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

• Published in: Lasers in medical science Vol. 33; no. 5; pp. 1009 - 1017
• Main Authors: Belcheva, A., El Feghali, R., Nihtianova, T., Parker, S.
• Format: Journal Article
• Language: English
• Published: London Springer London 01.07.2018; Springer Nature B.V
• Subjects: Acid resistance; Acids; Carbon dioxide; Carbon dioxide lasers; Data processing; Deionization; Demineralization; Demineralizing; Dental enamel; Dentistry; Diamond pyramid hardness; Distilled water; Drinking water; Enamel; Fluoride treatments; Fluorides; Flux density; Irradiation; Lasers; Medicine; Medicine & Public Health; Molars; Optical Devices; Optics; Original Article; pH effects; Phosphates; Photonics; Quantum Optics; Saliva; Teeth; Variance analysis; Prevention; Demineralization; Fluoride; Carbon dioxide laser; Microhardness; Enamel
• DOI: 10.1007/s10103-018-2446-4
• ISSN: 0268-8921

The aim of this in-vitro study was to evaluate positive effects of the carbon dioxide laser (CO 2 , 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, CO 2 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 CO 2 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/cm 2 . 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 CO 2 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 CO 2 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 CO 2 laser irradiation or fluoride alone.