In vitro evaluation of enamel demineralization after several overlapping CO2 laser applications

Preventing Enamel Caries Using Carbon Dioxide Laser and Silver Diamine Fluoride

Objective: This study was intended to investigate the caries prevention potential of carbon dioxide (CO₂) laser (λ = 10,600 nm) irradiation followed by application of silver diamine fluoride (SDF) to enamel. Materials and methods: Human enamel specimens were randomly allocated to four groups (n = 10 per group). Group 1 specimens were treated with SDF; Group 2 specimens were treated with a CO₂ laser; Group 3 specimens were irradiated with a CO₂ laser then treated with SDF, and Group 4 specimens received no treatment. All specimens were subjected to pH cycling for cariogenic challenge. Lesion depth, microhardness, surface morphology, and elemental analysis were assessed. Results: The lesion depths for Groups 1-4 were 33 ± 16, 80 ± 9, 18 ± 15, and 102 ± 9 μm, respectively (p < 0.001; Group 3 < Group 1 < Group 2 < Group 4). Knoop hardness values for Groups 1-4 were 61 ± 19, 68 ± 20, 78 ± 27, and 36 ± 8, respectively (p = 0.002; Group 4 < Groups 1, 2, and 3). The enamel in Group 4 but not in the other groups showed a roughened surface resembling an acid-etched pattern. Calcium-to-phosphorus molar ratios of Groups 1-4 were 1.68 ± 60.09, 1.61 ± 0.06, 1.69 ± 0.10, and 1.49 ± 0.10, respectively (p < 0.001; Group 4 < Groups 1, 2, and 3). Conclusions: Using the CO₂ laser or SDF separately enhanced the resistance of enamel to cariogenic challenge. Moreover, there was an additional effect of the combined use of the CO₂ laser and SDF for preventing enamel demineralization.

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.

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.