Ashraf, H., O. Dianat, R. Hajrezai, P. Paymanpour, and S. Azadnia. “Endodontic Treatment of a Double-Rooted Maxillary Second Molar With Four Canals: A Case Report”. Iranian Endodontic Journal, vol. 9, no. 4, Oct. 2014, pp. 304-6, doi:10.22037/iej.v9i4.6404.