Morphological and Structural Changes on Human Dental Enamel After Er:YAG Laser Irradiation: AFM, SEM, and EDS Evaluation

Abstract

Objective: The purpose of this study was to evaluate, using atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), the morphological and structural changes of the enamel after irradiation with the Er:YAG laser. Background data: A previous study showed that subablative Er:YAG laser irradiation produced undesirable morphological changes on the enamel surface, such as craters and cracks; however, the enamel acid resistance was not increased. Methods: Fifty-two samples of human enamel were divided into four groups (n ¼ 13): Group I was the control (no laser irradiation), whereas Groups II, III, and IV were irradiated with the Er:YAG 100 mJ (12.7 J /cm 2 ), 100 mJ (7.5 J/cm 2 ), and 150 mJ (11 J/cm 2 ), respectively, at 10 Hz with water spray. The morphological changes were observed by AFM and SEM. The weight percentages (wt%) of calcium (Ca), phosphorus (P), oxygen (O) and chlorine (Cl) were determined in the resultant craters and their periphery using EDS. Kruskal-Wallis and Mann-Whitney U tests were performed ( p 0.05) to distinguish significant differences among the groups. Results: The AFM images showed cracks with depths between 250 nm and 750 nm for Groups II and IV, respectively, and the widths of these cracks were 5.37 mm and 2.58 mm. The interior of the cracks showed a rough surface. The SEM micrographs revealed morphological changes. Significant differences were detected in Ca, P, and Cl in the crater and its periphery. Conclusions: AFM observations showed triangular-shaped cracks, whereas craters and cracks were evident by SEM in all irradiated samples. It was not possible to establish a characteristic chemical pattern in the craters.

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

“…Other studies also indicated topographical alterations including irregularities, craters and cracks in enamel and dentin specimens treated by Er:YAG or Er,Cr:YSGG lasers. 10,11,[20][21][22][23]30,33 The laser settings used in this study were selected in order to produce efficient enamel and dentin ablation, simulating the clinical conditions. Most of the previous studies used lower pulse repletion rates compared to that used in this study, but the number of microexplosions and the rate of ablation are directly dependent on this parameter.…”

The Effect of Energy Densities on the Shear Bond Strength of Self-Adhering Flowable Composite to Er:YAG Pretreated Dentin

“…It was demonstrated in previous studies that high level of energies increased dentin microhardness in the deepest area of the cavity until 60  μ m [31]. Consequently, the shear bond strength, in surfaces with lower energy density, was high due to fewer morphologic changes [32]. Bonding self-adhering flowable resin composite to laser irradiated dentin still remains a challenge because of the lack of information about alterations in collagen fibrils and mineral content promoted by Er:YAG laser irradiation.…”

Chemical Changes of Enamel Produced by Sodium Fluoride, Hydroxyapatite, Er:YAG Laser, and Combined Treatments

“…The distance between the tip and the sample was 1 mm, which was ensured by using a sheet of stainless steel (23 mm × 5 mm × 0 5 mm) that was fixed to the top of the laser handpiece. At this tip-sample distance, the exit tip and the laser beam had the same diameter, which was confirmed by a laminated infrared sensor screen (Lumitek International Inc., Ijamsville, MD, USA) [18,25,27,28]. Each sample was irradiated only once for 20 sec.…”

“…The crown was fixed to a glass slide with thermoplasticized epoxy resin (Allied, Rancho Dominguez, CA). Afterwards, a diamond wheel (South Bay Technology Inc.) was employed to obtain samples under constant irrigation [18,25,27,28].…”