Review of dental waterline safety. Examines the etiology and composition of dental waterline biofilms. Review of the varieties and contaminant levels of microorganisms present in dental unit biofilms. Understand the mechanics of dental units which promote the development of contaminated biofilm. Review of the potential for pathogenicity of microorganisms present in dental waterlines. Discusses cases of possible dental waterline contamination which allegedly resulted in secondary infection of patients or staff. Review of strategies for decreasing and/or eliminating the levels of microorganisms delivered by dental waterlines.