Effects of CO2 laser on fluoride uptake in enamel

Enamel Fluoride Uptake Determined Using the Microbiopsy Technique and Time-of-Flight Secondary Ion Mass Spectrometry: A Pilot Study

This study evaluated the suitability of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to assess enamel fluoride uptake (EFU) in comparison with the microbiopsy technique. Enamel specimens were exposed to equimolar solutions of fluoride prepared from sodium fluoride (NaF), stannous fluoride (SnF2), or amine fluoride (AmF). EFU was quantified by both techniques on the same specimens. EFU was found to be highest for samples treated with AmF, followed by SnF2 and NaF. Both methods yielded clearly interpretable, highly correlating (r = 0.95) data. ToF-SIMS can be considered a promising alternative to the microbiopsy technique for near-surface EFU assessment.

Combined Effect of Fluoride Mouthwash and Sub-ablative Er:YAG Laser for Prevention of White Spot Lesions around Orthodontic Brackets

Background:

Development of white spot lesions (WSLs) around orthodontic brackets compromises esthetics and necessitates additional dental treatments.

Objectives:

This study aimed to assess the efficacy of fluoride mouthwash combined with Er:YAG laser irradiation for the prevention of WSLs around orthodontic brackets.

Methods:

Orthodontic brackets were bonded to 50 bovine incisors. The entire tooth surface was coated with acid-resistant varnish except for a margin around the brackets. The microhardness of the teeth was measured at the respective area using the Vickers hardness test. The teeth were then randomly divided into five groups (n=10) of control (Gc), Orthokin fluoride mouthwash (Gf), 100 mJ/cm2 Er:YAG laser (Gl), laser + mouthwash (Glf), and mouthwash + laser (Gfl). Then, the teeth underwent pH cycling according to the standard protocol for demineralization. The microhardness of the teeth was measured again, and the percentage of change in microhardness was calculated. The amount of calcium released during pH cycling was quantified using atomic absorption spectroscopy. Data were analyzed using one-way ANOVA and Tukey’s test.

Results:

Calcium release (indicative of demineralization) in the Gf, Gfl, and Glf groups was significantly lower than that in the Gc and Gl groups (P<0.05). The reduction in surface microhardness was also the same in the five groups with no significant difference (P>0.05).

Conclusion:

Fluoride mouthwash combined with Er:YAG laser or Er:YAG laser alone cannot decrease the incidence of WSLs around orthodontic brackets compared to fluoride mouthwash alone.

Caries inhibition with CO2-laser during orthodontic treatment: a study protocol for a randomized split-mouth controlled clinical trial

Introduction

White spot lesions associated with orthodontic treatment are a common problem. Recent studies reported increased resistance to acid demineralization of enamel after sub-ablative CO₂-laser irradiation in a combination with fluoride application. The aim of the study is to assess the efficacy of CO₂-laser in combination with a fluoride varnish in the prevention, severity, and extent of white spot lesions during orthodontic treatment with fixed appliances.

Methods and analysis

This is a protocol for a randomized, split-mouth controlled, clinical trial. The participants will be children aged 12–18 years at high caries risk, requiring fixed orthodontic treatment. The vestibular surfaces of maxillary anterior teeth of eligible patients will be exposed to CO₂-laser irradiation in combination with fluoride therapy and fluoride therapy alone followed by bonding of orthodontic brackets. The patients will be recalled 6 and 12 months post-irradiation. Outcome measures will be visual examination with International Caries Detection and Assessment System criteria and SoproLife fluorescence. Data will be analyzed by Student’s t test for paired samples and proportional odds logistic regression model, p<0.05.

Ethics and dissemination

The study protocol has been approved by the Committee for Scientific Research Ethics, Medical University-Plovdiv, Bulgaria (Reference number P-605/27.03.2020, Protocol of approval No. 2/01.04.2021) and registered on a publicly accessible database. This research received institutional funding from the Medical University–Plovdiv, Bulgaria. The results will be presented through peer-reviewed publications and conference presentations.

Trial registration

ClinicalTrials.gov NCT04903275. Registered on June 2021.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06117-y.

In situ effect of CO2 laser (9.3 μm) irradiation, combined with AmF/NaF/SnCl2 solution in prevention and control of erosive tooth wear in human enamel

OBJECTIVES

This single-blind, controlled cross-over in situ study aimed to evaluate the effect of CO2 laser (9.3µm) irradiation, combined with AmF/NaF/SnCl2 solution on prevention and control of Erosive Tooth Wear (ETW) in human enamel.

MATERIALS AND METHODS

Two trial conditions were analyzed, Condition-1 as ETW-prevention (sound tooth surface) and Condition-2 as ETW-control (in vitro initial erosive lesion). The experiment was conducted in two phases, one with one without exposure to AmF/NaF/SnCl2 solution. A hundred and ninety-two samples of human enamel (3x3x1mm) were randomly divided into 4 experimental groups for each condition: (C) without treatment (negative control); (F) AmF/NaF/SnCl2 solution (positive control); (L) CO2 laser irradiation; (L+F) CO2 laser+AmF/NaF/SnCl2 solution. Twelve volunteers used a removable device each containing 8 samples per phase. Ex-vivo erosive challenges (4×5min/day) and rinsing protocol (1×30s/day) were performed. The surface loss was determined using optical profilometer (n=12 per group), and the surface morphology was observed with Scanning Electron Microscopy (n=3).

RESULTS

Condition-1 data were analyzed by one-way ANOVA and Condition-2 by two-way repeated measures ANOVA, both with Tukey post-hoc tests (α=5%). Condition-1: groups L (4.59 ±2.95µm) and L+F (1.58 ±1.24µm) showed significantly less surface loss in preventing ETW than groups C and F. Condition-2: in controlling the progression of ETW, L+F was the only group with no significant surface loss between initial erosive lesion (3.65 ±0.16µm) and after erosive challenge (4.99 ±1.17µm).

CONCLUSIONS

CO2 9.3µm laser application prevented and controlled ETW progression in human enamel, with greater efficiency when combined with AmF/NaF/SnCl2 solution application.

Effect of Er:YAG Laser Irradiation and Acidulated Phosphate Fluoride Therapy on Re-Mineralization of White Spot Lesions

Statement of the Problem:

Studies on the efficacy of erbium laser for enhancement of enamel resistance to acid attacks and its effects on fluoride uptake by the enamel are limited.

Purpose:

This study sought to assess and compare the effects of erbium-doped yttrium aluminum garnet (Er:YAG) laser irradiation and application of acidulated phosphate fluoride (APF) gel (alone and in combination) on remineralization of artificial white spot lesions (WSLs).

Materials and Method:

This in vitro, experimental study evaluated 90 buccal and lingual slabs of extracted human premolars. The specimens underwent pH cycling to induce WSLs. They were then randomly divided into 6 groups of caries-free positive control (c+), negative control with WSLs (ws), 1.23% APF gel applied on the enamel (F), Er:YAG laser irradiation (80 mJ, 10 Hz, and 8 J/cm²) of enamel (L), APF gel application followed by laser irradiation (FL), and laser irradiation followed by fluoride gel application (LF). The fluoride ion content of specimens was measured before and after the intervention using a potentiometer. Data were analyzed by ANOVA (p< 0.05).

Results:

APF gel application before/after laser irradiation maximally increased the fluoride uptake by the enamel (p= 0.000). Application of APF gel in group F and laser irradiation in group L increased fluoride uptake by the enamel, compared with groups 1 and 2 (p= 0.000). Laser- treated (L) and APF-treated (F) groups had no significant difference in this respect (p= 0.945). Maximum fluoride concentration was noted in combined laser and fluoride groups (FL=332.07ppm and LF=341.27ppm) with no significant difference between the two (p= 1.000).

Conclusion:

Er:YAG laser irradiation changes the chemical composition of enamel and probably promote its remineralization, especially when combined with APF gel application, which highlights its cariostatic potential.

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.

Effect of Erbium:Yttrium-Aluminum-Garnet Laser Combined with Mineralizing Agents on Microhardness of Demineralized Dentin

Objective The aim of this study was to assess the combined effect of erbium:yttrium-aluminum-garnet (Er:YAG) laser and mineralizing agents including casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and fluoride in improving the resistance of demineralized dentin at new demineralization process.

Materials and Methods One hundred and twenty healthy dentin surfaces were prepared and demineralized using acidic solutions. Primary microhardness was measured (h1), and samples were randomly divided into six groups. Each group received a different protocol as follows: Group A (control group): no additional treatment, Group B: applying a fluoridated gel, Group C: applying a CPP-ACP-containing cream, Group D: irradiation of Er:YAG laser, Group E: irradiation of Er:YAG laser combined with the application of a fluoridated agent, and Group F: irradiation of Er:YAG laser combined with the application of CPP-ACP-containing cream. Microhardness values were measured afterward (h2). Then, all the groups were re-exposed to acidic solution, and microhardness was measured for the third time (h3). The microhardness data were analyzed using analysis of variance and Scheffe's post hoc test.

Results Although application of mineralizing agents increased the microhardness of demineralized dentin in comparison with the control group, no significant difference was observed using two agents. Comparison of laser groups showed an increase in microhardness only after the irradiation of Er:YAG laser combined with the application of a fluoridated agent. Demineralizing process reduced the microhardness values in all the groups, but the application of a CPP-ACP agent caused the least reduction among the laser irradiated groups. Comparison of hardness changes at the beginning and end of the experiment did not show any significant differences between the groups.

Conclusion Comparison of treatment modalities used in this study exhibited that fluoride had the greatest impact on dentin resistance. Laser irradiation on demineralized dentin did not increase the hardness or resistance to acidic attacks.

Non-contact profilometry of eroded and abraded enamel irradiated with an Er:YAG laser

Literature has reported positive results regarding the use of lasers in the control of erosive lesions; however, evaluating whether they are effective in the control of the progression of erosive/abrasive lesions is important.

Effect of CO2 Laser and Fluoride Varnish Application on Microhardness of Enamel Surface Around Orthodontic Brackets

Introduction: Orthodontic treatment has many advantages such as esthetic improvement and self-esteem enhancement; yet it has some disadvantages such as increasing the risk of formation of white spot lesions, because it makes oral hygiene more difficult. It is rational to implement procedures to prevent these lesions. The present study was aimed to assess the effect of CO₂ laser and fluoride varnish on the surface of the enamel surface microhardness around the orthodontic braces. Methods: Eighty extracted premolar teeth were selected, scaled, polished with nonfluoridated pumic and metal brackets were bonded to them. Then, they were randomly allocated to 5 groups: control (neither fluoride nor laser is used on enamel surfaces), fluoride (4 minutes fluoride varnish treatment of the enamel surfaces), CO₂ laser (10.6 µm CO₂ laser irradiation of the teeth), laserfluoride (fluoride application after laser irradiation) and fluoride-laser (fluoride was applied and then teeth were irradiated with laser). After surface treatment around brackets on enamel, the samples were stored in 0.1% thymol for less than 5 days and then they were exposed to a 10-day microbiological caries model. Microhardness values of enamel were evaluated with Vickers test. One sample of each group (5 teeth from 80 samples) was prepared for SEM (scanning electron microscopy) and the data from 75 remaining teeth were analyzed with analysis of variance (ANOVA) and chi-square tests (α =0.05). Results: Microhardness mean values from high to low were as follow: fluoride-laser, laser-fluoride, laser, fluoride and control. Microhardness in fluoride-laser group was significantly higher compared with that of the control group. Distribution adhesive remnant index (ARI) scores were significantly different between groups and most of bond failures occurred at the enamel-adhesive interface in groups 2 to 5 and at the adhesive-bracket interface in the control group. Conclusion: Combination of fluoride varnish and CO2 laser irradiation can reduce enamel demineralization around orthodontic brackets.

In Vitro Comparison Of Fluoride Gel Alone and in Combination With Er,Cr:YSGG Laser on Reducing White Spot Lesions in Primary Teeth

Introduction: Laser therapy has been suggested as a method for caries-prevention, and ErCr:YSGG laser is increasingly used in dentistry. This study aimed to compare the efficacy of fluoride gel alone and in conjunction with Er,Cr:YSGG laser for remineralization of white spot lesions (WSLs) in primary teeth. Methods: This study was conducted on 20 primary teeth with WSLs extracted for orthodontic reasons. Three sections were made of each tooth at the site of WSLs. The surface area of WSLs was measured under a stereomicroscope at ×25 magnification. Samples were assigned to 3 groups of control (group 1), exposure to 1.23% APF gel for 4 minutes (group 2) and Er,Cr:YSGG laser (0.5 W power, 20 Hz frequency, 60% water, 40% air, pulse duration of 5±1 seconds) plus fluoride (group 3). All samples were stored in artificial saliva for 10 days and then the surface area of the WSLs was measured again under a stereomicroscope. Data were analyzed using the Kruskal-Wallis, MannWhitney and Wilcoxon signed rank tests. Results: The reduction in surface area of the WSLs was significantly different between the control and fluoride (P<0.001) and also the control and laser plus fluoride groups (P<0.001); the difference between fluoride and laser plus fluoride groups was not significant (P=0.265). Comparison of the surface area of WSLs before and after the intervention showed no significant difference in group one (P=0.737) while this difference in groups 2 (P<0.001) and 3 (P<0.001) was statistically significant. Conclusion: The results showed that Er,Cr:YSGG laser irradiation plus 1.23% APF gel was not significantly different from the application of fluoride gel alone in enhancing the remineralization of WSLs.

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.

Effect of silver diamine fluoride and ammonium hexafluorosilicate applications with and without Er:YAG laser irradiation on the microtensile bond strength in sound and caries-affected dentin

BACKGROUND AND OBJECTIVE

Cariostatic and preventive agents are applied to create caries-resistant dentin surfaces and may affect subsequent resin bonding. The aim of this study was to investigate the effect of different agents with and without Er:YAG laser irradiation on the microtensile bond strength (µTBS) of resin composite to sound dentin (SD) and caries-affected dentin (CAD), and to assess the morphological and chemical changes in the specimens.

MATERIALS AND METHODS

Ninety-six extracted molar teeth were divided into a control group (deionized water) and two experimental groups (ammonium hexafluorosilicate [SiF], silver diamine fluoride [SDF]), that subdivided according to different conditions (SD, CAD, SD+laser irradiation, CAD+laser irradiation). After treatment procedures, the teeth were restored and the µTBS was tested with a universal testing machine. Morover, 144 teeth were prepared and after treatment modalities; morphological changes of the surface were investigated and elemental analyses were performed using scanning electron microscope/energy dispersive spectroscopy (SEM-EDS). The data were analyzed using Kruskal-Wallis and Mann-Whitney U tests.

RESULTS

SDF and SiF applications reduced the µTBS values in both the SD and CAD subgroups (P < 0.05). Laser irradiation increased the µTBS values in the SiF group and the values were adversely affected in the SDF group (P < 0.05). Fluoride content of the specimens increased in all of the treatment groups, compared with the control group. Silver content was detected only in the SDF group, and silicon was detected only in the SiF group.

CONCLUSIONS

The µTBS values of resin composite, surface morphology and chemical characteristics of dentin were affected by the material type, dentin condition and laser irradiation and the use of SiF and SDF solutions under the resin restorations do not seem appropriate.

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.

In situ study of the anticariogenic potential of fluoride varnish combined with CO2 laser on enamel

OBJECTIVE

This in situ study evaluated the effect of fluoride varnish combined with CO2 laser in controlling enamel demineralization caused by cariogenic challenges.

DESIGN

In a crossover study conducted in 2 phases of 14 days each, 14 volunteers (n = 14) wore palatal appliances with bovine enamel slabs treated with fluoride varnish + CO2 laser (FV + CO2), fluoride varnish (FV), nonfluoride placebo varnish (PV) and nonfluoride placebo varnish + CO2 laser (PV + CO2). Drops of sucrose solution were dripped onto enamel slabs allowing the accumulation of biofilm. At the first phase, half of the volunteers received 4 enamel slabs treated with FV while the remainders received slabs exposed to the PV with and without CO2 laser. In the second phase, the vonlunteers were reversed treatments. The slabs were evaluated for cross-sectional microhardness (CSMH) and the concentration of loosely bound fluoride (CaF2) and firmly bound fluoride (FAp). The concentration of fluoride in biofilm were also determined.

RESULTS

Two-way ANOVA showed that the CSMH values were higher in laser-irradiated enamel, regardless of the fluoride varnish. Friedman test showed that FV group presented significantly larger amount of fluoride in biofilm (P < 0.05). In the enamel, the largest amount of fluoride was found in the groups FV + CO2, which was not different from FV (P > 0.05).

CONCLUSION

The synergistic effect of fluoride varnish and CO2 laser on enamel demineralization was not observed, however, CO2 laser reduces enamel demineralization.

CLINICAL SIGNIFICANCE

CO2 laser might reduce the demineralization of subsurface enamel, although its association with a high concentrated fluoride therapy may not result in a positive synergistic interaction.

Effects of diode laser therapy and stannous fluoride on dentin resistance under different erosive acid attacks

OBJECTIVE

This in vitro study aimed to evaluate the effect of a low intensity diode laser (λ=808 nm; 60 J/cm2) associated with stannous fluoride on the inhibition of dentin erosion by assessing percentage of superficial hardness loss (%SHL) and calcium release into the acid solution.

MATERIALS AND METHODS

Human root dentin slabs were assigned to eight groups (n=10), according to treatments (control, stannous fluoride, diode laser therapy, and the combination of stannous fluoride and laser therapy), and acid challenge (hydrochloridric or citric acid). All slabs were subjected to a previous 2 h acquired pellicle formation; laser and fluoride treatments were performed according to the groups. Subsequently, the slabs were exposed to erosive challenge (0.01 M hydrochloridric acid or citric acid 1% for 60 sec). Additionally, calcium released into the acid solution during erosive challenge was analyzed by photometric test. Data were analyzed by ANOVA followed by Tukey's test (p<0.05).

RESULTS

Mean values (±SD) for %SHL of treated groups did not present statistically significant differences, regardless of the erosive challenge. However, in relation to released calcium concentration, groups treated with laser presented statistically significant lower calcium loss under hydrochloridric acid challenge (p<0.001). To groups under citric acid attack, only the combination of treatments (p=0.037) was able to show a protective effect on dentin.

CONCLUSIONS

Under the conditions of this study, 808 nm diode laser with or without stannous fluoride could effectively reduce dentin surface loss under both acid exposures. Only calcium concentration analysis was sensitive enough to measure the effects under the tested conditions.

Topical Laser Application Enhances Enamel Fluoride Uptake and Tribological Properties

Topical fluoride treatment prevents dental caries. However, the resulting calcium-fluoride-like deposits are soft and have poor wear resistance; therefore, frequent treatment is required. Lasers quickly heat surfaces and can be made portable and suitable for oral remedies. We examined the morphology, nanohardness, elastic modulus, nanowear, and fluoride uptake of fluoride-treated enamel followed by CO2 laser irradiation for 5 and 10 sec, respectively. We found that laser treatments significantly increased the mechanical properties of the calcium-fluoride-like deposits. The wear resistance of the calcium-fluoride-like deposits improved about 34% after laser irradiation for 5 sec and about 40% following irradiation for 10 sec. We also found that laser treatments increased fluoride uptake by at least 23%. Overall, laser treatment significantly improved fluoride incorporation into dental tissue and the wear resistance of the protective calcium-fluoride layer.

Prevention of dentine caries using silver diamine fluoride application followed by Er:YAG laser irradiation: an in vitro study

To evaluate the preventive effect of Er:YAG laser (EYL) irradiation followed by silver diamine fluoride (SDF) application on dentine with cariogenic biofilm challenge. Twenty-four dentine slices were prepared from extracted sound human third molars. Each slice was cut into four parts for SDF application, followed by EYL irradiation (group SL), SDF application (group S), EYL irradiation (group L) and water (group W). The specimens were subjected to cariogenic biofilm challenge for 12 h, followed by immersion in a buffered remineralising solution containing calcium chloride and sodium hypophosphate for 12 h at 37 °C. Surface morphological changes in the specimens were examined using scanning electronic microscopy. Elemental analysis was performed using energy-dispersive X-ray spectrometry. Micro-mechanical properties were investigated by nano-indentation. The specimen surfaces of groups SL and L showed laser melting contours with narrowed dentinal orifices. Group S showed a partial tubular occlusion. A porous surface was observed in group W, indicating demineralisation. The mean (SD) fluoride weight percentages were 3.93 (0.91), 3.10 (0.61), 0.17 (0.09) and 0.32 (0.07) in groups SL, S, L and W, respectively, (p < 0.001; SL, S > L, W). The mean (SD) micro-hardness values in GPa were 1.84 (0.22), 0.49 (0.13), 0.41 (0.11) and 0.30 (0.06) in groups SL, S, L and W, respectively, (p < 0.001; SL > S > L, W). The mean (SD) elastic moduli in GPa were 75.1 (7.2), 20.0 (1.3), 24.3 (5.2) and 20.2 (2.8) in groups SL, S, L and W, respectively, (p < 0.001; SL > S, L, W). SDF application followed by EYL irradiation on a dentine surface increased its resistance to cariogenic biofilm challenge.

The effect of fractional CO2 laser irradiation on remineralization of enamel white spot lesions

This study investigated the combined effect of fractional CO(2) laser irradiation and fluoride on treatment of enamel caries. Sixty intact premolars were randomly assigned into four groups and then stored in a demineralizing solution to induce white spot lesions. Tooth color was determined at baseline (T1) and after demineralization (T2). Afterwards, the teeth in group 1 remained untreated (control), while group 2 was exposed to an acidulated phosphate fluoride (APF) gel for 4 min. In groups 3 and 4, a fractional CO(2) laser was applied (10 mJ, 200 Hz, 10 s) either before (group 3) or through (group 4) the APF gel. The teeth were then immersed in artificial saliva for 90 days while subjected to daily fluoride mouthrinse and weekly brushing. Color examinations were repeated after topical fluoride application (T3) and 90 days later (T4). Finally, the teeth were sectioned, and microhardness was measured at the enamel surface and at 30 and 60 μ from the surface. In both lased groups, the color change between T1 and T4 stages (∆E(T1-T4)) was significantly lower than those of the other groups (p < 0.05). Laser irradiation followed by fluoride application (group 3) caused a significant increase in surface microhardness compared to APF alone and control groups (p < 0.05). Microhardness at depths of 30 and 60 μ was also significantly greater in group 3 compared to those of all other groups (p < 0.05). Application of a fractional CO(2) laser before fluoride therapy is suggested for recovering the color and rehardening of demineralized enamel.

Potential Mechanism for the Laser-Fluoride Effect on Enamel Demineralization

Laser-induced prevention of dental caries has been studied extensively. However, the cariostatic mechanisms of a combined fluoride-laser treatment are not well-understood. Using micro- computed tomography (micro-CT), we quantified the effect of fluoride and/or Er:YAG laser treatment on enamel demineralization. The mean mineral loss (%/V) for each group was 4,870 ± 1,434 (fluoride followed by laser treatment), 6,341 ± 2,204 (laser treatment), 7,669 ± 2,255 (fluoride treatment), and 10,779 ± 2,936 (control). The preventive effect of the laser ( p < 0.001) and fluoride ( p = 0.010) treatment was statistically significant. Characterized by micro-x-ray diffraction (XRD) analysis, the significant contraction in the a-axis after both laser and combined laser/fluoride treatment was revealed (both p < 0.05). In conclusion, subablative low-energy Er:YAG laser irradiation following fluoride treatment may instantaneously transform enamel hydroxyapatite into fluoridated hydroxyapatite to reduce enamel solubility as a preventive treatment for enamel demineralization.

Prevention of toothbrushing abrasion of acid-softened enamel by CO(2) laser irradiation

OBJECTIVE

The aim of the present study was to evaluate the effect of CO(2) laser irradiation (10.6μm) at 0.3J/cm(2) (0.5μs; 226Hz) on the resistance of softened enamel to toothbrushing abrasion, in vitro.

METHODS

Sixty human enamel samples were obtained, polished with silicon carbide papers and randomly divided into five groups (n=12), receiving 5 different surface treatments: laser irradiation (L), fluoride (AmF/NaF gel) application (F), laser prior to fluoride (LF), fluoride prior to laser (FL), non-treated control (C). After surface treatment they were submitted to a 25-day erosive-abrasive cycle in 100ml sprite light (90s) and brushed twice daily with an electric toothbrush. Between the demineralization periods samples were immersed in supersaturated mineral solution. At the end of the experiments enamel surface loss was determined using a contact profilometer and morphological analysis was performed using scanning electron microscopy (SEM). For SEM analysis of demineralization pattern, cross-sectional cuts of cycled samples were prepared. The data were statistically analysed by one-way ANOVA model with subsequent pairwise comparison of treatments.

RESULTS

Abrasive surface loss was significantly lower in all laser groups compared to both control and fluoride groups (p<0.0001 in all cases). Amongst the laser groups no significant difference was observed. Softened enamel layer underneath lesions was less pronounced in laser-irradiated samples.

CONCLUSION

Irradiation of dental enamel with a CO(2) laser at 0.3J/cm(2) (5μs, 226Hz) either alone or in combination with amine fluoride gel significantly decreases toothbrushing abrasion of softened-enamel, in vitro.

Effect of a pulsed CO2 laser and fluoride on the prevention of enamel and dentine erosion

OBJECTIVE

The hypotheses of this study was that pulsed CO(2) laser (lambda=10.6 microm) treatment in combination (or not) with previous fluoride gel application could increase the resistance of enamel and dentine to erosion, throughout successive erosive challenges.

DESIGN

Thirty-two bovine specimens of enamel and of root dentine were flattened, polished and randomly assigned to the following treatments (n=8): fluoride (F), laser (L), fluoride+laser (FL) or no treatment as negative control (C). The treated specimens were submitted to demineralization (0.3% citric acid, pH 2.45, for 5 min) and remineralization (artificial saliva, for 60 min) cycles, three times a day, for 3 days. Dental surface loss as well as the concentration of calcium, phosphorus and fluoride in the demineralizing solutions were determined after each cycling day. Enamel and dentine were analysed separately using repeated measures ANOVA for ranks (alpha=0.05).

RESULTS

The association between fluoride and laser (FL) resulted in the lowest enamel and dentine surface loss values throughout the cycles, differing significantly from the control group. No clear benefit of FL over the F or L treatments was observed. There was a non-significant trend (p>0.05) for FL to release less calcium, phosphorus and fluoride into the demineralizing solutions when compared to the other groups.

CONCLUSIONS

Pulsed CO(2) laser (lambda=10.6 microm) alone was not able to prevent enamel or dentine surface losses due to erosion. Laser treatment in combination with fluoride showed some protection, but the effect does not appear to be synergistic.

Near-infrared hyperspectral imaging of teeth for dental caries detection

Near-infrared (NIR) is preferred for caries detection compared to visible light imaging because it exhibits low absorption by stain and deeper penetration into teeth. Hyperspectral images from 1000 to 2500 nm have been obtained for a total of 12 extracted teeth (premolars and molars) with different degrees of natural lesion. Analysis of the reflectance spectra suggests that light scattering by porous enamel and absorption by water in dentin can be used to quantify the lesion severity and generate a NIR caries score. Teeth were ground for histological examination after the measurements. The NIR caries score obtained correlates significantly (Spearman's correlation of 0.89, p<0.01) with the corresponding histological score. Results yield a sensitivity of >99% and a specificity of 87.5% for enamel lesions and a sensitivity of 80% and a specificity >99% for dentine lesions. The nature of the technique offers significant advantages, including the ability to map the lesion distribution rather than obtaining single-point measurements, it is also noninvasive, noncontact, and stain insensitive. These results suggest that NIR spectral imaging is a potential clinical technique for quantitative caries diagnosis and can determine the presence of occlusal enamel and dentin lesions.

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

OBJECTIVE

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

BACKGROUND DATA

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Effects of low power red laser on induced-dental caries in rats

OBJECTIVE

The purpose of this study was to investigate the effects of low power red laser associated with acidulated phosphate fluoride on the development of induced-dental caries in rats.

DESIGN

Dental caries were induced in molars of 40 rats divided into five groups: control group (CG), the teeth were not submitted to any treatment; laser group (LG), teeth were irradiated with a low power red laser (LPRL), power of 30 mW and dose of 5 J/cm(2); fluoride group (FG), teeth were treated with topical acidulated phosphate fluoride (APF) 1.23% applied for 4 min; laser+fluoride group (LFG), teeth were irradiated with LPRL followed by APF; fluoride+laser group (FLG), teeth were treated with APF followed by LPRL. The animals were killed after 48 days, and the first and second molars were extracted to analyze the caries lesion area, microhardness, and calcium and phosphorus ratio.

RESULTS

There were no statistical differences among FG, LFG, and FLG regarding to caries area and microhardness, although the caries area were smaller in LFG. Ca/P ratio did not show significant differences among all groups.

CONCLUSIONS

Although LPRL before APF application appeared to diminish the caries progression, LPRL did not present any additional benefit compared with acidulated phosphate fluoride on the prevention of induced-dental caries in rats.

Laser-induced compositional changes on enamel: A FT-Raman study

Preventive effects of lasers on enamel caries have been documented in the past few decades. However, its specific mechanism remains uncertain.

OBJECTIVES

To evaluate the laser-induced change of enamel compositions, including carbonate and organic matters using Fourier-transform Raman spectroscopy (FT-Raman).

METHODS

Twelve windows (1 mm x 1 mm), created on six defect-free primary incisors, were characterized by FT-Raman microscopy (1024 nm) before and after Er:YAG laser treatment (Fidelis) with 5.1 J/cm(2)-2 Hz-5s. To assess the statistical significance of laser effects, Raman peaks assigned to nu(1) phosphate, type-A/B carbonates, and organic matters were evaluated with the paired-samples t-test.

RESULTS

The standardized intensity of type B carbonate decreased significantly from 0.117 to 0.106 (p=0.029), whereas the standardized intensity of carbonate A remained unchanged (p=0.467). Related to organic matters, the standardized intensity of peaks at 2940 cm(-1) and in the ranges of 1200-1600 cm(-1) decreased significantly, with p=0.005 and p<0.001, respectively. Revealing enamel crystallinity, the bandwidth of nu(1) phosphate on lased surfaces appeared to be unaltered after laser treatment (p=0.477).

CONCLUSIONS

Laser treatment may provide caries-preventive effect on enamel through reduction of carbonate and modification of organic matters.

Increased fluoride uptake in human dental specimens treated with diode laser

The hypothesis of this study was the fact that diode lasers can increase the fluoride uptake in dental structures. The main objectives were: (1) to evaluate the effect of diode laser-NaF varnish combination on binding fluoride to dental enamel in an in vitro model and (2) to analyse outer enamel surface changes produced by the laser energy. After NaF enamel varnish and laser irradiation at different levels of energy, specimen surfaces were examined by environmental scanning electron microscopy. The incorporation of F(-) ion into the dental structure was quantitatively determined by using a fluoride ion-selective electrode. Results showed that the laser treatment significantly increased the binding of fluoride to the enamel surface without damaging it. The amount of F(-) estimated was 37 +/- 7 mg/l to the power of 5 W and 58 +/- 12 mg/l to the power of 7 W. These increases were significantly greater than the ones achieved by conventional topical fluoridation. The results were analysed and compared by Kruskal-Wallis and Dunn's multiple comparison tests, and significant statistical differences were found. These suggest that the NaF varnish-diode laser combination may be a useful option for the effective fluoridation of teeth.

Laser-fluoride effect on root demineralization

Although the individual cariostatic effects of laser and fluoride have been shown, the combined effect of CO(2) laser and fluoride on root demineralization remains uncertain and was the main aim of this study. By using a pH-cycling system and Polarized Light Microscopy, we demonstrated the synergistic effect of fluoride combined with CO(2) laser treatment on reducing root demineralization. The mean lesion depths (in microm) for each group were 160 +/- 14 (Control), 113 +/- 8 (Laser treatment alone), 111 +/- 6 (Fluoride treatment alone), and 25 +/- 7 (Fluoride followed by laser treatment). A significant laser-enhanced fluoride uptake, characterized by the ToF-SIMS analysis, was revealed by the 37% and 400% increments in loosely and firmly bound fluorides (both p < 0.002) in laser-irradiated areas, compared with the non-irradiated controls. In conclusion, there is a significant synergistic effect of combined CO(2) laser and fluoride treatment on the inhibition of root demineralization, possibly due to laser-enhanced fluoride uptake in the root.

Increased fluoride uptake and acid resistance by CO2 laser-irradiation through topically applied fluoride on human enamel in vitro

OBJECTIVES

The aim of the current in vitro study was to evaluate the effect of CO(2)-laser treatment immediately after applying amine fluoride solution on enamel. It was hypothesized that such a treatment would increase enamel fluoride uptake, and reduce dissolution rate and thermal surface alterations.

METHODS

Fluoride uptake was determined in 40 human enamel sections randomly assigned to four groups (n=10), which were either left untreated (1), exposed to a 1% amine fluoride solution for 15s without irradiation (2), irradiated for 15s with a continuous-wave carbon dioxide laser (3), or laser-treated for 15s through the amine fluoride solution applied immediately beforehand (4). Fluoride uptake was determined with an ion selective electrode after acid dissolution of the specimens (surface and subsurface layers). For the determination of acid resistance, another 40 enamel sections were treated according to the above protocol. Acid resistance was determined in surface and subsurface layers by measuring eluted calcium upon 3% lactic acid exposure with atomic absorption spectrometry. Enamel surface alterations after laser irradiation were monitored using scanning electron microscopy.

RESULTS

Laser irradiation through the fluoride solution led to significantly higher fluoride contents in the surface enamel layer compared to fluoride treatment alone or laser treatment alone (p=0.002). Laser treatment with or without fluoride resulted in an increased acid resistance of enamel specimens. Fewer surface alterations were observed upon SEM examination of specimens irradiated through the amine fluoride solution compared to counterparts treated with laser only.

CONCLUSIONS

CO(2) laser light application through an amine fluoride solution may be useful and effective in the prevention of caries.