Effect of Different Sterilizing Methods on the Corrosion of Dental Steel Bur: A Comparative Study

Objectives: To compare the corrosion of dental steel bur after sterile with different methods and sterilizing cycles.
Methods: Three hundred dental round steel burs were divided into two groups, dipped or not dipped with sodium nitrite, a rust inhibiting solution. Both two groups were later subjected to repeated sterilization by autoclave, hot-air oven or formaldehyde gas for 1, 3, 5, 10, and 15 cycles. Level of corrosions were measured by chemical reaction with 1,10-phenanthroline, energy dispersive x-ray spectrometer (EDX) and scanning electron microscope (SEM).
Results: Sterilizing the dental steel bur by autoclave either dipped or not dipped with sodium nitrite induce significant increase (p < 0.05) in corrosion level compare to other sterilizing methods as demonstrated by measured Fe3+ level. The corrosion in autoclave group started to be observed as early as the 3rd cycle and in all later cycles. On the contrary, sterilization with hot-air oven and formaldehyde gas did not induce a significant difference in Fe3+ level compared to control group even at the maximum sterilizing cycles tested. The measurement of element Fe/O ratio by mean of EDX show no difference between groups. Micrographs and SEM of dental burs sterilized by autoclave demonstrated obvious sign of corrosion compared to the other methods.
Conclusions: Sterilizing the dental steel burs with autoclave induces significant corrosion. Application of sodium nitrite could not prevent corrosion induced by sterilization of dental steel burs.