1. McGehee, W.H.O.; True, H.A.; and In-Skipp, E.E.: Operative Dentistry, 4th ed, New York: McGraw-Hill Book Co., 1956, p 192.
2. Gilmore, H.W.: Textbook of Operative Dentistry, St Louis: The C. V. Mosby Co., 1967, p 97.
3. Brackwell, R.E.: Black's Operative Dentistry, Vol 2, London: Medico-Dental Publishing Co., 1955, p 109.
4. Relationship between Hardness, Discoloration, and Microbial Invasion in Carious Dentin