1. Bennett, A.G.: Plastic Materials for Filling Teeth, Vol. II, American System of Dentistry by Wilbur H. Litch, Philadelphia: Lea Brothers & Co., 1887, p. 233.
2. Flagg, J.F.: Plastics and Plastic Filling, 1st ed. Philadelphia: Presley Blakeston, 1881, p. 54.
3. Kirk, E.C.: Dental Metallurgy. Part IV, Vol. III, American System of Dentistry by Wilbur H. Litch, Philadelphia: Lea Brothers & Co., 1887, p. 813.