title: 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
  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 = 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 μm and 2.58 μm. 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.
authors.affiliation: Centro de Investigación y Estudios Avanzados en Odontología de la Universidad Autónoma del Estado de México, Toluca, Estado de México.
authors.forename: Laura Emma
authors.initials: LE
authors.lastname: Rodríguez-Vilchis
authors.forename: Rosalía
authors.initials: R
authors.lastname: Contreras-Bulnes
authors.forename: Oscar Fernando
authors.initials: OF
authors.lastname: Olea-Mejìa
authors.forename: Ignacio
authors.initials: I
authors.lastname: Sánchez-Flores
authors.forename: Claudia
authors.initials: C
authors.lastname: Centeno-Pedraza
mesh_terms: D003743:Dental Enamel / Q000528:radiation effects* / Q000648:ultrastructure*; D006801:Humans; D053844:Lasers, Solid-State; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D013052:Spectrometry, X-Ray Emission; D018709:Statistics, Nonparametric; D013499:Surface Properties