Chemomechanical Disinfection

Question 1

What are the 3 design objectives?

Answer 1

• Create a continuously tapering funnel shape
• Maintain apical foramen in original position
• Keep apical opening as small as possible

Question 2

What does mechanical prep do?

Answer 2

This creates space to allows irrigating solutions and medicaments to more effectively eliminate micro-organisms from the root canal system

Question 3

What are the stages in mechanical prep?

7

Answer 3

prep of tooth
access cavity
create straight line
intial negotiation
coronal flaring
working length determination
apical prep

Question 4

What ISO size should the apical prep be?

Answer 4

size 25

Question 5

Why would a larger apical prep be advocated?

Answer 5

larger allows irrigation (ISO 30)

Question 6

What are the ideal properties of an irrigant?

2 most important

Answer 6

killing of biofilm microbes
detachment of biofilm

Question 7

What is the primary irrigant used?

Answer 7

NaOCl (sodium hypochlorite)

Question 8

How does NaOCl work chemically?

Answer 8

• NaOCl ionises in water into Na+ and the hypochlorite ion, OCl-
• Establishes equilibrium with hypochlorous acid (HOCl)
• Acid/Neutral HOCl predominates
• pH 9 and above OCl- predominates
• HOCl is responsible for antibacterial activity

Question 9

Why is NaOCl used?

Answer 9

potent antimicrobial activity
dissolves pulp remnants and collagen
only root canal irrigant that dissolves necrotic aand vital tissue
helps disrupt smear layer by acting on organic component

Question 10

What concentration of NaOCl is optimal?

Answer 10

3% (between 0.5 - 6%)

Question 11

Why is NaOCl dangerous near the apex of the tooth?

Answer 11

may leak out to surrounding tissues and cause damage

Question 12

What is the endoactivator a type of?

Answer 12

mechical agitation used to allow irrigant to reach apex

Question 13

What is the effect of NaOCl on root dentine?

Answer 13

increased conc reduces elasticity and flexural strength

Question 14

What is the smear layer and what does it do?

Answer 14

• Smear layer formed during preparation
• Organic pulpal material and inorganic dentinal debris
• Superficial 1-5μm with packing into tubules
• Bacterial contamination, substrate and interferes with disinfection
• Prevents sealer penetration

Question 15

What is the smear layer removed by?

Answer 15

second irrigant - 17% EDTA

NaOCl cannot remove smear layer by itself

Question 16

How does EDTA work and how is it used?

Answer 16

• EDTA is a chelating agent that is capable, when used with NaOCl, of removing smear layer
• 17% solution used
• 1 minute contact time necessary

Question 17

Why should NaOCl be aspirated before using EDTA?

Answer 17

mixing both creates a precipitate

Question 18

What are NaOCl complications?

Answer 18

• Discoloration of fabrics
• Ophthalmic injuries due to eye contact
• Apical extrusion leading to tissue necrosis - intracanal use, no more toxic than saline solution
• Allergic reactions

Question 19

Why is chlorhexidine good and how long does it last?

Answer 19

• Dentine medicated with CHX acquires antimicrobial substantivity.
• Adsorbtion of CHX prevents microbial colonisation for time beyond time of application
• Varying times, upto 12 weeks

Question 20

What are the limitations of chlorhexidine?

Answer 20

• Antibacterial activity – studies show conflicting results, may have similar activity to NaOCl.
• Less antifungal activity that NaOCl
• Somewhat active against biofilms, but unable to disrupt biofilms

Question 21

What is the interaction between chlorhexidine and NaOCl?

Answer 21

• Interaction with NaOCl forms para-chloroaniline (precipitate) making root canal brown
• Cytotoxic and carcinogenic
• Uncertain bioavailability

Question 21

What are the steps of irrigatation (with concentrations and chemicals)?

Answer 21

1. 3% NaOCl throughout instrumentation and at least 30mL after instrumentation complete with MDI – at least 10 minutes prior to obturation
2. 17% EDTA 1min penultimate rinse
3. 3% NaOCl final rinse

Question 22

Between irrigants what should be done?

Answer 22

Dry canal using absorbent paper points between irrigants