Boel, T. ., D. . Kartika, and L. Liliana. “Root Canal Configuration Of Permanent Mandibular First Molars Using Radiographic Tube Shift Technique On Dentistry Student Of University Of Sumatera Utara”. IIUM Medical Journal Malaysia, vol. 16, no. 2, Dec. 2017, doi:10.31436/imjm.v16i2.1098.