Endodontic Materials Flashcards
What are the seven main categories of endodontic materials?
- Instruments
- Irrigants
- Intra-canal medicaments
- Obturation materials
- Sealers
- Pulp Capping materials
- Root-end filling materials
What is the purpose of endodontic instruments in chemomechanical disinfection?
They remove soft and hard tissues, eliminate microorganisms, create space for disinfectants, and shape the canal for obturation.
Define stress and its different types in the context of endodontic instruments.
Stress is the deforming force per unit area. Types include tensile, compressive, shear, and torsional stress.
What is a stress concentration point, and why is it significant?
It is an area of increased stress due to abrupt shape changes, increasing the likelihood of instrument fracture.
How does strain relate to stress in an endodontic file?
Strain is the deformation response of the file under stress.
What is the difference between elastic and plastic deformation?
Elastic deformation is reversible within the elastic limit; plastic deformation is permanent and occurs when the elastic limit is exceeded.
At what point does a plastically deformed file break?
At the plastic limit, where the material can no longer withstand further deformation.
What are the causes of cyclic and torsional fatigue in endodontic instruments?
Cyclic fatigue occurs due to repeated tension/compression cycles; torsional fatigue occurs when a file binds in a canal and twists beyond its elastic limit.
How can cyclic and torsional fatigue be prevented during treatment?
Use proper glide path creation, crown-down technique, torque-controlled motors, and avoid abrupt curvatures.
What are the six types of endodontic instruments?
Manually operated
Low-speed instruments
Engine-driven nickel-titanium rotary instruments
Engine-driven shape-adaptive instruments
Engine-driven reciprocating instruments
Ultrasonic instruments.
What distinguishes engine-driven reciprocating instruments from rotary instruments?
Reciprocating instruments rotate back and forth, reducing stress and instrument separation risk, while rotary instruments rotate continuously.
What is work hardening
- Strengtheningofametalby plastic deformation
- Crystal structure dislocation
- Dislocations interact and create obstructions in crystal lattice
- Resistance to dislocation formation develops
- Observed work hardening
What is nitinol?
- Equiatomic alloy of nickel and titanium
- Exotic metal – does not conform to typical rules of mettalurgy
- Super-elasticity – application of stress does not result in usual proportional strain
What is the structure of NiTi and what are it’s qualities?
- Temperature-dependent structures martensite and austenite
- Crystal lattice structure altered by temperature or stress
- Character and proportions determine mechanical properties of the metal
- Martensite form, it is soft and ductile and easily deformed
- Austenitic form is quite strong and hard
What are shape memory alloys?
materials that can be deformed at one temperature but when heated or cooled, return to their original shape.
What are the components of an endodontic rotary instrument?
- Taper – diameter change along working surface
- Flute – groove to collect dentine and soft tissue
- Leading/Cutting edge – forms and deflects dentine chips
- Land – surface extending between flutes
- Relief – reduction in surface of land
- Helix angle – angle cutting axis forms with long axis of file
What are the essential properties an ideal irrigant should possess?
Debris removal
Lubrication
Organic/inorganic dissolution
Deep penetration, Antibacterial/antifungal/antiviral activity
Biofilm disruption
Biological compatibility
Structural integrity preservation.
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 the most commonly used irrigant in endodontics?
It dissolves organic matter, has strong antimicrobial properties, and effectively disrupts biofilms.
What determines the antibacterial activity of NaOCl?
The concentration, volume, contact time, mechanical agitation, and exchange rate.
Why must the smear layer be removed, and which agents are effective in its removal?
It prevents disinfectant penetration and sealer adhesion. 17% EDTA, 10% citric acid, and MTAD effectively remove it.
What hazardous by-product is formed when NaOCl interacts with CHX, and why is it concerning?
Parachloroaniline (PCA), which is cytotoxic and potentially carcinogenic.
What properties make an ideal obturation material?
Ease of manipulation
Dimensional stability
Excellent sealing ability
Non-irritancy
Moisture resistance
Antibacterial
Radiopaque
Non-discoloring
Sterile
Retrievable.
What are the differences between alpha and beta-phase gutta-percha?
Alpha-phase is naturally occurring and more flowable when heated
Beta-phase is used commercially and less adaptable.
What is the composition of gutta-percha cones?
20% gutta-percha, 65% zinc oxide, 10% radiopacifiers, 5% plasticizers.
What are the primary functions of endodontic sealers?
They seal voids, lateral canals, and spaces between dentinal walls and gutta-percha, preventing leakage and microbial infiltration.
How does the setting mechanism of zinc oxide eugenol-based sealers work?
Zinc oxide reacts with eugenol to form a hardened matrix, embedding zinc oxide particles.
What are the advantages and disadvantages of resin-based sealers?
They provide excellent sealing and flow but have initial toxicity and can be difficult to remove in retreatment
Why are glass ionomer sealers not used?
- Removal upon retreatment is difficult
- Minimal antimicrobial activity
- Little clinical data to support use
How does zinc oxide and eugenol set and how can this act as an irritant?
- Setting is a chemical process combined with physical embedding of zinc oxide in a matrix of zinc eugenolate
- Eugenolate formation constitutes hardening – CaOH accelerates this process so must be removed from canals
- Free eugenol which remains can act as an irritant
- Lose volume with time due to dissolution – resins can modify this
What are the qualities of calcium silicate sealers?
- High pH (12.8) during the initial 24 hours of the setting
- Hydrophilic
- Enhanced biocompatibility
- Does not shrink on setting
- Non-resorbable
- Excellent sealing ability
- Quick set - three to four hours – requires moisture
- Easy to use
What are the key differences between grey and white MTA?
Grey MTA contains tetracalcium aluminoferrite (causing discoloration) and has better setting characteristics; white MTA lacks this compound
Why does MTA have an extended setting time, and how does hydration affect its setting reaction?
It is a hydraulic cement that requires water for setting; hydration reactions are slow and differ between white and grey MTA.
How do bioceramic cements differ from conventional sealers?
They are highly biocompatible, hydrophilic, do not shrink, and have superior sealing ability.
According to the AAE, what are the biological and mechanical criteria for an ideal root filling?
Biocompatible, creates a fluid-tight seal, promotes periradicular healing, and prevents reinfection.
