Dye-assisted diode laser ablation of carious enamel and dentine

Impact of thermal photodynamic disinfection on root dentin temperature in vitro

BACKGROUND

Thermal photodynamic disinfection procedures have been proposed for adjunctive endodontic treatment. This study assessed photothermal disinfection relative to root dentin temperature and the thermal effects of simulated periodontal blood flow.

METHODS

Thirty freshly extracted human single-rooted teeth were prepared endodontically using a 45/.02 master apical file. The root surfaces were coated with wax and covered with thermoforming sheets, leaving a circumferential space of 0.25 mm after wax removal. The sheets were perforated to allow fluid circulation through the simulated periodontal space. Irradiation was performed in two groups of 30: I, 810 nm laser (1.5 W, continuous wave), 4 × 5 s; II, photothermal group: indocyanine green and 810 nm laser (200 mW, continuous wave), 20 s. Thermographic measurements were performed at different water flow rates (6, 2.6, 0 mL/min) with a baseline temperature of 37 °C. Nonparametric statistical analysis was performed (Wilcoxon).

RESULTS

The highest temperature change (median 7.52 °C, range 0.82-18.32 °C) was with 810 nm laser irradiation in group I, without any simulated blood flow. Fluid circulation resulted in a significant reduction in temperature changes in this group (median 2.14 °C, range 0.37-9.83 °C; p  < 0.05). The lowest temperature changes were in the photothermal group with a water flow rate of 6 mL/min (median 0.79 °C, range 0.00-3.88 °C; p < 0.05).

CONCLUSION

Photothermal disinfection of root canals can increase root canal dentin temperatures, but periodontal fluid circulation has a cooling effect on the outer root surface, reducing the risk of potential thermal injury to periodontal tissue.

Microbial Composition of Oral Biofilms after Visible Light and Water-Filtered Infrared a Radiation (VIS+wIRA) in Combination with Indocyanine Green (ICG) as Photosensitizer

In view of increasing antibiotic resistance, antimicrobial photodynamic therapy (aPDT) is an alternative treatment method used to eradicate the microbial community of oral biofilms that can be responsible for different oral infections. In order to investigate changes in the microbial composition after application of aPDT with visible light and water-filtered infrared A (VIS+wIRA) in combination with indocyanine green (ICG), oral microorganisms of the initial and mature biofilm were evaluated by mass spectrometry (MALDI-TOF-MS). To determine surviving microorganisms using MALDI-TOF-MS, an in situ biofilm was irradiated with VIS+wIRA for five minutes in the presence of ICG (300 and 450 µg/mL, respectively). Treatment with chlorhexidine (0.2%) served as positive control. Identified microorganisms of the initial biofilm treated with ICG showed a clear reduction in diversity. The microbial composition of the mature oral biofilm also showed changes after the implementation of aPDT, which mainly resulted in a shift in the percentage of bacterial species. The resulting destruction of the microbial balance within the oral biofilm by aPDT using VIS+wIRA and ICG can be seen as an advantageous supplementary approach in the adjunctive treatment of periodontitis and peri-implantitis.

Dynamic characterization of indocyanine green-assisted dental caries ablation with continuous diode laser using thermal imaging and fluorescence spectroscopy

We describe the time-resolved thermal changes in indocyanine green (ICG)-assisted diode laser ablation of dental caries as a potential technique for painless treatment based on the selective photoabsorption and controlled photothermal ablation. Static ablation mode produced a higher temperature rise compared with scanning mode due to localized accumulation of heat. A temperature rise between 45-80 and 70-95 °C was obtained after 20 s that corresponded to 29 and 80 W cm^-2, respectively. The temperature of the tooth surface increased by irradiation time, and it behaved linearly up to 70 °C at 29 and 80 W cm^-2. A maximum ablation per area of about 0.3 and 0.45 mg cm^-2 was achieved after 80 s exposure at 29 and 80 W cm^-2, respectively. A statistically significant difference is observed in mean carious teeth weight at various exposure times between low and high irradiances. A thermal penetration depth of 0.8-9 mm is determined for 1-100 s of exposure time. The IR thermal imaging of ICG temperature as a function of exposure time showed a linear increase for 60 s beyond which it deviated. The laser-induced fluorescence spectroscopy indicated that the ICG quality can be altered during the course of irradiation, which in our case, it corresponded to ≈ 78% loss of signal within 23 min of exposure. The caries removal experiment was performed within 100 s corresponding to ≈ 7% loss. We believe that the application of the above-combined technique can be utilized as a monitoring device to control the ablation interaction process.

Enhancing the detection of proximal cavities on near infrared transillumination images with Indocyanine Green (ICG) as a contrast medium: In vitro proof of concept studies

OBJECTIVES

The use of near infrared transillumination for caries detection is gaining recognition in daily practice. Differentiation between cavitated and non cavitated proximal lesions is recognized as a threshold for restorative treatment. This investigation focused on the use of a near infrared absorbent dye which may enhance the detection of cavitation on near infrared transillumination images.

MATERIALS AND METHODS

1: Natural teeth with artificial proximal cavitation were images with 3 different dyes to establish that near infrared absorbent dye can act like a contrast medium. 2: Natural teeth with natural cavitated lesions were used to investigate the contrast enhancing effect of indocyanine green (ICG) on near infrared transillumination images. 3: Artificial teeth with artificial cavitations were used to determine the best consistency of ICG as a contrast medium. 4: natural teeth with proximal lesions were used to confirm that ICG can differentiate between cavitated and non cavitated proximal lesions.

RESULTS

1: ICG enhanced the contrast of cavitations compared to other dyes (ANOVA; p < 0.05). 2: ICG enhanced the contrast of the cavitated area on natural lesions but not significantly (t-test; p > 0.05). 3: ICG in a gel form enhanced the detection of cavitated lesions when compared to liquid ICG (t-test; p < 0.05). 4: ICG gel was able to differentiate between cavitated and non cavitated proximal lesions (ANOVA; p < 0.05).

CONCLUSION

ICG can potentially be used as a contrast medium to enhance the detection of cavitated proximal lesions in vitro on near infrared transillumination images. A clinical study is required to validate these results in vivo.

Inactivation of oral biofilms using visible light and water-filtered infrared A radiation and indocyanine green

Aim: To investigate the antimicrobial photodynamic therapy (aPDT) of visible light and water-filtered infrared A radiation in combination with indocyanine green (ICG) on planktonic oral microorganisms as well as on oral biofilm. Methods: The irradiation was conducted for 5 min in combination with ICG. Treatment with chlorhexidine served as a positive control. The number of colony forming units and bacterial vitality were quantified. Results: All tested bacterial strains and salivary bacteria were killed at a level of 3log_10. The colony forming units of the initial mature oral biofilms were strongly reduced. The high bactericidal effect of aPDT was confirmed by live/dead staining. Conclusion: The aPDT using visible light and water-filtered infrared A radiation and ICG has the potential to treat periodontitis and peri-implantitis.

Indocyanine-green-assisted near-infrared dental imaging - the feasibility of in vivo imaging and the optimization of imaging conditions

X-ray-based imaging, including computed tomography, plays a crucial role in the diagnosis and surgery of impacted teeth that affects over 25% of the human population. But the greatest disadvantage of this technique is ionizing radiation risk to the patients. Here we describe a completely ionizing-radiation-free in vivo near-infrared (NIR) fluoresence dental imaging with indocyanine green (ICG) agent that has rarely been applied in dental imaging. Our method can acquire dental structure images within a short period (only 10 minutes after injection) without ionizing radiation risk. NIR enables the observation of dental structures that are not distinguishable under visible conditions. At prolonged 72 hours, only molar regions remained highlighted; the contrast between molar regions and surrounding tissues was prominent; this is particularly useful for in vivo dental imaging. Using the quantitative spectral analysis, we found the peak wavelengths of ICG fluorescence shifted along with the injection time: the peak wavelength shifted 8 nm (from 819 nm to 811 nm) in 0~72 hours. The injection methods of tail vein v.s. intradermal injections caused ~3 nm shift. ICG-assisted NIR fluorescence imaging can serve as a useful tool for in vivo real-time diagnosis in dental clinics and surgeries without ionizing radiation risk.

Indocyanine green MS/MS investigations using femtosecond laser-pulse photodissociation and collision-induced dissociation

The dissociation reactions of indocyanine green (also known as cardiogreen) have been studied in a Fourier-transform ion-cyclotron resonance mass spectrometer by the application of unimolecular, collision-induced dissociation and photodissociation using femtosecond laser pulses. Ions were prepared by electrospray ionization (ESI) in various solvents. Depending on the properties of the solvent mixture, the mono sodiated molecule could be measured through cation exchange in various compositions. Using a mixture of methanol/water/formic acid as solvent, protonated ions, formed by exchange of sodium, are predominantly observed. A mixture of isopropanol/formic acid leads to the addition of a further sodium cation to the molecule yielding an intense bi-sodiated ion signal. The photodissociation of the stored ions was achieved using pulses at a wavelength of 790 nm and approximately 150 fs pulse duration. The results show that only fs-photodissociation leads to the fragmentation of the different molecular structures, while in case of sodiated indocyanine green collision induced dissociation fails completely to observe any fragments. In all other investigated ion structures, the collision-induced-dissociation spectra show unspecified and little intense spectra. It is shown that fs-photodissociation mass spectrometry is the only method that leads to substance specific fragmentation for this sample. Furthermore, indocyanine green is known to form aggregation products. In the ion-cyclotron resonance experiment, the reactions of a dimeric cluster were also investigated. The necessary condition and the interference of the fragmentations with those of the monomer are discussed.

Effects of near infrared laser radiation associated with photoabsorbing cream in preventing white spot lesions around orthodontic brackets: an in vitro study

OBJECTIVE

The present study aims to investigate the effect of a low-power infrared laser on the inhibition of bovine enamel demineralization around orthodontic brackets.

BACKGROUND DATA

Near infrared lasers have been suggested as alternative approaches because they may produce an increase in resistance to dental caries.

METHODS

Forty-eight blocks of enamel obtained from bovine incisor teeth were divided into six groups: Group 1 (control), without treatment; Group 2 (C), photoabsorbing cream; Group 3 (CF), photoabsorbing cream with fluoride; Group 4 (L), irradiation with low-level infrared laser (λ=830 nm) at an energy density of 4.47 J/cm2; Group 5 (L+C), photoabsorbing cream followed by low-level infrared laser irradiation; and Group 6 (L+CF), photoabsorbing cream with fluoride followed by low-level infrared laser irradiation. After these procedures, the enamel blocks received an assortment of orthodontic brackets and were then submitted to pH cycling to simulate a highly cariogenic challenge. The enamel surface demineralization around the orthodontic brackets, according to the different treatments, was quantified by fluorescence loss analysis by quantitative light-induced fluorescence (QLF). The fluorescence loss, expressed as ΔF (percentage of loss fluorescence), was statistically examined by analysis of variance and the Tukey test.

RESULTS

The control group (-10.48±2.85) was statistically similar to Group C (-14.52±7.80), which presented the lowest values of ΔF when compared with Groups FC (-3.67±3.21), L (-2.79±1.68), CL (-1.05±0:50), and CFL (-0.60±0:43). However, Groups FC, L, CL, and CFL showed no statistically significant differences among them.

CONCLUSIONS

It can be concluded that both the low-level infrared laser and photoabsorbing cream with fluoride were effective in inhibiting the development of caries in enamel around orthodontic brackets, even in situations of high cariogenic challenge.

Dental enamel irradiated with a low-intensity infrared laser and photoabsorbing cream: a study of microhardness, surface, and pulp temperature

OBJECTIVE

The aim of this study was to assess the effect of low-intensity infrared laser light (λ=810 nm, 100 mW/cm(2), 90 sec, 4.47 J/cm(2), 9 J) with or without indocyanine green cream fluorinated or not fluorinated, using Knoop surface microhardness analysis.

BACKGROUND DATA

Lasers can be used as tools for the prevention of tooth enamel demineralization.

METHODS

The surface and pulp temperatures of the human deciduous tooth enamel were measured. For the analysis of surface hardness, a total of 48 specimens were prepared and randomly assigned into six groups (n=8/group): C (+), which received laser light; C(-), which received no treatment; cream (IV); cream and fluoride (IVF); cream and light (IVL); and cream and fluoride and light (IVFL). The specimens were subjected to treatment before demineralizing challenge by pH cycling. To analyze the surface and pulp temperatures, the samples were divided into the following groups (n=10): C(+), IVL, and IVFL.

RESULTS

The hardness analysis indicated that the groups that received irradiation had less hardness reduction following the demineralizing challenge (p<0.001), with IVFL and IVL presenting the lowest percentages of surface microhardness loss at 3.98% and 9.3%, respectively. Surface temperature analysis indicated a maximum increase of 74°C and a mean of 45.25°C and 45.95°C for the IVL and IVFL groups, respectively. Pulp temperature analysis indicated a higher mean increase of 2.40°C±0.65 in the IVL group.

CONCLUSIONS

These results suggest that the combination of cream and laser light possibly promoted protein denaturation of the tooth enamel organic matrix, which possibly decreased the loss of hardness without causing pulp damage.

Dental enamel irradiated with infrared diode laser and photo-absorbing cream: part 2--EDX study

OBJECTIVE

The effects of laser-induced compositional changes on the enamel were investigated by energy-dispersive X-ray fluorescence spectrometry (micro-EDX). After cariogenic challenge, we administered treatment of low-level infrared diode laser and a photo-absorbing cream (used to intensify the superficial light absorption).

BACKGROUND DATA

Dental caries is considered the most prevalent oral disease. A simple and noninvasive caries preventive regimen is treating tooth enamel with a laser, either alone or in combination with fluoride, which reduces enamel solubility and dissolution rates. High power lasers are still not widely used in private practice. Low-power near-infrared lasers may be an alternative approach. Energy-dispersive micro-EDX is a versatile and nondestructive spectroscopic technique that allows for a qualitative and quantitative elemental analysis of inorganic enamel components, such as calcium and phosphorus.

MATERIALS AND METHODS

Twenty-four extracted or exfoliated caries-free deciduous molars were divided into six groups: 1) control group (CTR-no treatment); 2) infrared laser treatment (L) (lambda = 810 nm, 100 mW/cm(2), 90 sec, 4.47 J/cm(2), 9 J); 3) infrared laser irradiation and photo-absorbing agent (CL); 4) photo-absorbing agent alone (C); 5) infrared laser irradiation and fluoridated photo-absorbing agent (FCL); and 6) fluoridated photo-absorbing agent alone (FC). Samples were analyzed using micro-EDX after two sets of treatments and pH cycling cariogenic challenges.

RESULTS

The CL group showed statistically significant increases in calcium and phosphorus (wt%) compared with the CTR group. The Ca/P ratio was similar in the FCL and CTR groups. There was a significant laser-induced reduction compared with the CTR group, and there was a possible modification of the organic balance content in enamel treated with laser and cream.

CONCLUSION

micro-EDX may be able to detect compositional changes in mineral phases of lased enamel under cariogenic challenge. Our results suggest that with a combined laser and photo-absorbing agent (CL) treatment, there was a possible disorganization of organic content in the tooth enamel with hydroxyapatite crystal reordering and reorganization.

Dental enamel irradiated with infrared diode laser and photoabsorbing cream: Part 1 -- FT-Raman Study

OBJECTIVE

The aim of this FT-Raman study was to investigate laser-induced compositional changes in enamel after therapy with a low-level infrared diode laser and a photoabsorbing cream, in order to intensify the superficial light absorption before and after cariogenic challenge.

BACKGROUND DATA

Dental caries remains the most prevalent disease during childhood and adolescence. Preventive modalities include the use of fluoride, reduction of dietary cariogenic refined carbohydrates, plaque removal and oral hygiene techniques, and antimicrobial prescriptions. A relatively simple and noninvasive caries preventive regimen is treating tooth enamel with laser irradiation, either alone or in combination with topical fluoride treatment, resulting in reduced enamel solubility and dissolution rates. Due to their high cost, high-powered lasers are still not widely employed in private practice in developing countries. Thus, low-power red and near-infrared lasers appear to be an appealing alternative.

MATERIALS AND METHODS

Twenty-four extracted or exfoliated caries-free deciduous molars were divided into six groups: control group (no treatment; n = 8); infrared laser treatment (L; n = 8) (810 nm at 100 mW/cm(2) for 90 sec); infrared diode laser irradiation (810 nm at 100 mW/cm(2) for 90 sec) and photoabsorbing cream (IVL; n = 8); photoabsorbing cream alone (IV; n = 8); infrared diode laser irradiation (810 nm at 100 mW/cm(2) for 90 sec) and fluorinated photoabsorbing agent (IVLF; n = 8); and fluorinated photoabsorbing agent alone (IVF; n = 8). Samples were analyzed using FT-Raman spectroscopy before and after pH cycling cariogenic challenge.

RESULTS

There was a significant laser-induced reduction and possible modification of the organic matrix content in enamel treated with the low-level diode laser (the L, IVL, and IVFL groups).

CONCLUSION

The FT-Raman technique may be suitable for detecting compositional and structural changes occurring in mineral phases and organic phases of lased enamel under cariogenic challenge.

Bactericidal effects of diode laser onStreptococcus mutans after irradiation through different thickness of dentin

BACKGROUND AND OBJECTIVES

A reliable method to eradicate the bacteria of residual carious dentin has not yet been developed. The aim of this study was to evaluate the antibacterial effect of a diode laser on Streptococcus mutans through different thickness (500, 1,000, and 2,000 microm) of human dentin. The thermal effect of laser irradiation was also investigated.

STUDY DESIGN/MATERIALS AND METHODS

Dentin specimens were inoculated with 2 microl of S. mutans on one side and irradiated by a diode laser on the other side with a power output ranging from 0.5 to 7 W. The laser tip was swept with the whole irradiation area of 7 mm x 3 mm at a speed of about 10 mm/second with a total irradiation time of 30 seconds. Cooling with distilled water (30 ml/minute) was applied simultaneously during laser irradiation. After laser irradiation, the bacteria was removed from the dentin surfaces and cultured for 48 hours at 37 degrees C anaerobically to assess the colony forming units (CFU) per ml. The morphology of the lased bacteria and the temperature rise during laser irradiation were observed by scanning electron microscope (SEM) and measured by thermocouple, respectively.

RESULTS

The results revealed that 7 W of laser power could kill 97.7% of CFU through 500 microm thickness of dentin. However, the bactericidal efficiency was significantly reduced as the dentin thickness was increased. The morphological changes of lased bacteria ranged from less affected such as loss of their wall bands and existence of minicells to more severely degenerated, such as disintegration and fusion of cells with pores on the cell wall. Only the dentin specimens with a thickness of 500 microm exhibited a temperature rise greater than 5.5 degrees C after receiving 5 or 7 W of laser irradiation.

CONCLUSIONS

A diode laser can eliminate the Streptococcus mutans of the residual carious dentin without inducing high pulpal temperature rise when the remaining dentin thickness is greater than 1 mm.

Assessment of a novel alternative to conventional formocresol-zinc oxide eugenol pulpotomy for the treatment of pulpally involved human primary teeth: diode laser-mineral trioxide aggregate pulpotomy

OBJECTIVE

The purpose of this study was to investigate whether a diode laser pulpotomy with mineral trioxide aggregate (MTA) sealing could be an acceptable alternative to the conventional formocresol pulpotomy and zinc oxide eugenol (ZOE) sealing in human primary teeth.

METHODS

A randomized, single-blind, split-mouth study was used with a sample of 16 children aged from 3 to 8 years (mean age=5.10 years). A total of 26 pairs of teeth from these 16 patients were selected based on clinical and radiographic criteria. One tooth from each pair was randomly assigned to either the laser-MTA pulpotomy group or the formocresol-ZOE pulpotomy group. All teeth were followed up clinically and radiographically at 2.3, 5.2, 9.5 and 15.7 months. All extracted failures were sectioned and photographed to assess possible reasons for this.

RESULTS

A total of seven laser-MTA-treated teeth were deemed to be radiographic failures (mean time until failure=9.1 months) compared to three formocresol-ZOE treated teeth (mean time until failure=12.5 months). These results were not significant using Fisher's exact test (P>0.05). Six of the laser-MTA failures and all three formocresol-ZOE failures exhibited furcal and/or periapical radiolucencies with or without pathologic root resorption. One of the laser-MTA failures displayed premature root resorption and is being observed for exfoliation. Analysis of photographs of teeth available for extraction revealed errors in clinical technique in addition to expected signs of a disease process such as the presence of granulation tissue and areas of pathologic root resorption.

CONCLUSIONS

The laser-MTA pulpotomy showed reduced radiographic success rates compared to the formocresol-ZOE pulpotomy at 15.7 months; however, these results were not statistically significant. Improved success rates among a larger patient sample and a longer follow-up period would be required for the laser-MTA pulpotomy to be considered a routine alternative to the conventional formocresol-ZOE procedure. Meticulous restorative techniques must be followed to ensure the success of laser-MTA pulpotomies.