Posts And Cores Flashcards
How to assess if RCT was successful?
Lacks of signs and symptoms clinically
No history or pain or discomfort
Not TTP
Not tender to buccal palpation
No sinus or swelling
Evidence of helping on radiographs
Functional and aesthetically good
If the tooth is RCT-ed, and we are restoring it, do we re RCT?
If GP was exposed to saliva for longer period-yes
If post-treatment disease is diagnosed -yes
Factors influencing if the tooth has good prosthodontic prognosis are:
Quantity and quality of remaining tooth tissue-most important factor
Ferrule effect
Remaining coronal tooth substance offers retention and resistance to bond to
” A metal ring or cap intended to embrace the tooth structure cervically to achieve root strengthening and prevent shattering of the root
1 mm width between post hole and the edge of the substrate, 2 mm height of tooth substrate
Benefits offered by ferrule:
Longer ferrule- increases fracture resistance
It resists lateral forces from the post and leverage from the crown in function
Increases retention and resistance of the crown-harder to pull it out etc
Provides anti-rotational features
Increases longevity of the post and core restorations
Less likely of failure or if it happens more chance of repairing
Crown and crown prep features needed for success
Ferrule (dentine axial wall height) of 2-3 mm
Parallel axial walls
Restoration must encircle the tooth
Margins on sound tooth tissue not restoration
Biological width not invaded
Tooth restored with a post but no ferrule have what complications?
Increase risk of:
Root fracture
Coronal-apical leakage
Recurrent caries
Dislodgement of crown/core
Periodontal injury-LoA, bone loss.. from the invasion of biological width
Is GP antimicrobial
No
How to clean the pulp chamber?
With alcohol as it removes extra sealer from the pulp chamber
Vitrebond is placed so the pulpal floor is completely sealed.
When do we place the post?
Immediately as we will be familiar with morphology and length of the roots( less chance of perforation or excessive GP removal). Apical seal won’t be disrupted. Decreases the chance of coronal leakage as there is no temporary crown or dressing though which leakage can happen
If delayed, the apical seal can be disturbed.
Size of the post
Depends on materials
Metal or non metal, adhesive or non adhesive
The length is required- more important than width. Longer the post-better retention (especially if longer than crown length)
We need at least4-5 mm of GP apically- needed for the seal as many lateral canals in that apical region
Width-needed for resistance and strength of the post to fracture.
Ideally, at least 1 mm diameter as the tip (less than the third of the thickness of the diameter of the root at the corresponding depth)
Every tooth has a different morphology
Wider post risks:
Increased risk of perforation, increased cervical strength, decreased impact resistance, reduced resistance.to root fracture
How to prepare post space
- Remove GP by chemical (solvents, but avoid due to risk of apical leakage), mechanical (best option, burs with non cutting tips so lower risk of perforation, not so much heat generated) and thermal (ultrasonic, system B-avoid as can disturb apical GP)
- Piezo reamer or parapost reamers used to complete the prep (gives parallel walls)- use after GP removed!
Cements used to cement posts
Should be insoluble, prevent microleakage
Should stick to radicular dentine to reinforce the tooth
Withstand fatigue (as they can cause microcracks)
Luting cements for posts
E.g. zinc phosphate or polycarboxylate:
No chemical bond, retention by mechanical means only
GIC
Depends on resin content (RMGIC)-not indicated for post cementation as exhibit hygroscopic expansion that can cause fracture of the roots
Conventional GIC- more resistant than zinc phosphate, and there is a degree of bonding to dentine
Resin based luting cements
Can reinforce the tooth, aid post retention, need conditioning of the dentine (etching) forming hybrid layer.
Use of sodium hypochlorite can affect this bond as is a strong oxidising agent, leaving oxygen rich layer on dentine that can inhibit polymerisation of the resin
If eugenol was used, also affects resin
Moisture sensitivity! - use self etch but can be less effective
Dual curing can be used
Self adhesive cement -
No pretreatment of root dentine- not so technically sensitive
Contain phosphoric acid that demineralises the dentine and infiltrates hard tissues
Advantages of adhesive cementation
Improved marginal adaptation/better fit
Improved apical seal
Increased post retention
Relieves stress in root canals as it sticks and distributes stress
Optimizes fracture patterns-if fracture happens, still a chance to repair it
Disadvantages of adhesive cementation
Difficult to access and see without magnification
Remnants of acid, debris from the prep may persis-bonding decreased by GP remnants, smear layer debris, sealer etc
Treatment objectives of restoring RCTed teeth
- Retain the tooth as a functional unit in the arch
- Maintain the coronal seal of RCS
- Protect and preserve remaining tooth structure
Factors to consider when planning a final restoration
Amount of sound supra gingival remaining tooth structure
Position of the tooth in the arch (molars 6x more likely to fail if no cuspal coverage)
Opposing dentition
Length, width and curvature of the root
Consequences of endo treatment upon a tooth
Brittleness
Proprioception ( reduced by 30%)
Fracture resistance
What is a post
Peg/pin used for fastening of the artificial crown/core to a natural tooth root
Usually made of metal/fiber material that is filled into the prepared canal , when combined with a core it provides retention and resistance for the artificial crown
It’s function is to retain the core NOT to reinforce the root structure
Restorative considerations for post retained restoration
If tooth has minimal access cavity and walls intact or has loss of one wall (MO, DO), loss of two walls (MOD)-no need for post
If tooth has lost 3 walls or has no walls at all- post IS required
Ferrule
The remaining walls of dentine extending coronal to the shoulder of the preparation provide what is known as ferrule effect - a protective effect resisting root fracture
2-3mm of coronal dentine is considered an optimal height to produce a ferrule but NOT LESS than 1.5 mm
Restoration lacking resistance form (ferrule) will fail long term regardless of the retentiveness of the post
Ferrule offers retention, resistance, substrate to bond to and strengthening of the root
Ferrule resist lateral forces which means that it increases retention and resistance of the restoration
Importance of ferrule - functional lever forces, lateral forces exterted during post insertion, wedging effect of tapered posts
It resists stresses which otherwise cause root fracture
Optimal post dimensions
Length - equal/ longer to the height of the crown, or 1/3-2/3 of the length of the root, more important than the width
Apical seal- 4-5 mm from the apex
Diameter/width - no more than 1/3 of the root diameter at that level, at least 1 mm at the tip
Curvature - only placed in the straight part of the canal
Retention increases with the width, but increasing the width does not improve retention (wider- increased risk of perforation, cervical stresses and decreased resistance to root fracture and impact resistance)
Post types
Prefabricated a d custom made ( direct or indirect)
Metal ( SS, titanium) and non metal ( glass or ceramic fiber)
Parallel or tapered (geometry)
Serrated, smooth and threaded
Metal vs fibre posts
Fiber- difficult to remove, tooth coloured- good aesthetics, compatible to adhesive systems, can be placed immediately, low elastic modulus/similar to dentine, can absorb/dissipate stress
Metal- useful in flared canal, custom made, if indirect - need impression, conserves tooth tissue which reduces risk of perforation compared to parallel-sided fibre post
When fibre post cannot be used
If there is less than 2-3 mm of ferrule( supragingival tooth structure) or if there is parafunction or deep overbite
-fiber post can debond at post cement interface and lead to recurrent caries
Tapered Vs parallel
Tapered- follows root form ensuring maximum remaining root dentine apically, stress concentration coronally, wedging effect (bad side), retained by cement (bad side)
Parallel- uniform stress distributing along length, increased pull-out strength, bad side - more tooth structure removed, stress concentration apically
Surface design of posts
Smoother it is -less retention
Increased retention comes from self-threading into the dentine
But this sets up fracture lines as it cuts its way into the canal
Installation pressure is subsequently relieved by root fracture
Optimal post design
Non threaded - avoid installation pressure created by threading posts that will later be relieved by root fracture
Parallel sided- avoids wedging forces
Cement retained - cement tends to distribute masticatory forces evenly
Types of cements for post
Adhesive resin cement- greater retention with adhesive resins, highest compressive strength, premature setting of the resin may not allow complete seating of post, bonding may be impaired by the presence of remnants of endodontic material
Glass ionomer cement- provides a wear chemical bond to dentine, retrievability is easier, fluoride release and anti-cariogenic effect, requires several days/weeks to reach maximum strength
RM GIC- fluoride release and anti-cariogenic effect, insoluble, provides good retention of prosthesis, imbibe water and expands with time
MECHANICALLY, an endodontic post should not:
- Break
- Break the root
- Distort or allow movement of the core and crown
A post needs:
Retention
Resistance
Resilience
Stiffness
Strength
The resistance of the post is influenced by:
Presence of ferrule
Presence of antirotational features
Post length and rigidity
If the post has higher Modulus of elasticity than dentine, where is the stress concentration
At the bottom of the post
Usually what happens in metal posts
This kind of post is prone to fail due to tooth fracture
If stiffness of a post is similar to the dentine, stress is?
Stress is dissipated by the coronal and the root dentine
This happens in fibre-based posts
This kind of post tends to fail due to debonding
What are 3 clinical and 6 radiographic findings to say endo was successful?
Clinical: no swelling/sinus, no signs and symptoms, not ttp
Radiographic: obturation to WL, reduction in periradicular radiolucency, bone healing, no coronal leakage, no secondary caries, narrower PDL space
What is active post?
Primary retention from root dentine via threads screwed into the wall of the root canal
Risk of vertical root fracture during placement as introduces great stress within the root during placement- wedging effect
Is should be avoided
What is passive post?
Passively placed in close contact to the dentine wall
Retention relies on the luting cement
(If adhesive cement improved retention)
Can be parallel or tapered
Parallel is more retentive that tapered but more constructive
Parallel less likely to cause root fracture than tapered
Luting cements for post
Should be insoluble and prevent microleakage
Should adhere to dentine
Should withstand fatigue forces
E.g. zinc phosphate, GIC..
Advantages and disadvantages of adhesive cementation
Advantages: improved marginal adaptation, improved apical seal, increased post retention, relives stress in root canal
Disadvantages: difficult access and vision without magnification, can be compromised by acid and debris left in RCS..
Desirable core properties
High compressive strength
Flexural strength
Dimensional stability
Ease of manipulation
Short setting time
Ability to bond to tooth and post
Where should margin of the core be?
At the sound tooth tissue
Because:
- fewer forces will be transmitted to the core restoration
- if finishing on the core, more interfaces exposed in the oral cavity
- if thin layer between restoration and tooth- can fracture and cause plaque retention, caries
Five requirements needed for crown and crown prep to be successful
Ferrule much be 2-3 mm in height
Parallel axial walls
Restoration must completely encircle the tooth
The margin must be on sound tooth tissue
Crown and crown prep must not invade biological width
Ferrule effect offers protection and what else
Provides anti rotational feature
Increases longevity of post and core restoration
When ferrule is present, failure of restoration can be retrievable
Increases fracture resistance of root treated teeth
Monoblock concept
A passive post system adhesively cemented and less rigid than metal post. This reduces incidence of root fracture. Bonding fibre post to root dentine can improve distribution of forces along the root and decrease the root fracture. A well adapted, adhesively cemented fibre post is considered the most retentive with the least stress generated on the canal walls. Adhesive cement acts as shock absorber. Modulus of elasticity is similar to dentine
chemical homogenity among components
Potentially can offer some reinforcement of remaining root structure.
Biocompatible
