Caries inhibition in vital teeth using 9.6-μm CO2-laser irradiation

Effect of CO2 Laser-Assisted Titanium Tetra-fluoride on Demineralization of Enamel Around Orthodontic Brackets

Introduction: One of the clinical problems following orthodontic treatment is white spot lesions around orthodontic brackets due to enamel demineralization. Confronting enamel demineralization during fixed treatments has long been a challenge for orthodontists. The aim of this in vitro study was to evaluate the effect of CO2 laser and Titanium Tetra-fluoride (TiF4) application on the prevention of enamel demineralization around orthodontic brackets. Methods: Eighty permanent premolars were selected and bonded with brackets. They were randomly divided into four groups (n=20): topical titanium tetra-fluoride gel 4% (TiF4), CO2 laser (10.6 μm wavelength for 10 seconds, peak power=291 W), fluoride+laser (F+L) and control (C). All specimens were demineralized for 10 days in a 0.2 M acetate buffer solution. The mean lesion depths were determined by using polarized light microscopy. Results: The mean depth of lesion was the highest in the C group and then decreased in the TiF4, CO2 laser, and F+L groups, respectively. The difference between all groups was significant (P<0.05), except for the CO2 laser and F+L groups. Conclusion: The lowest amount of demineralization around the orthodontic brackets was observed in the L+F group, followed by the CO2 laser, TiF4, and control groups, respectively.

The effects of low-level laser therapy and photodynamic therapy on oral health of fixed orthodontics patients. A systematic review and meta-analysis

Objective To investigate the effect of low-level laser and photodynamic therapy on the oral health, and periodontal tissue of fixed orthodontic patients and the effect of using photobiomodulation methods compared to routine plaque removal methods and the amount of plaque in fixed orthodontic patients. Method and materials First, the title and summary of related articles were collected by using the search strategy electronic databases PUBMED, EMBASE, Cochrane's CENTRAL, Scopus, ISI and all the articles that were published from the beginning to February 2023 were evaluated. The title, abstracts and full texts of all the relevant studies were reviewed respectively, and those meeting the criteria were entered into our study. Finally, the quality of the studies was examined and the results of the studies were pooled by means of random effects inverse variance meta-analysis. Results Eighteen randomized studies, conducted between 2015 and December 2022, were selected for meta-analysis. Five studies were conducted as split-mouth, twelve as parallel-group, and one as a cross-over design. Among the studies, five examined the effects of low-level laser therapy and twelve assessed the effects of photodynamic therapy. The meta-analysis revealed that photodynamic therapy significantly reduced probing depth compared to scaling (MD=-0.2 mm, P<0.001), though the difference does not seem to be clinically significant. But no significant differences between photodynamic therapy and scaling or low-level laser therapy and control groups in terms of plaque index, or bleeding on probing, gingival crevicular fluid volume, gingival recession, clinical attachment loss, bacterial load and concentrations of inflammatory substances across multiple follow-up periods. Conclusion Moderate evidence indicates that photodynamic therapy (PDT) is comparable to conventional methods in improving oral health, as measured by periodontal indices, inflammatory proteins, bacterial colonies, and white spot lesions, making it a suitable alternative. Limited evidence suggests low-level laser therapy (LLLT) may improve oral health, particularly addressing caries, but further research is needed.

Biophotonics in Dentistry

The aim of this review paper is to concentrate on the use and application of photonics in dentistry. More than one hundred review and research articles were comprehensively analysed in terms of applications of photonics in dentistry, including surgical applications, as well as dental biomaterials, diagnosis and treatments. In biomedical engineering, various fields, such as biology, chemistry, material and physics, come together in to tackle a disease/disorder either as a diagnostic tool or an option for treatment. Engineers believe that biophotonics is the application of photonics in medicine, whereas photonics is simply a technology for creating and connecting packets of light energy, known as photons. This review paper provides a comprehensive discussion of its main elements, such as photoelasticity, interferometry techniques, optical coherence tomography, different types of lasers, carbon nanotubes, graphene and quantum dots.

Demineralization Inhibition by High-Speed Scanning of 9.3 µm CO2 Single Laser Pulses Over Enamel

BACKGROUND AND OBJECTIVE

In vitro studies were conducted to evaluate the use of an automated system for high-speed scanning of single 9.3 µm CO₂ laser pulses in the inhibition of caries-like lesion formation in the enamel of extracted human molars. The effect of the laser in generating an acid-resistant layer and the effect of the layer on inhibiting surface mineral loss during pH cycling was explored.

STUDY DESIGN/MATERIALS AND METHODS

Laser irradiation was performed with fluences of 0.6, 0.8, and 1.0 J/cm² for single pulses of 1 mm diameter (1/e² ), with pulse durations of 17, 22, and 27 microseconds, respectively. The laser was scanned at a 750 Hz pulse repetition rate in an automated pattern covering an area of 7 mm² in 0.3 sec. Six treatment groups were investigated: three groups for each fluence for laser-only and three for laser irradiation with additional fluoride from a toothpaste slurry (sodium fluoride at 1100 ppm). Each group used non-irradiated areas, which included untreated controls for the laser-only groups and a fluoride-only treatment for the groups with additional fluoride. pH cycling was performed on both groups, followed by microhardness testing to determine the relative mineral loss (∆Z) from a caries-like formation and surface mineral loss (∆S).

RESULTS

Laser irradiation with the 9.3 µm CO₂ laser generated an acid-resistant layer of about 15 µm in depth. For the laser-irradiated samples with additional fluoride application, the relative mineral loss (∆Z) was 113 ± 63 vol%-µm, while for those with only fluoride application ∆Z was 572 ± 172 vol%-µm. At the highest fluence (1.0 J/cm² ) used, an 80.2% inhibition of caries-like lesion was measured by ∆Z. Using only laser irradiation at the highest fluence resulted in an inhibition of caries-like lesion of 79.5% for the irradiated samples (∆Z = 374 ± 149 vol%-µm) relative to the control (∆Z = 1826 ± 325 vol%-µm). Surface microhardness tests resulted in an inhibition of surface softening, as measured by the Knoop Hardness Value (KHN) (108 ± 33 KHN for laser irradiated with additional fluoride, for non-irradiated controls with fluoride only 52 ± 16 KHN). Inhibition of surface loss was observed for all laser fluences, but the maximum surface loss for the untreated control group was only 2.2 ± 0.49 µm.

CONCLUSIONS

The results demonstrate a significant benefit of the 9.3 µm CO₂ laser at fluences of 0.6, 0.8, and 1.0 J/cm² in caries-like lesion inhibition as measured by the relative mineral loss in depth and surface mineral loss, without significant damage to the enamel. Additionally, inhibition of surface softening and surface loss during pH cycling was observed. The surface loss was small compared with the overall lesion depth and thickness of the generated acid-resistant layer. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Fissure caries inhibition with a CO2 9.3-μm short-pulsed laser-a randomized, single-blind, split-mouth controlled, 1-year clinical trial

OBJECTIVES

The objective of this randomized, single-blind, split-mouth controlled, clinical trial was to evaluate whether the use of a short-pulsed 9.3-μm CO₂ laser increases the caries resistance of occlusal pit and fissures in addition to fluoride therapy over 12 months.

MATERIALS AND METHODS

A total of 60 participants, average age 13.1 years, were enrolled. At baseline, second molars were randomized into test and control, and assessed by ICDAS, SOPROLIFE, and DIAGNOdent. An independent investigator irradiated test molars with a CO₂ laser (wavelength 9.3 μm, pulse duration 4 μs, pulse repetition rate 43 Hz, beam diameter 250 μm, average fluence 3.9 J/cm², 20 laser pulses per spot). Test molars received laser and fluoride treatment, control teeth fluoride alone. Fluoride varnish was applied at baseline and at 6 months. After 6 and 12 months, teeth were again assessed.

RESULTS

A total of 57 participants completed the 6-month and 51 the 12-month recall. Laser-treated surfaces showed very slight ICDAS improvements over time with ICDAS change - 1 in 11% and 8%, no changes (ICDAS change 0) in 68% and 67%, and slightly worsened (ICDAS change 1) in 19% and 24% at 6- and 12-month recalls, respectively, and worsened by two scores in 2% at both recall time points. Control teeth showed significantly higher ICDAS increases, with 47% and 25% showing ICDAS change 0, ICDAS change 1 in 49% and 55%, and ICDAS change 2 in 4% and 20% at 6- and 12-month recalls, respectively. Differences in ICDAS changes between the groups were statistically significant (P = 0.0002 and P < 0.0001; Wilcoxon's signed-rank test, exact). A total of 22% of the participants developed ICDAS 3 scores on the control teeth.

CONCLUSIONS

Microsecond short-pulsed 9.3-μm CO₂ laser irradiation markedly inhibits caries progression in pits and fissures in comparison with fluoride varnish alone.

CLINICAL RELEVANCE

The 9.3-μm CO₂ laser irradiation of pits and fissures enhances caries resistance.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02357979.

The effect of CO2 9.3 μm short-pulsed laser irradiation in enamel erosion reduction with and without fluoride applications-a randomized, controlled in vitro study

The aim of this in vitro study was to evaluate the protective effect of short-pulsed CO₂ 9.3 μm laser irradiation against erosion in human enamel without and combined with TiF₄ and AmF/NaF/SnCl₂ applications, respectively, as well as compared to the protective effect of these fluoride treatments alone. After polishing, ninety enamel samples (3 × 3mm) were used for 9 different treatment groups: 4% TiF₄ gel (pH 1.5, 24,533 ppm F^-); AmF/NaF/SnCl₂ rinse (pH 4.5; 500 ppm F^-, 800 ppm Sn²); CO₂ laser (average power 0.58 W); CO₂ laser (0.58 W) + TiF₄; CO₂ laser (0.58 W) + AmF/NaF/SnCl₂; CO₂ laser (0.69 W); CO₂ laser (0.69 W) + TiF₄; CO₂ laser (0.69 W) + AmF/NaF/SnCl₂; negative control (deionized water). TiF₄ gel was brushed on only once before the first erosive cycling, while samples treated with AmF/NaF/SnCl₂ were daily immersed in 5 ml of the solution before cycling. Laser treatment occurred with a CO₂ laser (wavelength 9.3 μm, pulse repetition rate 100 Hz, pulse duration 14.6 μs/18 μs, average power 0.58 W/0.69 W, fluence 1.9 J/cm²/2.2 J/cm², beam diameter 0.63 mm, irradiation time 10 s, air cooling). TiF₄ was applied only once, while AmF/NaF/SnCl₂ was applied once daily before the erosive challenge. Surface loss (in μm) was measured with optical profilometry immediately after treatment, and after 5 and 10 days of erosive cycling (0.5% citric acid, pH 2.3, 6 × 2 min/day). Additionally, scanning electron microscopy investigations were performed. All application measures resulted in loss of surface height immediately after treatment. After 5 days, significantly reduced surface loss was observed after applying laser irradiation (both power settings) followed by applications of TiF₄ or AmF/NaF/SnCl₂ solution (p < 0.05; 2-way ANOVA and Tukey test) compared to fluoride application alone. After 10 days, compared to after 5 days, a reduced tissue loss was observed in all groups treated with AmF/NaF/SnCl₂ solution. This tissue gain occurred with the AmF/NaF/SnCl₂ application alone and was significantly higher when the application was combined with the laser use (p < 0.05). Short-pulsed CO₂ 9.3 μm laser irradiation followed by additional application of AmF/NaF/SnCl₂ solution significantly reduces the progression of dental enamel erosion in vitro.

In vitro CO2 9.3-μm short-pulsed laser caries prevention-effects of a newly developed laser irradiation pattern

Caries prevention with different lasers has been investigated in laboratory studies and clinical pilot trials. Objective of this in vitro study was to assess whether 9.3-μm microsecond short-pulsed CO₂ laser irradiation enhances enamel caries resistance without melting, with and without additional fluoride application. Seven groups of enamel, totaling 105 human enamel samples, were irradiated with 2 different carbon dioxide lasers with 2 different energy application systems (original versus spread beam; 9.3 μm wavelength, pulse repetition rate 43 Hz vs 100 Hz, fluence ranges from 1.4 to 3.9 J/cm², pulse duration 3 μs to 18 μs). The laboratory pH-cycling was performed with or without additional fluoride, followed by cross-sectional microhardness testing. To assess caries inhibition, the mean relative mineral loss delta Z (∆Z) was determined. To evaluate for melting, scanning electron microscopy (SEM) examinations were performed. For the non-laser control groups with additional fluoride use, the relative mineral loss (ΔZ, vol% × μm) ranged between 512 ± 292 and 809 ± 297 (mean ± SD). ΔZ for the laser-irradiated samples with fluoride use ranged between 186 ± 214 and 374 ± 191, averaging a 58% ± 6% mineral loss reduction (ANOVA, P < 0.01 to P < 0.0001). For the non-laser-treated controls without additional fluoride, the mineral loss increased (ΔZ 914 ± 422 to 1224 ± 736). In contrast, the ΔZ for the laser-treated groups without additional fluoride ranged between 463 ± 190 and 594 ± 272 (P < 0.01 to P < 0.001) indicative of 50% ± 2% average reduction in mineral loss. Enhanced caries resistance was achieved by all applied fluences. Using the spread beam resulted in enhanced resistance without enamel melting as seen by SEM. CO₂ 9.3-μm short-pulsed laser irradiation with both laser beam configurations resulted in highly significant reduction in enamel mineral loss. Modifying the beam to a more homogenous profile will allow enamel caries resistance even without apparent enamel melting.

Laser-assisted prevention of enamel caries: a 10-year review of the literature

Since the invention of lasers in dentistry, investigations in caries prevention by the use of laser radiation have been proposed. There are several mechanisms stated for this purpose such as photothermal and/or photochemical interaction processes with the enamel. Alone or in conjugation with topical fluoride application, this treatment modality may improve enamel acid resistance in high-caries-risk populations. Data collection was done by searching the keywords caries, prevention, and laser in PubMed, Embase, Web of Science, Cochrane Library, and Google Scholar. Lasing protocols of the collected literature and their effectiveness as well as examination methods used to verify treatment outcomes have been evaluated. One hundred eighteen publications were found for the last 10 years. The wavelengths investigated for caries prevention are mainly located in the near and the mid-infrared spectral range. In the evaluated period of time, investigations using CO₂; Er:YAG; Er,Cr:YSGG; Er:YLF; fundamental, second, and third harmonic generations of Nd:YAG; diodes; and argon ion lasers were found in the databases. Accounting for 39% of the literature, CO₂ laser was the most examined system for this purpose. Reviewing the literature in this narrative review showed that all laser systems presented a positive effect in varying degrees. Laser irradiation could be an alternative or synergistic to topical fluoridation for enamel caries prevention with longer lasting effect. Further research should be focused on selecting proper laser settings to avoid damage to enamel and developing effective evidence-based clinical protocols.

Influence of CO2 Laser Irradiation and CPPACP Paste Application on Demineralized Enamel Microhardness

Introduction: It has been suggested that the application of casein phosphopeptide-amorphous calcium phosphate paste (CPP-ACP) and CO2 laser irradiation on enamel could increase the resistance of enamel to caries and acid attacks. The aim of the current study was to compare the influence of CPP-ACP paste application and irradiation of CO2 laser on microhardness of demineralized enamel. Methods: Thirty sound maxillary extracted premolars were selected. The crowns were cut at the cervical line and were split into facial and palatal halves. Specimens were mounted in selfcure acrylic blocks in such way that the enamel surface was exposed to 4×4 mm. After a pH cycling of the specimens, they were randomly divided into 4 groups (n=15), as follows: CG: Control group, LAS: CO2 laser, CP: CPP-ACP and LASCP: laser combined CPP-ACP treatment. The Vickers microhardness of the specimens was measured (500 g load, 5 seconds, 3 points). Data were analyzed using one-way ANOVA and post hoc Tukey tests (α =0.05). Results: The lowest mean Vickers microhardness value was observed in CG group (192.57±50.87 kg/mm2 ) and the highest in LASCP group (361.86±22.22 kg/mm² ). There were significant differences between groups (P<0.001). The pairwise comparison of the groups revealed that there were significant differences between these groups: CG versus LAS, CP, LASCP (P<0.05) and LASCP versus LAS and CP (P<0.05). No significant difference between LAS group versus CP group (P>0.05) was observed. Conclusion: The results of the current study revealed that CO2 laser and CCP-ACP were effective for improvement of enamel hardness value after demineralization. Incorporation of CO2 laser irradiation and CCP-ACP paste application provides additional remineralizing potential for demineralized enamel.

Bond strength of etch-and-rinse and self-etch adhesive systems to enamel and dentin irradiated with a novel CO2 9.3 μm short-pulsed laser for dental restorative procedures

The objective of this study was to evaluate the influence of CO₂ 9.3 μm short-pulsed laser irradiation on the shear bond strength of composite resin to enamel and dentin. Two hundred enamel and 210 dentin samples were irradiated with a 9.3 µm carbon dioxide laser (Solea, Convergent Dental, Inc., Natick, MA) with energies which either enhanced caries resistance or were effective for ablation. OptiBond Solo Plus [OptiBondTE] (Kerr Corporation, Orange, CA) and Peak Universal Bond light-cured adhesive [PeakTE] (Ultradent Products, South Jordan, UT) were used. In addition, Scotchbond Universal [ScotchbondSE] (3M ESPE, St. Paul, MN) and Peak SE self-etching primer with Peak Universal Bond light-cured adhesive [PeakSE] (Ultradent Products) were tested. Clearfil APX (Kuraray, New York, NY) was bonded to the samples. After 24 h, a single plane shear bond test was performed. Using the caries preventive setting on enamel resulted in increased shear bond strength for all bonding agents except for self-etch PeakSE. The highest overall bond strength was seen with PeakTE (41.29 ± 6.04 MPa). Etch-and-rinse systems achieved higher bond strength values to ablated enamel than the self-etch systems did. PeakTE showed the highest shear bond strength with 35.22 ± 4.40 MPa. OptiBondTE reached 93.8% of its control value. The self-etch system PeakSE presented significantly lower bond strength. The shear bond strength to dentin ranged between 19.15 ± 3.49 MPa for OptiBondTE and 43.94 ± 6.47 MPa for PeakSE. Etch-and-rinse systems had consistently higher bond strength to CO₂ 9.3 µm laser-ablated enamel. Using the maximum recommended energy for dentin ablation, the self-etch system PeakSE reached the highest bond strength (43.9 ± 6.5 MPa).

A New Laser-Processing Strategy for Improving Enamel Erosion Resistance

In the present study, a new automatic laser-processing strategy allowing standardized irradiation of natural tooth areas was investigated. The objective was to find a combination of laser parameters that could cause over a 600°C temperature increase at the enamel surface while not damaging enamel, avoiding temperature change above 5.5°C in the pulp and increasing enamel erosion resistance. Seventy-seven bovine enamel samples were randomly divided into 6 laser groups and 1 negative control (C/no treatment/ n = 11). A scanning strategy (7 × 3 mm) was used for the CO₂ laser treatment (λ = 10.6 µm, 0.1-18 J/cm²) with different pulse durations-namely, 20 µs (G20), 30 µs (G30), 55 µs (G55), and 490 µs (G490), as well as 2 modified pulse distances (G33d, G40d). Measurements of temperature change were performed at the surface (thermal camera/50 Hz), at the underside (thermocouples), and at the pulp chamber using a thermobath and human molars ( n = 10). In addition, histology and X-ray diffraction (XRD/ n = 10) were performed. Erosion was tested using an erosive cycling over 6 d, including immersion in citric acid (2 min/0.05 M/pH = 2.3) 6 times daily. Surface loss was measured using a profilometer and statistical analysis with a 2-way repeated-measures analysis of variance (α = 0.05). Only G20 fulfilled the temperature requirements at the surface (619 ± 21.8°C), at the underside (5.3 ± 1.4°C), and at the pulp (2.0 ± 1.0°C), and it caused no mineral phase change and significant reduction of enamel surface loss (-13.2 ± 4.0 µm) compared to C (-37.0 ± 10.1 µm, P < 0.05). A laser-scanning strategy (20 µs/2 kHz/1.25 J/cm², 3.4 mm/s) has been established that fulfilled the criteria for biological safety and significantly increased enamel erosion resistance (64%) in vitro.

Effect of Nd:YAG and CO2 Laser Irradiation on Prevention of Enamel Demineralization in Orthodontics: In Vitro Study

OBJECTIVE

The aim of this study was to investigate Nd:YAG and CO₂ laser effects in the prevention of demineralization in deeper layers of enamel via successive acid challenge cycles.

BACKGROUND DATA

Lasers are promising in the prevention of enamel demineralization around the orthodontic brackets; however, there are very few studies that evaluate if the effects of treatment could be extended after successive acid challenge cycles due to permanent enamel structural alterations.

MATERIALS AND METHODS

Human enamel samples were divided into five groups (n = 12): G1-application of 1.23% acidulated fluoride phosphate gel (AFP, control); G2-Nd:YAG laser irradiation (0.6 W, 84.9 J/cm², 10 Hz, 110 μs, contact mode); G3-Nd:YAG laser irradiation associated with AFP; G4-CO₂ laser irradiation (0.5 W, 28.6 J/cm², 50 Hz, 5 μs, and 10 mm focal distance); and G5-CO₂ laser irradiation associated with AFP. The samples were submitted to successive acid challenge cycles. Quantitative light-induced fluorescence and scanning electron microscopy were used to assess enamel demineralization. The data were statistically compared (α = 5%).

RESULTS

G1: 50.87 ± 4.57; G2: 47.72 ± 2.87; G3: 50.96 ± 4.01; G4: 28.21 ± 2.19; and G5: 30.13 ± 6.38. The CO₂ laser groups had significantly lower mineral losses than those observed in all other groups after successive acid challenge cycles.

CONCLUSIONS

Only the CO₂ laser (10.6 μm) irradiation prevents enamel demineralization around the orthodontic brackets even after exposure to successive acid challenges. The CO₂ laser at 10.6 μm showed a deeper effect in enamel regarding caries prevention.

Influence of irradiation by a novel CO2 9.3-μm short-pulsed laser on sealant bond strength

The objective of this in vitro study was to evaluate whether irradiation of enamel with a novel CO₂ 9.3-μm short-pulsed laser using energies that enhance caries resistance influences the shear bond strength of composite resin sealants to the irradiated enamel. Seventy bovine and 240 human enamel samples were irradiated with a 9.3-μm carbon dioxide laser (Solea, Convergent Dental, Inc., Natick, MA) with four different laser energies known to enhance caries resistance or ablate enamel (pulse duration from 3 μs at 1.6 mJ/pulse to 43 μs at 14.9 mJ/pulse with fluences between 3.3 and 30.4 J/cm², pulse repetition rate between 4.1 and 41.3 Hz, beam diameter of 0.25 mm and 1-mm spiral pattern, and focus distance of 4-15 mm). Irradiation was performed "freehand" or using a computerized, motor-driven stage. Enamel etching was achieved with 37% phosphoric acid (Scotchbond Universal etchant, 3M ESPE, St. Paul, MN). As bonding agent, Adper Single Bond Plus was used followed by placing Z250 Filtek Supreme flowable composite resin (both 3M ESPE). After 24 h water storage, a single-plane shear bond test was performed (UltraTester, Ultradent Products, Inc., South Jordan, UT). All laser-irradiated samples showed equal or higher bond strength than non-laser-treated controls. The highest shear bond strength values were observed with the 3-μs pulse duration/0.25-mm laser pattern (mean ± SD = 31.90 ± 2.50 MPa), representing a significant 27.4% bond strength increase over the controls (25.04 ± 2.80 MPa, P ≤ 0.0001). Two other caries-preventive irradiation (3 μs/1 mm and 7 μs/0.25 mm) and one ablative pattern (23 μs/0.25 mm) achieved significantly increased bond strength compared to the controls. Bovine enamel also showed in all test groups increased shear bond strength over the controls. Computerized motor-driven stage irradiation did not show superior bond strength values over the clinically more relevant freehand irradiation. Enamel that is made caries-resistant with CO₂ 9.3-μm short-pulsed laser irradiation showed at least equal or significantly higher shear bond strength to pit and fissure sealants than non-laser-irradiated enamel. The risk of a sealant failure due to CO₂ 9.3-μm short-pulsed laser irradiation appears reduced. If additional laser ablation is required before placing a sealant, the CO₂ 9.3-μm enamel laser-cut showed equivalent or superior bond strength to a flowable sealant.

Caries inhibition with a CO2 9.3 μm laser: An in vitro study

BACKGROUND AND OBJECTIVES

The caries preventive effects of different laser wavelengths have been studied in the laboratory as well as in pilot clinical trials. The objective of this in vitro study was to evaluate whether irradiation with a new 9.3 μm microsecond short-pulsed CO2 -laser could enhance enamel caries resistance with and without additional fluoride applications.

STUDY DESIGN/MATERIALS AND METHODS

One hundred and one human tooth enamel samples were divided into seven groups. Each group was treated with different laser parameters (CO2 -laser, wavelength 9.3 μm, 43 Hz pulse-repetition rate, pulse duration between 3 µs at 1.5 mJ/pulse to 7 µs at 2.9 mJ/pulse). A laboratory pH-cycling model followed by cross-sectional microhardness testing determined the mean relative mineral loss delta Z (ΔZ) for each group to assess caries inhibition in tooth enamel by the CO2 9.3 µm short-pulsed laser irradiation. The pH-cycling was performed with or without additional fluoride.

RESULTS

The non-laser control groups with additional fluoride had a relative mineral loss (ΔZ, vol% × µm) that ranged between 646 ± 215 and 773 ± 223 (mean ± SD). The laser irradiated and fluoride treated samples had a mean ΔZ ranging between 209 ± 133 and 403 ± 245 for an average 55% ± 9% reduction in mineral loss (ANOVA test, P < 0.0001). Increased mean mineral loss (ΔZ between 1166 ± 571 and 1339 ± 347) was found for the non-laser treated controls without additional fluoride. In contrast, the laser treated groups without additional fluoride showed a ΔZ between 470 ± 240 and 669 ± 209 (ANOVA test, P < 0.0001) representing an average 53% ± 11% reduction in mineral loss. Scanning electron microscopical assessment revealed that 3 µs pulses did not markedly change the enamel surface, while 7 µs pulses caused some enamel ablation.

CONCLUSION

The CO2 9.3 µm short-pulsed laser energy renders enamel caries resistant with and without additional fluoride use. The observed enhanced acid resistance occurred with the laser irradiation parameters used without obvious melting of the enamel surface as well as after irradiation with energies causing cutting of the enamel. Lasers Surg. Med. 48:546-554, 2016. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Combined Tin-Containing Fluoride Solution and CO2 Laser Treatment Reduces Enamel Erosion in vitro

The aim of this in vitro study was to evaluate the effect of combined CO2 laser and tin-containing fluoride treatment on the formation and progression of enamel erosive lesions. Ninety-six human enamel samples were obtained, stored in thymol solution and, after surface polishing, randomly divided into 6 different surface treatment groups (n = 16 in each group) as follows: no treatment, control (C); one CO2 laser irradiation (L1); two CO2 laser irradiations (L2); daily application of fluoride solution (F); combined daily fluoride solution + one CO2 laser irradiation (L1F), and combined daily fluoride solution + two CO2 laser irradiations (L2F). Laser irradiation was performed at 0.3 J/cm2 (5 µs/226 Hz/10.6 µm) on day 1 (L1) and day 6 (L2). The fluoride solution contained AmF/NaF (500 ppm F), and SnCl2 (800 ppm Sn) at pH 4.5. After surface treatment the samples were submitted to an erosive cycling over 10 days, including immersion in citric acid (2 min/0.05 M/pH = 2.3) 6 times daily and storage in remineralization solution (≥1 h) between erosive attacks. At the end of each cycling day, the enamel surface loss (micrometers) was measured using a 3D laser profilometer. Data were statistically analyzed by means of a 2-level mixed effects model and linear contrasts (α = 0.05). Group F (-3.3 ± 2.0 µm) showed significantly lower enamel surface loss than groups C (-27.22 ± 4.1 µm), L1 (-18.3 ± 4.4 µm) and L2 (-16.3 ± 5.3 µm) but higher than L1F (-1.0 ± 4.4 µm) and L2F (1.4 ± 3.2 µm, p < 0.05). Under the conditions of this in vitro study, the tin-containing fluoride solution caused 88% reduction of enamel surface loss, while its combination with CO2 laser irradiation at 0.3 J/cm2 hampered erosive loss almost completely.

Effect of carbon dioxide laser irradiation on enamel surface microhardness around orthodontic brackets

INTRODUCTION

In this study, we aimed to determine the effect of carbon dioxide laser irradiation on enamel surface microhardness.

METHODS

In this single-blind interventional clinical trial, 16 patients needing at least 2 premolars extracted for orthodontic purposes participated. In each subject, 1 premolar was treated with the carbon dioxide laser (beam diameter, 0.2 mm; power, 0.7 W); the other was exposed to a visible guiding light as the control. A t-loop was ligated to the bonded brackets to increase caries risk. After at least 2 months, the teeth were extracted, and the surface microhardness was measured. Scanning electron microscope evaluation was performed on 1 sample from each group. Normal distribution of the data was assessed by the Kolmogorov-Smirnov and Shapiro-Wilks tests. Mean microhardness values of the 2 groups were compared using paired t tests.

RESULTS

The data had normal distributions. Means and standard deviations of the microhardness in the laser-treated and control groups were 301.81 ± 94.29 and 183.9 ± 72.08 Vickers hardness numbers, respectively; this was different significantly (P <0.001). Scanning electron microscopy showed the enamel surface melting in the laser-treated specimens.

CONCLUSIONS

Carbon dioxide laser treatment results in higher enamel surface microhardness around orthodontic brackets. Patients at high risk of caries might benefit from this intervention. Exact control of the laser irradiation parameters is recommended.

A method for monitoring enamel erosion using laser irradiated surfaces and optical coherence tomography

INTRODUCTION

Since optical coherence tomography (OCT) is well suited for measuring small dimensional changes on tooth surfaces, OCT has great potential for monitoring tooth erosion. Previous studies have shown that enamel areas ablated by a carbon dioxide laser manifested lower rates of erosion compared to the non-ablated areas. The purpose of this study was to develop a model to monitor erosion in vitro that could potentially be used in vivo.

METHODS

Thirteen bovine enamel blocks were used in this in vitro study. Each 10 mm × 2 mm block was partitioned into five regions, the central region was unprotected, the adjacent windows were irradiated by a CO2 laser operating at 9.3 µm with a fluence of 2.4 J/cm(2) , and the outermost windows were coated with acid resistant varnish. The samples were exposed to a pH cycling regimen that caused both erosion and subsurface demineralization for 2, 4 and 6 days. The surfaces were scanned using a time-domain polarization sensitive optical coherence tomography (PS-OCT) system and the degree of surface loss (erosion) and the integrated reflectivity with lesion depth was calculated for each window.

RESULTS

There was a large and significant reduction in the depth of surface loss (erosion) and the severity of demineralization in the areas irradiated by the laser.

CONCLUSION

Irradiation of the enamel surface with a pulsed carbon dioxide laser at sub-ablative intensities results in significant inhibition of erosion and demineralization under the acid challenge employed in this study. In addition, these results suggest that it may be feasible to modify regions of the enamel surface using the laser to serve as reference marks to monitor the rate of erosion in vivo.

Use of new minimum intervention dentistry technologies in caries management

Preservation of natural tooth structure requires early detection of the carious lesion and is associated with comprehensive patient dental care. Processes aiming to detect carious lesions in the initial stage with optimum efficiency employ a variety of technologies such as magnifying loupes, transillumination, light and laser fluorescence (QLF® and DIAGNOdent® ) and autofluorescence (Soprolife® and VistaCam®), electric current/impedance (CarieScan(®) ), tomographic imaging and image processing. Most fluorescent caries detection tools can discriminate between healthy and carious dental tissue, demonstrating different levels of sensitivity and specificity. Based on the fluorescence principle, an LED camera (Soprolife® ) was developed (Sopro-Acteon, La Ciotat, France) which combined magnification, fluorescence, picture acquisition and an innovative therapeutic concept called light-induced fluorescence evaluator for diagnosis and treatment (LIFEDT). This article is rounded off by a Soprolife® illustration about minimally or even non-invasive dental techniques, distinguishing those that preserve or reinforce the enamel and enamel-dentine structures without any preparation (MIT1- minimally invasive therapy 1) from those that require minimum preparation of the dental tissues (MIT2 - minimally invasive therapy 2) using several clinical cases as examples. MIT1 encompasses all the dental techniques aimed at disinfection, remineralizing, reversing and sealing the caries process and MIT2 involves a series of specific tools, including microburs, air abrasion devices, sonic and ultrasonic inserts and photo-activated disinfection to achieve minimal preparation of the tooth. With respect to minimally invasive treatment and prevention, the use of lasers is discussed. Furthermore, while most practices operate under a surgical model, Caries Management by Risk Assessment (CaMBRA) encourages a medical model of disease prevention and management to control the manifestation of the disease, or keep the oral environment in a state of balance between pathological and preventive factors. Early detection and diagnosis and prediction of lesion activity are of great interest and may change traditional operative procedures substantially. Fluorescence tools with high levels of magnification and observational capacity should guide clinicians towards a more preventive and minimally invasive treatment strategy.

Effect of pretreatment with an Er:YAG laser and fluoride on the prevention of dental enamel erosion

The aim of this study was to evaluate the effect of the Er:YAG laser and its association with fluoride (1.23% acidulate phosphate fluoride gel) on the prevention of enamel erosion. Sixty specimens were obtained from bovine enamel (4 × 4 mm), which were ground flat, polished, and randomly divided into five groups according to the preventive treatments: control-fluoride application; L--Er:YAG laser; L+F--laser + fluoride; F+L--fluoride + laser; L/F--laser/fluoride simultaneously. Half of the enamel surface was covered with nail varnish (control area), and the other half was pretreated with one of the preventive strategies to subsequently be submitted to erosive challenge. When the laser was applied, it was irradiated for 10 s with a focal length of 4 mm and 60 mJ/2 Hz. Fluoride gel was applied for 4 min. Each specimen was individually exposed to regular Coca-Cola® for 1 min, four times/day, for 5 days. Wear analysis was performed with a profilometer, and demineralization was assessed with an optical microscope. Data were analyzed using the Kruskal-Wallis test (wear)/Dunn test and ANOVA/Fisher's exact tests. The group L/F was similar to control group. The other groups showed higher wear, which did not present differences among them. In the demineralization assessment, the groups F+L and L/F showed lower demineralization in relation to the other groups. It can be concluded that none preventive method was able to inhibit dental wear. The treatments L/F and F+L showed lower enamel demineralization.

Effects of pulsed Nd:YAG laser on tensile bond strength and caries resistance of human enamel

This study aims to evaluate the effects of pulsed Nd:YAG laser on the tensile bond strength (TBS) of resin to human enamel and caries resistance of human enamel. A total of 201 human premolars were used in this in vitro study. A flat enamel surface greater than 4 × 4 mm in area was prepared on each specimen using a low-speed cutting machine under a water coolant. Twenty-one specimens were divided into seven groups for morphology observations with no treatment, 35% phosphoric acid etching (30 seconds), and laser irradiation (30 seconds) of pulsed Nd:YAG laser with five different laser-parameter combinations. Another 100 specimens were used for TBS testing. They were embedded in self-cured acrylic resin and randomly divided into 10 groups. After enamel surface pretreatments according to the group design, resin was applied. The TBS values were tested using a universal testing machine. The other 80 specimens were randomly divided into eight groups for acid resistance evaluation. Scanning electron microscope (SEM) results showed that the enamel surfaces treated with 1.5 W/20 Hz and 2.0 W/20 Hz showed more etching-like appearance than those with other laser-parameter combinations. The laser-parameter combinations of 1.5 W/15 Hz and 1.5 W/20 Hz were found to be efficient for the TBS test. The mean TBS value of 14.45 ± 1.67 MPa in the laser irradiated group was significantly higher than that in the untreated group (3.48 ± 0.35 MPa) but lower than that in the 35% phosphoric acid group (21.50 ± 3.02 MPa). The highest mean TBS value of 26.64 ± 5.22 MPa was identified in the combination group (laser irradiation and then acid etching). Acid resistance evaluation showed that the pulsed Nd:YAG laser was efficient in preventing enamel demineralization. The SEM results of the fractured enamel surfaces, resin/enamel interfaces, and demineralization depths were consistent with those of the TBS test and the acid resistance evaluation. Pulsed Nd:YAG laser as an enamel surface pretreatment method presents a potential clinical application, especially for the caries-susceptible population or individuals with recently bleached teeth.

Influence of CO2 (10.6 μm) and Nd:YAG laser irradiation on the prevention of enamel caries around orthodontic brackets

One possible undesirable consequence of orthodontic therapy is the development of incipient caries lesions of enamel around brackets. The aim of this study was to compare the effects of CO2 (λ = 10.6 μm) and Nd:YAG (λ = 1,064 nm) lasers associated or not with topical fluoride application on the prevention of caries lesions around brackets. Brackets were bonded to the enamel of 65 premolars. The experimental groups (n = 13) were: G1--application of 1.23% acidulated fluoride phosphate gel (AFP, control); G2--Nd:YAG laser irradiation (0.6 W, 84.9 J/cm(2), 10 Hz, 110 μs, contact mode); G3--Nd:YAG laser irradiation associated with AFP; G4--CO2 laser irradiation (0.5 W, 28.6 J/cm(2), 50 Hz, 5 μs, and 10 mm focal distance); and G5--CO2 laser irradiation associated with AFP. Quantitative light-induced fluorescence was used to assess enamel demineralization. The data were statistically compared (α = 5%). The highest demineralization occurred in the Nd:YAG laser group (G2, 26.15% ± 1.94). The demineralization of all other groups was similar to that of the control group. In conclusion, CO2 laser alone was able to control enamel demineralization around brackets at the same level as that obtained with topical fluoride application.

In-vivo occlusal caries prevention by pulsed CO2 -laser and fluoride varnish treatment--a clinical pilot study

BACKGROUND AND OBJECTIVES

High caries prevalence in occlusal pits and fissures warrants novel prevention methods. An 86% reduction in dental enamel smooth surface demineralization in-vivo following short-pulsed 9.6 µm-CO(2) -laser irradiation was recently reported. The objective of this study was to conduct a blinded 12-month-pilot clinical trial of occlusal pit and fissure caries inhibition using the same CO(2) -laser irradiation conditions.

STUDY DESIGN/MATERIALS AND METHODS

Twenty subjects, average age 14 years, were recruited. At baseline, second molars were randomized into test and control groups, assessed by International Caries Detection & Assessment System (ICDAS-II), SOPROLIFE light-induced fluorescence evaluator in daylight and blue-fluorescence mode and DIAGNOdent. An independent investigator irradiated test molars with a CO(2) -laser, wavelength 9.6 µm, pulse-duration 20 µs, pulse-repetition-rate 20 Hz, beam diameter 800 µm, average fluence 4.5 ± 0.5 J/cm(2), 20 laser pulses per spot. At 3-, 6- and 12-month recall teeth were assessed by ICDAS, SOPROLIFE and DIAGNOdent. All subjects received fluoride varnish applications at baseline and 6-month recall.

RESULTS

All subjects completed the 3-month, 19 the 6-month and 16 the 12-month recall. At all recalls average ICDAS scores had decreased for the test and increased for the control fissures (laser vs. control, 3-month: -0.10 ± 0.14, 0.30 ± 0.18, P > 0.05; 6-month: -0.26 ± 0.13, 0.47 ± 0.16, P = 0.001; 12-month: -0.31 ± 0.15, 0.75 ± 0.17, P < 0.0001; mean ± SE, unpaired t-test) being statistically significantly different at 6- and 12-month recalls. SOPROLIFE daylight evaluation revealed at 6- and 12-months statistically significant differences in changes between baseline and recall for test and control molars, respectively (laser vs. control, 6-month: 0.22 ± 0.13, 0.17 ± 0.09, P = 0.02; 12-month: 0.28 ± 0.19, 0.25 ± 0.17, P = 0.03). For SOPROLIFE blue-fluorescence evaluation mean changes in comparison to baseline for the control and the laser treated teeth were also statistically significant for the 6- and 12-month recall.

CONCLUSION

Specific microsecond short-pulsed 9.6 µm CO(2) -laser irradiation markedly inhibits caries progression in pits and fissures in comparison to fluoride varnish alone over 12 months.

Light therapy: complementary antibacterial treatment of oral biofilm

Conventional antibacterial treatment fails to eradicate biofilms associated with common infections of the oral cavity. Unlike chemical agents, which are less effective than anticipated, owing to diffusion limitations in biofilms, light is more effective on bacteria in biofilm than in suspension. Effectiveness depends also on the type and parameters of the light. We tested the phototoxic effects of non-coherent blue light (wavelengths, 400-500 nm) and CO(2) laser (wavelength, 10.6 μm), which have different mechanisms of action on the oral bacterium Streptoccocus mutans, in biofilm and on tooth enamel. Exposure of S. mutans in biofilm to blue light had a delayed effect on bacterial viability throughout the biofilm and a sustained antibacterial effect on biofilm newly formed by previously irradiated bacteria. A synergistic antibacterial effect between blue light and H(2)O(2) may enhance the phototoxic effect, which involves a photochemical mechanism mediated by reactive oxygen species (ROS) formation. The effect of CO(2) laser irradiation on the viability of S. mutans in biofilm on enamel samples appeared to be higher in the deep layers, due to heating of the enamel surface by the absorbed energy. Biofilms do not interfere with the chemical changes resulting from irradiation, which may increase the enamel's resistance to acid attack.

Influence of laser irradiation on pits and fissures: an in situ study

OBJECTIVE

The aim of this in situ study was to analyze the influence of the Er:YAG, Nd:YAG, and CO(2) lasers on the enamel acid resistance of pits and fissures.

BACKGROUND DATA

The laser tissue interaction has been studied as a method of preventing occlusal caries.

METHODS

Thirteen volunteers wore palatal acrylic appliances containing human occlusal enamel blocks that were divided into four groups (G1, control; G2, Er:YAG; G3, Nd:YAG; G4, CO(2)). Each palatal acrylic appliance was used in the four studied groups and was used for 14 consecutive days. A sucrose solution was applied to the specimens six times per day. The specimens were then sectioned in half, and a microhardness test was applied. The other halves were analyzed using polarized light microscopy to measure the caries-like lesion areas, and a morphological analysis was conducted using a scanning electron microscope (SEM).

RESULTS

For the statistical analysis of the data obtained from the microhardness test (Knoop hardness number. [KHN]) (α=5%), Fisher's exact test was performed, and the group means were as follows: G1, 247±71; G2, 258±70; G3, 272±73; and G4, 298±56. The results demonstrated that the control group was significantly different from G3 and G4, which presented higher microhardness values. The Wilcoxon signed-rank test was used to analyze the data obtained from the caries-lesion area measurements (mm(2)) (α=5%) (G1, 0.01±1.08; G2, 0.13±0.18; G3, 0.05±0.17; and G4, 0.09±0.22). The results no showed significant differences among the groups in this analysis.

CONCLUSIONS

Based on the results from the present study, it may be concluded that the CO(2) and Nd:YAG lasers increased the enamel acid resistance in pits and fissures.

Laser application in prevention of demineralization in orthodontic treatment

One common negative side effect of orthodontic treatment with fixed appliances is the development of incipient caries lesions around brackets, particularly in patients with poor oral hygiene. Different methods have been used to prevent demineralization such as fluoride therapy and application of sealant to prevent caries. The recent effort to improve the resistance against the demineralization is by the application of different types of lasers. The purpose of this review article is discussing the effects of laser in prevention of demineralization in orthodontic patients.

FTIR and SEM analysis of CO2 laser irradiated human enamel

OBJECTIVES

Considering the enamel chemical structure, especially carbonate band, which has a major role in the caries prevention, the objective of the present study was to assess the chemical alterations on the enamel irradiated with CO(2) laser by means of FTIR spectroscopy and SEM analysis.

DESIGN

The enamel surfaces were analysed on a spectrometer for acquisition of the absorption spectrum relative to the chemical composition of the control sample. The irradiation was conducted with a 10.6-μm CO(2) laser (0.55W, 660W/cm(2)). The carbonate absorption band at 1600-1291cm(-1) as well as the water absorption band at 3793-2652cm(-1) was measured in each sample after the irradiation. The water band was measured again 24-h after the irradiation. The band area of each chemical compound was delimited, the background was subtracted, and the area under each band was integrated. Each area was normalized by the phosphate band (1190-702cm(-1)).

RESULTS

There was a statistically significant decrease (p<0.05) in the water content after irradiation (control: 0.184±0.04; irradiated: 0.078±0.026), which increased again after rehydration (0.145±0.038). The carbonate/phosphate ratio was measured initially (0.112±0.029) and its reduction after irradiation indicated the carbonate loss (0.088±0.014) (p<0.05).

CONCLUSION

The 10.6-μm CO(2) laser irradiation diminishes the carbonate and water contents in the enamel after irradiation.