Cleaning of rotary nickel-titanium endodontic instruments

Aim To develop and evaluate an effective cleaning procedure for rotary nickel-titanium (NiTi) endodontic instruments. Methodology New rotary instruments (ProFile size 25/.04) were contaminated by preparing canals of extracted teeth. Three factors were evaluated to develop an effective cleaning sequence: dry or moist storage before cleaning; mechanical removal (brushing); and chemical dissolution in 1% NaOCl with ultrasonication. Debris on flutes was scored after staining in situ with Van Gieson's solution at x45 magnification. Debris was classified as stained or unstained particulate debris and organic film, and rated as none, slight, moderate or heavy. The effectiveness of a recommended cleaning sequence was tested on different instrument types and in private endodontic practices. Results All new instruments showed metallic spurs and fine particulate debris on the surfaces. After contamination, brushing alone removed most particulate debris, but did not remove organic film. NaOCl effectively removed organic film. Under laboratory conditions, the sequential cleaning procedures (moist storage, brushing followed by immersion in 1% NaOCl and ultrasonic cleaning) totally removed organic debris. Dry storage before cleaning or autoclaving with debris present reduced cleaning effectiveness (P < 0.001, one-way ANOVA). In three private practices, the cleaning protocol substantially reduced biological contamination, but complete cleaning was not always achieved (87% clean). Conclusion Complete removal of organic debris from instruments is feasible using a combination of mechanical removal and chemical dissolution, but requires meticulous attention to details.