The American Dental Association, "Treating Periodontal Disease: Scaling and Root Planing," accessed January 29, 2008  http://www.ada.org/prof/resources/pubs/jada/patient/patient_23.pdf 

The American Dental Association, "Plaque," accessed January 29, 2008  http://www.ada.org/public/topics/plaque.asp

Colgate World of Care, "What Is Tartar?" accessed January 24, 2008 http://www.colgate.com/app/Colgate/US/OC/Information/OralHealthBasics/CommonConcerns/PlaqueTartar/WhatisTartar.cvsp

United Stated National Library of Medicine & National Institutes of Health, "Dental calculus: recent insights into occurrence, formation, prevention, removal and oral health effects of supragingival and subgingival deposits," accessed January 24, 2008  http://www.ncbi.nlm.nih.gov/pubmed/9395117