29 - Sterilization, Disinfectants, Antisepsis

sterilization

destruction of all microbial forms, including endospores

• no bacteria, no viruses, no fungi, no spores remain

• physical method in dentistry → steam under pressure

  • other methods include dry heat, filtration, irradiation, gas vapor sterilization, chemical sterilants

endospores

obligate anaerobes survive in air by forming endospores

• classically members of Bacillus and Clostridium

  • B. stearothermophilus used for quality control of heat sterilization

  • B. anthracis used in biological warfare

• resistant structure → heat, irradiation, cold

  • impermeable cortex and outer coat

  • high calcium and dipiocolinic acid content

  • low water content

  • very low metabolic and enzyme activity

• central, subterminal, terminal location for classification

sterilization methods

• steam/most heat → autoclaving

• dry heat → dry ovens

• filtration → HEPA filters in industry

• irradiation → UV at 260 nm or ionizing radiation

• gas vapor sterilization

  • ethylene oxide → explosive

  • formaldehyde gas → carcinogenic

  • hydrogen peroxide gas → used in hospitals

• chemical sterilants

  • peracetic acid → oxidizing agent

  • glutaraldehyde → toxic

dental processing

all dental instruments should be ideally sterilized to protect patients and staff from cross-contamination; all other surfaces are to be disinfected

• decontamination → process of making reusable items safe for reuse and safe for staff to handle

• sequence: cleaning → disinfection → sterilization

  • washer disinfector (WD) → wash + 1min at 90ºC

  • steam autoclaves

    • type N → gravity displacement with steam

    • type B → vacuum stage before steam

      • better at sterilization because gets air out before steam enters, where air blocks steam penetration

      • wrapped/packaged sterile items keep sterility longer

• time and temperature:

  • steam autoclave, gravity displacement (type N): 30min at 121ºC

  • pre-vacuum sterilizer (type B): 3-4 min at 134ºC

  • pressure at 15psi

  • each autoclave and each cycle must be validated by test runs

• standard operating protocol (SOP) → concern for efficacy, compatibility, occupational health

autoclave vs hot-air oven

autoclaving is standard because moist heat works better than dry heat, especially against spores

• autoclave → shorter cycle

  • moist heat as protein denaturant to penetrate spores

  • residual moisture present

  • possible corrosion/rust

• chemiclave → intermediate cycle length

  • chemical hazards possible

• hot-air oven → long cycle

  • no residual moisture

  • can affect temper and brittleness

  • cycle interruption possible

  • risk of spontaneous combustion

indicators of sterility

• mechanical indicators → temperature and pressure gauges

• process indicators → chemical indicators (tape indicators)

  • turns color when goes through process, but not proof of sterility

• biological indicators → viable bacterial spores (prospores)

  • red before autoclaving; yellow color after 12hr incubation at 55ºC indicates failed sterilization

  • test whether highly resistant spores survived, strongest indicator

disinfection

destruction of most microbial forms, but spores and Mycobacterium tuberculosis may remain viable

• divided into high-, intermediate-, and low-level agents

• phenolic index → ratio of effectiveness of chemical compound compared with effectiveness of phenol solution

• modes of action:

  • damage bacterial membranes → chlorhexidine, quaternary ammonium compounds, alcohols, phenols

  • fixing cell membranes → formaldehyde, glutaraldehyde

  • oxidation → halogens (hypochlorite, iodine, bromides)

• factors in choosing a disinfectant → concentration, pH, neutralization by agents, stability, speed of action, absence of odor and toxicity, cost, environmental impact

• used for objects/surfaces

potency of disinfectants

• high-level → active against gram-positive and gram-negative spores, and M. tuberculosis

  • used for critical tools that touch exposed tissues (scalpels, burs)

• intermediate-level → kills M. tuberculosis, vegetative bacteria, most viruses, and fungi

  • only kills few spores

  • used for semi-critical items (mouth mirrors)

• low-level → kills most bacteria and most fungi

  • does not kill M. tuberculosis or spores

  • used for non-critical items (stethoscopes, lab sinks)

common disinfectants / antiseptics used in dentistry

• alcohols → ethanol and isopropanol

  • commonly used at 70% in water for skin antisepsis before injection

  • volatile, flammable

  • inactivated by organic material

• aldehyde → glutaraldehyde

  • tissue fixaive

  • not used in the US anymore

• bisguanides → chlorhexidine

  • widely used as antiseptic and plaque-controlling agent

    • 0.2% as oral antiseptic / plaque control

    • 2% solution in water as denture disinfectant

  • has substantivity because it is absorbed to hydroxyapatite and salivary mucus → keeps working after application

• halogen compounds → hypochlorites and iodine solutions

  • oxidizing agents that release halides

  • can rust metals

  • inactivated by organic materials

• phenolics → used for gross contamination

  • resist inactivation by organics

  • poorly virocidal and sporacidal but kill bacteria

antisepsis

use of antimicrobial agents on skin or mucosa to eliminate or inhibit microbes

• do not eliminate spores

• alcohols → ethanol and isopropanol 70-90%

• iodophors → 1-2mg of free iodine/L

• chlorohexidine → broad antimicrobial agent

  • slower acting than alochols