The above letter, published on 13 May 2016 (220: 429) only mentioned one author. The authors of the letter were: María Mercedes Suárez-Cunqueiro and Inmaculada Tomás, both of the Department of Stomatology, School of Medicine and Dentistry, Universidade de Santiago de Compostela, Spain. We apologise to the authors for this error and the inconvenience caused.