JVD 2020 #1 Endodontic Disinfection for Orthograde Root Canal Treatment in Veterinary Dentistry; Sasser

Question 1

Define biofilm

Answer 1

Sessile multicellular microbial community that is attached to a surface and enmeshed in a self-produced matrix of extracellular polymeric substance

Question 2

How much more resistant are bacteria within biofilms to antimicrobials?

Answer 2

100 to 1000-fold more resistant to antimicrobial agents

Question 3

Define smear layer

Answer 3

ultrafine layer of inorganic and organic substances, dentin particles, remnants of vital or necrotic pulp tissue, microorganisms and retained irrigants formed by shaping and irrigating the root canal

Question 4

What are the possible problems/sequela of the smear layer?

Answer 4

harbors microorg., reduces dentin permeability, compromises adequate disinfection by limiting disinfectant diffusion inside the dentinal tubules and is potential channel for microleakage

Question 5

What are the mechanical and chemical objectives of Irrigation in Endodontics?

Answer 5

flush out debris
lubricate the canal
dissolve organic & inorganic tissue
prevent formation of smear layer

Question 6

What are the biological objectives of Irrigation in Endodontics?

Answer 6

Highly effective against anaerobic and facultative microorg.
Inactivates toxins
Is nontoxic to vital tissue
Disinfects areas inaccessible to endo instruments

Question 7

Properties of an IDEAL irrigant for RCT?

Answer 7

1. Nonirritating to periapical tissues
2. Remains stable in solution
3. Prolonged, broad-spec antimicrobial effect
4. Active in presence of blood, serum and protein derivatives
5. Low surface tension
6. Does not stain
7. Does not induce cell-med immune response
8. Able to dissolve necrotic pulp and biofilm
9. Prevents or dissolves smear layer
10. Able to disinfect dentin/tubules
11. Non toxic/carcinogenic and doesn’t interfere with healing
12. No adverse effect on physical properties of exposed dentin
13. No adverse effects on sealing ability of filling materials

Question 8

Key points of Sodium Hypochlorite (NaOCl)

Answer 8

• Most commonly used irrigation solution b/c of ability to destroy variety of microbes and dissolve necrotic pulp and organic debris of smear layer
• Conc 0.5-6%
• in water, produces hypochlorous acid and chlorite ions–> dissolve organic tissues
• removes exposed collagen fibrils, which decreases adherence for E. faecalis
• Efficacy can be improved by incr temp of solution, volume, contact time (5-20m) and using agitation/activation methods
  
  • heating 0.5% NaOCl to 113F dissolved pulp as well as 5.25% root temp; Elevating temp to 140F resulted in complete pulp dissolution (diff study)
• Loses dissolving/antibact capacity within 2 mins–> replenish!

Question 9

What are the limitations/disadvantages of Sodium Hypochloriate (NaOCl) irrigating solution?

Answer 9

• It will not dissolve/remove the entire smear layer
• May negatively affect periapical tissues, if admin forcefully
• Implicated in hypersensitivity reactions due to phago. of neuts in periapical region
• Because it removes collagen fibrils when used as final irrigant- could interact and decrease bonding strength of resin-based canal sealer??
• 5.25% solution compared to 0.5% solution decreases the elastic modulus and flexural strength of dentin due to proteolytic action on collagen matrix (pot weaken tooth)

Question 10

Key Points Chlorhexidine (2% chlorhexidine gluconate) irrigant

Answer 10

• Strongly basic molecule with cationic charges capable of binding to negatively charged surfaces of bacteria– damaging cell wall
• Bactericidal at high conc and bacteriostatic at low conc
• Shown activity against Gram + & - bacteria and yeasts
• Sustantive antimicrobial activity by being readily adsorbed into the hydroxyapatite crystals of dentin and released back (tx residual bacteria)
• Differs from NaOCl as it does not remove collagen fibrils- may improve resin-dentin bond
• lower grade of toxicity locally & systemically compared to NaOCl– less likely tissue rxn with extrusion

Question 11

Limitations/Disadvantages of Chlorhexidine gluconate 2% irrigant

Answer 11

• Inability to dissolve organic debris compared to NaOCl
• Cannot destroy resistant biofilm structure
• Creates parachloroaniline insoluble precipitate when used with NaOCl
  
  • Parachloroaniline can cause cyanosis, carcinogenic, penetrates tubules and interferes with sealer

Question 12

Key points Ethylenediaminetetraacetic acid (EDTA) irrigant

Answer 12

• Demineralizing- used to remove the inorganic mineralized components of smear layer
• highly biocompatible
• normally conc 15-17% disodium EDTA liquid or paste
• Detergents frequently added to solution to aid in wetting of the root canal wall and increase penetration into the dentin
• Lubrication of hand or rotary files
• Most commonly used with or alternately with NaOCl to enhance cleaning/antimicro
• EDTA retains Ca-binding abilities when combined with NaOCl but NaOCl will lose some tissue-dissolving capacity

Question 13

Limitations/Disadvantages of EDTA irrigant

Answer 13

• Little to no antimicrobial effects
• When used by itself, incapable of removing entire smear layer and disinfection
• EDTA as a final irrigant demineralizes dentin, exposing collagen, and potentially creates ideal envir for residual E. faecalis to adhere

Question 14

Key points MTAD - “mixture of tetracycline, acid and detergent” irrigant

Answer 14

• Combination irrigant as alternative to EDTA as final rinse
• supplied as powder and liquid when mixed creates aqueous sol 3% doxycycline, 4.25% citric acid as a demineralizing agent and 0.5% polysorbate as a detergent
• Synergistic effects on disruption of bacterial cell walls and membranes, effectiveness against E. faecalis
• Increasing effectiveness of MTAD in eliminating smear layer by first irrigating canal with 1.3% sol of NaOCl
• has not demonstrated effects on flexural strength or elastic modulus of dentin- beneficial if using resin-based sealer
• Failed to demonstrate dentin disinfection against E. faecalis compared to 5.25% NaOCl

Question 15

Delivery of Endo Irrigants

Answer 15

• Critical component of chemical debridement and disinfection
• Irrigation dynamics depend on ability of irrigant sol to be dispersed to apical portion
  
  • penetration depth of needle, diameter and length of root canal, diameter of needle, irrigation pressure and velocity, type and angle of needle bevel
• needle–> flexible and has one side opening to prevent excess pressure/velocity apically
• Standard 25- or 31-mm endo needles shorter than many veterinary species canal lengths thus disinfection of most apical portion impossible

Question 16

Negative- pressure irrigation

Answer 16

• Irrigant delivered to the coronal access site and aspirated down the canal to the apical terminus of needle then drawn into the microcannula needle through a series of holes in terminal aspect.
• Microcanula needle has sequence of 12 laser drilled microscopic holes; manufactured in 32 and 50mm lengths making adaptation to the longer canals possible.
• Less risk of periapical exgtrusion of irrigant

Question 17

Manual canal irrigation

Answer 17

• Frequent replenishment of solutions, flusing debris from the root canal space with placement of irrigant in area of microorganisms
• Actual exchange of fluids occurs within 1.0 to 1.5mm apical to needle tip
• Wider needle enables more active flushing but risks wedging in canal limiting necessary backflow of irrigant and potential apical extrusion

Question 18

Key points of Intracanal Medicaments

Answer 18

• Use when standard disinfection and tissue disolution does not resovle pulpal bleeding during standard RCT
• Use as root canal dressing between 2 endo appointments
• Impede bacterial regrowth, supply continued disinfection and create a physical barrier in the root canal system
• Calcium hydroxide most commonly used as slurry with water or NaOCl
  
  • high pH provides sustained broad-spec antimicrobial, capacity to dissolve necrotic tissue remants, bacteria and by-products
  • Needs complete removal at 2nd appointment to reduce effect on sealer
  • may have limited action on biofilm and E. faecalis