1. 3. E. D. Coolidge, and M. K. Hine, Periodontology; clinical pathology and treatment of periodontal tissues . 3rd ed. Philadelphia, Lea and Febiger, 1958 . 431 p. (p. 431 -31 ).
2. Oral Hygiene Habits of Young Adults
3. 5. Irving Glickman, Clinical periodontology . Philadelphia, Saunders, 1958 . 951 p. (p. 951 -47 ).