A Pilot Study on Internal Contamination of Air-driven Slow-speed Handpieces

Objective: This study was designed to determine if the interior of slow-speed handpiece/prophy angle systems become contaminated during operation. Methods: One type of handpiece was attached to four different types of disposable prophy angles. Sterile handpieces were covered with plastic sleeves and the prophy angles were attached. Angle heads were submerged into 12.5 mL of 2.0 x 10⁶/mL Geobacillus stearothermophilus in 10% sheep’s blood. Rotating angle cups were then pressed against the beaker sides and released. The process was repeated 30 times within 60 seconds. Handpiece components were aseptically disassembled and the inside surfaces of the angle, nosecone, including the gears and the motor were sampled and aerobically incubated in TSB containing 0.25% glucose at 56⁰C for seven days. The process was tested in reverse when 0.1 mL of the spore-blood suspensions was inoculated onto the gears of sterilized motors. Rotating angle cups were submerged in beakers containing 12.5 mL of sterile phosphate buffered saline (PBS). Operation was as previously described. The PBS, the inside of the angle and nosecone, the gears of the nosecone and motor were sampled for contamination. Both methods were tested ten times for each prophy angle type. Results: In the 40 tests of handpieces contaminated at the prophy cup end, the spores traveled up and inside to the motor gears 14 times (35%). In the other 40 tests where the motor gears were contaminated, the test bacterium traveled down inside to the prophy cup and out in 27 instances (67%). All four types of prophy angles were exhibited contamination for both methods.

Conclusions: These data suggest that slow-speed handpiece motors can become contaminated with oral flora during use with prophy angles. Also, internal contaminants appear to be released out of the handpiece. It appears that unless properly sterilized, slow-speed handpieces pose a risk for cross-infection.