseline level.

CONCLUSION

The fluorescence quenching effect of these oxidizing agents needs to be considered when using laser fluorescence in assessing the quality of root canal debridement or disinfection.

Effects of Lasers and Their Delivery Characteristics on Machined and Micro-Roughened Titanium Dental Implant Surfaces

The aim of the study was to investigate the effects of neodymium: yttrium aluminium garnet (Nd:YAG) (1064 nm) and erbium: yttrium aluminium garnet (Er:YAG) (2940 nm) laser energy on titanium when delivered with conventional optics (focusing handpieces or plain ended optical fibres) or with a conical tip. Machined and micro-roughened implant discs were subjected to laser irradiation under a variety of energy settings either dry (without water) or wet (with water). Samples were scanned using a 3D non-contact laser profilometer and analysed for surface roughness, volume of peaks and the maximum diameter of the ablated area. Conical tip designs when used with both lasers showed no surface effect at any power setting on both machined and micro-roughened implant surfaces, regardless of the irrigation condition. When used with conventional delivery systems, laser effects on titanium were dose related, and were more profound with the Nd:YAG than with the Er:YAG laser. High laser pulse energies caused surface fusion which reduced the roughness of micro-roughened titanium surfaces. Likewise, repeated pulses and higher power densities also caused greater surface modifications. The presence of water reduced the influence of laser irradiation on titanium. It may be concluded that conical fibres can reduce unwanted surface modification, and this may be relevant to clinical protocols for debridement or disinfection of titanium dental implants.

Novel Approaches to Detect and Treat Biofilms within the Root Canals of Teeth: A Review

Biofilms located within the root canals of teeth are a unique and pressing concern in dentistry and in medical microbiology. These multispecies biofilms, which include fungi as well as bacteria, form in a protected site with low shear stress and low oxygen tension. Systemic antibiotics are of limited value because of the lack of blood flow of the site, and issues with innate and acquired resistance. Physical disruption using hand or rotary powered instruments does not reach all locations in the root canal system where biofilms are present. Alternative strategies including agitated irrigation fluids, continuous chelation, materials with highly alkaline pH, and antimicrobial nanoparticles are being explored to meet the challenge. Detection and quantification of biofilms using fluorescence-based optical methods could provide an indication of successful biofilm removal and an endpoint for physical and chemical treatments.

Identifying intestinal fibrosis and inflammation by spectroscopic photoacoustic imaging: an animal study in vivo

Crohn's disease (CD) is a chronic autoimmune disease characterized by obstructing intestinal strictures. Conventional imaging modalities can identify the strictures but cannot characterize whether a stricture is predominantly inflammatory or fibrotic. The purpose of this study is to examine the capability of photoacoustic (PA) imaging to characterize intestinal fibrosis and inflammation in vivo. Intestinal strictures in a rat model of CD were imaged with a PA-ultrasound parallel imaging system. Internal and external illuminations were attempted, both with transcutaneous PA signal reception. The PA signal magnitudes acquired at wavelengths targeting individual molecular components and the derived functional information showed significant differences between the inflammatory and fibrotic strictures, consistent with histological inflammation and fibrosis.

Dispersion of near-infrared laser energy through radicular dentine when using plain or conical tips

The aim of this study was to investigate the influence of tip design on patterns of laser energy dispersion through the dentine of tooth roots when using near-infrared diode lasers. Diode laser emissions of 810 or 940 nm were used in combination with optical fiber tips with either conventional plain ends or conical ends, to irradiate tooth roots of oval or round cross-sectional shapes. The lasers were operated in continuous wave mode at 0.5 W for 5 s with the distal end of the fiber tip placed in the apical or coronal third of the root canal at preset positions. Laser light exiting through the roots and apical foramen was imaged, and the extent of lateral spread calculated. There was a significant difference in infrared light exiting the root canal apex between plain and conical fiber tips for both laser wavelengths, with more forward transmission of laser energy through the apex for plain tips. For both laser wavelengths, there were no significant differences in emission patterns when the variable of canal shape was used and all other variables were kept the same (plain vs conical tip, tip position). To ensure optimal treatment effect and to prevent the risks of inadvertent laser effects on the adjacent periapical tissues, it is important to have a good understanding of laser transmission characteristics of the root canal and root dentine. Importantly, it is also essential to understand transmission characteristics of plain and conical fibers tips.

Activation of Alkaline Irrigation Fluids in Endodontics

In conventional endodontic treatment, alkaline solutions of sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) are used in combination to disinfect the root canal system and to eliminate debris and smear layers. An important concept that has emerged over recent years is the use of active physical methods for agitating these fluids to improve their penetration within areas that are not reached by endodontic instruments and to accelerate the chemical actions of these alkaline fluids against planktonic microorganisms, biofilms, soft tissue remnants and smear layers. Ultrasonic agitation and more recently pulsed lasers have emerged as two promising methods for activating endodontic irrigation fluids. Ultrasonic agitation with piezoelectric devices employs a moving tip, while laser agitation uses a stationary tip. Both methods cause cavitation, followed by implosions and shear forces which assist with debridement. Fluid streaming further enhances the activity of the fluids. While agitation enhances performance of irrigants, extrusion of fluids from the root canal during activation is a hazard that must be controlled.

In vitro performance of DIAGNOdent laser fluorescence device for dental calculus detection on human tooth root surfaces

OBJECTIVE

This study assessed the reproducibility of a red diode laser device, and its capability to detect dental calculus in vitro on human tooth root surfaces.

MATERIAL AND METHODS

On each of 50 extracted teeth, a calculus-positive and calculus-free root surface was evaluated by two independent examiners with a low-power indium gallium arsenide phosphide diode laser (DIAGNOdent) fitted with a periodontal probe-like sapphire tip and emitting visible red light at 655 nm wavelength. Laser autofluorescence intensity readings of examined root surfaces were scored on a 0-99 scale, with duplicate assessments performed using the laser probe tip directed both perpendicular and parallel to evaluated tooth root surfaces. Pearson correlation coefficients of untransformed measurements, and kappa analysis of data dichotomized with a >40 autofluorescence intensity threshold, were calculated to assess intra- and inter-examiner reproducibility of the laser device. Mean autofluorescence intensity scores of calculus-positive and calculus-free root surfaces were evaluated with the Student's t-test.

RESULTS

Excellent intra- and inter-examiner reproducibility was found for DIAGNOdent laser autofluorescence intensity measurements, with Pearson correlation coefficients above 94%, and kappa values ranging between 0.96 and 1.0, for duplicate readings taken with both laser probe tip orientations. Significantly higher autofluorescence intensity values were measured when the laser probe tip was directed perpendicular, rather than parallel, to tooth root surfaces. However, calculus-positive roots, particularly with calculus in markedly-raised ledges, yielded significantly greater mean DIAGNOdent laser autofluorescence intensity scores than calculus-free surfaces, regardless of probe tip orientation. DIAGNOdent autofluorescence intensity values >40 exhibited a stronger association with calculus (36.6 odds ratio) then measurements of ≥5 (20.1 odds ratio) when the laser probe tip was advanced parallel to root surfaces.

CONCLUSIONS

Excellent intra- and inter-examiner reproducibility of autofluorescence intensity measurements was obtained with the DIAGNOdent laser fluorescence device on human tooth roots. Calculus-positive root surfaces exhibited significantly greater DIAGNOdent laser autofluorescence than calculus-free tooth roots, even with the laser probe tip directed parallel to root surfaces. These findings provide further in vitro validation of the potential utility of a DIAGNOdent laser fluorescence device for identifying dental calculus on human tooth root surfaces.

Interstitial photoacoustic spectral analysis: instrumentation and validation

Photoacoustic (PA) spectral analysis (PASA) is a recently developed approach for quantifying molecular components and microscopic architectures in tissue. The PASA relies on signals with sufficient temporal length and narrow dynamic range for statistics based analysis. However, the optical and acoustic attenuation within the biological tissue make it difficult to acquire desirable signals from deep locations in biological tissue for PASA. This study proposes an interstitial PASA approach. By combining a fiber optics diffuser and a small aperture needle hydrophone, a fine needle PA probe facilitates PASA in deep tissue. A prototype probe has been fabricated and tested in quantifying the prostate cancer cell concentrations in vitro and lipid infiltrated hepatocyte in liver ex vivo. Experiment results show that the needle probe could potentially provide pathologic information of the tissues.

Radial-firing optical fiber tip containing conical-shaped air-pocket for biomedical applications

We report a novel radial-firing optical fiber tip containing a conical-shaped air-pocket fabricated by deforming a hollow optical fiber using electric arc-discharge process. The hollow optical fiber was fusion spliced with a conventional optical fiber, simultaneously deforming into the intagliated conical-shaped region along the longitudinal fiber-axis of the fiber due to the gradual collapse of the cavity of the hollow optical fiber. Then the distal-end of the hollow optical fiber was sealed by the additional arc-discharge in order to obstruct the inflow of an external bio-substance or liquid to the inner air surface during the surgical operations, resulting in the formation of encased air-pocket in the silica glass fiber. Due to the total internal reflection of the laser beam at the conical-shaped air surface, the laser beam (λ = 632.8 nm) was deflected to the circumferential direction up to 87 degree with respect to the fiber-axis.

Real-time evaluation of two light delivery systems for photodynamic disinfection of Candida albicans biofilm in curved root canals

Antimicrobial photodynamic therapy (APDT) combined with endodontic treatment has been recognized as an alternative approach to complement conventional root canal disinfection methods on bacterial biofilms. We developed an in  vitro model of bioluminescent Candida albicans biofilm inside curved dental root canals and investigated the microbial reduction produced when different light delivery methods are employed. Each light delivery method was evaluated in respect to the light distribution provided inside curved root canals. After conventional endodontic preparation, teeth were sterilized before canals were contaminated by a bioluminescent strain of C. albicans (CEC789). Methylene blue (90 μM) was introduced into the canals and then irradiated (λ = 660 nm, P = 100 mW, beam diameter = 2 mm) with laser tip either in contact with pulp chamber or within the canal using an optical diffuser fiber. Light distribution was evaluated by CCD camera, and microbial reduction was monitored through bioluminescence imaging. Our findings demonstrated that the bioluminescent C. albicans biofilm model had good reproducibility and uniformity. Light distribution in dental tissue was markedly dependent on the light delivery system, and this strategy was directly related to microbial destruction. Both light delivery systems performed significant fungal inactivation. However, when irradiation was performed with optical diffuser fiber, microbial burden reduction was nearly 100 times more effective. Bioluminescence is an interesting real-time analysis to endodontic C. albicans biofilm inactivation. APDT showed to be an effective way to inactivate C. albicans biofilms. Diffuser fibers provided optimized light distribution inside curved root canals and significantly increased APDT efficiency.

Activation of ethylenediaminetetraacetic acid by a 940 nm diode laser for enhanced removal of smear layer

Laser enhancement of ethylenediaminetetraacetic acid with cetrimide (EDTAC) has previously been shown to increase removal of smear layer, for middle-infrared erbium lasers. This study evaluated the efficiency of EDTAC activation using a near-infrared-pulsed 940 nm laser delivered by plain fibre tips into 15% EDTAC or 3% hydrogen peroxide. Root canals in 4 groups of 10 single roots were prepared using rotary files, with controls for the presence and absence of smear layer. After laser treatment (80 mJ pulse(-1) , 50 Hz, 6 cycles of 10 s), roots were split and the apical, middle and coronal thirds of the canal were examined using scanning electron microscopy, with the area of dentine tubules determined by a validated quantitative image analysis method. Lasing EDTAC considerably improved smear layer removal, while lasing into peroxide gave minimal smear layer removal. The laser protocol used was more effective for smear layer removal than the 'gold standard' protocol using EDTAC with sodium hypochlorite (NaOCl). In addition, lasers may also provide a benefit through photothermal disinfection. Further research is needed to optimise irrigant activation protocols using near-infrared diode lasers of other wavelengths.

Optical properties of root canal irrigants in the 300-3,000-nm wavelength region

In root canal therapy, irrigating solutions are essential to assist in debridement and disinfection. Their spread and action is often restricted by canal anatomy, requiring some form of activation. Lasers have been shown to be promising tools for this purpose (laser-activated irrigation (LAI)). For LAI to be effective, high absorption of radiation in the irrigant is essential. Although the absorption spectrum of water is well established, little is known about the optical properties of other irrigating solutions. Therefore, root canal irrigants (sodium hypochlorite (NaOCl), citric acid (CA), chlorhexidine (CHX), ethylenediaminetetraacetate (EDTA), water) were subjected to UV/Vis spectrophotometry in the 300-3,000-nm region using synthetic quartz cells with an optical path length of 1 mm. Transmission data were used to plot the transmission spectrum and calculate the absorption coefficient (α) of each irrigant. The transmission spectra of the tested solutions proved to follow the spectrum of pure water to a large extent. All tested solutions displayed absorption peaks around 1,450 nm (α ≈ 14 cm(-1)), 1,950 nm (α > 30 cm(-1)), and above 2,500 nm (α > 30 cm(-1)). NaOCl showed higher absorption than water in the UV region. Slightly higher absorption than water was noted for CHX (Corsodyl) around 513 nm and for CA between 1,600 and 1,800 nm and around 2,200 nm. The absorption in all tested solutions for wavelengths greater than 2,500 nm is very high, meaning a great potential for laser-activated irrigation. Other wavelengths eligible for LAI are located around 1,450 and 2,000 nm but require further investigation.

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.

Performance assessment of novel side firing safe tips for endodontic applications

During root canal or periodontal treatment, directing laser energy onto the walls of the root canal is essential for effective disinfection. This study assessed the performance of four different fiber modifications that have increased lateral emission, including three designs with safe tips to reduce irradiation directed toward the root apex. Free-running pulsed infrared lasers (Nd:YAG, Er:YAG, and Er,Cr:YSGG) and a diode laser (980 nm) were used in combination with plain ended (forward emitting) laser fibers; conical laser fibers, side firing honeycomb pattern fibers without a safe end; honeycomb fibers with silver coated ends, conical fibers with selectively abraded tips, and selectively abraded honeycomb fibers with silver coated tips (20 fibers for each laser type). Laser emissions forward and laterally were measured, and digital photographs and thermally sensitive paper used to record the emission profiles. Thermochromic dyes painted onto the root surface of an extracted tooth were used to explore the distribution of laser energy with different tips designs. All three safe tipped ends gave reduced emissions in the forward direction (range 17-59%), but had similar lateral emission characteristics. Fiber designs with reduced forward emission may be useful for various dental laser procedures.