CO2 laser irradiation enhances CaF2 formation and inhibits lesion progression on demineralized dental enamel—in vitro study

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.

The Effect of a Bioactive Oral System and CO2 Laser on Enamel Susceptibility to Acid Challenge

This study evaluated the structural changes of enamel treated by the Regenerate system and carbon dioxide (CO2) laser against acid challenge. Thirty human enamel slabs were prepared and assigned into three groups: Group I: untreated (control); Group II: treated with the Regenerate system; and Group III exposed to CO2 laser. All specimens were subjected to an acid challenge (pH 4.5–7.0) for 14 days. Specimens were evaluated and compared at 120 points using five Raman microspectroscopic peaks; the phosphate vibrations ν1, ν2, ν3, and ν4 at 960, 433, 1029, and 579 cm−1, respectively, and the carbonate at 1070 cm−1, followed by Vickers microhardness test. The ratio of carbonate to phosphate was correlated to the equivalent microhardness numbers. The intensities of phosphate peaks ν1, ν2, and ν4 were reduced in all groups post-acid challenge, while the carbonate and ν3 were significantly increased (p < 0.000). Surfaces treated by Regenerate exhibited higher peak intensity of phosphate and carbonate before and after pH-cycling (p < 0.05). The mineral content in enamel had a direct effect on tissue microhardness, and the CO2-lased surfaces showed a reduced carbonate content and higher microhardness values. Both approaches induced surface changes that can protect enamel against acid challenge resulting in a significant benefit for dental healthcare.

Ex-vivo effects of propolis quantum dots-nisin-nanoquercetin-mediated photodynamic therapy on Streptococcus mutans biofilms and white spot lesions

BACKGROUND

White spot lesions (WSLs) remain one of the most critical adverse sequelae of fixed orthodontic treatment, despite materials and techniques advances in orthodontics. WSLs seem to be a multi-factorial interaction including increased microbial plaque due to intrabuccal appliances that limit the oral-cleansing mechanism and change in the oral microbiome during fixed appliance wear. The aim of this study was to investigate the synergistic effect of propolis quantum dots (PQD), nisin (Nis), and quercetin nanoparticles (nQCT)-mediated photodynamic therapy (PQD-Nis-nQCT-mediated aPDT) in the eradication of Streptococcus mutans biofilms and the remineralization of WSLs ex-vivo.

MATERIALS AND METHODS

The cytotoxicity of PQD-Nis-nQCT composite on human gingival fibroblasts was evaluated using neutral red. Intracellular reactive oxygen species (ROS) generation following PQD-Nis-nQCT-mediated aPDT was measured. Enamel slabs were prepared and demineralized using a demineralization solution containing S. mutans. Demineralized enamel slabs were divided into 9 groups (n = 10) and treated in the following groups: 1) Artificial saliva (negative control), 2) 2% neutral sodium fluoride gel (NSF; positive control or treatment control, 3) PQD, 4) Nis, 5) nQCT, 6) Nis-nQCT, 7) PQD-Nis-nQCT 8) Blue laser irradiation (light), 9) PQD-Nis-nQCT with irradiation (PQD-Nis-nQCT-mediated aPDT). Then, the surface changes, microhardness, and surface topography of the demineralized slabs were examined following each treatment using DIAGNOdent Pen reading, digital hardness tester, and SEM, respectively. After the determination of minimum biofilm eradication concentration (MBEC) of PQD, Nis, and nQCT by microtiter plate assay, the synergistic antimicrobial effects of PQD and Nis-nQCT were determined via evaluation of fractional biofilm eradication concentration (FBEC) index. The anti-biofilm effects of each treatment on S. mutans were assessed using a colorimetric assay. The virulence‑associated gtfB gene expression was assessed following PQD-Nis-nQCT-mediated aPDT by quantitative real‑time PCR.

RESULTS

PQD-Nis-nQCT at 2048 µg/mL had no significant cell cytotoxicity on human gingival fibroblasts compared to the control group (P > 0.05). A significantly increased (7.6 fold) in intracellular ROS was observed following PQD-Nis-nQCT-mediated aPDT (13.9 ± 1.41) when compared to the control (1.83 ± 0.13). Following each treatment, the microhardness of the demineralized enamel surface significantly increased except for the artificial saliva (negative) and blue laser irradiation groups. The highest change in microhardness improvement was detected in the PQD-Nis-nQCT-mediated aPDT group (P < 0.05). Also, DIAGNODent Pen reading revealed the highest significant improved change in the level of mineralization degree in the PQD-Nis-nQCT-mediated aPDT group. Nis and blue light irradiation groups, like the artificial saliva-treated demineralized enamel slabs (control group), did not lead to remineralization (P > 0.05). Also, the PQD-Nis-nQCT-mediated aPDT treatment results obtained from SEM revealed that remineralization of demineralized enamel slabs in that group has significantly improved compared to the others. Light-activated nQCT, PQD, Nis-nQCT, and PQD-Nis-nQCT composite significantly reduced pre-formed biofilms of S. mutans compared with unactivated forms of test materials. The relative expression level of the virulence gtfB gene was significantly decreased (7.53-fold) in the presence of PQD-Nis-nQCT-mediated aPDT (P < 0.05).

CONCLUSION

PQD-Nis-nQCT-mediated aPDT can be used for the eradication of S. mutans biofilms and remineralization of WSLs. The found in vitro efficacy should be tested further through clinical studies.

Human Enamel Fluorination Enhancement by Photodynamic Laser Treatment

Poor oral hygiene leads to serious damages of theteeth’s surface enamel such as micro-abrasions and acid erosion. These alterations combined with bacterial plaque result in cavity appearance. Prophylactic measures include various techniques for enamel surface restoration. Fluorination is one of the most important treatments for this purpose. Therefore, in the present research, we investigated the classical fluorination treatment compared with laser photodynamic fluorination performed on human enamel samples with poor surface quality. Three sample groups were investigated: veneer (F), inlay (I), and crowns (C). The general morphologic aspect was investigated by scanning electron microscopy (SEM), and the specific details such as the fine microstructure and nanostructure were investigated by atomic force microscopy (AFM) of the surface roughness. The samples were also investigated by Fourier transformed infrared attenuated total reflectance (FTIR-ATR) to evidence the fluorination effect on the enamel surface. Results showed that all initial samples had an altered state with micro-abrasions and erosion with mineral loss, which increase the surface roughness. The F group was the most damaged, having a higher roughness, and the I group was less damaged. Classic fluorination treatment partially restored the enamel by local re-mineralization, but did not obtain the parameters of healthy enamel. However, a significant decrease of the roughness was observed (statistical relevance p = 0.001 with the Breusch–Pagan Test). This fact was supported by the presence of newly formed fluorides in the FTIR-ATR spectra. The photodynamic laser fluorination restores the enamel in an enhanced manner by a strong re-mineralization, which implies a significant roughness value decrease comparable to healthy enamel. The Breusch–Pagan Test confirmed the relevance with p = 0.001. This is due to an extended re-mineralization abundant in fluoride crystals as observed by AFM and FTIR. Statistical p-values regarding laser application were in the range of 0.02–0.06, supporting its relevance in the fluorination effect. The final conclusion is that the photodynamic effect is able to favor the newly formed fluoride deposition onto the affected sites of the enamel surface.

The effects of combining erbium, chromium: Yttrium-scandium-gallium-garnet laser irradiation with fluoride application in controlling the progression of enamel erosion

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Fluoride alone increased the microhardness of the enamel surface.

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Fluoride alone halted the progression of enamel erosion.

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Laser irradiation before fluoride-induced similar effects as fluoride alone.

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Laser irradiation alone did not prevent the progression of enamel erosion.

Objective

Increasing enamel resistance to acid may be useful for preventing cavitation and could reduce changes in the enamel’s microhardness. Topical fluoride application and laser irradiation promote acid resistance of dental substrates. The aim of the study was to assess the efficacy of erbium, chromium: yttrium-scandium-gallium-garnet laser irradiation in combination with fluoride application to control enamel erosion.

Design

Sixty human premolar specimens were prepared (N = 60) and were randomly assigned to 5 groups, twelve specimens in each group (n = 12/group) according to surface treatment. The groups were as follows: group 1 (C): control with no treatment; group 2 (F): application of 1.23% acidulated phosphate fluoride gel alone; group 3 (L): laser irradiation alone; group 4 (F+L): acidulated phosphate fluoride gel followed by laser irradiation; group 5 (L+F): laser irradiation followed by acidulated phosphate fluoride gel. All the specimens were eroded 10 min in citric acid. Baseline measurements were performed using a Vickers microhardness tester before surface treatment. Subsequently, all specimens were subjected to a 60 min erosion-remineralization cycle for five days followed by measurements of the final surface microhardness. Statistical comparisons were performed by a one-way analysis of variance and Tukey’s post hoc analysis.

Results

The control, laser, and fluoride + laser groups showed a statistically significant decrease in microhardness values between baseline and post-erosion measurements (P < 0.05), indicating that these treatments could not prevent erosion progression. However, the fluoride and laser + fluoride groups showed a significant increase in microhardness values compared to baseline.

Conclusions

Our results suggest that compared to that of the control group, acidulated phosphate fluoride application as well as laser irradiation prior to fluoride application increased enamel surface microhardness and prevented the progression of enamel erosion.

Effects of 10,600 nm Carbon Dioxide Laser on Remineralizing Caries: A Literature Review

Objective: To study the effects of carbon dioxide (CO₂) lasers (λ = 10,600 nm) on remineralizing dental caries. Methods: This study involved performing a systematic search of English articles archived in the PubMed, Scopus, and Web of Science databases. The keywords used to identify the relevant articles were ((CO₂ laser) OR (carbon dioxide laser)) AND ((dental caries) OR (tooth remineralization)). Publications before 2019 were selected. The titles and abstracts of the initially identified articles were screened. Duplicate records, reviews, and irrelevant studies were removed. Full texts were retrieved for publications that studied the effects of CO₂ lasers on remineralizing dental caries. Results: The search identified 543 potentially relevant publications. A total of 285 duplicate records were removed. Sixteen articles were included in this review. Four studies reported that CO₂ lasers inhibited bacterial growth. The growth of cariogenic bacteria, mainly Streptococcus mutans, on an irradiated tooth surface was slower compared with nonirradiated ones. Four studies investigated the reduction of the demineralization of enamel with cariogenic challenge. They found that CO₂ lasers reduced the carbonate content of mineralized tissues and increased the microhardness of enamel. Nine studies used CO₂ lasers associated with topical fluorides in remineralizing dental caries. The results of the synergistic effect of laser irradiation and fluoride application with regard to the inhibition of caries progression varied among these studies, whereas laser irradiation could enhance fluoride uptake to demineralized mineral tissues. Conclusions: CO₂ laser irradiation increased acid resistance and facilitated the fluoride uptake of caries-like lesions. In addition, it reduced the growth of cariogenic bacteria.

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

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

Efficacy of diode and CO2 lasers along with calcium and fluoride-containing compounds for the remineralization of primary teeth

Background

This study aimed to assess the efficacy of a 980-nm diode and 10.6-μm CO₂ laser accompanied by tricalcium phosphate-5% sodium fluoride (fTCP) and casein phosphopeptide amorphous calcium phosphate (CPP-ACP) for the remineralization of primary teeth.

Methods

In total, 117 extracted primary anterior teeth were randomly divided into eight experimental and one control group: (I) control (polished enamel), (II) fTCP varnish, (III) fTCP + diode laser, (IV) fTCP + CO₂ laser, (V) CPP-ACP, (VI) CPP-ACP + diode laser, (VII) CPP-ACP + CO₂ laser, (VIII) diode laser, and (IX) CO₂ laser. The microhardness of 12 samples in each group and the enamel porosity of one sample in each group were assessed before and after demineralization and 28 days after remineralization. Data were analysed using two-way ANOVA.

Results

Significant differences existed in microhardness (P = 0.004) and percentage of remineralization (P < 0.001) after remineralization among the material groups such that the highest mean was noted in the CPP-ACP group. No significant difference was noted in microhardness (P = 0.052) or percentage of remineralization (P = 0.981) after remineralization among the laser groups. In all groups, porosities increased after demineralization and slightly decreased after remineralization; the greatest reduction in porosity of the material groups was noted in the fTCP group, and the CO₂ group among the laser groups. The interaction effect of materials and lasers was not significant (P > 0.05).

Conclusion

The highest microhardness was achieved after remineralization with CPP-ACP. The efficacy of the diode and CO₂ lasers was the same. No synergistic effect was found between materials and lasers.

Trial registration

This is not a human subject research.

Effects of Laser and Fluoride on the Prevention of Enamel Demineralization: An In Vitro Study

Introduction: Investigations have demonstrated that fluoride is an essential element in preventive dentistry. However, there are still controversies about the preventive effects of various kinds of laser. The aim of this study was to examine the effect of diode laser irradiation (810 nm) with or without fluoride therapy in the prevention of deciduous enamel demineralization. Methods: Sixty deciduous molar crowns were randomly assigned to 6 groups: C: received no treatment; F: fluoride varnish application; 2L: 2 times diode laser irradiation; 4L: 4 times diode laser irradiation; F2L: 2 times laser irradiation over fluoride varnish; F4L: 4 times laser irradiation over fluoride varnish. Teeth in all groups were subjected to a pH-cycling process to produce artificial caries-like lesions. Results: The analysis of variance (ANOVA) of microhardness values indicated a significant great effect for laser, fluoride, and the interaction of laser- fluoride on reducing the final microhardness value (P<0.001). However, the 2L group was an exception. Despite the 4L group, it did not show a significant prevention of enamel microhardness loss (P=0.125). These 2 groups exhibited different effects in the absence of fluoride (P _2L-4L=0.05) while in the presence of the fluoride varnish, no statistically significant difference was observed between them (P _F2L-F4L=0.257). Moreover, no statistically significant difference was observed between the laser-fluoride combination group and the fluoride group (P _F2L-F=0.133, P _F4L-F=0.926). Conclusion: Our results suggest that fluoride varnish, diode laser, and their combination decrease the loss of the enamel microhardness value and potentially prevent deciduous enamel demineralization. However, the combination of laser and fluoride was not more effective than fluoride.

The Self-Assembling Peptide P11-4 Prevents Collagen Proteolysis in Dentin

The major goal in restorative dentistry is to develop a true regenerative approach that fully recovers hydroxyapatite crystals within the caries lesion. Recently, a rationally designed self-assembling peptide P11-4 (Ace-QQRFEWEFEQQ-NH2) has been developed to enhance remineralization on initial caries lesions, yet its applicability on dentin tissues remains unclear. Thus, the present study investigated the interaction of P11-4 with the organic dentin components as well as the effect of P11-4 on the proteolytic activity, mechanical properties of the bonding interface, and nanoleakage evaluation to artificial caries-affected dentin. Surface plasmon resonance and atomic force microscopy indicated that P11-4 binds to collagen type I fibers, increasing their width from 214 ± 4 nm to 308 ± 5 nm ( P < 0.0001). P11-4 also increased the resistance of collagen type I fibers against the proteolytic activity of collagenases. The immediate treatment of artificial caries-affected dentin with P11-4 enhanced the microtensile bonding strength of the bonding interface ( P < 0.0001), reaching values close to sound dentin and decreasing the proteolytic activity at the hybrid layer; however, such effects decreased after 6 mo of water storage ( P < 0.05). In conclusion, P11-4 interacts with collagen type I, increasing the resistance of collagen fibers to proteolysis, and improves stability of the hybrid layer formed by artificial caries-affected dentin.

Influence of Ultrapulsed CO2 Laser, before Application of Different Types of Fluoride, on the Increase of Microhardness of Enamel In Vitro

Objective

To evaluate the influence of ultrapulsed CO₂ laser in combination with commercial fluoride products in order to verify the increase of microhardness of artificial enamel caries lesions.

Materials and Methods

Bovine enamel specimens were prepared, and artificial enamel caries lesions were created. Teeth were randomly divided into 5 groups (n=10): treated with laser (L), laser + neutral fluoride gel 2% (LNF), laser + acidulated phosphate fluoride gel 1.23% (LAFG), laser + acidulated fluoride mousse 1.23% (LAFM), and laser + fluoride varnish 5% (LFV). Microhardness was evaluated at baseline, after caries induction, after CO₂ laser irradiation + fluoride treatment in the 1st week, and after fluoride treatment at 3rd and 5th week.

Results

There was a decrease in microhardness in all groups after artificial enamel caries lesion formation; no increase in microhardness was found in the first and third weeks in all groups (p > 0.05). In the fifth week, an increase in microhardness occurred in all groups (p < 0.05).

Conclusion

Although CO2 laser irradiation in combination with different commercial fluoride products was capable of increasing microhardness on enamel caries lesions in bovine tooth enamel it is necessary to confirm these results by testing the isolated effect of fluoride on enamel surface microhardness. Also, although microhardness was higher in the fluoride varnish group than in the other groups in the fifth week it is not possible to discard the best effect of fluoride varnish treatment on absence of artifacts that may occur with the other fluoride treatments.

Clinical Relevance

In order to prove that CO2 laser may contribute to an increase in microhardness when applied to enamel lesions in combination with different commercial fluoride products it is necessary to conduct additional studies. Also, higher microhardness of fluoride varnish group should be carefully considered.

The effect of diode laser irradiation associated with photoabsorbing agents containing remineralizing materials on microhardness, morphology and chemical structure of early enamel caries

Background

This study investigated the effects of laser irradiation associated with photo-absorbing agents containing sodium fluoride (NaF), MI paste Plus or Remin Pro® on microhardness and surface structure of white spot lesions (WSLs).

Material and Methods

Fifty-six premolars were divided into two halves, then immersed in a demineraling solution to induce WSLs. The samples were divided into 8 groups by treatment (n=12) : (1) control, (2) diode laser (810 nm, 500 mW, 90 s), (3) NaF, (4) MI Paste plus, (5) Remin Pro®, (6) NaF + Laser, (7) MI Paste Plus + Laser, (8) Remin Pro® + Laser. Microhardness was measured before and after remineralization treatments. Two samples from each group were selected for SEM analysis.

Results

Microhardness increased significantly after all treatments with the exception of control, Laser and Remin Pro® groups (p >0.05). ANOVA revealed no significant difference in initial microhardness (P=0.21), whereas a significant difference was noted after treatment (P=0.009). The application of sodium fluoride with or without laser irradiation produced the highest microhardness among the groups (p<0.05). SEM analysis revealed some cracks on lased enamel and non-homogenous coatings of minerals after the use of remineralizing products.

Conclusions

The use of NaF either alone or combined with laser irradiation was the most effecttive strategy for increasing microhardness of WSLs. The application of diode laser through photoabsorbing agents containing sodium fluoride or MI Paste Plus did not produce any additional effects in enhancing remineralization of WSLs, whereas the combined application of diode laser with Remin Pro® was effective.

Key words:CPP-ACP, Enamel caries, fluoride, Hydroxyapatite, Low level laser, Microhardness, Remineralization, casein phosphopeptide amorphous calcium phosphate.

Biomimetic Mineralizing Agents Recover the Micro Tensile Bond Strength of Demineralized Dentin

Biomimetic remineralization is an approach that mimics natural biomineralization, and improves adhesive procedures. The aim of this paper was to investigate the influence of Dentin Caries-like Lesions (DCLL)-Producing Model on microtensile bond strength (μTBS) of etch and rinse adhesive systems and investigate the effect of remineralizing agents such as Sodium Fluoride (NaF), MI Paste™ (MP) and Curodont™ Repair (CR) on caries-affected dentin (n = 6). Nine groups were established: (1) Sound dentin; (2) Demineralized dentin/Chemical DCLL: (3) Demineralized dentin/Biological DCLL; (4) Chemical/DCLL + NaF; (5) Chemical/DCLL + MP; (6) Chemical/DCLL + CR; (7) Biological/DCLL + NaF; (8) Biological/DCLL + MP; (9) Biological/DCLL + CR. Then all dentin blocks were subjected to a bonding procedure with Adper™ Single Bond 2 adhesive system/Filtek Z350XT 4 mm high block, following this they were immersed in deionized water/24 h and then sectioned with ≅1 mm² beams. The μTBS test was conducted at 1 mm/min/500 N loading. Failure sites were evaluated by SEM (scanning electron microscopy (150×). μTBS data were submitted to factorial ANOVA and Tukey’s test (p < 0.05). The highest values were found when demineralized dentin was treated with MP and CR, regardless caries lesion depth (p < 0.05). There was a predominance of adhesive/mixed in the present study. It was concluded that the use of the artificial dentin caries production models produces differences in the μTBS. Additionally MP and CR remineralizing agents could enhance adhesive procedures even at different models of caries lesion.

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

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

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

OBJECTIVE

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

BACKGROUND DATA

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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