L19. Chemomechanical Disinfection

Question 1

What is the origin of periodontal disease?

Answer 1

Bacterial, fungal and viral - developed into biofilms

Question 2

What are oral biofilms?

Answer 2

Complex communities of microorganisms, embedded within a complex ECM, that are adherent to the dentinal surface and resistant to changes/ attempt of removal

Question 3

What are the clinical objectives of endodontic therapy?

Answer 3

• Remove canal contents;

- Eliminate infection.

Question 4

What is chemomechanical disinfection?

Answer 4

• Mechanical processes to debride and shape the RCs;

- Supplemented by chemical means to enhance biofilm disruption.

Question 5

What are Dr Herbert Schilder’s design objectives?

Answer 5

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

(these create space to allow irrigating solutions and medicaments to effectively eliminate micro-organisms)

Question 6

What is the minimum size of master file usually recommended for apical preparation?

Answer 6

25 (30 for stainless steel files)

25: 0.25mm
30: 0.30mm

Question 7

Why is a minimum apical file size important?

Answer 7

Adequate space preparation for irrigation

Question 8

What are the two main key properties of an endodontic irrigant?

Answer 8

• Killing of biofilm microbes;

- Detachment of biofilm.

Question 9

State some other ideal properties of an endodontic irrigant.

Answer 9

• Low cost;
• Washing action;
• Reduction of friction;
• Improving cutting of dentine by the instruments;
• Temperature control;
• Dissolution of organic and inorganic matter;
• Good penetration within the root canal system;
• Killing of planktonic microbes;
• Non-toxic to periapical tissue;
• Non-allergenic;
• Does not react with negative consequences with other dental materials;
• Does not weaken dentine.

Question 10

What irrigant is typically used in endodontics?

Answer 10

Sodium hypochlorite (NaOCl)

Question 11

With regards to laboratory studies, why is sodium hypochlorite typically the irrigant of choice?

Answer 11

Shows to be very effective at killing and dislodging the biofilm

Question 12

What can NaOCl offer, that other irritants can’t?

Answer 12

Also dissolves organic remnants (necrotic pulp tissue), this helps to disrupt the smear layer

Question 13

What component of NaOCl provides the antimicrobial activity?

Answer 13

Hypochlorous acid (HOCl)

[the buffer ion which predominates in acidic/ neutral environments]

Question 14

What is the concentration range of NaOCl used in endodontics?

Answer 14

0.5-6%

Question 15

What concentration of NaOCl is typically used at GDH&S?

Answer 15

3% (sweet spot - effective but less side effects)

Question 16

Why does effective irrigation of a root canal system require a relatively large volume of NaOCl?

Answer 16

NaOCl quickly looses activity so must be replenished

Question 17

Why is it important to use an endodontic needle to apply irrigant?

Answer 17

• To improve apical irrigation;

- So irrigant flows where we want it to go (not straight through constriction - this can cause nerve damage).

Question 18

What are endoactivators and why are they used?

Answer 18

• Ultrasonic (?) instruments;

- Used in root canals to improve mechanical agitation of debris removal/ biofilm disruption, alongside irrigant.

Question 19

What is an alternative to an endoactivator?

Answer 19

Mechanical agitation - use of GP cone to pump in and out

Question 20

What problems are associated with use of NaOCl?

Answer 20

• Possible effect on dentine properties;
• Inability to remove smear layer by itself;
• Effect on organic material.

Question 21

What effects can NaOCl have on dentine properties?

Answer 21

• Dissolve/ modify organic content;

- Modulus of elasticity and flexural strength can decrease with an increase in NaOCl (as penetration does).

Question 22

What is the smear layer in endodontics?

Answer 22

• Formed during preparation;
• Organic pulpal material and inorganic dentinal debris;
• Packs into tubules;
• Interferes with disinfection;
• Prevents sealer penetration

Question 23

What is used to remove the smear layer?

Answer 23

17% EDTA solution (1-min contact time required)

[EDTA is a chelating agent]

Question 24

What other risks organic are there when using NaOCl in a dental setting?

Answer 24

• Fabrics (discolouration);
• Ophthalmic injuries (can lead to blindness);
• Tissue necrosis due to apical extrusion;
• Allergies;
• Can interact with other materials/ solutions used and produce cytotoxic/ carcinogenic byproducts.

Question 25

Why is sodium hypochlorite often favoured over chlorhexidine digluconate?

Answer 25

• CHX has similar antimicrobial properties to NaOCl;

- BUT less effective at disrupting biofilms.

Question 26

What is the proposed protocol for cleaning a root canal, after shaping has been carried out?

Answer 26

• 3% NaOCl throughout instrumentation;
• At least 30mL NaOCl irrigation after instrumentation;
• 17% EDTA 1-min penultimate rinse;
• 3% NaOCl final rinse.

[dry canal using paper points in between irrigants]