RESEARCH ARTICLE Effect of Er:YAG laser irradiation on deciduous enamel roughness and bacterial adhesion: An in vitro study Bernardo Teutle-Coyotecatl 1 | Rosalía Contreras-Bulnes 1 | Rogelio José Scougall-Vilchis 1 | Argelia Almaguer-Flores 2 | Laura Emma Rodríguez-Vilchis 1 | Ulises Velazquez-Enriquez 1 | Jesús  Angel Arenas Alatorre 3 1 Universidad Autónoma del Estado de México, Facultad de Odontología, Centro de Investigación y Estudios Avanzados en Odontología (CIEAO). Jesús Carranza esq. Paseo Tollocan, Colonia Universidad, Toluca, Estado de México, México, C.P. 50130. 2 Universidad Nacional Autónoma de México, Facultad de Odontología, Laboratorio de Genética Molecular, Circuito Escolar s/n, Ciudad Universitaria, Delegación Coyoacán, Mexico 3 Universidad Nacional Autónoma de México, Instituto de Física, Circuito Escolar s/n, Ciudad Universitaria, Delegación Coyoacán, Mexico Correspondence Rosalía Contreras Bulnes, Universidad Autónoma del Estado de México, Facultad de Odontología, Centro de Investigación y Estudios Avanzados en Odontología (CIEAO). Jesús Carranza esq. Paseo Tollocan, Colonia Universidad, Toluca, Estado de México. México, C.P. 50130. Email: rcontrerasb@uaemex.mx Review Editor: Mingying Yang ABSTRACT Laser irradiation has been proposed as a preventive method against dental caries since it is capable to inhibit enamel demineralization by reducing carbonate and modifying organic matter, yet it can produce significant morphological changes. The purpose of this study was to evaluate the influence of Er:YAG laser irradiation on superficial roughness of deciduous dental enamel and bacterial adhesion. Fifty-four samples of deciduous enamel were divided into three groups (n = 18 each). G1_control (nonirradiated); G2_100 (7.5 J/cm 2 ) and G3_100 (12.7 J/cm 2 ) were irradiated with Er:YAG laser at 7.5 and 12.7 J/cm 2 , respectively, under water irrigation. Surface roughness was measured before and after irradiation using a profilometer. Afterwards, six samples per group were used to measure bacterial growth by XTT cell viability assay. Adhered bacteria were observed using confocal laser scanning microscopy (CLSM) and a scanning electron microscopy (SEM). Paired t-, one-way analysis of variance (ANOVA), Kruskal-Wallis and pairwise Mann–Whitney U tests were performed to analyze statistical differences (p < .05). Before treatment, samples showed homogenous surface roughness, and after Er:YAG laser irradiation, the surfaces showed a significant increase in roughness values (p < .05). G3_100 (12.7 J/cm 2 ) showed the highest amount of Streptococcus mutans adhered (p < .05). The increase in the roughness of the tooth enamel surfaces was pro- portional to the energy density used; the increase in surface roughness caused by laser irradiation did not augment the adhesion of Streptococcus sanguinis; only the use of the energy density of 12.7 J/cm 2 favored significantly the adhesion of S. mutans. KEYWORDS bacterial adhesion, enamel, erbium laser, preventive dentistry, roughness, streptococci 1 | INTRODUCTION As an alternative to fluoride, laser irradiation has been tested as a method to prevent enamel demineralization (Ana, Bachmann, & Zezell, 2006). Sev- eral experiments in vitro have demonstrated that a proper laser treatment may prevent such demineralization by reducing enamel diffusion (Liu, Hsu, Teo, & Teoh, 2013; Maung, Wohland, & Hsu, 2007), through chemical (Díaz-Monroy et al., 2014; Liu & Hsu, 2007; Zamudio-Ortega et al., 2014a) and morphological changes (Hossain et al., 2000). The laser microablasive process causes vaporization of water and dental organic components Received: 8 March 2019 Revised: 21 May 2019 Accepted: 16 July 2019 DOI: 10.1002/jemt.23354 Microsc Res Tech. 2019;1–9. wileyonlinelibrary.com/journal/jemt © 2019 Wiley Periodicals, Inc. 1