CO2 laser inhibitor of artificial caries-like lesion progression in dental enamel

Effect of Casein Phosphopeptide-Amorphous Calcium Phosphate, Proanthocyanidin, Carbon Dioxide Laser Remineralization on the Bond Integrity of Composite Restoration Bonded to Caries-Affected Dentin

Objective: Assessment of different remineralizing pretreatment casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), proanthocyanidin (PA), carbon dioxide laser (CO2), eggshell solution (ES) on the shear bond strength (SBS) of resin composite bonded to remineralized carious-affected dentin (CAD). Materials and methods: Eighty human molars were collected with occlusal caries that extended about halfway into the dentin. Using a water-cooled, low-speed cutting saw, a flat, mid-coronal dentin surface was exposed. CAD was differentiated from healthy dentin. Based on the remineralizing agent used on the CAD surface, the teeth were arbitrarily allocated into five groups (n = 10). Group 1: no remineralizing agent, Group 2: CPP-ACP, Group 3: 6.5% PA solution, Group 4: CO2 laser, and Group 5: ES solution. All samples were bonded to composite and light cured and thermocycled. SBS and failure mode analysis were performed using universal testing and stereomicroscope 40 × . Using SPSS, SBS, and failure mode data were analyzed using analysis of variance and Tukey's honesty significant difference (HSD) test Results: Group 3 (6.5% PA solution; 15.59 ± 1.44 MPa) samples established the maximum bond integrity. Nevertheless, Group 1 (No remineralizing agent; 11.19 ± 1.21 MPa) exhibited the minimum outcome of bond strength. Intergroup comparison analysis showed that Group 1 (No remineralizing agent), Group 2 (CPP-ACP), and Group 4 (CO2 laser) established comparable values of bond strength (p > 0.05). Likewise, Group 3 (6.5% PA solution) and Group 5 (EA solution) also revealed equivalent bond integrity (p > 0.05). Conclusions: PA and ES are considered potential remineralizing agents used for caries-affected dentin surfaces in improving bond integrity to composite resin. However, further studies are advocated to extrapolate the findings of this study.

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.

Investigating the efficacy of a varnish containing gallic acid on remineralization of enamel lesions: an in vitro study

This study evaluated the efficacy of a formulated remineralizing gallic acid (GA) varnish in treating artificial enamel caries lesions. Fifty-five intact bovine incisors were collected. Enamel blocks (5 × 9 mm) were prepared. A third of each block's surface remained intact. Primary carious lesions were induced on the middle and bottom thirds of the blocks by immersing the samples in a demineralization solution for 6 h. The bottom third of the blocks were further remineralized by randomly applying 0.5%, 2%, or 8% GA varnishes and 2.26% fluoride varnish (V varnish, Vericom, Seoul, Korea), or the varnish base without active ingredients (n = 11 each). The specimens were immersed in a remineralizing solution for 4 h and then subjected to a 2-hour immersion in the demineralizing solution. After six days of pH cycling, the surface microhardness was measured at depths of 30, 75, and 120 μm. The percentage of surface microhardness recovery (SMHR%) was compared among the groups using the Shapiro-Wilk, ANOVA, and Tukey HSD post-hoc tests (α = 0.05). The SMHR% of all experimental groups was higher than the control group at 30 μm (p < 0.05). The 0.5% GA varnish showed the highest SMHR% at all depths; however, the difference with the other experimental groups was significant at a depth of 30 μm (p < 0.05). The SMHR% of the fluoride and the 2% and 8% GA varnishes was comparable at all depths. All treatments potentially remineralize enamel lesions, with 0.5% GA varnish having the greatest effect, particularly on the top surface layer. As such, this newly developed varnish may emerge as a promising alternative to fluoride varnish.

Evaluation of ER;CR:YSGG Laser and Remineralization Agents on Mineral Density and Ion Levels of Primary and Permanent Enamel

Objective: The aim of this study is to evaluate the efficacy of two different fluoride varnishes used alone or in combination with laser treatment on permanent and primary tooth enamel. Methods: Ninety-six primary and 96 permanent molar samples were divided into six groups. The levels of calcium, phosphorus, fluoride, and silver ions of each sample were analyzed using energy-dispersive X-ray spectroscopy (EDS). Six different treatments were applied to 12 different groups (n = 15) as control (g1/G1), fluoride varnish (g2/G2), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP)-fluoride varnish (g3/G3), laser (g4/G4), laser+fluoride varnish (g5/G5), and laser+CPP-ACP-fluoride varnish (g6/G6). After the procedures, ion levels were reanalyzed with EDS. The teeth were subjected to the artificial caries-forming procedure and ion levels were again evaluated by EDS. One sample from each group was prepared separately for the focused ion beam-scanning electron microscope measurement; initial and final images were recorded. The obtained data were statistically analyzed with the SPSS 23.0 program. Results: Compared with the initial measurement, phosphorus percentages increased in most of the groups in the last measurement. Calcium percentages of primary teeth increased in the last measurement, except for the g1 group, but in permanent teeth, there was an increase only in the G6 group. There was a statistically significant difference between g1/G1 and g6/G6 groups in the last measurement of phosphorus and calcium percentages. Conclusions: The combined use of laser with CPP-ACP-fluoride varnish enhanced remineralization in the primary and permanent teeth. However, in permanent teeth, the use of laser alone was not as effective as in primary teeth. Therefore, combined usage with CPP-ACP-fluoride varnish can enhance its efficacy. This in vitro study was approved by the local ethics committee of Hacettepe University (Project No.: GO 20/441).

The preventive/therapeutic effect of CO2 laser and MI Paste Plus® on intact and demineralized enamel against Streptococcus mutans (In Vitro Study)

Background

To evaluate the preventive and therapeutic effects of CO2 laser and MI paste plus on intact and demineralized enamel surfaces and their impact on bacterial adhesion. Methods: 160 enamel slabs were prepared and randomly allocated into two main groups; sound and demineralized enamel (n = 80 per group), in which specimens were immersed in a demineralizing solution (50 mM acetic acid, pH 4.5) for 72 h at 37 °C. Each group was further divided into four subgroups (n = 20); the control (un treated surfaces), surfaces treated by CO2 laser, MI paste plus (Recaldent™, GC corporation/Germany), and those received a combination of CO2 and MI paste plus. Streptococcus Mutans biofilm was isolated, quantified, and then applied on treated enamel surfaces and incubated anaerobically for 24 h and then quantified by colony-forming unit (CFU). Meanwhile, surface changes were assessed by Vickers microhardness and Scanning Electron Microscope combined with Energy-Dispersive X-Ray Spectroscopy (SEM-EDX). Results: The combined use of CO2 laser followed by MI paste plus significantly (p < 0.000) enhanced surface microhardness of sound and demineralized enamel with a significant reduction in bacterial counts. However, each technique alone was beneficial as they exhibited higher microhardness with lower bacterial viability in comparison to the control. The treatment of demineralized enamel surfaces with MI paste significantly reduced the number of bacterial colonies with the presence of dispersed mineral deposits over the surface.

Conclusions

The combined use of CO2 laser and MI paste plus was effective as a preventive and/or therapeutic measures in enhancing surface properties of enamel and reducing the bacterial viability.

Cold plasma enamel surface treatment to increase fluoride varnish uptake

Among the available methods of enamel strengthening, fluoride varnish (FV) treatment has relatively better results. On the other hand, cold plasma technology has shown promising capacities in sterilizing the environment, surface modification, and improving adhesion. Accordingly, this study aimed to increase the adhesion of FV to the enamel surface to prolong the enamel interaction with FV with subsequently increased fluoride uptake by enamel. Emphasizing that the change in adhesion is evidence-based and has not been explicitly measured. For this purpose, we randomly divided twenty bovine teeth into two groups A (consisting of four teeth) and B (composed of four subgroups, each containing four teeth). Samples of group A and one specimen of each subset B investigated the effect of using Helium-DBD (He-DBDJ), Argon (ArJ), and Air-DBD jet on the enamel surface. Other B specimens are devoted to studying the release of FV fluoride ions from processed enamel. Two diagnostic techniques, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), have been utilized to examine the samples' surface morphology and chemical analysis, respectively. Finally, the release of fluoride ions into distilled water was measured by an ion-selective electrode (ISE). SEM images showed that ArJ and Air-DBD significantly damaged enamel hexagonal structures, whereas, in the case of He-DBDJ, the hexagonal structures have only altered from convex to concave. EDX indicated an increase in calcium to phosphorus ratio and the amount of fluoride and sodium uptake on the enamel surface layer in the group processed with He-DBDJ plasma. The latter helps restore the damaged parts of the enamel. Analysis of fluoride released from the FV did not show a significant change owing to plasma processing (P ≤ 0.112). The combination of cold plasma and fluoride varnish treatment on the enamel surface might be considered as a more promising approach to increasing enamel resistance to tooth decay.

Caries inhibition of simulated active caries lesions with CO2 laser irradiation and fluoride

It has been well established that CO₂ laser irradiation can be used to transform the mineral phase of dental enamel to make it more resistant to acid dissolution. The purpose of this study was to investigate if carbon dioxide laser irradiation and topical fluoride can be used to treat incipient caries lesions to inhibit further progression, i.e. treat active lesion surfaces as opposed to sound surfaces prior to subjecting them to an acid challenge. Simulated active caries lesions were produced on twenty eight bovine enamel samples using a pH cycling model and those surfaces were irradiated by a 9.4 μm CO₂ laser and treated with topical fluoride. Changes in the surface morphology, acid resistance, and permeability were measured using digital microscopy, optical coherence tomography (OCT), and SWIR reflectance surface dehydration rate measurements at 1950 nm after exposure to a further acid challenge. There was a significant reduction (P < 0.05) of further lesion progression for lesion windows treated with CO₂ laser irradiation followed by the application of an acidulated phosphate fluoride gel compared to the untreated lesion windows on each sample. Treatment by laser irradiation alone was not effective. The degree of lesion inhibition was not as high as has been previously observed for laser irradiated sound enamel surfaces exposed to an acid challenge.

Demineralization prevention with a new antibacterial restorative composite containing QASi nanoparticles: an in situ study

OBJECTIVES

To investigate whether a newly developed dental composite with quaternary ammonium silica dioxide (QASi) nanoparticles incorporated with other fillers into the restorative material demonstrates antibacterial activity by reducing enamel demineralization in an in situ gap model.

MATERIALS AND METHODS

Twenty subjects wearing a lower removable partial denture (RPD) with acrylic flanges on both sides of the mouth were recruited into the 4-week in situ study. The gap model consisted of an enamel slab placed next to a composite, separated by a 38-μm space. In the split-mouth design on one side of the RPD, the composite was the Nobio Infinix composite (Nobio Ltd., Kadima, Israel), and the contralateral side used a control composite. Each participant received enamel slabs from one tooth. The gap model was recessed into the RPD buccal flange, allowing microbial plaque to accumulate within the gap. After 4 weeks of continuous wearing, decalcification (∆Z mineral loss) of the enamel slabs adjacent to the gap was determined by cross-sectional microhardness testing in the laboratory.

RESULTS

The ∆Z for the antibacterial composite test side was 235±354 (mean±standard deviation [SD]; data reported from 17 participants) and statistically significantly lower compared to ∆Z of the control side (774±556; mean±SD) (paired t-test, P<0.0001; mean of test minus control -539 (SD=392), 95% confidence interval of difference: -741, -338).

CONCLUSIONS

This in situ clinical study showed that composites with QASi antibacterial particles significantly reduced demineralization in enamel adjacent to a 38-μm gap over a 4-week period in comparison to a conventional composite.

CLINICAL RELEVANCE

Composites with QASi nanoparticle technology have the potential to reduce the occurrence of secondary caries.

TRIAL REGISTRATION

ClinicalTrials.gov #NCT04059250.

Effects of 9,300 nm Carbon Dioxide Laser on Dental Hard Tissue: A Concise Review

A carbon dioxide laser at 9,300 nm has a high absorption affinity for water and a shallow depth of penetration. It can be used for soft tissue surgery and hemostasis. Besides, it matches well with the absorption characteristic of hydroxyapatite in enamel and dentine. Therefore, the laser possesses a great ability for energy transfer to dental hard tissues. It has a low risk of thermo-damage to the dentine-pulp complex because it has a shallow depth of heat absorption. Hence, the laser is safe for dental hard tissue preparation. A carbon dioxide laser at 9,300 nm can effectively alter the chemical structure of teeth. It increases the ratio of calcium to phosphorus and converts the carbonated hydroxyapatite to the purer hydroxyapatite of enamel and dentine. It can alter the surface morphology of a tooth through surface melting, fusion, and ablation of dentine and enamel. At higher power, it removes caries lesions. It can enhance the success of restoration by increasing the bond strength of dental adhesives to the dentine and enamel. A carbon dioxide laser at 9,300 nm can also be used with fluoride for caries prevention. The advancement of technology allows the laser to be delivered in very short pulse durations and high repetition rates (frequency). Consequently, the laser can now be used with high peak power. The objective of this review is to discuss the effects and potential use of a 9,300 nm carbon dioxide laser on dental hard tissue.

Use of a novel 9.3-μm carbon dioxide laser and silver diamine fluoride: Prevention of enamel demineralisation and inhibition of cariogenic bacteria

OBJECTIVE

To investigate the effects of a 9.3-μm carbon dioxide (CO₂) laser and silver diamine fluoride (SDF) on the prevention of enamel demineralisation and inhibition of cariogenic bacteria.

METHODS

Enamel blocks were applied with Laser (Group-1), SDF (Group-2), Laser + SDF (Group-3) and no treatment (Group-4), and then subjected to an 8-day pH-cycling for cariogenic challenge. Lesion depth and cross-sectional micro-hardness were assessed. Surface morphological and chemical changes were studied using scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). For the antibacterial activity, treated enamel blocks were incubated with Streptococcus mutans. The biofilm morphology, kinetics and viability were assessed by SEM, colony-forming units (CFUs) and confocal laser scanning microscope (CLSM), respectively.

RESULTS

Lesion depths (μm) for Group-1 to Group-4 were 88 ± 21, 26 ± 11, 13 ± 9 and 115 ± 25, respectively (p < 0.001; Group-2 and Group-3 < Group-1 < Group-4). Group-3 had a significantly higher cross-sectional micro-hardness than the other three groups. EDS determined that Group-4 had the lowest calcium-to-phosphorus molar ratio among the groups (p < 0.001). SEM images showed apparent bacteria accumulation on enamel surfaces in Group-4, but not in other groups. Log CFUs for Group-1 to Group-4 were 6.2 ± 0.6, 2.9 ± 0.8, 2.2 ± 1.1 and 7.3 ± 0.3, respectively (p < 0.001; Group-2 and Group-3 < Group-1 < Group-4). CLSM images revealed that live bacteria dominated in Group-4, but not in other groups.

SIGNIFICANCE

The irradiation with a 9.3-μm CO₂ laser alone can prevent the demineralisation of enamel and reduce the adhesion of cariogenic bacteria. Moreover, adding SDF can significantly increase the preventive effect and antibacterial ability.

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 Remineralizing Agents With/Without CO2 Laser Irradiation on Structural and Mechanical Properties of Enamel and its Shear Bond Strength to Orthodontic Brackets

Introduction: Remineralizing agents may be used for the treatment of white spot lesions (WSLs) prior to bracket bonding. However, some concerns exist regarding their possible interference with the etching and bonding process, negatively affecting the bond strength. This study aimed to assess the effect of two remineralizing agents with/without CO₂ laser irradiation on the mechanical properties and shear bond strength (SBS) of demineralized enamel to the orthodontic bracket. Methods: This study evaluated 60 premolar teeth in 6 groups (n=10) as follows: (I) sound enamel, (II) demineralized enamel, (III) Nupro remineralizing agent (N), (IV) Nupro and CO₂ laser (N/L), (V) Teethmate remineralizing agent (T), and (VI) Teethmate and CO₂ laser (T/L). The remineralizing agents were applied to the enamel surfaces after their immersion in a demineralizing solution for 5 days. In groups IV and VI, the CO₂ laser with a 10.6 μm wavelength, 10 ms pulse duration, a 50 Hz repetition rate, 0.3 mm beam diameter and 0.7 W power was irradiated after applying the remineralizing agents. Brackets were bonded to the enamel surfaces and SBS was measured by a universal testing machine. For the assessment of enamel microhardness, 20 sections of molar teeth were divided into 4 groups (n=5; N, N/L, T, T/L) and their microhardness was measured before demineralization, after demineralization and after remineralization. X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM) and energy-dispersive spectrometry (EDS) were carried out to assess the formation of hydroxyapatite. The atomic percentages of the C, O, P, Ca, Na, Si, F and Ca/P ratio were determined by EDS analysis. Results: The SBS significantly decreased in group II (P<0.001). There was no significant difference among the groups I, III, IV, V and VI (P<0.05). This finding was similar to the microhardness results, which showed an increase in microhardness after remineralization (P<0.05), with no difference among the remineralizing agents. The Ca/P ratio was the highest in the Nupro group and the lowest in the demineralized group. Conclusion: Remineralizing agents can significantly improve the microhardness and structural properties of demineralized enamel to a level similar to that of sound enamel with no adverse effect on SBS to orthodontic brackets.

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.

The Effect of Titanium Tetrafluoride Treatment and the CO2 Laser on Acid Resistance of Human Enamel

Introduction: Titanium tetrafluoride (TiF4 ) is deemed more effective than the previous fluoride compounds. To enhance the effect of the fluoride compounds, researchers have suggested their association with lasers, although there are conflicting results in this area. We evaluated the acid resistance of enamel after treatment with the CO₂ laser and TiF4 . Methods: Thirteen human premolar teeth were sectioned into 5 parts and each segment was assigned to a study group: co (control): without treatment, AF: enamel treatment with APF 1.23% for 4 minutes, TF: enamel treatment with TiF4 4% for 1 minute, TF-L: enamel treatment with TiF4 4% and then the CO₂ laser (Peak power: 1 W, pulse duration: 10 ms, interval time: 500 ms, Beam spot size: 0.2 mm, distance: 2 cm), L-TF: enamel treatment with the CO₂ laser and then TiF4 4%. Each sample was kept for 7 days in acidic solution of hydroxyethyl cellulose at pH=4.5, and the amount of the calcium ion released in the solution was measured by atomic absorption spectrometry. Data were analyzed by ANOVA and Bonferroni tests. The significance level was set at 0.05. Results: The average concentration of the calcium ion released in acidic solution was 197.46, 153.30, 99.23, 61.23, 55.46 ppm in the groups respectively. There was a significant difference between the study groups (P<0.0001). Only the difference between TF-L and L-TF was not significant (P>0.05). Conclusion: The loss of calcium from the enamel samples in the groups treated with a combination of the laser and TiF4 was significantly lower than the groups treated with fluoride alone, or the control group. It did not make a significant difference whether the CO₂ laser was applied before or after TiF4 .

Influence of Er, Cr: YSGG (2780 nm) and Nanosecond Nd: YAG Laser (1064 nm) Irradiation on Enamel Acid Resistance: Morphological and Elemental Analysis

BACKGROUND

Enamel demineralisation is an initial step of the serious dental problem including dental caries, white spot lesions and dental erosion.

AIM

Compare the effect of Er, Cr: YSGG (λ = 2780 nm) and nanosecond Nd: YAG (λ = 1064 nm) laser on enamel acid resistance.

MATERIAL AND METHODS

Thirty non-carious human premolars, extracted for orthodontic reasons, were used. The experimental groups (n = 10 each group) were: Group I, untreated (control); Group II, Er, Cr: YSGG laser irradiation (0.75 W, 20 Hz, 140 μs, 10 s); Group III, nanosecond pulsed Nd: YAG laser irradiation (0.8 W, 10 Hz, 7 ns, 10 s). Scanning electron microscope and Energy Dispersive X-ray Spectroscopy (EDX) were used to assess acquired enamel resistance to PH cycling.

RESULTS

After subjecting the three experimental groups to PH cycling, scanning electron microscopic examination revealed irregular porous dissoluted enamel surface in group I. However, groups II and III demonstrated partially dissoluted enamel surface. EDX analysis demonstrated the lowest mean percentage decrease in calcium and phosphorus content in group II followed by group III, then the highest mean percentage decrease was observed in untreated group I. One-way ANOVA revealed significant differences (p < 0.0001) between the tested groups.

CONCLUSIONS

Both Er, Cr: YSSG and nanosecond Nd: YAG laser irradiation were able to improve the acid resistance of enamel. However, enamel surface treated with Er, Cr: YSSG laser showed the lowest mean percentage decrease of calcium and phosphorus (highest acid resistance).

Preventive effects of carbon dioxide laser and casein phosphopeptide amorphous calcium phosphate fluoride varnish on enamel demineralization: A comparative, in vitro study

AIM

The aim of the present study was to compare the effects of carbon dioxide (CO₂ ) laser and casein phosphopeptide amorphous calcium phosphate (CPP-ACP)fluoride varnish on enamel demineralization.

METHODS

Human teeth were randomly assigned to three groups. The enamel was treated with fluoride varnish, 10.6 μm CO₂ laser, or no treatment (control), followed by 9 days of pH cycling. Baseline and final FluoreCam images were used to quantify the area, intensity, and impact of demineralization; cross-sectional microhardness was used to measure the mechanical properties of the enamel.

RESULTS

There were statistically-significant changes in the area, intensity and impact of demineralization in the control and laser groups (P < 0.05), but not in the fluoride group. The control group showed a significantly greater area and impact of enamel demineralization compared to the fluoride group. The area of demineralization in the laser group was significantly greater than that of the fluoride group. Enamel demineralization of the laser and control groups was comparable. The fluoride group showed statistically-significant harder enamel than the control at 20, 40, and 60 μm depths; the laser group enamel was significantly harder than the control at 20 and 40 μm depths. The fluoride group showed statistically-significant harder enamel than the laser group at 20 μm depth.

CONCLUSIONS

CPP-ACP fluoride varnish is more effective than CO₂ in preventing enamel demineralization.

Assessment of Inhibition of Mineral Loss from Human Tooth Enamel by Carbon Dioxide Laser and 1.23% Acidulated Phosphate Fluoride

Aims and Objectives

The efficacy of carbon dioxide (CO₂) laser irradiation combined with fluoride in inhibiting enamel demineralization has been demonstrated by several laboratory investigations. However, there are very few reports about the in situ or in vivo caries preventive effect of CO₂ laser combined with topical fluoride on dental enamel. Hence, an in situ study was designed and carried out to assess inhibition of mineral loss from human tooth enamel by CO₂ laser and 1.23% acidulated phosphate fluoride (APF).

Material and Methods

Impressions of upper and lower arch of the volunteers were made in alginate impression material. Study models were poured, duplicated, and duly labeled. On the working model, appliances were fabricated in acrylic resin to fit the upper dental arch of the volunteers. Four enamel slabs (one from each group) were fitted on the palatal surface of the appliance as close as possible to posterior teeth. Surfaces of slabs were kept below the outer surface of acrylic. The analysis was done using SPSS version 15 (SPSS Inc., Chicago, IL, USA) Windows software program.

Results

Statistically significant increase in inhibition of mineral loss of enamel slabs when treated individually or in a combination of low power CO₂ laser and 1.23% APF solution. The application of 1.23% APF solution after low power CO₂ laser treatment showed maximum inhibition of mineral loss.

Conclusion

The combined use of this specific laser treatment plus fluoride was more successful than either laser treatment or fluoride alone in the inhibition of mineral loss in the mouth. The results of this study also suggest that the combination of low power laser treatment with fluoride therapy may be effective as a caries inhibition treatment.

Er,Cr:YSGG Laser Energy Delivery: Pulse and Power Effects on Enamel Surface and Erosive Resistance

BACKGROUND

High power lasers have been suggested as a useful tool for dental caries and erosion prevention due to the increase of enamel acid resistance.

OBJECTIVE

to evaluate the effect of Er,Cr:YSGG (erbium,chromium:yttrium, scandium, gallium, garnet) laser irradiation pulse frequency and power on enamel surface and acid erosion resistance.

METHODS

By combining pulse frequency (5-75 Hz) and power settings (0.10-1.00 W), 20 irradiated groups and one nonirradiated control group were tested. A total of 63 bovine enamel blocks (n = 3/group) were prepared for surface hardness and roughness evaluation, performed in three phases: baseline, after irradiation, and after erosive challenge. Enamel blocks were irradiated with Er,Cr:YSGG laser with MZ8 tip (iPlus; Waterlase, Biolase, CA) for 30 sec according to experimental group and submitted. Erosive challenge consisted of four cycles alternating immersion in 0.01 M HCl (5 mL/mm²; 2 min; at 37°C) and immersion in artificial saliva for 3 h. Analysis of variance (three-way ANOVA), Tukey's test, and Pearson correlation were performed for the statistical analysis (p < 0.05).

RESULTS

After irradiation, groups irradiated with pulse frequency of 10 and 15 Hz showed a decrease in surface hardness. After erosive challenge, 5 and 75 W groups showed increase in surface hardness; 0.25, 0.5, 0.75, and 1 W groups showed minor alterations in surface roughness.

CONCLUSIONS

the irradiation of Er,Cr:YSGG laser with different parameters of power and pulse frequency settings may alter enamel surface and erosive resistance differently. Pulse frequency of 30 Hz and power of 0.50 W was considered the best parameter to prevent enamel acid erosion.

SEM Evaluation of Enamel Surface Changes and Enamel Microhardness around Orthodontic Brackets after Application of CO2 Laser, Er,Cr:YSGG Laser and Fluoride Varnish: An In vivo Study

Introduction

One of the most undesirable consequences of orthodontic treatment is occurrence of enamel demineralization around orthodontic brackets. Numerous in vitro studies have reported the prevention of enamel demineralization by surface treatment with lasers and fluoride varnish.

Aim

To evaluate the changes on the enamel surface and microhardness around orthodontic brackets after surface treatment by CO₂ laser, Er, Cr:YSGG laser and fluoride varnish in vivo.

Materials and Methods

A double blind interventional study was carried out on 100 premolars which were equally divided into five groups, out of which one was the control group (Group 0). The intervention groups (Group I to IV) comprised of patients requiring fixed orthodontic treatment with all 4 first premolars extraction. Brackets were bonded on all 80 premolars which were to be extracted. Enamel surface treatment of Groups I, II and III was done by CO₂ laser, Er, Cr:YSGG laser and 5% sodium fluoride varnish respectively and Group IV did not receive any surface treatment. A modified T-loop was ligated to the bracket and after two months, the premolars were extracted. Surface changes were evaluated by Scanning Electron Microscopic (SEM) and microhardness testing. Comparison of mean microhardness between all the groups was assessed using post-hoc test with Bonferroni correction.

Results

Group I showed a melted enamel appearance with fine cracks and fissures while Group II showed a glossy, homogenous enamel surface with well coalesced enamel rods. Group III showed slight areas of erosions and Group IV presented areas of stripped enamel. Significant difference was observed between the mean microhardness (VHN) of Group I, Group II, Group III, Group IV and Group 0 with p<0.001. A significant difference of p<0.001 was observed while comparing Group I vs II,III,IV,0 and Group II vs III,IV,0. However, difference while comparing Group III vs IV was p=0.005 and difference between the mean microhardness of Group 0 vs Group III was non significant.

Conclusion

Surface treatment with Er,Cr:YSGG laser causes a positive alteration of the enamel surface increasing its ability to resist demineralization with optimum microhardness as compared to CO₂ laser and sodium fluoride varnish.

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).

Influence of multi-wavelength laser irradiation of enamel and dentin surfaces at 0.355, 2.94, and 9.4 μm on surface morphology, permeability, and acid resistance

OBJECTIVE

Ultraviolet (UV) and infrared (IR) lasers can be used to specifically target protein, water, and mineral, respectively, in dental hard tissues to produce varying changes in surface morphology, permeability, reflectivity, and acid resistance. The purpose of this study was to explore the influence of laser irradiation and topical fluoride application on the surface morphology, permeability, reflectivity, and acid resistance of enamel and dentin to shed light on the mechanism of interaction and develop more effective treatments.

METHODS

Twelve bovine enamel surfaces and twelve bovine dentin surfaces were irradiated with various combinations of lasers operating at 0.355 (Freq.-tripled Nd:YAG (UV) laser), 2.94 (Er:YAG laser), and 9.4 μm (CO₂ laser), and surfaces were exposed to an acidulated phosphate fluoride gel and an acid challenge. Changes in the surface morphology, acid resistance, and permeability were measured using digital microscopy, polarized light microscopy, near-IR reflectance, fluorescence, polarization sensitive-optical coherence tomography (PS-OCT), and surface dehydration rate measurements.

RESULTS

Different laser treatments dramatically influenced the surface morphology and permeability of both enamel and dentin. CO₂ laser irradiation melted tooth surfaces. Er:YAG and UV lasers, while not melting tooth surfaces, showed markedly different surface roughness. Er:YAG irradiation led to significantly rougher enamel and dentin surfaces and led to higher permeability. There were significant differences in acid resistance among the various treatment groups.

CONCLUSION

Surface dehydration measurements showed significant changes in permeability after laser treatments, application of fluoride and after exposure to demineralization. CO₂ laser irradiation was most effective in inhibiting demineralization on enamel while topical fluoride was most effective for dentin surfaces. Lasers Surg. Med. 49:913-927, 2017. © 2017 Wiley Periodicals, Inc.

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.

Influence of Multi-Wavelength Laser Irradiation of Enamel and Dentin Surfaces on Surface Morphology and Permeability

UV and IR lasers can be used to specifically target protein, water, and the mineral phase of dental hard tissues to produce varying changes in surface morphology. In this study, we irradiated enamel and dentin surfaces with various combinations of lasers operating at 0.355, 2.94, and 9.4 μm, exposed those surfaces to topical fluoride, and subsequently evaluated the influence of these changes on surface morphology and permeability. Digital microscopy and surface dehydration rate measurements were used to monitor changes in the samples overtime. The surface morphology and permeability (dehydration rate) varied markedly with the different laser treatments on enamel. On dentin, fluoride was most effective in reducing the permeability.

Synergistic effect of fluoride and laser irradiation for the inhibition of the demineralization of dental enamel

Both laser irradiation and fluoride treatment alone are known to provide increased resistance to acid dissolution. CO₂ lasers tuned to a wavelength of 9.3 μm can be used to efficiently convert the carbonated hydroxyapatite of enamel to a much more acid resistant purer phase hydroxyapatite (HAP). Further studies have shown that fluoride application to HAP yields fluoroapatite (FAP) which is even more resistant against acid dissolution. Previous studies show that CO₂ lasers and fluoride treatments interact synergistically to provide significantly higher protection than either method alone, but the mechanism of interaction has not been elucidated. We recently observed the formation of microcracks or a "crazed" zone in the irradiated region that is resistant to demineralization using high-resolution microscopy. The microcracks are formed due to the slight contraction of enamel due to transformation of carbonated hydroxyapatite to the more acid resistant pure phase hydroxyapatite (HAP) that has a smaller lattice. In this study, we test the hypothesis that these small cracks will provide greater adhesion for topical fluoride for greater protection against acid demineralization.

Influence of a pulsed CO2 laser operating at 9.4 μm on the surface morphology, reflectivity, and acid resistance of dental enamel below the threshold for melting

Below the threshold for laser ablation, the mineral phase of enamel is converted into a purer phase hydroxyapatite with increased acid resistance. Studies suggest the possibility of achieving the conversion without visible surface alteration. In this study, changes in the surface morphology, reflectivity, and acid resistance were monitored with varying irradiation intensity. Bovine enamel specimens were irradiated using a CO 2 laser operating at 9.4 ?? ? m with a Gaussian spatial beam profile—1.6 to 3.1 mm in diameter. After laser treatment, samples were subjected to demineralization to simulate the acidic intraoral conditions of dental decay. The resulting demineralization and erosion were assessed using polarization-sensitive optical coherence tomography, three-dimensional digital microscopy, and polarized light microscopy. Distinct changes in the surface morphology and the degree of inhibition were found within the laser-treated area in accordance with the laser intensity profile. Subtle visual changes were noted below the melting point for enamel that appear to correspond to thresholds for denaturation of the organic phase and thermal decomposition of the mineral phase. There was significant protection from laser irradiation in areas in which the reflectivity was not increased significantly, suggesting that aesthetically sensitive areas of the tooth can be treated for 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.

FT-Raman spectroscopic characterization of enamel surfaces irradiated with Nd:YAG and Er:YAG lasers

Background. Despite recent advances in dental caries prevention, caries is common and remains a serious health problem. Laser irradiation is one of the most common methods in preventive measures in recent years. Raman spectroscopy technique is utilized to study the microcrystalline structure of dental enamel. In this study, FT-Raman spectroscopy was used to evaluate chemical changes in enamel structure irradiated with Nd:YAG and Er:YAG lasers.

Methods. We used 15 freshly-extracted, non-carious, human molars that were treated as follows: No treatment was carried out in group A (control group); Group B was irradiated with Er:YAG laser for 10 seconds under air and water spray; and Group C was irradiated with Nd:YAG laser for 10 seconds under air and water spray. After treatment, the samples were analyzed by FT-Raman spectroscopy.

Results. The carbonate content evaluation with regard to the integrated area under the curve (1065/960 cm^–1) exhibited a significant reduction in its ratio in groups B and C. The organic content (2935/960 cm^-1) area exhibited a significant decrease after laser irradiation in group B and C.

Conclusion. The results showed that the mineral and organic matrices of enamel structure were affected by laser irradiation; therefore, it might be a suitable method for caries prevention.

Chemical and Morphological Changes of Primary Teeth Irradiated with Nd:YAG Laser: An Ex Vivo Long-Term Analysis

OBJECTIVE

The aim of this study was to assess any long-term chemical and morphological Nd:YAG laser modifications on irradiated primary enamel.

BACKGROUND DATA

Previous studies on irradiated primary human enamel employed methodologies that evaluated the short-term effects only.

METHODS

One hundred and eighty-six irradiated (with and/or without fluoride) primary enamel teeth from high-caries-risk children, which were exfoliated over a 1-year period, were collected, and the sample surface area was submitted for scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray energy-dispersive spectrometry (EDS). The subsurface was analyzed by Knoop microhardness and light microscopy (LM). Data were analyzed by one way ANOVA and Tukey tests (α=0.05) and Kruskall-Wallis and Tukey tests (α=0.05).

RESULTS

FTIR analysis revealed a higher concentration of phosphate and carbonate in the irradiated (0.987±0.064) and lower concentration in the control groups (1.477±0.310). SEM analysis showed that the control samples exhibited a slightly smoother surface than the irradiated groups. The EDS analysis did not show any differences in the amount of calcium, phosphorus, or fluoride among the groups. The microhardness analysis revealed that sealant (249.86±7.15) and laser irradiation (262.44±22.69) led to higher hardness values than the negative control group (128.35±25.19). LM indicated significantly reduced caries formation in the laser (5.35±5.38%) and the laser plus acidulated phosphate fluoride (APF) groups (10.35±0.88%) compared with the negative control group (72.56±12.86%).

CONCLUSIONS

Even with the limitations of the present study, these results suggest that Nd:YAG irradiation clinically modified the chemical composition of the enamel surface regardless of fluoride concentration, which successfully inhibited demineralization of primary tooth enamel over a 1-year period without significant morphological changes.

In situ Mineral Loss Inhibition by CO2 Laser and Fluoride

Laser and fluoride treatments have been shown to inhibit enamel demineralization in the laboratory. However, the intra-oral effects of this association have not been tested. This study assessed in situ the effect of a Transversely Excited Atmospheric CO2 laser (λ = 9.6 μm) and the use of pressure fluoridated dentifrice on enamel demineralization. During two 14-day phases, 17 volunteers wore palatal appliances containing human enamel slabs assigned to treatment groups, as follows: (1) non-fluoride dentifrice, (2) CO2 laser irradiation plus non-fluoride dentifrice, (3) fluoride dentifrice, and (4) CO2 laser irradiation plus fluoride dentifrice. A 20% sucrose solution was dripped onto the slabs 8 times per day. The specimens treated with laser and/or fluoridated dentifrice presented a significantly lower mineral loss when compared with those from the non-fluoride dentifrice group. The results suggested that CO2 laser treatment of enamel inhibits demineralization in the human mouth, being more effective when associated with fluoride.

Effects of CO2 laser irradiation on matrix-rich biofilm development formation-an in vitro study

BACKGROUND

A carbon dioxide (CO₂) laser has been used to morphologically and chemically modify the dental enamel surface as well as to make it more resistant to demineralization. Despite a variety of experiments demonstrating the inhibitory effect of a CO₂ laser in reduce enamel demineralization, little is known about the effect of surface irradiated on bacterial growth. Thus, this in vitro study was preformed to evaluate the biofilm formation on enamel previously irradiated with a CO₂ laser (λ = 10.6 µM).

METHODS

For this in vitro study, 96 specimens of bovine enamel were employed, which were divided into two groups (n = 48): 1) Control-non-irradiated surface and 2) Irradiated enamel surface. Biofilms were grown on the enamel specimens by one, three and five days under intermittent cariogenic condition in the irradiated and non-irradiated surface. In each assessment time, the biofilm were evaluated by dry weigh, counting the number of viable colonies and, in fifth day, were evaluated by polysaccharides analysis, quantitative real time Polymerase Chain Reaction (PCR) as well as by contact angle. In addition, the morphology of biofilms was characterized by fluorescence microscopy and field emission scanning electron microscopy (FESEM). Initially, the assumptions of equal variances and normal distribution of errors were conferred and the results are analyzed statistically by t-test and Mann Whitney test.

RESULTS

The mean of log CFU/mL obtained for the one-day biofilm evaluation showed that there is statistical difference between the experimental groups. When biofilms were exposed to the CO₂ laser, CFU/mL and CFU/dry weight in three day was reduced significantly compared with control group. The difference in the genes expression (Glucosyltransferases (gtfB) and Glucan-binding protein (gbpB)) and polysaccharides was not statically significant. Contact angle was increased relative to control when the surface was irradiated with the CO₂ laser. Similar morphology was also visible with both treatments; however, the irradiated group revealed evidence of melting and fusion in the specimens.

CONCLUSION

In conclusion, CO₂ laser irradiation modifies the energy surface and disrupts the initial biofilm formation.

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.

Evaluation of enamel surface modification using PS-OCT after laser treatment to increase resistance to demineralization

At laser intensities below ablation, carbonated hydroxyapatite in enamel is converted into a purer phase hydroxyapatite with increased acid resistance. Previous studies suggested the possibility of achieving the conversion without surface modification. This study attempts to evaluate the thresholds for the modification without additional changes in physical and optical properties of the enamel. Bovine specimens were irradiated using an RF-excited CO₂ laser operating at 9.4-µm with a pulse duration of 26-µs, pulse repetition rates of 100-1000 Hz, with a Gaussian spatial beam profile - 1.4 mm in diameter. After laser treatment, the samples were subjected to acid demineralization for 48 hours to simulate acidic intraoral conditions of a caries attack. The resulting demineralization and erosion were assessed using polarization sensitive OCT (PS-OCT) and 3D digital microscopy. The images from digital microscopy demonstrated a clear delineation between laser protected zones without visual changes and zones with higher levels of demineralization and erosion. Distinct changes in the surface morphology were found within the laser treated area in accordance with the Gaussian spatial beam profile. There was significant protection from the laser in areas that were not visually altered.

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.

CO₂ laser emission modes to control enamel erosion

Considering the importance and prevalence of dental erosion, the aim of this in vitro study was to evaluate the influence of different modes of pulse emission of CO2 laser associated or not to acidulated phosphate fluoride (APF) 1.23% gel, in controlling enamel erosion by profilometry. Ninety-six fragments of bovine enamel were flattened and polished, and the specimens were subjected to initial erosive challenge with hydrochloric acid (pH = 2). Specimens were randomly assigned according to surface treatment: APF 1.23% gel and gel without fluoride (control), and subdivided according to the modes of pulse CO2 laser irradiation: no irradiation (control), continuous, ultrapulse, and repeated pulse (n = 12). After surface treatment, further erosive challenges were performed for 5 days, 4 × 2 min/day. Enamel structure loss was quantitatively determined by a profilometer, after surface treatment and after 5 days of erosive challenges. Two-away ANOVA revealed a significant difference between the pulse emission mode of the CO2 laser and the presence of fluoride (P ≤ 0.05). The Duncan's test showed that CO2 laser irradiation in continuous mode and the specimens only received fluoride, promoted lower enamel loss than that other treatments. A lower dissolution of the enamel prisms was observed when it was irradiated with CO2 laser in continuous mode compared other groups. It can be concluded that CO2 laser irradiation in continuous mode was the most effective to control the enamel structure loss submitted to erosive challenges with hydrochloric acid.

Effects of CO2 laser irradiation combined with fluoride application on the demineralization, mechanical properties, structure, and composition of enamel

We investigated the effects of CO2 laser irradiation combined with acidulated phosphate fluoride (APF) application on the demineralization of enamel. APF gel was applied to the buccal enamel of human premolars and CO2 laser was applied. After the specimens were immersed in demineralization solution for 72 h, they were subjected to depth-dependent micro-CT and nanoindentation analyses. Micro-X-ray diffraction and X-ray photoelectron spectroscopy were performed to analyze the surfaces. Some surface regions of the enamel in specimens that were laser-irradiated with low output and APF-treated showed significantly higher values of MD and hardness than specimens treated with APF alone. A higher fluoride concentration in the enamel surface was observed in specimens treated with CO2 laser irradiation plus APF gel application. In conclusion, CO2 laser irradiation with low output is preferable to improve acid resistance.

CO2 laser and topical fluoride therapy in the control of caries lesions on demineralized primary enamel

This study evaluated the effect of CO₂ laser irradiation and topical fluoride therapy in the control of caries progression on primary teeth enamel. 30 fragments (3 × 3 × 2 mm) from primary canines were submitted to an initial cariogenic challenge that consisted of immersion on demineralizing solution for 3 hours and remineralizing solution for 21 hours for 5 days. Fragments were randomly assigned into three groups (n = 10): L: CO₂ laser (λ = 10.6 μm), APF: 1.23% acidulated phosphate fluoride, and C: no treatment (control). CO₂ laser was applied with 0.5 W power and 0.44 J/cm² energy density. Fluoride application was performed with 0.1 g for 1 minute. Cariogenic challenge was conducted for 5 days following protocol previously described. Subsurface Knoop microhardness was measured at 30 μm from the edge. Obtained data were subjected to analysis the variance (ANOVA) and Duncan test with significance of 5%. It was found that the L group showed greater control of deciduous enamel demineralization and were similar to those of APF group, while being statistically different from C group (P ≤ 0.05) that showed the lowest microhardness values. It was concluded that CO₂ laser can be an additional resource in caries control progression on primary teeth enamel.

Laser-Casein phosphopeptide effect on remineralization of early enamel lesions in primary teeth

Background

The aim of this study was to assess the effect of Nd:YAG laser irradiation following casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) application on calcium and phosphate concentration and surface microhardness (SMH) of enamel surface in artificial white spot lesions of primary teeth.

Material and Methods

Eighty teeth with artificial white spot lesions were randomly divided into four groups: (A) distilled and deionized water, (B) Nd:YAG laser, (C) CPP-ACP crème, & (D) CPP-ACP plus laser. SMH was measured using Vickers diamond indenter in Vickers Hardness Number (VHN). Two samples of each group were analyzed using scanning electron microscope (SEM). The results were analyzed with the SPSS 17/win.

Results

The subjects of group D demonstrated a significant increase in the calcium and phosphate contents of enamel surface compared to those of groups A (P < 0.001, P < 0.001), B (P < 0.001, P < 0.001) and C (P = 0.024, P = 0.04), respectively. A statistically significant difference was seen for mean VHN between groups A and B (P = 0.002). SEM evaluations confirmed the results.

Conclusions

The combination of Nd:YAG laser and CPP-ACP crème could be recommended as an effective preventive modality for remineralizing of white spot lesions in primary teeth.

Key words:CPP-ACP, enamel remineralization, microhardness, Nd:YAG, primary teeth, SEM.

Potential of CO2 lasers (10.6 µm) associated with fluorides in inhibiting human enamel erosion

This in vitro study aimed to investigate the potential of CO2 lasers associated with different fluoride agents in inhibiting enamel erosion. Human enamel samples were randomly divided into 9 groups (n = 12): G1-eroded enamel; G2-APF gel; G3-AmF/NaF gel; G4-AmF/SnF2 solution; G5-CO2 laser (λ = 10.6 µm)+APF gel; G6-CO2 laser+AmF/NaF gel; G7-CO2laser+AmF/SnF2solution; G8-CO2 laser; and G9-sound enamel. The CO2 laser parameters were: 0.45 J/cm2; 6 μs; and 128 Hz. After surface treatment, the samples (except from G9) were immersed in 1% citric acid (pH 4.0, 3 min). Surface microhardness was measured at baseline and after surface softening. The data were statistically analyzed by one-way ANOVA and Tukey's tests (p < 0.05). G2 (407.6 ± 37.3) presented the highest mean SMH after softening, followed by G3 (407.5 ± 29.8) and G5 (399.7 ± 32.9). Within the fluoride-treated groups, G4 (309.0 ± 24.4) had a significantly lower mean SMH than G3 and G2, which were statistically similar to each other. AmF/NaF and APF application showed potential to protect and control erosion progression in dental enamel, and CO2 laser irradiation at 0.45J/cm2 did not influence its efficacy. CO2 laser irradiation alone under the same conditions could also significantly decrease enamel erosive mineral loss, although at lower levels.

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.

Monitoring the inhibition of erosion by a CO2 laser with OCT

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. Teeth surfaces were irradiated with a carbon dioxide laser at low sub-ablative fluence to create an acid-resistant reference layer without damaging the enamel. The laser treated areas were compared with the unprotected areas using OCT during exposure to a pH cycling model for up to 6 days. The laser treated areas markedly reduced the rate of erosion.