1. Skinner, E.W. , and Phillips, R.W.: The Science of Dental Materials , 6th ed, Philadelphia : W. B. Saunders Co., 1967, p 285.
2. Peyton, F.A. ; Asgar, K.; Charbeneau, G.T.; Craig, R.G.; and Myers, G.E.: Restorative Dental Materials, 3rd ed, St. Louis: C. V. Mosby Co., 1968 , p 287.
3. Anderson, J.N. : Applied Dental Materials, 3rd ed, Oxford: Blackwell Scientific Publications, 1967, p 68.