Objectives: The purpose of this study was to identify the stains causing infections in dental clinics by analyzing bacterial contamination, as well as to suggest improvements for infection control in dental clinics. Methods: In this study, a questionnaire survey of 47 dental hospitals and clinics located in Gyeonggi-do and Incheon, South Korea was administered from June 2013 to September 2013 and used to investigate the practice rates of infection control by dental hygienists and to analyze the bacterial contamination levels in dental offices. Results: In the studied institutions, the bacterial contamination levels of water lines were $20.9{ imes}10^3$ colony forming units (CFU)/mL for three-way syringes, $12.7{ imes}10^3CFU/mL$ for high-speed handpieces and $9.8{ imes}10^3CFU/mL$ for gargling water. The bacterial contamination levels of surfaces were $44.9{ imes}10^3CFU/mL$ in cuspidors, higher than in unit chairs ($2.9{ imes}10^3CFU/mL$) and light handles ($6.7{ imes}10^3CFU/mL$). The mean bacterial cell count of water lines and surfaces was relatively high in all establishments founded 11 years ago or more, and the mean bacterial cell count of waterline handpieces was $6.27{ imes}10^3CFU/mL$ in establishments founded between one and five years ago, $11.16{ imes}10^3CFU/mL$ six to ten years ago and $20.04{ imes}10^3CFU/mL$ 11 years ago or more, which suggests that earlier foundation is associated with higher bacterial contamination levels with a statistical difference (p<0.01). Similarly, the mean bacterial cell count of cuspidors using water from water lines was also $70.16{ imes}10^3CFU/mL$ in at least 11-year-old establishments, statistically significantly higher among in one- to five-year-old ($4.61{ imes}10^3CFU/mL$) and six- to ten-year-old clinics ($47.89{ imes}10^3CFU/mL$) (p<0.05). Conclusion: This study may be utilized to improve the bacterial contamination levels in dental offices by controlling the characteristics and environmental factors of dental offices that affect the microbial contamination of waterlines and surfaces in such institutions.