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Sven-Erik Hamp; Sture Nyman; Jan Lindhe. (1975). Periodontal treatment of multi rooted teeth. : Results after 5 years. , 2(3), 126–135. doi:10.1111/j.1600-051x.1975.tb01734.x 
An interview with Sci-Hub Founder Alexandra Elbakyan,Who exactly should pay for academic research