Sterilization

• Bacteriostatic


  Growth inhibited; inhibition reversed when agent removed
• Bactericidal


  Irreversible lethal effect, kills bacteria
• Sterilization


  Render incapable of reproduction; Destruction or removal of all forms of life
• Earle H Spalding (Temple University, Philadelphia. 1939) devised a rational approach to disinfection & sterilisation
• Items based on degree of risk


  • Critical
  • Semi-critical
  • Non critical
• Disinfection


  Use of bactericidal chemical agents to destroy the potential infectivity of inanimate objects (exception being bacterial spores)
• Antisepsis


  Topical application of chemicals to a body surface to kill or inhibit pathogens
• Death rate of bacteria


  1. Decreasing rate proportional to number of bacteria

  2. Longer time to reach sterility
• D value


  Dose of agent required to reduce the population to 1/10
• If n = 5 (phenol), doubling the concentration of the drug will reduce the time required to achieve the same extent of inactivation 32 fold
• Increase in temperature


  Increase in activity of agent, Killing by heat alone
• Rates of sterilization can increase like chemical reactions, eg. three times for every rise of 10o C (Q10= 3)
• Q10 EtOH = 50 for S.typhimurium, 10 for S.aureus
• Thermal Death point


  Lowest temperature that sterilizes a 24hr culture in broth pH 7 in 10 min
• Pasteurization


  Disinfect and postpone spoilage, 62oC for 30 min, efficient against milk borne pathogens
• In vitro exposure of organisms to an agent in liquid medium with subsequent tests for viability, or by direct application of the agent to cultures on solid media, only shows that agent is either bacteriostatic or bactericidal
• Moist Heat - Boiling @ 100o C


  • Acts by denaturing proteins
  • Immersion for 10 -20 min destroys all vegetative cells and most spores
• Moist Heat - Steam Sterilization (Autoclaving)


  • Uses moist heat in the form of saturated steam under pressure in an air tight vessel
  • Relies on steam, pressure, temperature & time
  • Most commonly used - 121oC applied for 15 - 20 min, maybe longer depending on materials being sterilized
  • May use higher temp. and pressure for shorter periods, (132oC for 5 mins)
  • Must be monitored- mechanical, chemical and biological indicators
• Dry Heat


  • As proteins dry, denaturation resistance increases
  • Much less efficient than moist heat - uses higher temp.
  • Ultimate dry heat sterilisation is incineration-100% effective
  • Proper use of dry heat ovens provides effective sterilization in dental practices - Hold Temp. at 160oC for 2 hrs ( preheating recommended to allow heat penetration)
  • Disadvantages - destruction of rubber and plastic, melting of solder on impression trays etc.
  • Advantages - Good preservation of cutting edges, no corrosion caused by water vapour
• Radiation


  • Ultra violet (260nm) - poor penetration, damages DNA, used to reduce airborne infection in operating theatres & surfaces
  • X -ray and g Rays (0.001-10nm) - Good penetration, produces damage to biological molecules (DNA), uses - Sterilization of filters, syringes, needles, Petri dishes & Food
• Filtration


  • Seitz filters made of cellulose & asbestos, Sintered Glass, Membrane filters, Cellulose acetate, Cellulose nitrate, Teflon, 0.04 - 0.45mm
• Risks in the Dental Clinic


  • Oral micro-organisms
  • Handpieces
  • Dental instruments
  • Surgical dressings
  • Medicaments
  • injectables
• Transmission routes in Dental Clinic


  • Direct - Oral Cavity, Hands
  • Direct - Spray syringes, Bracket tables, Chair switches, Drawer handles, Light handles, Telephone
  • Airborne - Nose, Throat
• Cavity preparation and Ultrasonic scaling (sub-gingival) produces aerosols containing blood and saliva- Bio-aerosols
• Bio-aerosols contain bacteria and viruses such as influenza, Hep B, Hep C and HIV
• Infection control measures in Dental Practice

  • Universal barrier techniques- gloves, high filtration face masks
  • Rubber Dam
  • Patient positioning
  • Clean air systems – Extra Oral-Vacuum Aspirator
  • High volume evacuator
• Clinics need to be maintained as a clean area for infection control
• Instrument processing in Dental Practice


  • Pre-cleaning- mechanical removal of proteinaceous organic material
  • Application of a suitable disinfectant
• Hand washing before and after treatment of each patient