Chemomechanical Disinfection Flashcards
What are the 3 design objectives?
- Create a continuously tapering funnel shape
- Maintain apical foramen in original position
- Keep apical opening as small as possible
What does mechanical prep do?
This creates space to allows irrigating solutions and medicaments to more effectively eliminate micro-organisms from the root canal system
What are the stages in mechanical prep?
7
prep of tooth
access cavity
create straight line
intial negotiation
coronal flaring
working length determination
apical prep
What ISO size should the apical prep be?
size 25
Why would a larger apical prep be advocated?
larger allows irrigation (ISO 30)
What are the ideal properties of an irrigant?
2 most important
killing of biofilm microbes
detachment of biofilm
What is the primary irrigant used?
NaOCl (sodium hypochlorite)
How does NaOCl work chemically?
- 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
Why is NaOCl used?
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
What concentration of NaOCl is optimal?
3% (between 0.5 - 6%)
Why is NaOCl dangerous near the apex of the tooth?
may leak out to surrounding tissues and cause damage
What is the endoactivator a type of?
mechical agitation used to allow irrigant to reach apex
What is the effect of NaOCl on root dentine?
increased conc reduces elasticity and flexural strength
What is the smear layer and what does it do?
- 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
What is the smear layer removed by?
second irrigant - 17% EDTA
NaOCl cannot remove smear layer by itself
How does EDTA work and how is it used?
- EDTA is a chelating agent that is capable, when used with NaOCl, of removing smear layer
- 17% solution used
- 1 minute contact time necessary
Why should NaOCl be aspirated before using EDTA?
mixing both creates a precipitate
What are NaOCl complications?
- 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
Why is chlorhexidine good and how long does it last?
- Dentine medicated with CHX acquires antimicrobial substantivity.
- Adsorbtion of CHX prevents microbial colonisation for time beyond time of application
- Varying times, upto 12 weeks
What are the limitations of chlorhexidine?
- 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
What is the interaction between chlorhexidine and NaOCl?
- Interaction with NaOCl forms para-chloroaniline (precipitate) making root canal brown
- Cytotoxic and carcinogenic
- Uncertain bioavailability
What are the steps of irrigatation (with concentrations and chemicals)?
- 3% NaOCl throughout instrumentation and at least 30mL after instrumentation complete with MDI – at least 10 minutes prior to obturation
- 17% EDTA 1min penultimate rinse
- 3% NaOCl final rinse
Between irrigants what should be done?
Dry canal using absorbent paper points between irrigants
