A 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 becomes contaminated. Methods: Two types of handpieces were attached to 7 different types of disposable prophy angles and 1 type of reusable metal prophy angle. Sterile handpieces were covered with plastic sleeves and the 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 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, gears of the nosecone and motor were sampled and aerobically incubated in TSB containing 0.25% glucose at 56^oC for 7 days. The process was tested in reverse when 0.1 mL of the spore-blood suspension was inoculated onto the gears of sterilized motors. Angle heads 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 160 tests of handpieces contaminated at the prophy cup end, the spores traveled down and inside the motor gears 47 times (29%). In another 160 tests where the motor gears were contaminated, the spores traveled up inside to the prophy cup and out in 74 instances (46%). All types of prophy angles and handpieces 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.