Enamel diffusion modulated by Er:YAG laser

Effect of Er:YAG Laser Irradiation on Preventing Enamel Caries: A Systematic Review and Meta-Analysis

Caries is a global health problem, and its prevention has become a main goal of modern dentistry. Laser irradiation is believed to have potential in preventing dental caries. The purpose of this systematic review and meta-analysis was to evaluate whether Er:YAG laser irradiation has the potential to prevent enamel caries. Based on inclusion and exclusion criteria, PubMed, Web of Science, and EMBASE databases were searched; 2 reviewers independently used these search strategies to review titles and abstracts, with no language or date restrictions, up to June 2023. For the quantitative analysis, continuous variables were analysed by standard mean difference (SMD) with a 95% confidence interval (CI). The statistical analyses were conducted using Review Manager and Cochrane Collaboration (2020). A total of 51 potentially eligible studies were identified, of which 16 in vitro studies were eventually included in the quantitative meta-analysis. Three studies showed a low risk of bias, and 13 studies a medium risk of bias. In general, there was no significant difference between the calcium ions released under acidic conditions after laser irradiation. The final results indicated that after Er:YAG laser irradiation, enamel could maintain higher surface microhardness in acidic environments, as well as smaller lesion depth and less mineral loss, revealing its potential in preventing enamel caries. However, the effect of laser irradiation on the release of calcium ions in acidic solutions and the surface microhardness of demineralised enamel was not significant. Therefore, more in vitro and clinical trials are needed in to evaluate whether Er:YAG laser irradiation can effectively prevent enamel caries in clinical settings.

Remineralization effects of Er,Cr:YSGG and/or bioactive glass on human enamel after radiotherapy-an in vitro study

The aim was to evaluate the effects of Er,Cr:YSGG and/or bioactive glass 45S5 (BG) on the chemical and physical properties of enamel after radiotherapy. Third molar crowns were cut in half (buccal-lingually), and the mid part of the labial/oral surface was subjected to different protocols. All samples were treated with standard 70 Gy. After radiotherapy, enamel was treated with either Er,Cr:YSGG (2780 nm; pulse 60 μs) and BG or only BG, and control samples were kept in deionized water. Vickers microhardness, scanning electron microscopy (SEM), and characteristic X-ray spectroscopy (EDS) were performed before, after radiotherapy, and after treatment. Analysis of variance (ANOVA) was used. A significant drop in enamel microhardness was observed after radiotherapy (p < 0.001). After Er,Cr:YSGG and BG or BG alone, there was a significant increase in microhardness (p < 0.001), which was on average significantly higher compared to the initial measurements for Er,Cr:YSGG with BG (p < 0.001), but not observed in BG alone (p = 0.331). After radiotherapy, SEM showed increased surface roughness with eroded prisms. Er,Cr:YSGG and BG or BG alone both showed disorderly packed glass particles on the enamel surface. Radiotherapy noticeably reduced the concentrations of calcium and phosphorus. Er,Cr:YSGG and BG treatment increased the concentrations of calcium, sodium, phosphorus, and silicate. BG treatment alone increased the concetration of calcium and phosphorus. Directly induced radiotherapy led to potential damage of enamel, but afterwards treatment with Er,Cr:YSGG laser and BG resulted in a higher increase of enamel microhardness compared to BG alone, reflecting in a possible better remineralization effect.

Rehardening of Eroded Enamel with CPP-ACFP Paste and CO2 Laser Treatment

BACKGROUND

Diet and lifestyle can destroy tooth structure due to the dissolution of enamel by acidic beverages. The present study evaluated the effect of CO2 laser irradiation and CPP-ACFP (casein phosphopeptide and amorphous calcium phosphate with fluoride) paste on the remineralization of enamel eroded by carbonated soft drinks.

METHODS

In the present in vitro study, 46 human sound premolar teeth were sectioned mesiodistally to achieve 84 samples. Fourteen samples were assigned to the positive control group (G1), and the remaining samples were immersed in 500 mL of cola drink for 2 minutes, followed by rinsing with distilled water for 10 seconds. This procedure was carried out three times to create erosive lesions. Then, the 60 eroded samples were randomly assigned to five groups of G2 to G6 in terms of the treatment as follows: negative control (G2), CO2 laser irradiation (G3), CPP-ACFP paste (G4), CO2 laser irradiation followed by CPP-ACFP paste application (G5), and CPP-ACFP paste application followed by CO2 laser irradiation (G6). The mean surface microhardness of the enamel surface was evaluated and determined at three points for each sample. Data were analyzed with one-way ANOVA and Tukey HSD tests (α = 0.05).

RESULTS

The highest and the lowest hardness values were recorded in the G1 (314 ± 12 kg/mm2) and G2 (213.7 ± 12 kg/mm2) groups, respectively. ANOVA revealed significant differences between the study groups (P < 0.001). Two-by-two comparisons showed significant differences between the G2 group and the other groups, indicating the efficacy of all the treatment modalities in tooth remineralization and rehardening procedures (P < 0.05). Only in group G6, the enamel microhardness was not significantly different from the G1 positive control group (P > 0.05).

CONCLUSION

Considering the parameters used in the present study, CO2 laser irradiation or CPP-ACFP paste application alone increased eroded enamel's surface hardness; however, their sequential application was more effective in rehardening the eroded enamel's surface to near-normal levels.

Effect of the usage of Er,Cr:YSGG laser with and without different remineralization agents on the enamel erosion of primary teeth

The aim of the present study was to evaluate the effects of different remineralization agents associated with erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) (0.5 W power, 20 Hz frequency, 60% water, 40% air, 25 mJ pulse energy, 8.84 J/cm² fluence, 60 μs pulse duration, 600 μm tip diameter, and an approximate 1-1.5 mm distance to the target) laser irradiation on erosion induced by the consumption of carbonated drinks in human primary enamel. There were 8 groups and 10 primary teeth in each g0roup. The distribution was as follows: group 1, casein phosphopeptide-amorphous calcium phosphate with fluoride (CPP-ACPF); group 2, Er,Cr:YSGG laser+CPP-ACPF; group 3, fluor varnish; group 4, Er,Cr:YSGG Laser+fluoride varnish; group 5, ROCS® medical mineral gel; group 6, Er,Cr:YSGG laser + ROCS® medical mineral gel; group 7, Er,Cr:YSGG laser; and group 8, artificial saliva. The samples in the groups were submerged in artificial saliva and acid twice a day for 6 s at 6-h intervals and were then exposed to an erosion cycle 15 times. In the groups in which the Er,Cr:YSGG laser was applied in combination with the remineralization agents, the laser application was made first, and then the remineralization agents were applied for 4 min in each group. The Friedman and Wilcoxon signed-rank tests and the Bonferroni correction were used in statistical analyses, and the significance level was taken as p < 0.05. According to the results, all agents had a statistically significant difference (groups 1, 2, 3, 4, and 6: p = 0.005, p < 0.017; groups 5 and 7: p = 0.007, p < 0.017) between BL-RM periods. However, all agents had a statistically significant remineralization effect on primary teeth enamel (groups 1, 2, 3, 6, and 7: p = 0.005, p < 0.017; group 4: p = 0.011, p < 0.017) except that group 5 (p = 0.074, p < 0.017) between DM-RM periods. The coadministration of an agent with the laser did not make any difference at a statistical level (p = 0.804, p > 0.05). The results were supported by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. As a result of this study, CPP-ACPF had a notable impact in terms of the remineralization effect on eroded enamel, and the Er,Cr:YSGG laser alone may be an alternative method, which may be related to the modified hydroxyapatite structure, 38.5% H_0.56Ca_4.56O₁₃P₃Y_0.44, that was determined in XRD analysis.

Effect of Er:YAG laser irradiation on deciduous enamel roughness and bacterial adhesion: An in vitro study

Laser irradiation has been proposed as a preventive method against dental caries since it is capable to inhibit enamel demineralization by reducing carbonate and modifying organic matter, yet it can produce significant morphological changes. The purpose of this study was to evaluate the influence of Er:YAG laser irradiation on superficial roughness of deciduous dental enamel and bacterial adhesion. Fifty-four samples of deciduous enamel were divided into three groups (n = 18 each). G1_control (nonirradiated); G2_100 (7.5 J/cm² ) and G3_100 (12.7 J/cm² ) were irradiated with Er:YAG laser at 7.5 and 12.7 J/cm² , respectively, under water irrigation. Surface roughness was measured before and after irradiation using a profilometer. Afterwards, six samples per group were used to measure bacterial growth by XTT cell viability assay. Adhered bacteria were observed using confocal laser scanning microscopy (CLSM) and a scanning electron microscopy (SEM). Paired t-, one-way analysis of variance (ANOVA), Kruskal-Wallis and pairwise Mann-Whitney U tests were performed to analyze statistical differences (p < .05). Before treatment, samples showed homogenous surface roughness, and after Er:YAG laser irradiation, the surfaces showed a significant increase in roughness values (p < .05). G3_100 (12.7 J/cm² ) showed the highest amount of Streptococcus mutans adhered (p < .05). The increase in the roughness of the tooth enamel surfaces was proportional to the energy density used; the increase in surface roughness caused by laser irradiation did not augment the adhesion of Streptococcus sanguinis; only the use of the energy density of 12.7 J/cm² favored significantly the adhesion of S. mutans.

Evaluation of a clinical preventive treatment using Er,Cr:YSGG (2780 nm) laser on the susceptibility of enamel to erosive challenge

The purpose of this in vitro study was to evaluate the effect of a clinical preventive treatment using Er,Cr:YSGG laser irradiation on bovine enamel susceptibility after erosive challenge. Twelve sound bovine incisors were used and twenty-four enamel specimens were prepared in total. Two experimental groups (n = 12) were assigned as follows: Group 1 was the control group and in Group 2, the enamel specimens were irradiated with an Er,Cr:YSGG (2780 nm) laser system for 20 s, with average output power of 0.25 W, pulse repetition rate at 20 Hz without water or air flow and the pulse duration was fixed at 140 μsec. The tip diameter was 600 μm, the tip to tissue distance was 1 mm, the speed of handpiece movement was 2 mm/s, the power density was 88.34 W/cm², and the fluence was 31.25 J/cm². The specimens were submitted to erosive challenge using a common soft drink. Surface microhardness changes, surface roughness changes, and surface loss were evaluated after erosive challenge. The data were statistically analyzed using one-way ANOVA and Tukey's post-hoc test at a level of significance a = 0.05. Er,Cr:YSGG laser-treated enamel exhibited significantly less decrease in surface microhardness and significant less surface loss compared to control enamel after the erosive challenge (p < 0.05). The experimental groups did not show significant differences in surface roughness increase after the erosive challenge (p > 0.05). Er,Cr:YSGG laser treatment may be promising for the limitation of enamel erosive tooth wear induced by excessive consumption of soft drinks. Clinical studies are needed to clarify whether this protective effect is clinically significant.

Adhesion of Streptococcus mutans and Streptococcus sanguinis on Er:YAG Laser-Irradiated Dental Enamel: Effect of Surface Roughness

Objective: To determine surface roughness caused by Er:YAG laser irradiation and its effect on the increase in bacterial adhesion. Background: Er:YAG laser was proposed as a strategic device to reduce caries by its ability to generate chemical and structural changes in tooth enamel; in turn, it produces undesirable effects on the tooth surface that could increase its roughness and allow a greater accumulation of microorganisms. Methods: Eighty-four samples of human enamel were divided into seven groups (n = 12): G1_control (no laser irradiation); G2_100/H₂O, G3_200/H₂O, and G4_300/H₂O were irradiated with Er:YAG laser (12.7, 25.5, and 38.2 J/cm², respectively) under water irrigation. In addition, G5_100, G6_200, and G7_300 were irradiated with the energy densities described above and no water irrigation. Surface roughness measurements were recorded before and after treatment using a profilometer. Afterward, three samples per group were incubated in a microorganism suspension for the tetrazolium salt (XTT) assay. Biofilm morphology was observed using scanning electron microscopy and confocal laser scanning microscope. One-way analysis of variance and t-tests were performed for statistical analysis (p < 0.05). Results: There were no statistically significant differences in roughness values in the G5_100 group before and after treatment, but there were statistically significant differences observed in the other groups evaluated (p < 0.05). No significant differences in adhesion of both strains were detected in irradiated groups compared with G1_control. Conclusions: The increase in roughness on dental enamel surfaces was proportional to the irradiation conditions. However, the increase in surface roughness caused by Er:YAG laser irradiation did not affect Streptococcus mutans and S. sanguinis adhesion.

Structural and Morphological Changes in Human Dentin after Ablative and Subablative Er:YAG Laser Irradiation

INTRODUCTION

This study investigated the influence of Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) laser on microhardness, chemical composition and subsurface morphology of dentin cavity walls.

METHODS

Forty sound human premolars were selected and randomly assigned into four groups. Class V cavities were prepared either with an Er:YAG laser (groups 1 and 2; 15 Hz, 250 mJ for enamel, 10 Hz, 200 mJ for dentin) or with a high speed handpiece (groups 3 and 4). The specimens in groups 1 and 3 served as the control, whereas those in groups 2 and 4 were exposed to subablative laser irradiation following cavity preparation (10 Hz, 50 mJ). After bisecting the specimens, one half was subjected to microhardness assessment and the other half was evaluated by SEM-EDS analysis.

RESULTS

Microhardness was significantly greater in the specimens prepared by both ablative and subablative laser irradiation (group 2) than that of the bur-prepared cavities (groups 3 and 4) (P < 0.05). The quantity of calcium ion was significantly greater in cavities prepared by the Er:YAG laser (groups 1 and 2) compared to that of the bur cavities (groups 3 and 4) (P < 0.05). Subablative irradiation improved microhardness and weight percentage of calcium ion in both laser and bur cavities, but the difference was not significant compared to that of the relevant control group (P > 0.05).

CONCLUSION

Cavity preparation with an Er:YAG laser could be considered as an alternative to the conventional method of drilling, as it enhances the mechanical and compositional properties of lased dentin, especially when combined by subablative irradiation.

Er:YAG laser irradiation to control the progression of enamel erosion: an in situ study

This in situ study evaluated the effect of Er:YAG laser irradiation in controlling the progression of enamel erosion-like lesions. Fifty-six enamel slabs (330 KHN ± 10 %) with one fourth of the surface covered with resin composite (control area) were submitted to initial erosion-like lesion formation with citric acid. The slabs were divided into two groups: irradiated with Er:YAG laser and non-irradiated. Fourteen volunteers used an intraoral palatal appliance containing two slabs, in two phases of 5 days each. During the intraoral phase, in a crossed-over design, half of the volunteers immersed the appliance in citric acid while the other half used deionized water, both for 5 min, three times per day. Enamel wear was determined by an optical 3D profilometer. ANOVA revealed that when deionized water was used as immersion solution during the intraoral phase, lower values of wear were showed when compared with the groups that were eroded with citric acid, whether irradiated or non-irradiated with Er:YAG laser. When erosion with citric acid was performed, Er:YAG laser was not able to reduce enamel wear. Small changes on enamel surface were observed when it was irradiated with Er:YAG laser. It may be concluded that Er:YAG laser irradiation did not reduce the progression of erosive lesions on enamel submitted to in situ erosion with citric acid.

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.

In vitro evaluation of the effects of different treatment procedures on dentine tubules

OBJECTIVE

The objective of this preliminary study was to evaluate the occluding effect of topical gaseous ozone application and Er:YAG laser on human dentine tubules by scanning electron microscopic (SEM) analysis.

METHODS

Twenty-four dentine specimens were divided into three groups. Group I, including specimens treated only with citric acid, served as the control. Group II was treated with Er:YAG (30 Hz 60 mJ, 10 sec), and Group III received only topical gaseous ozone application (10 sec at level 2). Diameters and the number of open dentinal tubules per 100 μm(2) were counted from SEM photomigrophraphs at ×2000 magnification.

RESULTS

In terms of diameters and numbers of open dentinal tubules per 100 μm(2), both treatment modalities presented significant occlusion. The mean values of the diameters and the number of open dentinal tubules per 100 μm(2) were observed in Group I, Group II, and Group III, in decreasing order. Significant differences were found among the groups in favor of the topical gaseous ozone applied group.

CONCLUSIONS

The dentine tubules in both treatment groups were occluded, however more marked occlusion were seen in ozone treated group.

Influence of the irradiation distance and the use of cooling to increase enamel-acid resistance with Er:YAG laser

OBJECTIVES

The aim of this study was to assess the influence of irradiation distance and the use of cooling in the Er:YAG laser efficacy in preventing enamel demineralization.

METHODS

84 enamel blocks were randomly assigned to seven groups (n=12): G1: control group - no treatment, G2-G7: experimental groups treated with Er:YAG laser (80mJ/2Hz) at different irradiation distances with or without cooling: G2: 4mm/2mL; G3: 4mm/no cooling; G4: 8mm/2mL; G5: 8mm/no cooling; G6: 16mm/2mL; G7: 16mm/no cooling. The samples were submitted to an in vitro pH cycles for 14 days. Next, the specimens were sectioned in sections of 80-100microm in thickness and the demineralization patterns of prepared slices were assessed using a polarized light microscope. Three samples from each group were analyzed with scanning electronic microscopy. Analysis of variance and the Fisher test were performed for the statistical analysis of the data obtained from the caries-lesion-depth measurements (CLDM) (alpha=5%).

RESULTS

The control group (CLDM=0.67mm) was statistically different from group 2 (CLDM=0.42mm), which presented a smaller lesion depth, and group 6 (0.91mm), which presented a greater lesion depth. The results of groups 3 (CLDM=0.74mm), 4 (CLDM=0.70mm), 5 (CLDM=0.67mm) and 7 (CLDM=0.89mm) presented statistical similarity. The scanning electronic microscopy analysis showed ablation areas in the samples from groups 4, 5, 6 and 7, and a slightly demineralized area in group 2.

CONCLUSIONS

It was possible to conclude that Er:YAG laser was efficient in preventing enamel demineralization at a 4-mm irradiation distance using cooling.