Study protocol for an online questionnaire survey on symptoms/signs, protective measures, level of awareness and perception regarding covid-19 outbreak among dentists: a global survey - Campus, Guglielmo Giuseppe; Diaz-Betancourt, Marcela; Cagetti, Maria Grazia; Carvalho, Joana Christina; Carvalho, Thiago Saads; Cortés-Martinicorena, Javier F; Deschner, James; Douglas, Gail V. A; Giacaman, Rodrigo Andrés; MacHiulskiene, Vita; Manton, David J; Ramos-Gómez, Francisco J; et al. (International Journal of Environmental Research and Public Health, 2020)