Brubaker L, Richter HE, Barber MD, Hsu Y, Rahn DD, Menefee S, Visco A, Spino C, Martin S, Meikle SF. Pelvic floor disorders clinical trials: participant recruitment and retention. Int Urogynecol J. 2013 Jan 1;24(1):73-9.
Rothman KJ, Glass RL, Espinal F, Velez H. Caries-free teeth in the absence of fluoride ion. J Public Health Dent. 1972;32(4):225-8. doi: 10.1111/j.1752-7325.1972.tb03977.x