1. U.S. pat. No. 3,066,112 (1962).
2. U.S. pat. No. 3,179,623 (1965).
3. U.S. pat. No. 3,194,783 (1965).
4. Philips' Science of Dental Materials; W. B. Saunders Co.: Philadelphia, 1996, 10th ed.
5. ; Applied Dental Materials; Blackwell Science Ltd.: London, 1998, 8th ed.