M2: Sterilisation and disinfection

Question 1

Define sterilisation

Answer 1

Removal/inactivation of all micro-organisms from an article including bacteria, viruses, fungi and spores

Question 2

Define disinfection

Answer 2

Removal/inactivation of some micro-organisms from an article usually excluding bacterial spores

Question 3

Define antiseptic

Answer 3

Substance which destroys or inhibits growth of micro-organisms which can be applied onto living tissue such as open wounds or abrasions

Question 4

Define asepsis

Answer 4

The state of being free from living organisms

Question 5

What are the 4 main methods of steralisation

Answer 5

1. Heat
2. Irradiation
3. Gas
4. Filtration

Question 6

What is moist heat

Answer 6

This is more effective in sterilisation than dry heat and requires temperatures above 100 degrees which is attained by raising the pressure of steam in the autoclave vessel which is saturated with water vapour

Question 7

When is dry heat used

Answer 7

1. Incineration is used for pathological waste materials
2. Red heat and flaming are types of dry heat
3. Hot air sterilisers
4. Microwaves are not reliable for sterilisation

Question 8

What is irradiation

Answer 8

When ionising radiation (gamma, x-rays and accelerated electrons) are used for commercial sterilisation of single used items

Question 9

What is gaseous sterilisation

Answer 9

When ethylene oxide (penetrative and non-corrosive gas) is used for sterilisation of one use items

Question 10

What is filtration

Answer 10

This is a sterilisation technique used to exclude bacteria from fluids (0.22um = pore size filter) - most viruses can pass through

Question 11

Give an example of a biological sterilisation indicator

Answer 11

Bacillus spp; the strip will be cultured after sterilisation and if there is growth, the process has not been successful

Question 12

Give an example of a non-biological sterilisation indicator

Answer 12

• Externally calibrated thermocouple linked to a time monitor
• Autoclave tape and Brownes’ tubes show that apparatus has reached the correct temperature
• TST indicator strips

Question 13

What are the 5 main methods of disinfection

Answer 13

1. Moist heat
2. UV radiation
3. Gasses (formaldehyde gas)
4. Filtration
5. Chemicals

Question 14

What are the classes of disinfectants

Answer 14

• Alcohols (isopropanol and ethanol)
• Aldehydes (glutaraldehyde)
• Biguanides (chlorhexidine)
• Halogens (hypochlorites, iodophors, providone iodine)
• Phenolics
• Peroxygenated compounds
• Surface-active agents

Question 15

What is more sensitive to disinfection

Answer 15

Gram-positive bacteria are more sensitive to disinfection than gram-negative; mycobacteria and fungal spores are highly resistant; enveloped or lipophilic viruses are relatively sensitive (HIV) and hydrophilic viruses are less susceptible, Hep B is resistant

Question 16

What are the three main sources of infection in the dental surgery

Answer 16

1. Patients suffering from the infections disease
2. Patients in the prodromal stage of infections
3. Individuals who are carriers of pathogenic micro-organisms

Question 17

What are the three main ways of infection transmission in the dental surgery

Answer 17

1. By direct contact of tissues with skin or body fluids
2. By droplets containing infectious agents
3. Via contaminated instruments which have not been rendered safe for reuse

Question 18

What are the pros and cons of autoclave sterilisation

Answer 18

This is steaming under pressure

Strengths = low running costs 
Weaknesses = apparatus is expensive, rusts dental instruments

Question 19

What are the pros and cons of chemiclave

Answer 19

No longer used; various microbiocidal substances at high temperatures usually in vapour form

Strengths = doesn't rust dental instruments, cycles cannot be interrupted 
Weaknesses = long cycle time, vapours may be harmful, machine needs careful maintenance, chemicals involved are expensive

Question 20

What are the pros and cons of hot air ovens

Answer 20

Hot air sterilisation

Strengths = very cheap to run 
Weaknesses = long cycle, not reliable even when fitted with circulatory fans, damages instruments, sterilisation cycles can be interrupted