Performance assessment of novel side firing safe tips for endodontic applications

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.

Functionalized Nanoparticles Activated by Photodynamic Therapy as an Antimicrobial Strategy in Endodontics: A Scoping Review

The eradication of endodontic pathogens continues to be the focus of the search for new root canal system (RCS) disinfection strategies. This scoping review provides a comprehensive synthesis of antimicrobial photodynamic therapy (aPDT) using nanoparticles (NPs) as an alternative to optimize RCS disinfection. A systematic search up to March 2021 was carried out using the MEDLINE, EMBASE, Scopus, Lilacs, Central Cochrane Library, and BBO databases. We included studies focused on evaluating the activation of NPs by aPDT in inoculated root canals of human or animal teeth or bacterial cultures in the laboratory. The selection process and data extraction were carried out by two researchers independently. A qualitative synthesis of the results was performed. A total of seventeen studies were included, of which twelve showed a substantial antibacterial efficacy, two assessed the substantivity of the disinfection effect, and three showed low cytotoxicity. No adverse effects were reported. The use of functionalized NPs with photosensitizer molecules in aPDT has been shown to be effective in reducing the bacteria count, making it a promising alternative in endodontic disinfection. Further studies are needed to assess the development of this therapy in in vivo conditions, with detailed information about the laser parameters used to allow the development of safe and standardized protocols.

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.

Spatial effect of conical angle on optical-thermal distribution for circumferential photocoagulation

A uniformly diffusing applicator can be advantageous for laser treatment of tubular tissue. The current study investigated various conical angles for diffuser tips as a critical factor for achieving radially uniform light emission. A customized goniometer was employed to characterize the spatial uniformity of the light propagation. An ex vivo model was developed to quantitatively compare the temperature development and irreversible tissue coagulation. The 10-mm diffuser tip with angle at 25° achieved a uniform longitudinal intensity profile (i.e., 0.90 ± 0.07) as well as a consistent thermal denaturation on the tissue. The proposed conical angle can be instrumental in determining the uniformity of light distribution for the photothermal treatment of tubular tissue.

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.

Temperature Development on the External Root Surface During Laser-Assisted Endodontic Treatment Applying a Microchopped Mode of a 980 nm Diode Laser

OBJECTIVE

The aim of this article was to investigate the temperature increase of the external root surface during laser-assisted endodontic treatment using a diode laser (980 nm) in a microchopped mode.

METHODS

Ten freshly extracted, human maxillary incisors with mature apices were collected, prepared to size F4 at working length (ProTaper; Dentsply Maillefer, Ballaigues, Switzerland), mounted to a holder, and irradiated (using spiral movements in coronal direction) with a diode laser (GENTLEray 980 Classic Plus; KaVo, Biberach, Germany) with a 200 μm fiber in four different treatment groups: Group 1 (control group) was irradiated in six cycles of 5-sec irradiation/20-sec pause with 2.5 W in the pulse mode. Groups 2 to 4 were irradiated at six cycles of 5-sec irradiation/20-sec pause in the microchopped mode (Group 2-1.6 W; Group 3-2.0 W; Group 4-2.5 W). The applied mode was 25 ms on/25 ms off. Within the on period, the laser delivered an intermittent sequence of energy complexes and the maximum output was equal to the nominated output of the device (12 W). Canals were kept moist by sterile saline irrigation in between irradiations, and temperature changes were continuously measured using a thermal imaging camera. Recordings were analyzed by a mixed model (analysis of variance [ANOVA] for repeated measurements).

RESULTS

The highest mean of temperature rise, 1.94°C ± 1.07°C, was measured in Group 4, followed by Group 3 (1.74°C ± 1.22°C) and Group 2 (1.58°C ± 1.18°C). The lowest increase occurred in Group 1 (1.06°C ± 1.20°C). There was a significant difference (p = 0.041) between the groups. Significant differences were found between Groups 1 and 4 (p = 0.007) and 1 and 2 (p = 0.035). In addition, a marginally significant difference between Groups 1 and 2 (p = 0.052) was noted. There was no significant difference between Groups 2, 3, and 4. Despite the low mean values reported, the highest temperature increase (+5.7°C) was measured in one of the specimens of treatment Group 2 at the middle third.

CONCLUSIONS

Under the conditions used and within the limitations of the study, the microchopped diode laser irradiation is a safe possible treatment option in laser-assisted endodontic treatment, concerning the temperature elevation on the external root surface.

Adaptation and penetration of resin-based root canal sealers in root canals irradiated with high-intensity lasers

This research analyzed the quality of resin-based sealer adaptation after intracanal laser irradiation. Extracted teeth (n = 168) were root canal treated and divided into four groups, according to dentin surface treatment: no laser; Nd:YAG laser (1.5 W, 100 mJ, 15 Hz); diode laser (2.5 W in CW), and Er:YAG laser (1 W, 100 mJ, 10 Hz). The teeth were divided into four subgroups according to the sealer used: AH Plus, EndoREZ, Epiphany, and EpiphanySE. For testing the sealing after root canal obturation, the penetration of silver nitrate solution was measured, whereas to evaluate the adaptation and penetration of the sealer into the dentin, environmental scanning electron microscopy (ESEM) was used. The ESEM images were analyzed using a four-grade criteria score by three evaluators. The inter-examiner agreement was confirmed by Kappa test and the scores statistically compared by the Kruskal-Wallis' test (p < 0.05). Both adaptation and sealer penetration in root canals were not affected by the laser irradiation. Nd:YAG and diode laser decreased the tracer penetration for AH Plus, whereas EndoREZ and EpiphanySE performances were affected by Nd:YAG irradiation (p < 0.05). It can be concluded that intracanal laser irradiation can be used as an adjunct in endodontic treatment; however, the use of hydrophilic resin sealers should be avoided when root canals were irradiated with Nd:YAG laser.

Photodynamic therapy: An adjunct to conventional root canal disinfection strategies

Although chemical-based root canal disinfectants are important to reduce microbial loads and remove infected smear layer from root dentin, they have only a limited ability to eliminate biofilm bacteria, especially from root complexities. This paper explores the novel photodynamic therapy (PDT) for antimicrobial disinfection of root canals. The combination of an effective photosensitizer, the appropriate wavelength of light and ambient oxygen is the key factor in PDT. PDT uses a specific wavelength of light to activate a non-toxic dye (photosensitizer), leading to the formation of reactive oxygen species. These reactive oxygen molecules can damage bacterial proteins, membrane lipids and nucleic acids, which promote bacterial cell death. In, addition PDT may enhance cross-linking of collagen fibrils in the dentin matrix and thereby improving dentin stability. The concept of PDT is plausible and could foster new therapy concepts for endodontics. The available knowledge should enable and encourage steps forward into more clinical-oriented research and development. This article discusses PDT as related to root canal disinfection, including its components, mechanism of action, reviews the current endodontic literature and also highlights the shortcomings and advancements in PDT techniques.

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.

Laser-induced agitation and cavitation from proprietary honeycomb tips for endodontic applications

Cavitation and agitation generated by lasers in fluid-filled root canals create fluid movement and shear stresses along the root canals walls, enhancing removal of the smear layer and biofilm. When used with sodium hypochlorite and EDTA, laser activation of aqueous fluids can increase the efficiency of debridement and disinfection of root canals. However, the use of forward-firing laser fibers with such solutions poses a risk of driving fluid past the root apex, which could cause postoperative complications. The purpose of this study was to evaluate the mechanism of fluid agitation caused by a novel honeycomb tip. Glass capillary tubes filled with distilled water were used to replicate single-tooth root canals. A 980 nm pulsed diode laser was used with 200 μm diameter plain tips, tube-etched conical tips, and honeycomb tips. To record fluid movements, the tubes were backlit and imaged using a digital camera attached to a microscope. The honeycomb tips generated agitation with fluid movement directed onto the walls, while both the conventional plain fibers and the conical tips created fluid movement largely in a forward direction. The use of honeycomb tips alters the pattern of fluid agitation, and this laterally directed effect might lower the risk of fluid extrusion beyond the apex.

Antibacterial efficacy of photosensitizer functionalized biopolymeric nanoparticles in the presence of tissue inhibitors in root canal

INTRODUCTION

Application of antibacterial nanoparticles to improve root canal disinfection has received strong interest recently. The current study aims to assess the antibacterial effect of a novel photosensitizer (rose bengal functionalized chitosan nanoparticles [CSRBnp]) to eliminate bacteria in the presence of various root canal constituents that are known to inhibit the antibacterial efficacy of root canal disinfectants.

METHODS

The synthesized CSRBnp were evaluated for size, charge, and singlet oxygen release. The antibacterial effect of CSRBnp was tested on planktonic Enterococcus faecalis with or without pretreatment by using different inhibiting agents such as dentin, dentin-matrix, pulp tissue, bacterial lipopolysaccharides, and bovine serum albumin (BSA). Bacterial survival was assessed in a time-dependent manner. The antibacterial effects after photodynamic activation on CSRBnp, a cationic photosensitizer (methylene blue), and an anionic photosensitizer (rose bengal [RB]) in the presence of inhibitors were also evaluated.

RESULTS

CSRBnp were 60 ± 20 nm in size and showed reduced rate of singlet oxygen release as compared with methylene blue and RB. Pulp and BSA inhibited the antibacterial effect of CSRBnp (without photoactivation) significantly (P < .05) even after 24 hours of interaction. In case of photodynamic therapy, the pulp and BSA significantly inhibited the antibacterial activity of all 3 photosensitizers. CSRBnp showed residual effect and completely eliminated the bacteria after 24 hours of interaction after photodynamic therapy.

CONCLUSIONS

The inherent antibacterial activity of polycationic chitosan nanoparticles and the singlet oxygen released after photoactivation of RB synergistically provided CSRBnp the potential to achieve significant antibacterial efficacy even in the presence of tissue inhibitors within root canals.

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.

Optodynamic energy-conversion efficiency during an Er:YAG-laser-pulse delivery into a liquid through different fiber-tip geometries

When an erbium-laser pulse is directed into water through a small-diameter fiber tip (FT), the absorption of the laser energy superheats the water and its boiling induces a vapor bubble. We present the influence of different FT geometries and pulse parameters on the vapor-bubble dynamics. In our investigation, we use a free-running erbium: yttrium aluminum garnet (Er:YAG) (λ=2.94 μm) laser that was designed for laser dentistry. Its pulse is directed into the water through FTs with a flat and conical geometry. Our results show that in the case of the conical FT, a spherical bubble is induced, while a channel-like bubble develops for the flat FT. The ratio between the mechanical energy of the liquid medium and the pulse energy, which we call the optodynamic energy-conversion efficiency, is examined using shadow photography. The results indicate that this efficiency is significantly larger when a conical FT is used and it increases with increasing pulse energy and decreasing pulse duration. The spherical bubbles are compared with the Rayleigh model in order to present the influence of the pulse duration on the dynamics of the bubble's expansion.

Apical microleakage and SEM analysis of dentin surface after 980 nm diode laser irradiation

This study evaluated the effect of 980-nm diode laser on apical microleakage and intraradicular dentin morphology. Roots of 110 mandibular incisors were used in the study: 92 for microleakage test and 18 for scanning electron microscopy (SEM). Roots were randomly assigned to 3 groups according to the irrigating solution (water, NaOCl and NaOCl/EDTA) and were divided into 3 subgroups according to the laser irradiation protocol (without irradiation, irradiated at 1.5 W and irradiated at 3.0 W). Two specimens of each subgroup were prepared for SEM. The remaining roots were filled with AH Plus and gutta-percha. Apical leakage was assessed by ink penetration and data were analyzed statistically by ANOVA and Tukey-Krammer test (α=0.05). SEM analysis showed intensification of changes with increase of laser power as well as variations according to the irrigating solution. Modified smear layer was observed in specimens treated with water and irradiated with laser. Roots irrigated with NaOCl/EDTA had lower levels of infiltration (0.17 ± 0.18 mm) differing significantly (p<0.05) from those of roots irrigated with water (0.34 ± 0.30 mm), but similar (p>0.05) to those irrigated with NaOCl (0.28 ± 0.29 mm). Non-irradiated roots had lower levels of infiltration (0.10 ± 0.14 mm), differing (p<0.05) from those irradiated at 1.5 W (0.32 ± 0.22 mm) and 3.0 W (0.37 ± 0.32 mm). The 980 nm diode laser modified dentin morphology and increased apical microleakage.