Evaluation of crystalline changes and resistance to demineralization of the surface of human dental enamel treated with Er:YAG laser and fluoride using x-ray diffraction analysis and Vickers microhardness

Abstract

This study aimed to investigate the changes in crystalline structure and resistance to demineralization of human dental surface enamel treated with erbium-doped yttrium aluminium garnet laser (Er:YAG) laser and fluoride.The enamel surfaces were divided into four groups according to the treatment process including, (L): irradiated with Er:YAG; (F): treated with acidulated phosphate fluoride gel (LF): Pre-irradiated surfaces with Er:YAG subjected to acidulated phosphate fluoride gel and (FL): laser irradiation was performed on the fluoridated enamel surface. Before and after the treatment procedure, the samples were evaluated using X-ray diffraction, scanning electron microscope (SEM) and the Vickers microhardness test. The surface microhardness values also were measured after a pH-cycling regime and acid challenge.The a-axis of all lased groups was contracted after treatment procedure. Measurement of the area under the peaks showed the highest crysallinity in the FL group. The hardness values of all laser treated samples significantly reduced after treatment procedure compared to the F group (p ⩽ 0.001). The morphological observations showed remarkable changes on the lased enamel surfaces including cracks, craters and exposed prisms.These findings suggest, irradiation of the Er:YAG laser accompanying with fluoride application can induce some beneficial crystalline changes regarding the acid-resistance

Chemical and morphological changes of femtosecond laser‐irradiated enamel using subablative parameters

“…Enamel ablation by femtosecond lasers has been demonstrated by several authors (Chen et al, 2015; Chen et al, 2016; Le, Bertrand, & Vilar, 2016; Loganathan, Santhanakrishnan, Bathe, & Arunachalam, 2021; Yuan, Zheng, Sun, Wang, & Lyu, 2017). Nevertheless, there is no detailed characterization of femtosecond laser‐irradiated surfaces using subablative parameters, since previous studies have demonstrated the ability of high‐power lasers with subablative parameters to make dental enamel more acid‐resistant (Behroozibakhsh et al, 2018; Chang et al, 2017). The role of laser irradiation in caries prevention has been widely studied with a focus on the increase of caries resistance caused by a decrease in the enamel demineralization rate (Geraldo‐Martins et al, 2013; Tavares et al, 2012).…”

“…On the other hand, the pulsed mode allows a thermal relaxation between one pulse and another, reducing the heat propagation into the tissue inner layers (Chen, Li, Sun, Wang, & Lü, 2016). However, irradiation in the conventional pulsed mode with short pulses generates a strong thermal shock wave, which can cause damage to the surfaces of dental tissues, such as cracks and fissures (Behroozibakhsh, Shahabi, Ghavami‐Lahiji, Sadeghian, & Nazari, 2018). Consequently, the positive effects of irradiation on the acid resistance of the enamel would be reduced since the presence of cracks and fissures would make the enamel surface more susceptible to the diffusion of microorganisms and acids present in the dental biofilm fluid (Behroozibakhsh et al, 2018).…”

“…As the pulse duration of a femtosecond laser is shorter than the thermal relaxation time of the tissues, dentin or enamel is ionized before the occurrence of thermal diffusion, restricting the generation of thermal effects (Petrov, Pecheva, Walmsley, & Dimov, 2018). In preliminary studies of minimally invasive enamel and dentin ablation using femtosecond laser, different irradiation parameters were tested to choose optimal parameters for ablation with no collateral damage or overheating of the dental tissue (Behroozibakhsh et al, 2018; Chen et al, 2015; Chen et al, 2016; Petrov et al, 2018).…”

Micro-computed tomography in preventive and restorative dental research: A review

“…Several indirect methods have been introduced to estimate the mineral content of dental structures, such as optical coherence tomography (as a modality to measure optical properties), 17 microhardness, 18 and nanoindentation. 19 Direct approaches to measuring mineral content include transverse microradiography and micro-CT. CT is a nondestructive method of 3D tissue reconstruction for biological systems, whereas the traditional gold-standard method of transverse microradiography is destructive and time-consuming.…”