Seminar 10: Restoring After RCT Flashcards
What direction does peritubular dentine run?
Outwards radially
What direction does the collagen mesh run in dentine?
Perpendicular to tubules
Water can be found in two forms in dentine, they are?
Bound
Unbound
Where is bound water found in dentine?
Hydrogen bonded to collagen to prevent fibres joining to each other
Where is unbound water found in dentine?
Inside the tubules
What is the function of unbound water in dentine?
To exert a hydrostatic pressure when pressure is applied to the dentine
Why does dehydrated dentine fracture more than hydrated dentine?
Less water
Unable to undergo plastic strain
What happens to the calcium in dentine upon dehydration?
Calcium depletes and increase risk of fracture of dentine also when dehydrated
What happens to collagen in dehydrated dentine?
The shrink and pull tighter pulling HAP crystals in dentine closer causing it to become brittle
Why does dentine lose its cushioning ability once dehydrated?
Due to loss of water
What features increase risk of fracture post RCT?
- Less guarding
- Altered mechanical properties of dentine
- Loss of tooth tissue: loss of marginal ridge!!!
- Loss of proprioceptive feedback
- Effects of chemicals during RCT
What are the three principles of restoring root treated teeth?
- Preserve remaining tooth - odds ratio of x10
- Ensure stress is distributed favourably amongst remaining tooth
- Seal against coronal leakage
Survival of RCT teeth at 8-10 years is ?
Gulbivala and Ng 2019
87%
Which teeth are at greatest risk of fracture ?
Root treated molars
Those last in the arch
Immature ant teeth
MOD plastic restorations esp premolars
What effect does NaOCl have on dentine?
Effects organic matrix
Reduces flexural strength
Osmotic pressure during irrigation drives water out
What effect does EDTA have in dentine?
Disrupts inorganic matrix
Exposed collagen matrix to damage by NaOCl
To what depth does NaOCl and EDTA affect dentine?
0.3-0.5mm deep
What impact does size of dentinal tubules have on depth of NaOCl/EDTA penetration?
Wider tubules greater depth of effect
Younger teeth are more susceptible to chemicals since tubules are wider
What effect does CaOH have on dentine?
Deproteinates dentine
Caustic
What factors make non root treated teeth fracture ?
Tertiary dentine formation
Ageing
Sclerosis
Restorability assessment prior to RCT should be carried out. What should this include?
Space available
Remaining tooth
Occlusion
How much ferrule needed for success of restoration ?
2mm height and width around circumference of tooth
To increase amount of tooth structure present what can be done to the root?
Extrude
In which occlusal circumstance are anterior teeth loaded axially?
In class 3 malocclusion
What type of movements should be avoided on root treated teeth?
Excursions
What are the features of posts that affect their function?
Length- not longer than height of clinical crown- better stress distribution to the alveolar bone and tensile strength of apical root is greater than coronal root Diameter Shape Surface Diaphragm 2.Need to leave 4-5mm of GP apical to ensure apical seal maintained 3. Need at least 2mm of ferrule and dentine needs to be 1mm thick helps with resisting lateral forces and fracture resistance 4. Tip should be no more than 1/3 of diameter of the root 5. Not exceed the diameter of the shaped canal
Why do fibre posts offer more favourable characteristics ?
They flex allowing for deformation so root fracture tends to be more coronal in the root
What is the benefit of a parallel post?
Offer greater retention per unit length
What are the risks with parallel posts?
Can generate greater stresses
What are the risks with tapered posts?
- less retentive
- can generate a wedging effect but this can be reduced by placing a shoulder
What is the key determinant for retention of a post ?
Post length
What should you consider when determining ideal post length?
- Length of root canal filling- always leave 3mm apically
- where bone loss present ensure post extended to beyond bone level
- post should be similar height to crown
What is difference between cast and wrought posts ?
Cast: melted and poured
Wrought: this has been worked and shaped
Between cast and wrought post which should have a greater diameter?
Cast since they are weaker than wrought
What type of metal post would you use in a narrow canal?
Wrought
The diameter of post is more important for?
Post strength
What type of surface configuration for posts exist ?
Smooth
Rough
Serrated
Threaded
What function do diaphragms play in posts?
Can help prevent fracture and stresses concentrating in the apical region
Why is it better to have an onlay than crowns in cracked teeth?
- Onlays prevent cusp flexure
- Crowns cause thinning of the walls causing bracing to take place further down the tooth resulting in whole crown snapping off
What is the effect of 5.25% of NaOCl on dentine according to Sim et al 2000?
Reduces elasticity and strength
Increases stiffness
