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

The Effect of Er:YAG Laser Irradiation Combined With Fluoride Application on the Resistance of Primary and Permanent Dental Enamel to Erosion

Introduction: Erosion is an important cause of tooth mineral loss. The combined use of lasers and fluoride has been introduced as a novel modality for the prevention of enamel demineralization. This study aimed to assess the effect of Er:YAG laser combined with fluoride application on primary and permanent enamel resistance to erosion. Methods: Eighty enamel specimens of permanent (n=40) and primary (n=40) molars were prepared and randomly assigned to 4 groups: C-control (no pretreatment), F-acidulated phosphate fluoride (APF) gel, FL-APF gel application followed by Er:YAG laser irradiation, and LF-Er:YAG laser irradiation followed by the application of APF gel . The specimens were then submitted to pH cycling using Coca-Cola (pH=2.4). Enamel micro-hardness was measured using the Vickers microhardness tester before pretreatment and after the erosive process. The collected data were analyzed using the Kolmogorov-Smirnov test, two-way ANOVA and repeated measures ANOVA. Results: The micro-hardness of both permanent and primary enamel specimens significantly decreased after the erosive process (P < 0.05). In the permanent enamel specimens, the greatest reduction in micro-hardness was noted in groups C and F, while the least reduction was noted in group FL. However, these differences were not statistically significant (P > 0.05). In the primary enamel specimens, the greatest reduction in micro-hardness was noted in groups C and LF, while the least reduction was noted in group F. These differences were not statistically significant (P > 0.05). Conclusion: Within the limitations of this study, Er:YAG laser irradiation combined with fluoride application could not prevent erosion in permanent and primary enamel during the erosive process.

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.

Variation on Molecular Structure, Crystallinity, and Optical Properties of Dentin Due to Nd:YAG Laser and Fluoride Aimed at Tooth Erosion Prevention

This in vitro study evaluated the compositional, crystalline, and morphological effects promoted by Nd:YAG laser on root dentin, and verified the effects of laser and topical acidulated phosphate fluoride application (APF-gel) on dentin erosion. 180 bovine dentin slabs were randomized into 4 groups (n = 45): G1–untreated, G2–APF-gel (1.23% F⁻, 4 min), G3–Nd:YAG (1064 nm, 84.9 J/cm², 10 Hz), and G4–APF-gel application followed by Nd:YAG laser irradiation. The compositional, crystalline, and morphological effects promoted by treatments were investigated on five samples of each experimental group. The other samples were submitted to a 5-day, 10-day, or 15-day erosive and abrasive demineralization and remineralization cycling in order to create erosion lesions. The area and depth of lesions, as well as the optical attenuation coefficient, were assessed, and all data were statistically analysed (p < 0.05). Nd:YAG laser promoted the reduction of carbonate, the formation of tetracalcium phosphate, as well as the melting and recrystallization of the dentin surface. Laser significantly decreased the area and depth of erosion lesions and altered the optical attenuation coefficient when compared to untreated and APF-gel groups, but the association of APF-gel and laser did not promote an additional effect. Nd:YAG laser irradiation can be a promissory treatment to prevent dentin erosion and the abrasion process.

Effect of the carbon dioxide 10,600-nm laser and topical fluoride gel application on enamel microstructure and microhardness after acid challenge: an in vitro study

The aim of this in-vitro study was to evaluate positive effects of the carbon dioxide laser (CO₂, 10,600 nm) with acidulated phosphate fluoride (APF) gel on enamel acid resistance. Twenty extracted human third molars (40 surfaces) were randomly assigned into four groups: group C, untreated control; group L, CO₂ laser alone group; group F, APF 1.23% fluoride gel; and group FL, APF 1.23% gel and laser. Samples from group L were irradiated with a CO₂ laser for 30s. The parameter settings used were average power, 0.73 W; time on, 100 μs; time off, 40 ms; tip-to-tissue distance, 20 mm; tip diameter 700 μm; and energy density with movements, 5 J/cm². Samples from group F were treated with the APF gel for 4 min, and the gel was washed off with distilled water. The enamel samples from group FL were treated with APF gel for 4 min and then irradiated with the CO₂ laser for 30s without removing the gel. Each enamel sample was placed in 50 ml soft drink (pH = 2.75) for 10 min then rinsed with deionized water and stored in artificial saliva at 37 °C for 1 h. Samples were assessed for Vickers hardness number (VHN) before and after treatments and subjected to SEM analysis. Data were analyzed using a one-way analysis of variance (ANOVA) and Tukey's test (α < 0.05). After the acid challenge, the untreated C group was demineralized to a great extent and the enamel surface was with the lowest mean score of microhardness. The observed VHN in the control (C group) had a mean value of 176.13, the scores in the CO₂ laser group (L group) were with mean value of 238.40, the F group with a mean value of 218.45, and the fluoride-treated and laser-irradiated FL group-with a mean of 268.28 VHN. Paired t test performed to compare groups C, L, F, and FL has shown that group FL has greater resistance to decrease in microhardness of dental enamel (P ≤ 0.05) on exposure to acidic protocol. After the acid challenge, the fluoride-treated and laser-irradiated samples (group FL) showed the least diminution in enamel surface microhardness. The sub-ablative carbon dioxide laser irradiation in combination with fluoride treatment is more effective in protecting enamel surface and resisting demineralization than CO₂ laser irradiation or fluoride alone.

In Vitro Evaluation of Dentin Hydraulic Conductance After 980 nm Diode Laser Irradiation

BACKGROUND

Dentin hypersensitivity treatments are based on the physical obliteration of the dentinal tubules to reduce hydraulic conductance. The aim of the present study is to evaluate the hydraulic conductance of bovine root dentin after irradiation with a 980-nm diode laser, with or without associated fluoride varnish.

METHODS

Sixty bovine root dentin specimens were divided into six groups (n = 10 in each group): G1, G3, and G5 (0.5 W, 0.7 W, and 1 W diode laser, respectively); G2, G4, and G6 (fluoride varnish application + 0.5 W, 0.7 W, and 1 W diode laser, respectively). The dentin hydraulic conductance was evaluated at four time periods with a fluxmeter: 1) with smear layer, 2) after 37% phosphoric acid etching, 3) after the treatments, and 4) after 6% citric acid challenge. After the dentinal fluid flow measurements, specimens were also evaluated for mineral composition using energy dispersive X-ray spectroscopy (EDS).

RESULTS

Analysis demonstrated a better result with increased irradiation power (P < 0.001), especially if the diode laser irradiation was associated with the application of fluoride varnish (P < 0.001), ensuring a greater reduction in permeability. Considering the groups treated only with laser irradiation, the 1 W group was superior when compared with the 0.5 W and 0.7 W irradiated groups immediately after treatment (P < 0.001). After citric acid testing, all groups showed similar results, except when comparing the 1 W groups with the 0.5 W groups (P = 0.04). EDS results of the irradiated groups showed an increase in the proportion of calcium and phosphorus ions, which demonstrates a superficial composition modification after laser treatments.

CONCLUSION

Laser irradiation of exposed dentin promoted significant reduction in the dentin hydraulic conductance, mainly with higher energy densities and association with fluoride varnish.