To sterilize a metal dental instrument, if a steam sterilizer is unavailable, the next most effective method is to boil it in water for 15 minutes.

• A. Boiling it in water for 15 minutes
• B. Dipping it into a concentrated acid solution
• C. Heating it in a hot air oven at 160°C for 20 minutes
• D. Washing it in soap and water

Answer: (A)

The idea being tested is how different sterilization methods compare in killing microorganisms, especially with metal instruments. Steam under pressure is the most reliable and quickest way to sterilize because the high-temperature, moist steam penetrates and destroys microbes, including spores. If that isn’t available, boiling in water provides moist heat at 100°C with enough exposure time to achieve sterility for many pathogens, making it the best practical alternative among the given options. It is more effective for sterilization than dry heat or cleaning alone, and it’s far more reliable than simply washing with soap and water or using a harsh chemical bath.

Dipping in concentrated acid is not a safe or dependable sterilization method for dental instruments and can be corrosive and hazardous. Heating in a hot air oven at 160°C for 20 minutes uses dry heat, which takes longer to sterilize and is less effective for reaching all microbes in a one-step process. Washing with soap and water cleans debris but does not achieve sterilization. So boiling water for 15 minutes stands out as the most effective available method among the choices when steam sterilization isn’t an option.