Extra Positive Air Pressure to Prevent Microbial Contamination in Dental Handpieces: An Experimental Study

Objectives: This study aims to evaluate the effect of applying extra positive air pressure (AP) in dental handpieces (HPs) on preventing external bacterial penetration. Materials and methods: To investigate the suck-back phenomenon during HP operation, we examined the correlation between AP variations and the occurrence of suck-back under controlled conditions. To assess the suck-back phenomenon during HP operation, AP changes were evaluated by monitoring water displacement using a glass tube or a manometer. An extra AP supplier (EAPS) was connected to the exhaust airlines of the HP and operated for 5 seconds to control AP. To evaluate whether AP control could prevent bacterial penetration into the HP, bioburden tests were conducted by immersing the HP in five bacterial cultures during operation. This allowed for the assessment of microbial contamination risk under different AP-controlled conditions. Results: The manometer measurements revealed a maximum negative AP of –2.11 kPa immediately after HP operation and gradually decreased over the next 9 seconds. However, no negative AP was observed when the EAPS was activated after the HP operation. Bacteria were detected on the internal HP components when extra positive AP was not sufficiently applied following the HP operation. Conclusion: If sufficient extra positive AP is not applied after HP operation, bacteria can penetrate the HP, posing a risk of microbial contamination. However, applying extra positive AP of at least 0.1 MPa to the exhaust airflow for a minimum of 5 seconds effectively prevents microbial contamination.